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  • Calcium  (997)
  • Allgemeine Physik
  • Theoretische Chemie
  • Strömungsmechanik
  • Springer  (1,003)
  • American Institute of Physics (AIP)  (5)
  • 1
    ISSN: 1432-1238
    Keywords: Key words Propofol ; Disodium edetate ; Calcium ; Magnesium ; Parathyroid hormone ; Sedation ; Chelation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To evaluate the effects of propofol and propofol containing disodium edetate (ethylenediaminetetraacetic acid [EDTA]) on the parathyroid-calcium axis in normal subjects. Design: Randomised, double-blind, age-stratified, crossover trial. Setting: Single centre. Patients: A total of 50 healthy subjects. Interventions: Each subject was randomised to receive propofol or propofol containing EDTA on day 1 and the alternate treatment between days 15 and 29, with a 2-week washout period in between. On the day of treatment, subjects received a bolus of trial medication (1 or 2 mg/kg) followed by a 60-minute observation period. At the end of 60 minutes, subjects received trial medication infused for 60 minutes at 1 of 4 randomised infusion rates (25, 50, 100, or 200 μg/kg per min). Subjects were monitored for an additional 60 minutes following the infusion. Measurements and Results: Blood pressure, heart rate, respiratory rate, oxygen saturation, blood ionised calcium concentration, serum total magnesium concentration, serum intact parathyroid hormone (PTH) level, and plasma EDTA level were assessed at periodic intervals during and following the bolus and continuous infusion of trial medication. Mean arterial pressure significantly decreased (p 〈 0.05) following the bolus injection of both trial medications and returned to baseline at 60 minutes; it significantly decreased again during the continuous infusion and returned to baseline during recovery. Heart rate and respiratory rate fluctuated in both groups with significant increases and decreases throughout the study period following the bolus injection; both returned to baseline during the recovery period in each group. Ionised calcium and total magnesium concentrations remained within normal limits and were unchanged in response to both study medications. PTH levels significantly increased following the bolus injection of both study drugs. The increase in PTH levels was greater with higher doses of study medication during the infusion period. There was no difference in the response of blood pressure, heart rate, respiratory rate, or PTH levels between propofol and propofol with EDTA. EDTA levels increased significantly during the infusion of propofol with EDTA, reaching mean levels of 240 ng/mL. Conclusions: The results of this study indicate that propofol increases PTH levels in normal subjects; however, propofol with EDTA does not alter ionised calcium or total magnesium concentrations.
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  • 2
    ISSN: 1432-2145
    Keywords: Key words Antimonate localization ; Calcium ; Embryo sac ; Ovule ; Plumbago zeylanica
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Calcium was localized in ovules of Plumbago zeylanica from 1 day before anthesis to 3 days after anthesis using potassium antimonate and transmission electron microscopy in pollinated and emasculated flowers. At 1 day before anthesis, embryo sacs (containing an egg cell, a central cell and zero to three accessory cells) appear mature and contain abundant calcium precipitates (ppts), in contrast to nucellar cells. At anthesis, the vacuoles of nucellar cells have enlarged, and micropylar cells, in particular, are heavily labeled with calcium ppts. As pollen tubes elongate through ovular tissues, ppts diminish in ovular cells and become concentrated in the pollen tube cell wall. After fertilization, the calcium ppts sharply diminish in fertilized ovules; in unfertilized ovules, calcium ppts remain abundant up to 3 days after anthesis (when unfertilized ovules are shed). The distribution of calcium in the ovule changes in apparent response to fertilization, suggesting that calcium content may be related to the attraction and receipt of the pollen tube. In contrast with conventionally-organized embryo sacs with synergids, Plumbago accumulates calcium in the egg cell.
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  • 3
    ISSN: 1423-0127
    Keywords: Calcium ; Cell ; Channels, store-operated ; Calcium influx, capacitative ; Vasopressin ; Smooth muscle, vascular ; Thapsigargin ; Lanthanum ; Nifedipine ; A7r5
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Objective: The purpose of this study was to evaluate the contribution of capacitative calcium influx to intracellular calcium levels during agonist-induced stimulation of vascular smooth muscle cells.Methods: Aortic vascular smooth muscle cells (A7r5) were loaded with Indo-1 and intracellular calcium transients were measured. Cells were challenged with either arginine vasopressin (0.5 µM) or thapsigargin (1 µM). Lanthanum (1 mM) was used to block capacitative calcium influx through store-operated channels. Calcium traces were analyzed for basal, peak and plateau responses. Recordings were derivatized and integrated to gain additional information. Nonlinear regression provided a time constant that describes restoration of ionic equilibrium involving both sequestration and extrusion pathways.Results: Stimulation of cells with thapsigargin produced a non-L-type calcium influx that was attenuated by lanthanum. Cells excited with vasopressin exhibited a rapid calcium increase followed by a gradual decrease to a plateau level. Lanthanum pretreatment prior to stimulation caused no significant change in baseline, peak or plateau calcium levels as compared to control. Lanthanum caused no significant change in maximal calcium release rate, calcium integrals or time constant as compared to control.Conclusions: Capacitative calcium entry can occur in vascular smooth muscle cells, but does not appear to contribute significantly to the vasopressin response.
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  • 4
    ISSN: 1432-136X
    Keywords: Key words Action potential ; Calcium ; Heart failure
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Global contractile heart failure was induced in turkey poults by furazolidone feeding (700 ppm). Abnormal calcium regulation appears to be a key factor in the pathophysiology of heart failure, but the cellular mechanisms contributing to changes in calcium fluxes have not been clearly defined. Isolated ventricular myocytes from non-failing and failing hearts were therefore used to determine whether the whole heart and ventricular muscle contractile dysfunctions were realized at the single cell level. Whole cell current- and voltage-clamp techniques were used to evaluate action potential configurations and L-type calcium currents, respectively. Intracellular calcium transients were evaluated in isolated myocytes with fura-2 and in isolated left ventricular muscles using aequorin. Action potential durations were prolonged in failing myocytes, which correspond to slowed cytosolic calcium clearing. Calcium current-voltage relationships were normal in failing myocytes; preliminary evidence suggests that depressed transient outward potassium currents contribute to prolonged action potential durations. The number of calcium channels (as measured by radioligand binding) were also similar in non-failing and failing hearts. Isolated ventricular muscles from failing hearts had enhanced inotropic responses, in a dose-dependent fashion, to a calcium channel agonist (Bay K 8644). These data suggest that changes in intracellular calcium mobilization kinetics and longer calcium-myofilament interaction may be able to compensate for contractile failure. We conclude that the relationship between calcium current density and sarcoplasmic reticulum calcium release is a dynamic process that may be altered in the setting of heart failure at higher contraction rates.
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  • 5
    ISSN: 1432-136X
    Keywords: Key words Strontium ; Calcium ; Rumen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The net absorption rates of strontium ions from the ovine reticulo-rumen, isolated in situ in trained conscious animals, were measured under controlled conditions. A linear positive response was obtained from the addition of Sr2+ ions to the artificial rumen fluid. This increase in the absorption of Sr was reflected in an increase in the plasma Sr concentration. In contrast to the discrimination observed elsewhere in favour of the absorption of Ca relative to Sr, the absorption rate of Sr from the reticulo-rumen was significantly greater than that of Ca, from solutions containing the same molar concentration. A graded increase in the Sr concentration in the ruminal fluid from 1 mmol/l to 4 mmol/l led to a corresponding reduction in the absorption rate of Ca but an increase in that of phosphate. The latter result is similar to that observed when the intra-ruminal concentration of Ca2+ ions is increased. It is suggested that Ca and Sr share a common pathway for absorption from the reticulo-rumen and that this may involve coupling with the absorption of phosphate ions.
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  • 6
    Electronic Resource
    Electronic Resource
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    Journal of comparative physiology 170 (2000), S. 581-588 
    ISSN: 1432-136X
    Keywords: Key words Short chain fatty acids ; Calcium ; Rumen ; Sheep
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Net Ca2+ and Mg2+ absorption rates were measured in vivo from buffer solutions placed in the washed reticulo-rumen, isolated in situ in 30 conscious, trained sheep. An increase in concentration of short chain fatty acids (SCFA) in the buffer, over the range 0–50 mM, was shown to stimulate the net rates of absorption of Ca2+ and Mg2+ ions from the rumen. Similarly, the results of in vitro experiments, carried out with ovine rumen epithelium mounted in short-circuited Ussing chambers, showed that the absence of SCFA from the chamber fluid resulted in a reduction in Jnet Ca2+ caused by reduced flux of Ca2+ ions in the mucosal to serosal direction (Jms Ca2+). The addition of 1 mM acetazolamide, an inhibitor of carbonic anhydrase, to the ruminal buffer used in the in vivo experiments led to significant reductions in the net absorption rates of Ca2+and Mg2+ ions in the presence of SCFA (50 mmol l−1) but not in the absence of SCFA. However, in the in vitro experiments, the addition of 60 μM ethoxyzolamide had no significant effect on Jnet Ca2+. A reduction in pH of the intraruminal buffer in vivo from 6.8 to 5.4 led to significant increases in the net absorption rates of Ca2+and Mg2+ ions, an effect which was duplicated for Ca2+ in preliminary in vitro experiments in which the pH of the mucosal buffer was reduced from 7.4 to 5.4. This stimulatory effect was confined to Jms Ca2+ and Jnet Ca2+. Ussing chambers were also used to demonstrate that Jnet Ca2+ was reduced by a high transmural potential difference (PD), caused by voltage clamping, independently of the mucosal K+ concentration. Both unidirectional Ca2+ fluxes consisted of a PD-dependent and a K+-insensitive PD-independent component. The latter may be represented by a Ca2+/2H+ antiporter. It is postulated that SCFA, and to a lesser extent H2CO3, can stimulate Jms Ca2+ by activation of an apical Ca2+/2H+ antiporter through the provision of protons within the ruminal epithelial cell. A mild reduction in ruminal pH may also lead to a similar stimulation of this putative electroneutral exchange.
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  • 7
    ISSN: 1615-6102
    Keywords: Biomineralization ; Calcium ; Calcium oxalate ; Crystal ; Cytoskeleton ; Pistia stratiotes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Crystal idioblasts are cells which are specialized for accumulation of Ca2+ as a physiologically inactive, crystalline salt of oxalic acid. Using microautoradiographic, immunological, and ultrastructural techniques, the process of raphide crystal growth, and how crystal growth is coordinated with cell growth, was studied in idioblasts ofPistia stratiotes. Incorporation of45Ca2+ directly demonstrated that, relative to surrounding mesophyll cells, crystal idioblasts act as high-capacity Ca2+ sinks, accumulating large amounts of Ca2+ within the vacuole as crystals. The pattern of addition of Ca2+ during crystal growth indicates a highly regulated process with bidirectional crystal growth. In very young idioblasts,45Ca2+ is incorporated along the entire length of the needle-shaped raphide crystals, but as they mature incorporation only occurs at crystal tips in a bidirectional mode. At full maturity, the idioblast stops Ca2+ uptake, although the cells are still alive, demonstrating an ability to strictly regulate Ca transport processes at the plasma membrane. In situ hybridization for ribosomal RNA shows young idioblasts are extremely active cells, are more active than older idioblasts, and have higher general activity than surrounding mesophyll cells. Polarizing and scanning electron microscopy demonstrate that the crystal morphology changes as crystals develop and includes morphological polarity and an apparent nucleation point from which crystals grow bidirectionally. These results indicate a carefully regulated process of biomineralization in the vacuole. Finally, we show that the cytoskeleton is important in controlling the idioblast cell shape, but the regulation of crystal growth and morphology is under a different control mechanism.
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  • 8
    ISSN: 1615-6722
    Keywords: Schlüsselwörter Osteoporose ; Frakturen ; Risikofaktoren ; Densitometrie ; Hypogonadimus ; Glucocorticoidtherapie ; Calcium ; Vitamin D ; Bisphosphonate ; Key Words Osteoporosis ; Fractures ; Densitometry ; Risk factors ; Hypogonadism ; Glucocorticoid therapy ; Calcium ; Vitamin D ; Bisphosphonates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Abstract Background: Osteoporotic fractures occur frequently also in men. Epidemiologic data from Germany indicate that more than 900,000 men are affected by osteoporotic fractures. Diagnosis and therapy of male osteoporosis are hampered by a lack of clinical studies. Diagnosis: Risk factor analysis, conventional spine X-rays, bone densitometry and a limited number of serum and urine analyses contribute to the diagnosis of osteoporosis and the assessment of future fracture risk. Bone densitometry at the femoral neck is superior to measurements at the lumbar spine because of the high prevalence of degenerative changes at the lumbar spine in elderly men. Major risk factors for osteoporosis are hypogonadism, glucocorticoid therapy, hypercalciuria, gastrointestinal disease, and high alcohol consumption. In individual cases, bone histology or additional biochemical studies are needed to establish the cause of osteoporosis. Therapy: Calcium and vitamin D deficits should be substituted both in prevention and treatment of male osteoporosis. Testosterone replacement therapy is effective in hypogonadism. In primary osteoporosis and in corticosteroid-induced osteoporosis, bisphosphonates (cyclical etidronate, alendronate) and fluorides are therapeutic options. Conclusion: Important principles in the care of men with osteoporosis are the transfer of knowledge established for postmenopausel osteoporosis and the rigorous search for secondary osteoporosis aiming at treatment of the underlying cause.. Large prospective randomized trials aiming at the reduction of fracture rate in male osteoporosis are missing. They are urgently needed.
    Notes: Zusammenfassung Hintergrund: Epidemiologische Daten für Deutschland lassen darauf schließen, dass bei ¨ber 900 000 Männern eine manifeste Osteoporose mit Frakturen vorliegt. Diagnostik und Therapie bei diesen Patienten sind durch Datenmangel bei bisher unzureichenden Studien erheblich erschwert. Diagnostik: Die Diagnostik der Osteoporose des Mannes umfasst die Risikofaktoranalyse, die konventionelle Röntgendiagnostik der Wirbelsäule, die Densitometrie und ein Basislabor. Die Knochendichtemessung sollte bei älteren Männern bevorzugt am Schenkelhals durchgeführt werden, da an der Wirbelsäule die Messung durch häufige degenerative Veränderungen weniger zuverlässig ist. Wesentliche Risikofaktoren sind langfristige Glucocorticoidtherapie, Hypogonadismus, Hyperkalzurie, gastrointestinale Erkrankungen und Aklkoholabusus. In unklaren Fällen können eine gezielte ergänzende Laboruntersuchung und eine Knochenhistologie zur differentialdiagnostischen Einordnung erforderlich werden. Therapie: Sowohl in der Prävention der Osteoporose des Mannes als auch in der Basistherapie bei manifester Osteoporose sollten ein Calciumdefizit und ein Vitamin-D-Mangel ausgeglichen werden. Bei nachgewiesenem Hypogonadismus erfolgt eine Testosteronsubstitution. Bei der primären Osteoporose und bei corticosteroidinduzierter Osteoporose sind Bisphosphonate (zyklisches Etidronat, Alendronat) und Fluoride therapeutische Optionen. Schlussfolgerung: Wichtige Prinzipien in der Betreuung von Männern mit Osteoporose sind die Übernahme von Erfahrungen, die bei Frauen mit postmenopausaler Osteoporose gewonnen wurden, und die systematische Suche nach sekundären Osteoporoseformen mit dem Ziel einer kausalen Therapie. Große randomisierte Studien mit dem Ziel der Frakturreduktion fehlen für die Osteoporose des Mannes. Sie sind für die Zukunft dringlich zu fordern.
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  • 9
    ISSN: 1615-6102
    Keywords: Dunaliella ; Calcium ; Sodium ; Transport ; Na+-Ca2+ exchanger ; Algae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The countertransport of Ca2+ and Na+ across the membranes of the unicellular fresh-water algaChlamydomonas reinhardtii CW-15 and twoDunaliella species differing in salt tolerance was studied. All algae used are devoid of cell walls. The calcium uptake by twoDunaliella species depended markedly on the intracellular sodium concentration. This calcium uptake was accompanied by Na+ release. For 15 and 30 s after artificial gradient formation (Naint + greater than Naext +) the ratio of released Na+ to absorbed Ca2+ was 3∶1 and 4∶1, respectively. For the extremely halotolerantD. salina, the apparent Michaelis constant of the Ca2+ uptake was 33 μM, and for the marine halotolerant algaD. maritima, it was equal to 400 μM, presuming more efficient Na+-for-Ca2+ exchange inD. salina cells. Ouabain, an inhibitor of Na+/K+-ATPase, suppressed Na+ transfer by 25%, whereas the agents blocking Ca2+-channels did not affect the transport of Ca2+ and Na+. The oppositely directed transmembrane Ca2+ and Na+ transfer was shown to depend on the external concentrations of Na+ and H+. In the fresh-water algaC. reinhardtii CW-15 (Naext + greater than Naint +), the direction of Ca2+ and Na+ fluxes across the plasma membrane was opposite to those described for Dunaliella cells. The results obtained point to the ability of the Na+-Ca2+ exchanger function in plasma membranes of algal cells.
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  • 10
    ISSN: 1439-6327
    Keywords: Key words Fatigue ; Skeletal muscle ; Calcium ; Sarcoplasmic reticulum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Repeated activation of skeletal muscle causes fatigue, which involves a reduced ability to produce force and slowed contraction regarding both the speed of shortening and relaxation. One important component in skeletal muscle fatigue is a reduced sarcoplasmic reticulum (SR) Ca2+ release. In the present review we will describe different types of fatigue-induced inhibition of SR Ca2+ release. We will focus on a type of long-lasting failure of SR Ca2+ release which is called low-frequency fatigue, because this type of fatigue may be involved in the muscle dysfunction and chronic pain experienced by computer workers. Paradoxically it appears that the Ca2+ released from the SR, which is required for contraction, may actually be responsible for the failure of SR Ca2+ release during low-frequency fatigue. We will also discuss the relationship between gross morphological changes in muscle fibres and long-lasting failure of SR Ca2+ release. Finally, a model linking muscle cell dysfunction and muscle pain is proposed.
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  • 11
    ISSN: 1432-1459
    Keywords: Key words Motor neurone ; Astrocyte ; Human ; Tissue culture ; ALS ; Glutamate ; Calcium ; SOD-1
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Defining the basis of the selective cell vulnerability of motor neurones (MN) represents the key issue in amyotrophic lateral sclerosis (ALS), and tissue culture models are the ideal system for the identification of the MN specific features at the single cell level. Neurone-astrocyte metabolic interactions, which have a critical role in MN through glutamatergic toxicity, have been mostly defined in vitro. Ca++ metabolism, which appears to play a critical role in inducing MN loss in ALS, has been successfully studied using in vitro cell models. Furthermore, primary cultures demonstrated that apoptotic or necrotic death of neurones after injury depends upon the cell energetic status. Superoxide dismutase-1 (SOD-1) mutations were successfully expressed in cultured rodent MNs, providing a critical assay to sequence the molecular processes responsible for MN degeneration due to the identified genetic defect. The recent identification of genes that separate humans from apes further increases the value of the human in vitro models to better understand specific human cellular properties. Purified human MNs and astrocytes can today be obtained from the human embryonic spinal cord anterior horns. Interactions at the single cell level can be dissected using the cDNA amplification techniques. The effects of molecules affecting MN survival, neurite extension, and metabolism can easily be defined in vitro, gaining a critical mass of information of immediate clinical application in the treatment of patients affected by ALS. Understanding the properties of human MNs in vitro represents today a significant and critical tool that can easily be reached after extension of the available knowledge from non-primate to human research. Human MN culture studies can greatly contribute to identifying the primitive critical cellular events responsible for the MN degeneration observed in ALS and to gaining crucial information ¶on new therapeutical agents.
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  • 12
    ISSN: 1432-1335
    Keywords: Key words Proteinase-activated receptors ; PAR-1 ; PAR-4 ; Astrocytoma cells ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The proteinase-activated receptor 1 (PAR-1) was characterized as a functional receptor for thrombin in cells from different brain tumor entities. Whether PAR-1 alone accounts for thrombin-induced effects in human cancer cells, or whether other PAR contribute is unknown. We established primary cultures from two neurosurgically removed human astrocytomas and investigated intracellular signaling roles of PAR-1 and PAR-4 by estimating the effect of α-thrombin and PAR-activating peptides on [Ca2+]i mobilization in single astrocytoma cells. α-Thrombin or the PAR-1-activating peptide SFLLRN induced a transient calcium mobilization. This suggests the involvement of PAR-1 in α-thrombin-induced calcium signaling in human astrocytoma cells. In addition, a second, PAR-4-dependent, mechanism exists. This was deduced from the findings that a further calcium signal could be observed in human astrocytoma cells stimulated with α-thrombin after SFLLRN and the PAR-4-activating peptide GYPGQV also induced a calcium response. In addition, the observation that trypsin, known to activate both PAR-2 and PAR-4, but not the specifically PAR-2-activating peptide SLIGRL induced calcium signaling is a further indication of functional PAR-4-type thrombin receptors in human astrocytoma cells. This is the first report demonstrating a signaling role for a dual thrombin receptor system in human tumor cells.
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  • 13
    ISSN: 1432-1238
    Keywords: Key words Adult respiratory distress syndrome ; Calcium ; Chelating agents ; Magnesium ; Propofol ; Sedation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To determine whether the addition of disodium edetate (EDTA) to propofol significantly alters mineral metabolism, adverse events, and outcome in critically ill medical patients with acute pulmonary dysfunction. Design: Multicentre, double-randomised, double-blind, comparative trial. Setting: Medical intensive care units of 5 health centres. Patients: A total of 85 haemodynamically stable men and women aged 18–81 years who had pulmonary dysfunction or adult respiratory distress syndrome as a primary diagnosis or complication and who were expected to require at least 48 hours of sedation and mechanical ventilation. Interventions: Patients were randomised to receive propofol with or without EDTA and then to 1 of 2 sedation levels: light (Modified Ramsay Sedation Scale [MRSS] score of 2 to 3) or deep (MRSS score of 4 to 5). Propofol was administered by continuous infusion at an initial rate of 5 μg/kg per min and titrated as needed. Measurements and Results: Approximately 63 % of patients had a high severity of illness as indicated by an Acute Physiology and Chronic Health Evaluation II score ≥ 19. As expected, these patients had a higher mortality rate but did not require a higher dose of propofol or propofol with EDTA. Extensive evaluation of cation homeostasis showed that ionised calcium and magnesium concentrations remained remarkably stable during treatment. Total calcium concentration was low as a result of hypoalbuminemia. Parathyroid hormone (PTH) concentration was elevated in both study groups at baseline, on day 4, and at the end of sedation. There were no significant differences in electrolyte levels and no progression to renal dysfunction. There were also no significant differences in haemodynamic or adverse-event profiles. Treatment-related adverse events occurred in 5 patients in each group; 4 of these (in 3 patients receiving propofol and 1 patient receiving propofol with EDTA) were considered serious. Because a large percentage of patients experienced a change in sedation level, no analyses were performed using sedation level. Conclusions: The addition of EDTA to propofol does not alter calcium and magnesium homeostasis in critically ill patients with acute pulmonary dysfunction. The reason for the elevation in PTH concentrations in such patients is not known.
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  • 14
    ISSN: 1432-1238
    Keywords: Key words Propofol ; Disodium edetate ; Critical illness ; Calcium ; Magnesium ; Homeostasis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objective: To compare propofol with disodium edetate (EDTA) and propofol without EDTA when used for the sedation of critically ill surgical intensive care unit (ICU) patients. Design: Prospective, randomised, multicentre trial. Patients: A total of 122 surgical ICU patients who required intubation and mechanical ventilation. Interventions: Patients were randomised to receive either propofol or propofol plus EDTA (propofol EDTA) by continuous infusion for sedation. Measurements and Results: The addition of EDTA to propofol had no effect on calcium or magnesium homeostasis, renal function, haemodynamic function, or efficacy when used for the sedation of surgical patients in the ICU. The most common adverse events were hypotension, atrial fibrillation, and hypocalcaemia. In this trial, a greater number of serious adverse events and adverse events leading to withdrawal occurred in the propofol group relative to the propofol EDTA group. There was a significantly lower crude mortality rate at 7 and 28 days for the propofol EDTA group compared with the propofol group. There were no statistically significant differences between groups with respect to depth of sedation. Conclusion: The propofol EDTA formulation had no effect on calcium or magnesium homeostasis, renal function, or sedation efficacy compared with propofol alone when used for sedation in critically ill surgical ICU patients. There was a significant decrease in mortality in the propofol EDTA group compared with the propofol group. Further investigations are needed to validate this survival benefit and elucidate a possible mechanism.
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  • 15
    ISSN: 1432-198X
    Keywords: Key words Nephrocalcinosis ; Furosemide ; Chlorothiazide ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  A previous study on furosemide-induced nephrocalcinosis (NC) showed only partial resolution of the calcifications after discontinuation of the diuretic. We investigated whether treatment with chlorothiazide (CTZ) will expedite the resolution of established furosemide-induced NC. Seventy-eight weanling male Sprague-Dawley rats were divided into eight groups. Three groups were studied for 1 week: A, control; B, furosemide 40 mg/kg per 24 h; C, CTZ 100 mg/kg per 24 h. Five groups were studied for 5 weeks: D, control; E, F, G, furosemide 40 mg/kg per 24 h for 1 week followed by 4 weeks of observation (E), CTZ 50 mg/kg per 24 h (F), and CTZ 100 mg/kg per 24 h (G) and; and CTZ 100 mg/kg per 24 h (H) for 5 weeks. At the end of each study period urine and blood were collected, one kidney was studied histologically and the contralateral ashed for quantitative calcium (Ca) analysis. Animals in group B developed NC with a kidney Ca content of 1,844±203 µg/g dry tissue compared with group A 248±86 (P〈0.05) and group C 256±56 (P〈0.05). There were no differences among the three groups with regard to creatinine clearance, urine phosphate (P) or Ca excretion, although the latter tended to be lower in group C. Animals in group E showed a reduction in the magnitude of NC, with kidney Ca of 550±398 µg/g dry tissue, which was lower than in group B (P〈0.05) but still higher than in groups D (140±27) (P〈0.05) or H (162±63) (P〈0.05). Kidney Ca content in groups F (497±142) and G (489±271 µg/g dry tissue) was similar to that in group E. There were no differences among the five groups with regard to creatinine clearance or urine P excretion. Urine Ca excretion was significantly lower in groups F and G than groups D and E. We conclude that once established, NC caused by furosemide is not affected by CTZ therapy in spite of the anticalciuric property of the latter.
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  • 16
    ISSN: 1573-4935
    Keywords: Calcium ; lateral diffusion ; PDGF receptor
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract When the receptors for platelet-derived growth factor (PDGF) are activatedthey aggregate, become tyrosine-phosphorylated and elicit a cascade ofdown-stream signals, including mobilization of Ca2+ from intra- andextracellular stores. Receptor mobility in the plane of the membrane isa prerequisite for receptor aggregation and further signalling. Using humanforeskin fibroblasts (AG 1523) and fluorescence recovery afterphotobleaching (FRAP), we therefore assessed the lateral mobilitycharacteristics of PDGF-β2 receptors by their diffusioncoefficient (D), and fraction of mobile receptors (R). This was done oncells stimulated with either normal human serum (NHS) or PDGF underdifferent Ca2+-conditions. The results suggest that both intra- and extracellular free Ca2+influence the mobility characteristics of the PDGF-β2receptor. Interestingly, the extracellular Ca2+ seems to imposegeneral restrictions on the mobility of receptors, since R increased whenextracellular Ca2+ was quenched with EGTA, whereas intracellularclamping of Ca2+ transients with MABTAM (BAPT/AM) primarily affectedD. When both intra- and extracellular Ca2+ were quenced, D remainedlow and R high, further supporting the proposition that they achievedistinct effects. Inhibition of tyrosine phosphorylation with Erbstatin,partly inhibited the NHS effects and released PDGF-induced receptorimmobilization. Ratio imaging with Fura-2 displayed that both NHS and PDGFinduced changes in intracellular free [Ca2+]. In view of the presentdata it might have important effects on the state of the receptor in themembrane, for instance by regulating its lateral mobility, communicationwith other receptors and signalling functions in the membrane.
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  • 17
    ISSN: 1437-9813
    Keywords: Key words Insulinoma ; Arterial stimulation ; Calcium ; Localization ; Children
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The role of pre- and intraoperative procedures for the localization of insulinomas has been extensively debated. We report a case of successful treatment using preoperative selective intra-arterial calcium injection and intraoperative glucose monitoring. A 12-year-old boy with hypoglycemic attacks had a large insulinoma in the head of the pancreas on computed tomography. Preoperative selective angiography combined with arterial stimulation-venous sampling (ASVS) by intra-arterial injection of calcium revealed no other insulinomas in the body and tail of the pancreas. Elevation of serum glucose on intraoperative monitoring confirmed complete enucleation of the insulinoma. Preoperative ASVS can accurately localize an insulinoma, and may help to increase the success rate of surgery and avoid blind pancreatectomy.
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  • 18
    ISSN: 1438-2385
    Keywords: Key words Lysozyme ; Calcium ; Interaction ; Ultrafiltration ; Donnan effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: 2+ transmission was modified from 80% to 120% by pH acting on the positive charge of lysozyme. The action of pH in addition to that of increasing lysozyme concentration gave rise to very variable Ca2+ transmission, whereas an increase in ionic strength reduced these effects. Thus, these results highlighted the need for caution before carrying out ion/protein binding studies, for instance by increasing the ionic strength.
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  • 19
    ISSN: 1435-5604
    Keywords: Key words Zinc ; Calcium ; Bone metabolism ; Bone growth ; Newborn rats
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The effect of zinc on bone growth in newborn rats supplied with lactation by maternal rats was investigated. Newborn rats were killed between 1 and 35 days after birth. Increasing age caused a significant increase in zinc content, calcium content, and alkaline phosphatase activity in the femoral-diaphyseal and metaphyseal tissues, while the bone deoxyribonucleic acid (DNA) content was significantly decreased because of elevation of mineral content. Oral administration of zinc sulfate (2.0 mg/100 g body weight; four times at 24-h intervals) to maternal rats from 1 day after birth induced a significant increase in zinc, alkaline phosphatase activity, DNA, and calcium content in the femoral-diaphyseal and metaphyseal tissues of newborn rats compared with those 7 or 14 days old. The results indicate that the increase in bone components results from lactation with zinc-containing milk of maternal rats. The femoral-metaphyseal tissues of newborn rats obtained at 7 days after birth were cultured for 24 h in a medium containing either vehicle or zinc sulfate (10−6 to 10−4 M) in vitro. Bone alkaline phosphatase activity and calcium and DNA content were significantly increased by zinc addition. These increases were completely prevented by the presence of dipicolinate (10−3 M), a chelator of zinc ion, or cycloheximide (10−6 M), an inhibitor of protein synthesis. The present study suggests that zinc plays a role in the development of bone growth in newborn rats.
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  • 20
    ISSN: 1435-5604
    Keywords: Key words Kidney stone ; Calcium ; Oxalate ; Ca-oxalate crystal ; AAA Ca (active absorbable algal calcium)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In nine normal subjects, four men and five women between 23 and 49 years of age, 800 mg calcium was orally administered as active absorbable algal calcium (AAA Ca) (A) and calcium carbonate (CaCO3) (B), to compare with non-calcium-containing placebo (C) in a crossover design. Calcium, oxalate, osmolality, creatinine, and pH were measured in the first three morning urine samples and Ca/osmolality, Ca/osmolality/body weight, Ca/creatinine, and oxalate/osmolality were calculated to correct for urine dilution. Ca × oxalate product was also calculated, and Ca oxalate crystal in the sediment was microscopically examined, semiquantitatively estimated as −, +, ++, or +++, and numerically expressed as 0, 1, 2, or 3, respectively. Urinary Ca excretion was similar in groups A and B, but significantly larger than in group C, regardless of the method of correction for dilution. Urinary oxalate excretion with correction for osmolality, however, was significantly lower in A than in B and C, which gave similar values. Urine pH was similar among all three groups. Ca × oxalate product was significantly higher in C than in A, but A and B were not significantly different. AAA Ca appeared to decrease urinary oxalate excretion and Ca × oxalate product more efficiently than CaCO3, suggesting the possibility of inhibiting the formation of Ca × oxalate kidney stones.
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  • 21
    ISSN: 1432-2277
    Keywords: Key words Machine preservation ; Marginal donor ; Kidney ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Pulsatile preservation offers the advantage of pretransplant assessment of donor kidneys. Selected electrolyte concentrations of machine perfusate were measured over time in order to: (1) describe electrolyte changes in perfusate during the pulsatile preservation of expanded-criteria donor (ECD) kidneys, and (2) to assess the prognostic significance of these characteristics to early graft function. One hundred and fifty ECD kidneys were preserved in our laboratory between 1 January 1995 and 11 January 1997. ECD kidneys were defined as those requiring pretransplant biopsy. Kidneys were grouped by the presence or absence of delayed graft function (DGF), and perfusion parameters were measured every hour during pulsatile perfusion. All kidneys were preserved by continuous hypothermic pulsatile perfusion using Belzer II solution. Renal flow is decreased and renal resistance is increased in the presence of DGF in machine-preserved ECD kidneys. In addition, ionized calcium concentration of the machine perfusate is significantly elevated in the DGF group compared with the No DGF group (0.091 vs 0.054, P = 0.0016). The incidence of DGF is significantly lower in the ECD kidney. Among the pretransplant variables of donor characteristics, perfusion parameters and histology, perfusion parameters are highly predictive of early graft function. In addition, we found that ionized calcium concentration in the perfusate is significantly elevated in kidneys exhibiting DGF, which may have implications for assessing the suitability of donor kidneys for transplantation.
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  • 22
    ISSN: 1432-2145
    Keywords: Key words.Brassica ; Calcium ; Epidermis ; Host/Pathogen ; Pollen/stigma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Parallels have been explored between the early stages of stigmatic penetration by pollen tubes and the infection of epidermal cells by fungal pathogens. In a striking resemblence to events following the infection of Hordeum sp. by Erysiphe graminis, X-ray microanalysis has revealed the accumulation of calcium at the stigmatic surface following pollinations in Brassica oleracea. X-ray mapping strongly indicates the calcium to be localised at the points at which either the pollen grain or its tube makes contact with the surface of the stigmatic papilla. No definitive measures were made of the concentration of calcium at these sites, but controls indicated the levels to be well in excess of those found in the cytosol. X-ray microanalysis at the pollen/stigma interface failed to detect the presence of silicon, an element frequently accumulated by epidermal cells in response to pathogenic challenge. The phenylpropanoid biosynthesis pathway is activated by many plant hosts following infection by fungal pathogens, and the accumulation of autofluorescent material in the stigma 24 h after contact with self pollen strongly indicates this pathway also to be activated after pollination. The timing of this response, however, suggests that phenolic products are unlikely to be involved in the rejection of self pollen. These data are discussed in the perspective of current views of defence systems present in angiosperm epidermal cells, and why these mechanisms fail to identify and reject incompatible pollen tubes.
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  • 23
    ISSN: 1432-0533
    Keywords: Key words Apoptosis ; Atrophy ; Calcium ; Phytanic acid ; Purkinje cell
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Cerebellar atrophy, consequent to the postdevelopmental degeneration and loss of Purkinje cells and granular neurons, has been identified in three patients with rhizomelic chondrodysplasia punctata (RCDP). Cerebellar atrophy in our two chronic patients was symmetrical, but the vermis and medial portions of both hemispheres, particularly the dorsal lobules, displayed more severe atrophy than the lateral hemispheres. The distal tips of folia showed the greatest neuronal loss. Residual Purkinje cells showed progressive degenerative changes that appeared to be due, in part, to their topography. The precise mode of death of Purkinje cells in RCDP has not been established, but it does not appear to be mediated by entrance into the cell cycle or by ubiquitination; however, alterations in intracellular calcium levels and mitochondria may be involved. Elevated serum/CSF phytanic acid, decreased levels of tissue plasmalogens and increased chronological age are believed to play synergistic pathogenetic roles in this lesion.
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  • 24
    ISSN: 1423-0127
    Keywords: Myocytes single ; Cesium ; Voltage and current tails ; Na-Ca exchange ; Calcium ; Cadmium ; Nickel
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The mechanisms by which different concentrations of cesium modify membrane potentials and currents were investigated in guinea pig single ventricular myocytes. In a dose-dependent manner, cesium reversibly decreases the resting potential and action potential amplitude and duration, and induces a diastolic decaying voltage tail (Vex), which increases at more negative and reverses at less negative potentials. In voltage-clamped myocytes, Cs+ increases the holding current, increases the outward current at plateau levels while decreasing it at potentials closer to resting potential, induces an inward tail current (Iex) on return to resting potential and causes a negative shift of the threshold for the inward current. During depolarizing ramps, Cs+ decreases the outward current negative to inward rectification range, whereas it increases the current past that range. During repolarizing ramps, Cs+ shifts the threshold for removal of inward rectification negative slope to less negative values. Cs+-induced voltage and current tails are increased by repetitive activity, caffeine (5 mM) and high [Ca2+]o (8.1 mM), and are reduced by low Ca2+ (0.45 mM), Cd2+ (0.2 mM) and Ni2+ (2 mM). Ni2+ also abolishes the tail current that follows steps more positive than ECa. We conclude that Cs+ (1) decreases the resting potential by decreasing the outward current at more negative potentials, (2) shortens the action potential by increasing the outward current at potentials positive to the negative slope of inward rectification, and (3) induces diastolic tails through a Ca2+-dependent mechanism, which apparently is an enhanced electrogenic Na-Ca exchange.
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  • 25
    ISSN: 1432-0789
    Keywords: Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus ; Intercropping
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  A litter bag technique was used to study the decomposition and release of N, P, K, Ca, and Mg from Leucaena leucocephala and L. pallida prunings and cattle manure in a hedgerow intercropping trial conducted in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping or alley farming) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. Manure was the most resistant to decomposition, losing only 15% of its dry matter (DM) in 15 weeks, compared to 41–57% lost by leucaena prunings. Large quantities of K (up to 104 kg ha–1) were mineralized from prunings and manure, but Ca and Mg were mostly immobilized. More N and P were released from prunings than from manure, which resulted in net immobilization of these nutrients in the initial stages of decomposition and net mineralization in later stages. Between the leucaenas more N was mineralized and less Ca and Mg were immobilized when L. leucocephala prunings were applied than when L. pallida prunings were applied. Fertilizer N increased DM decomposition and N mineralization. Mineralization of the nutrients was constrained by lignin and polyphenol contents. It is concluded that leucaena mulch and cattle manure may be significant sources of N and K for crop growth, but external sources of P, Ca and Mg may be required, particularly in acid soils which have low contents of these nutrients. However, this fertility effect has to be evaluated against the competition effect of trees to predict crop response.
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  • 26
    ISSN: 1432-0789
    Keywords: Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  Balances between nutrients applied or mineralized and nutrients removed in maize grain and stover were calculated in a hedgerow intercropping experiment in which Leucaena leucocephala and L. pallida prunings and cattle manure were applied. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. In control treatments, nutrient depletion per season was in the order of 7–19 kg N ha–1, 4–12 kg P ha–1, 10–26 kg K ha–1, 0–2 kg Ca ha–1 and 3–6 kg Mg ha–1. N fertilizer reversed the depletion of N, but it accelerated the depletion of the other nutrients. Manure and at least two applications of leucaena prunings resulted in net positive balances of N, K, and Ca between amounts applied or mineralized and amounts removed by maize. The amounts of P and Mg applied with, or mineralized from, prunings or manure were insufficient to offset the negative balances of these nutrients.
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  • 27
    ISSN: 1432-0789
    Keywords: Key words Alley cropping ; Calcium ; Magnesium ; Nitrogen ; Phosphorus ; Leaf pruning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract  The effects of Leucaena leucocephala and L. pallida prunings and cattle manure on maize nutrient uptake and yield were investigated in a hedgerow intercropping trial in the Ethiopian highlands. Hedgerow intercropping (also called alley cropping) is an agroforestry system in which trees are grown in dense hedges between alleys where short-cycle crops are grown. The hedges are pruned periodically during the cropping period and the prunings are added to the soil as green manure. For each leucaena species, the experiment had 16 treatments resulting from a factorial combination of four levels of leucaena leaf prunings (no prunings applied; first prunings applied; first and second prunings applied; first, second and third prunings applied), two levels of air-dried cattle manure (0 and 3 t dry matter ha–1) and two levels of N fertilizer (0 and 40 kg N ha–1 as urea). Uptake of N, P and K increased significantly with application of the three nutrient sources, but uptake of Ca and Mg either did not respond or decreased with application of prunings and manure. All the three factors increased maize grain and stover yields significantly, usually with no significant interactions between the factors. At least two applications of prunings were required to significantly increase nutrient uptake and maize yield. Maize in the row closest to the hedge did not respond to these nutrient inputs. It is concluded that hedgerow intercropping, with or without manure application, can increase crop yields moderately (to 2–3 t ha–1 maize grain yields) in the highlands, but P, Ca and Mg may have to be supplied from external sources if they are deficient in the soil. Additional N is still required for higher yields (〉4 t ha–1 maize grain yields). However, quantification of the competition effects of the trees is also required to confirm these results.
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  • 28
    ISSN: 1432-069X
    Keywords: Key words Keratinocyte ; UVB ; Apoptosis ; Calcium ; p53
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Normal human keratinocytes are stimulated to proliferate in serum-free medium containing subphysiological concentrations of calcium (0.09 mM, low calcium). In this study, we examined the effect of increased levels of extracellular calcium (2.0 mM, normal calcium) on UVB-induced apoptosis. Apoptosis was assessed by changes in cellular morphology, annexind V-FITC flow cytometry, and the formation of internucleosomal DNA ladders. High doses of UVB induced keratinocytes grown in low calcium medium to undergo apoptosis. In contrast, keratinocytes grown for 72 h in normal calcium medium were completely resistant to UVB-induced apoptosis. No apoptosis was observed even at UVB doses as high as 1200 J/m2. However, despite the lack of UVB-induced cell death, keratinocytes grown in normal calcium medium lost the ability to proliferate following high levels of UVB irradiation. High doses of UVB also increased the expression of the differentiation-specific proteins involucrin and cytokeratin 10 in a dose-dependent manner. In addition, growth in normal calcium medium lowered the UVB-induced stimulation of the p53 protein and altered the normal subcellular localization pattern of p53. UVB irradiation of human keratinocytes grown in normal calcium medium may be inducing further cell differentiation in the absence of overt cell death.
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  • 29
    ISSN: 1434-0879
    Keywords: Key words Nephrolithiasis ; Kidneys ; Calcium ; oxalate crystallization ; Inter-α-inhibitor ; Bikunin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Our earlier studies indicated that members of the inter-α-inhibitor (IαI) family of glycoproteins may play an important role in urolithiasis. Indeed bikunin, the light chain of IαI is a potent inhibitor of calcium oxalate crystallization. In order to understand this role, the distribution of IαI and its related proteins, as well as the expression of bikunin, were studied in normal and nephrolithic rats. In normal rats, IαI immunoreactivity was located mainly in proximal tubules. However, in nephrolithic rats, in addition to proximal tubules, the staining was intensively extended to tubules in the corticomedullary junction. Furthermore, by using polymerase chain reaction technique, we demonstrated that gene encoding for bikunin was activated in kidneys of nephrolithic rats. We have previously demonstrated increased staining for osteopontin in association with calcium oxalate crystal deposition in rat kidneys. Others have shown an increase in osteopontin production by renal epithelial cells on exposure to calcium oxalate crystals. Based on these observations we conclude that kidney cells possess an auto-defense system against calcium oxalate crystallization and stone formation in which members of the IαI family may be closely involved.
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  • 30
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    Electronic Resource
    Springer
    ISSN: 1126-5442
    Keywords: Key words Muscle ; Calcium ; Halothane ; Isoflurane ; Calmodulin ; SR
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract It is proposed that volatile anesthetics act through the modification of Ca2+ homeostasis in excitable cells. To test this hypothesis, cardiac and skeletal muscles were used as models to examine Ca2+ response, and Ca2+ regulatory and delivery mechanisms. I found that halothane did not alter Ca2+ binding to cardiac troponin C. However, halothane and isoflurane reversibly decreased the Ca2+ affinity of calmodulin at low anesthetic concentration, and irreversibly increased the Ca2+ affinity of calmodulin at high anesthetic concentration. The volatile anesthetics also increased the permeability of light fraction of sarcoplasmic reticulum (SR) to Ca2+. I conclude that volatile anesthetics alter calcium homeostasis in cardiac and skeletal muscles. This work was in part performed in collaboration with Giovanni Salviati and the author benefited from Salviati's work in similar areas.
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  • 31
    ISSN: 1615-2573
    Keywords: Force—interval relation ; Sarcoplasmic reticulum ; Calcium ; Extrasystole ; Compensatory pause
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary We have reported that the postextrasystolic potentiation (PESP) decays in alternans or monotonically, respectively, depending on whether the first postextrasystolic beat interval has a compensatory pause or not, in the canine left ventricle. To get better mechanistic insight into the alternans PESP decay, we hypothesized that the myocardial mechanical restitution and potentiation could partly account for both types of PESP decay. To test this hypothesis, we simulated PESP decay on a computer using a documented equation combining myocardial mechanical restitution and potentiation. We changed the first postextrasystolic beat interval after a fixed extrasystolic beat interval without changing regular and other postextrasystolic beat intervals. The simulated PESP decayed in alternans or monotonically as a function only of the first postextrasystolic beat interval. Thus, the myocardial mechanical restitution and potentiation could partly account for both alternans and monotonic decay of PESP. We conclude that myocardial mechanical restitution and potentiation may partly underlie the initial two alternating beats, the first beat being the most potentiated and the second beat being the most depressed, of alternans PESP decay in the canine heart.
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  • 32
    ISSN: 1615-6102
    Keywords: Papaver rhoeas ; Self-incompatibility ; Calcium ; Signal transduction ; Cell-cell recognition
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary In recent years self-incompatibility (SI) has come to be recognised as an important model system for studying cell-cell interactions and signalling in flowering plants. In this article we discuss the intracellular events associated with the SI response in the field poppy,Papaver rhoeas. The SI response inP. rhoeas is known to involve a Ca2+-based signalling pathway, activated following molecular interactions on the surface of incompatible pollen tubes. Evidence demonstrates that, following a transient increase in the concentration of cytosolic free Ca2+ ([Ca2+];) initiated by the SI response, phosphorylation of certain cytosolic proteins occurs, followed by activation of pollen gene expression. The magnitude of this transient Ca2+ wave and the localisation of cytosolic [Ca2+]i following the SI response are discussed. We also describe the character of the proteins specifically phosphorylated in the SI response and the nature of the protein kinases involved in their phosphorylation. Finally, we consider the possibility that the end result of the SI response inP. rhoeas may be analogous to programmed-cell-death mechanisms such as those seen in developmental processes and defence responses in various plant cells.
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  • 33
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    Electronic Resource
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    Protoplasma 206 (1999), S. 234-240 
    ISSN: 1615-6102
    Keywords: Cilia ; Calcium ; Acetylcholine ; Trachea ; Epithelium ; Video microscopy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary This report summarizes our recent work on the role of intracellular Ca2+ ([Ca2+]i) in regulating mammalian ciliary beat frequency (CBF). CBF from a single ovine cilium and [Ca2+]i from the same cell were measured by digital video phase contrast microscopy and fura-2 ratiometric imaging video microscopy, respectively. Cells were stimulated with two exposures to 10 μM acetylcholine (ACh). CBF was recorded during the first and [Ca2+]i during the second stimulation. ACh increased [Ca2+]i and CBF transiently with indistinguishable kinetics and, early in culture, even induced [Ca2+]i oscillations and ciliary frequency modulations with the same peak-to-peak time interval. Cells treated with 1 μM thapsigargin, an inhibitor of the endoplasmic-reticulum Ca2+-ATPase, showed transient [Ca2+]i and CBF increases, again with similar kinetics, which often remained at an elevated plateau. Application of ACh to cells pretreated with thapsigargin produced decreases in both [Ca2+]i and CBF. Finally, changing extracellular Ca2+-concentrations induced corresponding changes in [Ca2+]i that were associated with kinetically similar CBF changes. These data strongly suggested that [Ca2+]i is a critical signal to regulate CBF in mammalian tracheal epithelial cells. In an initial effort to provide constraints on the number and type of reactions that link changes in [Ca2+]i to changes in CBF, simultaneous recordings of both signals from a single cell were analyzed. Such recordings provided higher resolution of the kinetic responses of CBF and [Ca2+]i to ACh as well as they allowed direct assessment of the coupling between [Ca2+]i and CBF. Simultaneous measurements revealed that [Ca2+]i and CBF were perfectly correlated within the CBF measurement time resolution, except for the period of the fastest changes in both signals during the initial ACh exposure. There, changes in CBF lagged the changes in [Ca2+]i by 1–3 ciliary beat cycles (ca. 150–450 ms).
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  • 34
    ISSN: 1615-6102
    Keywords: Calcium ; Electron energy loss spectroscopy ; Embryo sac ; Torenia fournieri ; Fertilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Calcium distribution in ovules ofTorenia fournieri was studied by electron energy loss spectroscopy and transmission electron microscopic visualization of calcium antimonate precipitates. High calcium levels were found in the ovules ofT. fournieri. Calcium is situated mainly in extracellular regions before fertilization, including the surface of embryo sac, in the mucilage, and among the cells of the egg apparatus. Intracellular calcium was found only in the nucellar cells around the embryo sac and in the epidermis of the central axis and funiculus. After pollination, a labyrinthine structure (coralloid-like cell wall formation) develops on the micropylar surfaces of the egg apparatus that contain high levels of calcium. Calcium levels increase in the degenerating synergid after the penetration of the pollen tube. Calcium-antimonate precipitates are abundant in vacuoles of the disrupted synergid and pollen tube cytoplasm.
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  • 35
    ISSN: 1573-7322
    Keywords: Calcium ; hypochlorous acid ; protein oxidation ; zinc ; dithiothreitol
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Reperfusion injury in ischemic myocardium may be caused by neutrophil oxidants such as hypochlorous acid (HOCl). In view of the close association between intracellular Ca2+ ([Ca2+]i) and cellular injury, we examined the ability of [Ca2+]i to affect HOCl injury in cardiac muscle. [Ca2+]i was modulated by bathing isolated, isometrically contracting, rat papillary muscles in normal (2.5 mM), low (0.5 mM), or high (5.0 mM) extracellular Ca2+ ([Ca2+]o), or with 1 µM nifedipine, an L-type Ca2+ channel antagonist, and 1 µM Bay K8644, an L-type Ca2+ channel agonist. In normal [Ca2+]o, HOCl (300 µM) caused a rapid decline in contractile function, the onset of contracture, and a decrease in protein sulfhydryl levels (P-SH). Ryanodine, an inhibitor of the sarcoplasmic reticulum Ca2+ release channel, protected against injury. Dithiothreitol (DTT) partially restored the lost function and P-SH. Lowering the [Ca2+]i with low [Ca2+]o or nifedipine resulted in a surprising potentiation of HOCl injury, and the inhibition of DTT-induced recovery. Raising [Ca2+]i with high [Ca2+]o or Bay K8644 resulted in protection against injury. Our previous studies have demonstrated an HOCl-induced increase in [Zn2+]i. Since Ca2+ can protect against the intracellular effects of Zn2+, we therefore propose that HOCl injury may be caused by the binding of mobilized Zn2+ to P-SH, and that increased [Ca2+]i protects against this injury Our data therefore provide an explanation for the lack of clinical efficacy of Ca2+ channel blockers with early phase acute myocardial infarction, and may therefore have significant clinical implications.
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  • 36
    ISSN: 1432-198X
    Keywords: Key words Aluminum ; Calcium ; Hyperparathyroidism ; Phosphate
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  In patients with chronic renal insufficiency, phosphate retention is a major factor in the development of secondary hyperparathyroidism, renal osteodystrophy, and soft tissue calcification, and may contribute to progression of renal failure. Prevention of phosphate retention with dietary and pharmacological means, along with the administration of calcitriol, may prevent or reverse secondary hyperparathyroidism. With more-advanced renal failure, phosphate binders become necessary to maintain phosphate balance and to prevent hyperphosphatemia. Because of toxicity, aluminum-containing phosphate binders are no longer used. Currently, calcium-containing phosphate binders, such as calcium carbonate and calcium acetate, are the most widely prescribed. Although calcium salts eliminate the problems associated with aluminum toxicity, they often result in transient hypercalcemia, requiring discontinuation of calcitriol and the use of low-calcium dialysate. Several new non- aluminum- and non-calcium-containing phosphate binders are currently at various stages of development, and may provide an alternative to the currently used binders. It is unlikely, however, that the newer compounds will completely replace calcium salts, since mild hypercalcemia may be necessary in chronic renal failure patients to suppress parathyroid hormone production. Other areas of investigation must include the development of drugs to inhibit soft tissue and renal calcifications, and to enhance urinary phosphate excretion.
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  • 37
    ISSN: 1432-2013
    Keywords: Key words Cardiomyocyte ; Calcium ; Insulin-dependent diabetes mellitus ; Fura-2 ; Taurine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The present study investigated the acute effects of taurine on intracellular Ca2+ ([Ca2+]i) in normal and diabetic cardiac myocytes. [Ca2+]i was monitored using fura-2 in single myocytes isolated from control or streptozotocin-treated rats and paced at frequencies between 0.33 Hz and 2.0 Hz in the absence or presence of 20 mM taurine. Increasing stimulus frequency resulted in significant increases in resting and peak [Ca2+]i, and amplitude of the Ca2+ transient in both control and diabetic myocytes. The amplitude of the Ca2+ transient and the extent of its increase with increasing frequency was, however, significantly lower in the diabetic myocytes. Taurine significantly increased resting [Ca2+]i, peak [Ca2+]i, and the amplitude of the Ca2+ transient in both control and diabetic myocytes at all stimulus frequencies examined. The degree of potentiation of the Ca2+ transient decreased with increasing stimulus frequency in control cells but not in diabetic cells. In the absence of taurine the decay of the Ca2+ transient was significantly slower in diabetic than control myocytes. Taurine was without significant effect on the time course of the Ca2+ transient decay in control cells, however, in diabetic cells it significantly accelerated the rate of decay. The data demonstrate directly that taurine is able to increase [Ca2+]i and the amplitude of the Ca2+ transient in both normal and diabetic cardiac myocytes. In addition several of the effects of taurine appeared to be more pronounced in diabetic than control cells.
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  • 38
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    Pflügers Archiv 437 (1999), S. 417-422 
    ISSN: 1432-2013
    Keywords: Key words Caffeine ; Calcium ; Efflux ; Frog ; Potassium ; Skeletal muscle
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The exposure of frog skeletal muscle to caffeine (3–4 mM) generates an increase of the K+ (42K+) efflux rate coefficient (k K,o) which exhibits the following characteristics. First it is promoted by the rise in cytosolic Ca2+ ([Ca2+]i), because the effect is mimicked by ionomycin (1.25 µM), a Ca2+ ionophore. Second, the inhibition of caffeine-induced Ca2+ release from the sarcoplasmic reticulum (SR) by 40 µM tetracaine significantly reduced the increase in k K,o (Δk K,o). Third, charybdotoxin (23 nM), a blocker of the large-conductance Ca2+-dependent K+ channels (BKCa channels) reduced Δk K,o by 22%. Fourth, apamin (10 nM), a blocker of the small-conductance Ca2+-dependent K+ channels (SKCa channels), did not affect Δk K,o. Fifth, tolbutamide (800 µM), an inhibitor of KATP channels, reduced Δk K,o by about 23%. Sixth, Ba2+, a blocker of most K+ channels, did not preclude the caffeine-induced Δk K,o. Seventh, omitting Na+ from the external medium reduced Δk K,o by about 40%. Eight, amiloride (5 mM) decreased Δk K,o by 65%. It is concluded that the caffeine-induced rise of [Ca2+]i increases K+ efflux, through the activation of: (1) two channels (BKCa and KATP) and (2) an external Na+-dependent amiloride-sensitive process.
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  • 39
    ISSN: 1432-2013
    Keywords: Key words Colon ; Chloride secretion ; Potassium channel ; SK channel family ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  Bradykinin (BK)-stimulated colonic Cl– secretion was studied in T84 colonic adenocarcinoma cells by measuring BK (50 nM)-evoked changes in cytosolic free [Ca2+] ([Ca2+]i), membrane conductance and transepithelial ion transport. In T84 cells grown on impermeable supports, BK stimulated a transient increase in [Ca2+]i as assessed by fura-2 ratio imaging. In cell-attached, patch-clamp recordings, BK transiently activated low-conductance K channels. These channels were activated/inactivated reversibly in inside-out patches by switching [Ca2+]i in the bath between 30 nM and 100 nM. Excised channels recorded with 160 mM [K+] in bath and pipette exhibited an inwardly rectifying current/voltage-relation, conductances of 10±1 pS and 34±4 pS (n=10) at positive and negative voltages, respectively, and a 15-fold lower permeability for Na+ than for K+. The mean open probability of these channels did not depend on voltage but increased with increasing [Ca2+]i with an apparent concentration for a half-maximal response (EC50) of 110 nM, resembling that of hSK4 K+ channels. Application of the reverse transcriptase-polymerase chain reaction technique showed hSK4 messenger ribonucleic acid (mRNA) to be expressed in T84 cells. Macroscopic currents in T84 cells showed a similar dependence on [Ca2+]i. Whole cell conductance (in nS/10pF) increased from 0.5±0.1 (n=6) at 10 nM [Ca2+]i in the pipette solution to 1.5±0.2 (n=7) at 100 nM, and to 2.0±0.5 (n=7) at 1 µM due to activation of a K+ conductance. In Ussing-chambered T84 monolayers grown on filters, BK did not evoke a short-circuit current (I sc). When, however, the monolayers were pre-stimulated by forskolin (1 µM), BK further enhanced Cl–secretion (ΔI sc=21±5 µA/cm2, n=10) transiently and biphasically. In conclusion, BK enhances cyclic adenosine monophosphate-stimulated Cl– secretion in T84 cells, probably via basolateral, Ca2+-liganded activation of low-conductance hSK4-type K+ channels.
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  • 40
    ISSN: 1432-2048
    Keywords: Key words:Chara (rhizoid ; protonema) ; Calcium ; Calcium channel ; Fluorescent-dihydropyridine ; Gravitropic tip growth
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. The localization of cytoplasmic free calcium and a dihydropyridine (DHP) receptor, a putative calcium channel, was recorded during the opposite graviresponses of tip-growing Chara rhizoids and Chara protonemata by using the calcium indicator Calcium Crimson and a fluorescently labeled dihydropyridine (FL-DHP). In upward (negatively gravitropically) growing protonemata and downward (positively gravitropically) growing rhizoids, a steep Ca2+ gradient and DHP receptors were found to be symmetrically localized in the tip. However, the localization of the Ca2+ gradient and DHP receptors differed considerably during the gravitropic responses upon horizontal positioning of the two cell types. During the graviresponse of rhizoids, a continuous bowing downward by differential flank growth, the Ca2+ gradient and DHP receptors remained symmetrically localized in the tip at the centre of growth. However, after tilting protonemata into a horizontal position, there was a drastic displacement of the Ca2+ gradient and FL-DHP to the upper flank of the apical dome. This displacement occurred after the apical intrusion and sedimentation of the statoliths but clearly before the change in the growth direction became evident. In protonemata, the reorientation of the growth direction started with the appearence of a bulge on that site of the upper flank which was predicted by the asymmetrically displaced Ca2+ gradient. With the upward shift of the cell tip, which is suggested to result from a statolith-induced displacement of the growth centre, the Ca2+ gradient and DHP receptors became symmetrically relocalized in the apical dome. No major asymmetrical rearrangement was observed during the following phase of gravitropic curvature which is characterized by slower rates of bending. Labeling with FL-DHP was completely inhibited by a non-fluorescently labeled dihydropyridine. From these results it is suggested that FL-DHP labels calcium channels in rhizoids and protonemata. In rhizoids, positive gravitropic curvature is caused by differential growth limited to the opposite subapical flanks of the apical dome, a process which does not involve displacement of the growth centre, the calcium gradient or calcium channels. In protonemata, however, it is proposed that a statolith-induced asymmetrical relocalization of calcium channels and the Ca2+ gradient precedes, and might mediate, the rearrangement of the centre of growth, most likely by the displacement of the Spitzenkörper, to the upper flank, which results in the negative gravitropic reorientation of the growth direction.
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  • 41
    Electronic Resource
    Electronic Resource
    Springer
    Planta 208 (1999), S. 38-45 
    ISSN: 1432-2048
    Keywords: Key words: Auxin ; Calcium ; Coleoptile growth ; K+-inward rectifier (channel) ; pH ; Zea (coleoptile protoplasts)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Potassium is taken up by maize (Zea mays L.) coleoptile cells via a typical plant inward rectifier (K ir ). Sufficient conductance of this channel is essential in order to maintain auxin-stimulated cell elongation. It was therefore investigated whether the activity of this channel is subject to direct or indirect control by this growth hormone. Patch-clamp measurements of whole coleoptile protoplasts revealed no appreciable effect of externally applied 10 μM or 100 μM α-naphthaleneacetic acid (NAA) on the activity of K ir over test periods of ≥ 18 or ≥ 8 min, respectively. When, however, K ir was recorded in the cell-attached configiuration and 10 μM NAA administered to the bath medium, the conductance of K ir increased significantly in 13 out of 18 protoplasts over the control. This rise occurred at a fixed protoplast voltage after a lag period of less than 10 min and exhibited no voltage dependency. The absence of response to NAA of protoplasts in the whole-cell configuration indicates that auxin perception and channel control is linked via a soluble cytoplasmic factor and that this mediator is washed out or modified upon perfusion of the cytoplasm with pipette solution. To search for this expected diffusible factor the K ir current was recorded before and after elevation of Ca2+ and H+ in the cytoplasm. In the whole-cell configuration the increase in Ca2+ from a nanomolar value to 〉1 μM by means of Ca2+-release from the caged precursor Na2-DM-nitrophen left K ir unaffected. The whole-cell K ir conductance was also not affected upon addition of 10 mM Na+-acetate to the bath medium, an operation used to lower the cytoplasmic pH. This excludes a primary role for the known auxin-evoked rise in cytoplasmic Ca2+ and H+ in K ir activity. We postulate that another, as yet unknown, mechanism mediates the auxin-evoked stimulation of the number of active K ir channels in the plasma membrane.
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  • 42
    ISSN: 1432-2013
    Keywords: Key words Ca buffering ; Calcium ; Sarcoplasmic reticulum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  This paper outlines a simple method of estimating both the Ca-buffering properties of the cytoplasm and the time-course of changes of sarcoplasmic reticulum (s.r.) Ca concentration during systole. The experiments were performed on voltage-clamped ferret single ventricular myocytes loaded with the free acid of fluo-3 through a patch pipette. The application of caffeine (10 mM) resulted in a Na-Ca exchange current and a transient increase of the free intracellular Ca concentration ([Ca2+]i). The time-course of change of total Ca in the cell was obtained by integrating the current and this was compared with the measurements of [Ca2+]i to obtain a buffering curve. This could be fit with a maximum capacity for the intrinsic buffers of 114±18 µmol l–1 and K d of 0.59±0.17 µM (n=8). During the systolic rise of [Ca2+]i, the measured changes of [Ca2+]i and the buffering curve were used to calculate the magnitude and time-course of the change of total cytoplasmic Ca and thence of both s.r. Ca content and Ca release flux. This method provides a simple and reversible mechanism to measure Ca buffering and the time-course of both total cytoplasmic and s.r. Ca.
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  • 43
    ISSN: 1432-2013
    Keywords: Key words Ca-ATPase ; Calcium ; Carboxyeosin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The effects of carboxyeosin, an inhibitor of the sarcolemmal Ca-ATPase, were studied on intracellular Ca and membrane currents in isolated rat ventricular myocytes. In the absence of carboxyeosin, 150-ms-duration depolarizing pulses from –40 to 0 mV resulted in an L-type Ca current on depolarization and a Na-Ca exchange ”tail” current on repolarization. The calculated entry of Ca on the L-type current was 1.3 times greater than the efflux via the Na-Ca exchange. The addition of carboxyeosin (20 µM) resulted in either an increase of the Na-Ca exchange current or a decrease of the L-type Ca current such that the Ca entry and efflux were exactly equal. These results suggest that, under control conditions, a carboxyeosin-sensitive Ca-ATPase contributes about 24% of the total Ca efflux from the cell and, therefore, that the sarcolemmal Ca-ATPase has a significant role in regulation of sarcolemmal Ca fluxes.
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  • 44
    ISSN: 1432-2013
    Keywords: Key words Muscle ; Calcium ; Relaxation ; Cross-bridges ; Diazo-2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The aim of this study was to compare the effects of increased concentrations of MgADP, inorganic phosphate (Pi) and H+ ([MgADP], [Pi] and [H+], respectively) on the rate of relaxation in two different muscle types: skinned muscle fibres from the frog Rana temporaria and myofibrillar bundles from the giant Pacific acorn barnacle Balanus nubilus. Relaxation transients are produced by the photolysis of diazo-2 and are well fitted with a double exponential curve, giving two rate constants: k1 [5.6±0.1 s–1 for barnacle, n=30; 26.3±0.7 s–1 for frog, n=14 (mean±SEM)] and k2 [0.6±0.1 s–1 in barnacle, n=30; 10.4±1.0 s–1 in frog, n=14 (mean±SEM)], at 10°C. Decreasing the pH by 0.5 pH units did not significantly affect k1 for barnacle relaxation [5.6±0.1 s–1 (mean±SEM), n=15] compared to the decrease in k1 of 40% seen in frog. Use of the Ca2+-sensitive fluorescent label acrylodan on barnacle wild-type troponin C demonstrated that decreasing the pH from 7.0 to 6.6 only alters the pCa50 value by 0.23 in the cuvette, while stopped-flow experiments with acrylodan revealed no significant change in koff from the labelled protein [322±32 s–1 at pH 7.0 and 381±24 s–1 (mean±SEM) at pH 6.6]. Increasing [MgADP] by 20 µM (50 µM added ADP) from control values of 50 µM in frog decreased k1 to 12.3±0.4 s–1 (mean±SEM, n=8), and at 400 µM MgADP, k1=9.6±0.1 s–1 (mean±SEM, n=12). In barnacle, 500 µM MgADP had a much smaller effect on k1 (4.0±0.9 s–1, mean±SEM, n=8). Increasing the free [Pi] from the contaminant level of 0.36 mM to 1.9 mM slowed k1 by ≈15% in barnacle [4.8±0.8 s–1, mean±SEM, n=7], compared to a ≈30% reduction seen in frog. We conclude that the differences between barnacle and frog seen here are most probably due to different isomers of the contractile proteins, and that events underlying the crossbridge cycle are the same or similar. We interpret our results according to a model of crossbridge transitions during relaxation.
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  • 45
    ISSN: 1432-2013
    Keywords: Key words Amperometry ; Botulinum neurotoxin ; Calcium ; Exocytosis ; Neuroendocrine cells ; PC12 cells ; SNAREs ; Syntaxin ; Transfection
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  We examined the effect on exocytosis in PC12 neuroendocrine cells of transient transfection with the specific endoprotease Botulinum neurotoxin C1 light chain (BoNT/C1), which cleaves syntaxin and SNAP-25. The effects of toxin expression on basal and evoked exocytosis were determined in cell population measurements and also in a single-cell transfection-amperometry assay. Co-expression of BoNT/C1 with human growth hormone (hGH) as a marker of secretory granules in transfected cells resulted in a 95% inhibition of hGH release evoked either by the purinergic agonist ATP or by depolarization with 55 mM K+. In addition, basal hGH release was also inhibited to the same extent. The high level of co-transfection efficiency revealed by this extent of inhibition was exploited in a high-resolution single-cell assay based on cell detection by expression of enhanced green fluorescent protein (EGFP) and analysis of evoked dopamine release by amperometry using a carbon fibre microelectrode. Cells expressing EGFP alone showed population responses and single-cell amperometric responses indistinguishable from those of control non-transfected cells. In contrast, co-expression of BoNT/C1 with EGFP resulted in an almost complete inhibition of current transients due to exocytosis evoked by ATP. These results establish and validate a single-cell assay of transfection-amperometry for analysing the effects of specific proteins on exocytosis.
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  • 46
    ISSN: 1530-0358
    Keywords: Vitamins ; Calcium ; Micronutrients ; Recurrence ; Chemoprevention ; Adenoma ; Colorectal neoplasia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract INTRODUCTION: Although some have suggested that certain vitamins or calcium supplements may reduce adenoma recurrence, our own prior retrospective study found no such effects. The purpose of this case-control study was to further investigate whether regular vitamin or calcium supplement intake influenced the incidence of recurrent adenomatous polyps in patients with previous neoplasia who were undergoing follow-up colonoscopy. METHODS: This study enrolled 1,162 patients who underwent colonoscopy by one of three surgeons at Columbia-Presbyterian Medical Center in New York City between March 1993 and February 1997. Of these patients 448 (250 males) had a previous diagnosis of colorectal neoplasia (cancer, adenomas, or dysplasia). Of these, 183 (40.8 percent) had an adenoma at the index colonoscopy. Information was collected on personal and family history of colonic diseases, cigarette smoking, medication, and vitamin and micronutrient supplement usage on a questionnaire that was completed by the patients before the colonoscopy. Odds ratios were obtained by unconditional logistic regression analysis, adjusting for age and gender, and used adenoma recurrence at index colonoscopy as the outcome. RESULTS: The mean interval between colonoscopic examinations was 37 months for the recurrent adenoma group and 38 months for the nonrecurrent group of patients (P = not significant). In this case-control study we found a protective effect for the use of vitamin supplements in general (any vitamin) on the recurrence of adenomas (odds ratio, 0.41; 95 percent confidence interval, 0.27–0.61). Specifically, this protective effect was observed for the use of multivitamins (odds ratio, 0.47; 95 percent confidence interval, 0.31–0.72), vitamin E (odds ratio, 0.62; 95 percent confidence interval, 0.39–0.98), and for calcium supplementation (odds ratio, 0.51; 95 percent confidence interval, 0.27–0.96). Nonsignificant protective effects were noted for carotene/vitamin A, vitamin D, and vitamin C. CONCLUSIONS: The use of multivitamins, vitamin E, and calcium supplements were found to be associated with a lower incidence of recurrent adenomas in a population of patients with history of previous colonic neoplasia. Prospective, randomized trials are needed to better assess the impact of these agents and to determine whether the use of these supplements is associated with a protective effect against recurrent adenomas.
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  • 47
    ISSN: 1530-0358
    Keywords: Smooth muscle ; Internal anal sphincter ; Rectum ; Nifedipine ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract INTRODUCTION: Glyceryl trinitrate reduces anal resting pressure and aids the healing of anal fissures. However, some patients develop tachyphylaxis and the fissure fails to heal, suggesting that other agents are needed. This study assesses the effects of nifedipine (a calcium channel antagonist) in modulating resting tone and agonist-induced contractions in human internal anal sphincter (IAS) and rectal circular muscle. METHODS: Smooth muscle strips from the IAS and rectal circular muscle from ten patients undergoing surgical resection were mounted for isometric tension recording in a superfusion organ bath. The effects of noradrenaline and carbachol were assessed in the presence of various perfusates. RESULTS: IAS strips developed tone and spontaneous activity. Noradrenaline produced dose-dependent contractions. In calcium-free Krebs solution, tone and activity were abolished and no contractions were elicited in response to noradrenaline. Nifedipine also abolished tone and spontaneous activity, but contractions to noradrenaline were only slightly attenuated. In contrast, rectal smooth muscle strips developed spontaneous activity but no resting tone and contracted in response to carbachol. In calciumfree Krebs solution, the spontaneous activity and carbachol contractions were abolished. Addition of nifedipine to the perfusate abolished spontaneous activity and greatly reduced contractions. DISCUSSION: These data suggest that spontaneous activity and resting tone are dependent on extracellular calcium and flux across the cells. Agonist-induced contraction in the IAS is attributable mainly to the release of calcium from intracellular stores, whereas rectal circular smooth muscle depends principally on extracellular calcium entering the cell for contraction. The attenuation of contractions in both tissues and the abolition of resting tone in the IAS suggest that nifedipine may be useful in the management of patients with anorectal disorders.
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  • 48
    ISSN: 1437-773X
    Keywords: Key words X-ray microanalysis ; Mitochondria ; Hippocampal CA1 ; Repeated brief cerebral ischemia ; Calcium ; Aluminum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract To elucidate the interrelationship between delayed neuronal death and calcium accumulation, an X-ray microanalysis technique was used to detect the elemental composition of deposits in mitochondria and nuclei after three 3-min bilateral common carotid arterial occlusion at 1-h intervals. Morphological changes in the CA1 pyramidal neurons were also observed. After 3 days of ischemia-recirculation, damaged mitochondria, electron-dense deposits in mitochondria, and rupture of nuclear membranes were evident. Calcium and aluminum were detected in those electron deposits in the mitochondria and nuclei. These findings support the hypothesis on delayed calcium-related cell death. Accumulation of aluminum in mitochondria and nuclei may be an additional factor involved in delayed neuronal death.
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  • 49
    ISSN: 1438-2385
    Keywords: Key words Infant formulas ; Components ; Calcium ; In vitro dialysability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Abstract  The in vitro methods proposed for estimating calcium bioavailability can be useful in studying the effect of dietetic factors. The aim of our work was to study the possible influence of different infant formula components – calcium, phosphorus, lactose, citric acid, ascorbic acid and proteins – on calcium bioavailability, considering dialysability to be an estimate of bioavailability. The 1981 method of Miller et al. with slight modifications (concerted action no 10 – FLAIR project) was applied to 18 commercial infant formulas of six different types: adapted, follow-up, preterm, hydrolysates, lactose-free and soy-based. Significant positive linear correlations between the amount of calcium dialysed and the calcium and phosphorus contents were found. However, there were no statistically significant correlations between the amount of calcium dialysed and the lactose, ascorbic acid or citric acid contents, In the case of proteins an exponential relationship was found between the amount of calcium dialysed and the protein content.
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  • 50
    ISSN: 1432-072X
    Keywords: Key words Heat shock ; Ethanol ; cAMP ; Protein ; kinase A ; cGMP ; Inositol phosphates ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Exposure of growing hyphae of Neurospora crassa to heat shock (44 °C) or ethanol (2.6 M) for 1 h induced a significant increase in the cAMP level, which reached a maximum approximately 2 min after the beginning of treatment and then decreased to control values despite continued heat or ethanol exposure. A 10-s heat shock or a 5-s ethanol shock also resulted in a transient cAMP increase 2 min after the pulse. Heat shock or ethanol treatment led to an increase in the amount of catalytic subunits of the cAMP-dependent protein kinase A in the nucleus almost synchronously with the increase of cAMP in the cytoplasm. The concentration of cGMP decreased a few seconds after the beginning of heat shock (44 °C) or ethanol treatment (2.6 M) to approximately 50% of the control level. Exposure to heat shock (44 °C, 1 h) led to an increase in the amount of inositol phosphates 0.5–2 min after the onset of heat shock. Thereafter, inositol phosphate levels dropped to control values despite continued heat exposure. Incubation of growing hyphae with cAMP or 8-Br-cAMP led to a two- to threefold increase of inositol phosphates 10–300 s after the beginning of incubation. Heat treatment furthermore caused a rapid release of calcium from vacuoles as determined by Fura-2 measurement of the calcium content released from isolated vacuoles. These heat-shock-dependent second messenger changes may play a role in the heat-shock-induced phase shifts of the circadian clock and heat-shock-induced conidiation.
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  • 51
    ISSN: 1432-0983
    Keywords: Key words Ergosterol ; Antifungal ; Calcium ; Fenpropimorph ; Azole ; ERG24 gene
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract ERG24 is the structural gene for the C14-sterol reductase in yeast. A lack of activity in that enzyme, mediated either by the morpholine fungicides or the insertional inactivation of ERG24, causes the accumulation of the aberrant sterol ignosterol. Cells producing this sterol are unable to grow aerobically in the routine laboratory medium, YPD. However, growth does occur on a synthetic defined medium. A novel calcium-dependent phenotype associated with alterations in the ergosterol biosynthetic pathway in yeast is described. In addition, reduction of yeast growth with an azole inhibitor of the C-14 sterol de-methylase was also modulated by an excess of calcium ions in the culture medium. These results define a new effect of ergosterol deficiency and provide important practical implications for utilizing morpholine and azole sterol biosynthetic-inhibiting fungicides.
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  • 52
    ISSN: 1432-1238
    Keywords: Key words Blood vessels ; Kidney ; Renal circulation ; Renal vascular resistance ; Calcium ; Ionized calcium ; Rat
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Objectives: Calcium may be indicated in critically ill patients for hemodynamic support. Its well-known action includes peripheral vasoconstriction. Vascular effects of calcium are unknown, however, in the presence of hypertension or in combination with calcium channel blocking drugs, commonly prescribed in the treatment of hypertension. The renal vessels of the spontaneously hypertensive rat (SHR) represent a suitable study model, because their vascular reactivity closely agrees with that in hypertensive humans. The present study should clarify (a) are the renal vessels of SHR responsive to high and low ionized calcium ([Ca++] within the clinical ranges? (b) because release of nitric oxide is calcium ion dependent, are renal vascular responses altered after inhibition of NO synthase? (c) are vascular responses of SHR to hypercalcemia altered by the calcium channel blocking drug verapamil? Animals and interventions: We compared isolated kidneys of SHR and those of two strains of age-matched normotensive rats (NTR) in their responses to high and low [Ca++]. They were perfused with oxygenated, warmed (37 °C) albumin containing Krebs-Henseleit buffer. In protocol A (n = 8 for each rat strain) steady state high [Ca++] (1.88 mmol/l) and low [Ca++] (0.55 mmol/l) were instituted in randomized order. In protocol B (n = 8 for each rat strain) interventions identical to those of protocol A were instituted after inhibition of NO synthase with NG monomethyl-L-arginine (L-NMMA). In protocol C, high and low [Ca++] levels were instituted in SHR after verapamil pretreatment. At each [Ca++] we measured changes in renal flow at constant perfusion pressures of 100 and 150 mm Hg. Results: In SHR (perfusion pressure 100 mm Hg), high [Ca++] induced a decrease in renal flow (–11.8 ± 1.8 % of control), which was significantly greater (p 〈 0.05) than the change (− 6.1 ± 1.5 and − 6.9 ± 1.4 % of control) recorded in the two normotensive strains. In SHR (perfusion pressure 150 mmHg), high [Ca++] induced a decrease in renal flow (− 12 ± 1.3 % of control), also significantly greater (p 〈 0.05) than the changes (− 6.2 ± 1.1 and −5.8 ± 1.7 % of control) in the two normotensive strains. Similar differences and significances were again observed after L-NMMA pretreatment. In SHR, verapamil prevented renal vascular responses in SHR to both high and low [Ca++]. Conclusions: First, renal vascular responses to high [Ca++] in SHR are exaggerated. At the upper end of the hypercalcemia range the observed changes in renal flow at constant perfusion pressure were modest, however, and with lesser degrees of hypercalcemia they may be anticipated to be even less pronounced. Second, effects of high [Ca++] were abolished after verapamil. If these findings are clinically applicable, they are of interest when calcium is infused in patients with hypertension.
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  • 53
    ISSN: 1432-1106
    Keywords: Key words Weaver mice ; Heterozygote ; Cerebellar granule cells ; Calcium ; GIRK2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract  The pleiotropic weaver disease is caused by the mutation of a single amino acid in the G-protein-linked inwardly rectifying K+ channel, GIRK2. In homozygous (wv/wv) animals, the disease is characterized by loss of cerebellar and dopaminergic mesencephalic neurons as well as testicular cells, which produce ataxia, fine tremors, and sterility, respectively. Heterozygous (wv/+) animals show no obvious motor impairments, although some loss of both cerebellar and dopaminergic neurons is observed and wv/+ males become sterile at 3.5 months of age. Abnormal influxes of Na+ and Ca2+ have been linked to cerebellar cell death in wv/wv animals, but it’s not clear whether similar changes are observed in wv/+ animals. To discover whether changes in K+-channel function or intracellular Ca2+ concentrations ([Ca2+]i) play a role in the augmented cell loss observed in wv/+ animals when compared with +/+ animals, we studied cultured cerebellar granule cells prepared from either wv/+ or +/+ animals. Resting [Ca2+]i was elevated in wv/+ relative to +/+ animals. Further, depolarizations of cells with elevated K+ solutions elicited much smaller changes in [Ca2+]i in wv/+ animals than in +/+ animals, presumably due to altered GIRK2 channel function. Both wv/+ and +/+ cells showed similar changes in [Ca2+]i when cells were depolarized by glutamate (1 mM), suggesting that both glutamate receptors and Ca2+ channels were unchanged in wv/+ animals. In summary, our results suggest that wv/+ cerebellar granule cells exhibit elevated resting [Ca2+]i levels and altered K+-channel function, which may contribute to the developmental abnormalities and increased cell death observed.
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  • 54
    ISSN: 1432-2145
    Keywords: Key words Calmodulin ; mRNA ; Calcium ; Pollen tube ; Agapanthus umbellatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  Pollen tube growth is a vital process for angiosperm fertilisation and is dependent on the presence of a tip-focused gradient of cytosolic free calcium ([Ca2+]c). In order to clarify some of the target molecules which convey the Ca2+ signal information, we investigated calmodulin distribution during tube growth. Fluorescently labelled calmodulin was pressure microinjected into pollen tubes and its distribution monitored by confocal microscopy. Calmodulin distributes evenly throughout the cell, but some of its binding sites form a V-shaped collar behind the apical region. This specific association dissipates upon growth arrest, and suggests an interaction of calmodulin with cytoskeletal-bound target proteins. The distribution of calmodulin mRNA was also analysed by microinjection of fluorescently labelled mRNA. No specific pattern was observed, with an even localisation in the body of tube and a lower concentration in the cell apex. Studies with localised application of inhibitors/activators indicate that calmodulin plays a crucial role in tip elongation but does not direct tube orientation.
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  • 55
    ISSN: 1432-069X
    Keywords: Key words Urocanic acid ; Keratinocyte ; Histamine ; Adenylate cyclase ; Calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract UVB irradiation causes suppression of delayed hypersensitivity. Various photoreceptors and mediators of these changes have been proposed, one of which is cis-urocanic acid formed from the naturally occurring trans-urocanic acid in the epidermis on exposure to UV irradiation. The mechanism by which cis-urocanic acid alters the immune system is not fully clarified, but it acts through different mechanisms, perhaps via histamine or histamine-like receptors. Histamine stimulation of keratinocytes induces activation of adenylate cyclase leading to an accumulation of cyclic AMP and an increase in intracellular Ca2+. Thus we investigated the effects of cis-urocanic acid on these transmembrane signaling systems in keratinocytes. Normal human keratinocytes were cultured in serum-free KGM medium. Cyclic AMP was measured by radioimmunoassay. Alterations in intracellular Ca2+ in single living keratinocytes were measured using an inverted fluorescence microscope and an ARGUS-200/CA digital imaging system. Cis-urocanic acid itself did not induce adenylate cyclase activation in cultured normal human keratinocytes. Cis-urocanic acid inhibited histamine-induced cyclic AMP accumulation. It did not affect keratinocyte growth, and did not induce an increase in intracellular Ca2+, but did attenuate the histamine-induced increase in intracellular Ca2+ but not that induced by epinephrine. Cis-urocanic acid acts on keratinocytes via modulation of the effects of histamine.
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  • 56
    ISSN: 1430-3418
    Keywords: Calcium ; Polarity ; Growth ; Signalling ; Cell volume control ; Fucus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This review addresses the role of cytosolic Ca2+in the regulation of embryonic polarity, polarised growth and osmotic control of cell volume with particular emphasis on the marine alga Fucus. Evidence is presented that the control of cell elongation in plants and algae requires the co-ordinate control of cell turgor and vesicle exocytosis, all of which are regulated by cytosolic Ca2+. In the Fucus embryo, polarised growth of the rhizoid cell requires sustained elevation of Ca2+ at the rhizoid apex whereas osmotic cell volume control is effected by transient elevations of cytosolic Ca2+. The mechanisms by which these signals are generated and their different downstream responses are discussed. Answers to questions of how specificity of signalling can be achieved by signal-response pathways which share common components will require more detailed knowledge of the interactions between different components and the spatial and temporal patterns of their activation.
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  • 57
    ISSN: 1432-0428
    Keywords: Keywords Insulin ; Insulin resistance ; Platelets ; Vascular Smooth Muscle ; Calcium ; cGMP ; cAMP ; Nitric oxide ; Prostacyclin.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Type of Medium: Electronic Resource
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  • 58