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  • 1
    ISSN: 1432-136X
    Keywords: Aequorin ; Calcium ; Sarcoplasmic reticulum ; Contraction ; Excitation-contraction coupling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Steps involved in excitation-contraction coupling in mammalian myocardium have been derived using a relatively limited number of animal species. However, the use of animal models for investigations into excitation-contraction coupling in normal and disease states has encompassed a wide range of animal species. We addressed the question as to whether excitation-contraction coupling as currently understood applies to intracellular calcium handling in myocardium from multiple mammalian species, amphibian, and avian myocardium. The bioluminescent calcium indicator aequorin was used to record intracellular calcium transients in both ventricular and atrial tissue. We report that in all mammalian and avian species studied the calcium transient recorded in both ventricular and atrial myocardium is monophasic and reflects calcium release and re-uptake by the sarcoplasmic reticulum. In contrast, the Ca2+ transient recorded from salamander myocardium is prolonged relative to mammalian and avian myocardium, and appears to reflect in part trans-sarcolemmal calcium entry. Only in diseased myocardium derived from human and swine myocardium was a second component detected in the calcium transient. These data indicate that sarcoplasmic reticulum calcium handling is pivotal in excitation-contraction coupling for multiple species with differing physiologies. Also, in disease states, intracellular calcium handling is often affected with resultant alterations in the time-course and/or configuration of the calcium transient.
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  • 2
    ISSN: 1432-1424
    Keywords: cell-to-cell junctions ; ionic coupling ; calmodulin ; anticalmodulin drugs ; calcium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary In many cell systems, the permeability of membrane junctions is modulated by the cytoplasmic level of free Ca++. To examine whether the calcium-dependent regulatory protein calmodulin is involved in this process, the ability of anticalmodulin drugs to influence the cell-to-cell passage of injected current and an organic tracer was tested using standard intracellular glass microelectrode techniques. Several antipsychotics and local anesthetics were found to block junctional communication in the epidermis of the beetleTenebrio molitor. Treatment of the epidermis with chlorpromazine (0.25 mM) raised intercellular resistance two- to threefold within 20 to 25 min; cell-to-cell passage of electrical current was abolished within 41±5 min. Loss of electrotonic coupling was accompanied by a block in the cell-to-cell movement of the organic tracer carboxyfluorescein. The reaction is fully reversible, with normal electrotonic coupling being restored within 2 to 4 hr. Other antipsychotics and local anesthetics had similar effects on cell coupling. The order of potency found was: trifluoperazine〉thioridazine〉 d-butaclamol〉chlorprothixine=chlorpromazine〉 l-butaclamol〉 dibucaine〉tetracaine. The relative uncoupling potencies of these drugs correlate well with their known ability to inhibit calmodulin-dependent phosphodiesterase activity. Other anesthetic compounds, procaine and pentobarbital, did not block cell-to-cell communication. Altering the extracellular Ca++ concentration did not affect the rate of uncoupling by antipsychotics, while chelation of extracellular Ca++ with EGTA raised electrotonic coupling. The effect of three metabolic inhibitors on coupling was also examined. Iodoacetate uncoupled the epidermal cells while DNP and cyanide did not. These results are discussed in terms of possible mechanisms by which calmodulin may control junctional communication in this tissue.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Pflügers Archiv 395 (1982), S. 75-77 
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Vascular smooth muscle ; Reversibly hyperpermeable cells ; Calcium indicators ; Aequorin ; Phenylephrine ; Angiotensin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The bioluminescent calcium indicator aequor in was successfully loaded into vascular smooth muscle cells ofAmphiuma tridactylum by either microinjection or a new method which makes the cells reversibly hyperpermeable. Both gave similar results; however, the latter method produced larger signals. Vasoconstrictors produced a sustained contraction and a light (calcium) response consisting of two component: a large transient followed by a smaller, sustained response. Electrical stimulation produced a light transient that was much briefer than the contraction. These results suggest that tension can be maintained in smooth muscle in the presence of lower calcium levels than those present during force development.
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  • 4
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Mammalian cardiac muscles ; Reversibly hyperpermeable cells ; Calcium indicators ; Aequorin ; Isoproterenol ; Caffeine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The bioluminescent calcium indicator aequorin was successfully loaded into mammalian working myocardium of ferrets by a chemical procedure which makes the cells reversibly hyperpermeable through exposure to Ethylenebis-(oxyethylenenitrilo) tetraacetic acid (EGTA). After undergoing the loading procedure, developed tension at Lmax was 103±26% of the control, which indicates that the muscles regained normal function. The configurations of the aequorin signals (i.e., calcium transients) and their responses to drugs were the same as reported after microinjection of aequorin. The peak of the Ca++ transient determined by the method of fractional luminescence at 3s intervals of stimulation, 2.5mM [Ca++]o, 22.5°C was 1.1μM; this value is similar to that reported for microinjection. These results indicate that the chemical loading procedure is a useful alternative to microinjection for loading aequorin into mammalian working myocardium.
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  • 5
    ISSN: 1432-2013
    Keywords: Excitation-contraction coupling ; Cell calcium ; Cardiac muscle ; Thyroid hormone ; Aequorin
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract The purpose of this study was to determine the influence of thyroid hormone on tension development and the intracellular calcium transient in mammalian ventricular muscle. A hyperthyroid (H) state was induced in ferrets by subcutaneous injection ofl-thyroxine, 0.3 mg/kg daily, for 2–3 weeks. One-half of the age matched control group (C) were injected with vehicle. Aequorin was loaded into the cells of ferret papillary muscles by a chemical procedure. The muscles were stimulated at 0.33 Hz and isometric tension and the calcium transient were simultaneously recorded at 30°C. Peak isometric tension in mN/mm2 (±SD) was 15.4±7.2 and 16.2±7.9 for C (n=8) and H (n=9) respectively. The time to peak tension and time to 80% relaxation from peak of tension were reduced by 22% and 28% respectively in H compared to C. After stimulation, the calcium transient reached a maximum in 56±6 ms in C and in 47±5 ms in H. The time to 80% decay of the peak calcium transient was 95±8 ms and 68±5 ms for C and H respectively. The ratio of the aequorin luminescence at the peak of the calcium transient over the calculated maximum luminescence,L max, were compared and they were not different. At 22°C Log (L/L max) was −3.3±0.1 in C (n=4) and −3.4±0.3 in H (n=3). These results indicate that the thyroid state influences the time course of the calcium transient and are consistent with the abbreviation in the duration of contraction that is observed in the hyperthyroid state.
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  • 6
    ISSN: 0730-2312
    Keywords: genome ; calmodulin ; smooth muscle ; immunohistochemistry ; heart ; development ; protein kinase ; tissue selective ; calcium ; signal transduction ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Chemistry and Pharmacology , Medicine
    Notes: We report that the genetic locus that encodes vertebrate smooth muscle and nonmuscle myosin light chain kinase (MLCK) and kinase-related protein (KRP) has a complex arrangement and a complex pattern of expression. Three proteins are encoded by 31 exons that have only one variation, that of the first exon of KRP, and the genomic locus spans approximately 100 kb of DNA. The three proteins can differ in their relative abundance and localization among tissues and with development. MLCK is a calmodulin (CaM) regulated protein kinase that phosphorylates the light chain of myosin II. The chicken has two MLCK isoforms encoded by the MLCK/KRP locus. KRP does not bind CaM and is not a protein kinase. However, KRP binds to and regulates the structure of myosin II. Thus, KRP and MLCK have the same subcellular target, the myosin II molecular motor system. We examined the tissue and cellular localization of KRP and MLCK in the chicken embryo and in adult chicken tissues. We report on the selective localization of KRP and MLCK among and within tissues and on a differential distribution of the proteins between embryonic and adult tissues. The results fill a void in our knowledge about the organization of the MLCK/KRP genetic locus, which appears to be a late evolving regulatory paradigm, and suggest an independent and complex regulation of expression of the gene products from the MLCK/KRP genetic locus that may reflect a basic principle found in other eukaryotic gene clusters that encode functionally linked proteins. J. Cell. Biochem. 70:402-413, 1998. © 1998 Wiley-Liss, Inc.
    Additional Material: 5 Ill.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Cardiovascular drugs and therapy 1 (1988), S. 621-624 
    ISSN: 1573-7241
    Keywords: calcium ; congestive heart failure ; internal calcium ; calcium overload
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
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  • 8
    ISSN: 1572-9729
    Keywords: calcium ; fine roots ; nitrogen ; northern hardwood ; nutrient dynamics ; seasonality ; soils ; sulfur ; vegetation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Seasonal dynamics of S, Ca and N were examined at the Huntington Forest, a northern hardwood ecosystem in the central Adirondacks of New York for a period of 34 months (1985–1988). Solute concentrations and fluxes in bulk precipitation, throughfall (TF) and leachates from the forest floor, E horizon and B horizon were quantified. Both above and below-ground elemental fluxes mediated by vegetation (e.g. uptake, litter inputs, and fine roots production) were also determined. The roles of abiotic and biotic processes were ascertained based on both changes in solute concentrations through the strata of the ecosystem as well as differences between dormant and growing seasons. Concentrations of SO4 2−, NO3 −, NH4 + and Ca2+ were greater in TF than precipitation. Forest floor leachates had greater concentrations of SO4 2−, NO3 − + NH4 + and Ca2+ (9, 6 and 77 µeq L−1, respectively) than TF. There were differences in concentrations of ions in leachates from the forest floor between the dormant and growing seasons presumably due to vegetation uptake and microbial immobilization. Concentrations and fluxes of NO3 − and NH; were greatest in early spring followed by a rapid decline which coincided with a demand for N by vegetation in late spring. Vegetation uptake (44.7 kg N ha−1 yr−1 ) could account for the low leaching rates of N03 −. Within the mineral soil, changes with soil depth and the absence of seasonal patterns suggest that cation exchange (Ca+) or anion sorption (SO4 2−) are primarily responsible for regulating solute concentrations. The increase in SO4 2− concentration after leachates passed through the mineral soil may be attributed to desorption of sulfate that was adsorbed during an earlier period when SO4 2− concentrations would have been greater due to elevated S inputs.
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