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  • 1
    ISSN: 0921-4534
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Physics
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Ca2+ signalling ; diabetes mellitus ; glucose insulin secretion ; islets of Langerhans ; oscillations pancreatic beta cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Mechanisms of pulsatile insulin release in man were explored by studying the induction of oscillatory Ca2+ signals in individual beta cells and islets isolated from the human pancreas. Evidence was provided for a glucose-induced closure of ATP-regulated K+ channels, resulting in voltage-dependent entry of Ca2+. The observation of step-wise increases of capacitance in response to depolarizing pulses suggests that an enhanced influx of Ca2+ is an effective means of stimulating the secretory activity of the isolated human beta cell. Activation of muscarinic receptors (1–10 μmol/l carbachol) and of purinergic P2 receptors (0.01–1 μmol/l ATP) resulted in repetitive transients followed by sustained elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i). Periodic mobilisation of intracellular calcium was seen also when injecting 100 μmol/l GTP-γ-S into beta cells hyperpolarized to −70 mV. Individual beta cells responded to glucose and tolbutamide with increases of [Ca2+]i, manifested either as large amplitude oscillations (frequency 0.1–0.5/min) or as a sustained elevation. Glucose regulation was based on sudden transitions between the basal and the two alternative states of raised [Ca2+]i at threshold concentrations of the sugar characteristic for the individual beta cells. The oscillatory characteristics of coupled cells were determined collectively rather than by particular pacemaker cells. In intact pancreatic islets the glucose induction of well-synchronized [Ca2+]i oscillations had its counterpart in 2–5 min pulses of insulin. Each of these pulses could be resolved into regularly occurring short insulin transients. It is concluded that glucose stimulation of insulin release in man is determined by the number of beta cells entering into a state with Ca2+-induced secretory pulses.
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  • 3
    ISSN: 1432-0428
    Keywords: Beta cells ; islets ; insulin ; diabetes mellitus ; pancreas
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary In vitro studies on purified rat beta cells have indicated a functional diversity among insulincontaining cells. Intercellular differences were found in the rates of glucose-induced insulin synthesis and release. They are attributed to differences in cellular thresholds for glucose utilization and oxidation, as can be caused by varying activities in rate limiting steps such as glucokinase-dependent phosphorylation. The percent of functionally active beta cells increases dose-dependently with the glucose concentration, making cellular heterogeneity and its regulation by glucose major determinants for the dose-response curves of the total beta-cell population. Beta cells which are already responsive to low glucose concentrations are characterized by a higher content in pale immature granules; their activated biosynthetic and secretory activity accounts for preferential release of newly-formed hormone by the total beta-cell population. At any glucose level, the amplitude of insulin release depends on the percent glucose-activated cells and their cyclic AMP content, an integrator of (neuro)hormonal influences. The in vitro described heterogeneity in beta-cell functions may bear physiological relevance as several of its characteristics are also detectable in intact pancreatic tissue; furthermore, in vitro signs of heterogeneity can be altered by prior in vivo treatment indicating that they express properties of the cells in their in situ configuration. Elevated basal levels of (pro)insulin may reflect the existence of an increased number of beta cells that are activated at low physiologic glucose concentrations. Reductions in stimulated insulin levels can be caused by decreased numbers of beta cells that are activated at the prevailing glucose concentration or by insufficient cyclic AMP levels in beta cells, possibly as a result of inadequate signalling from hormones of local or distal origin. Only few markers are currently available with which to explore these mechanisms in vivo. Additional markers and tests should help assess the possible role of variations in beta-cell heterogeneity in the pathogenesis of diabetes mellitus.
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  • 4
    ISSN: 1432-0428
    Keywords: Keywords Diabetes mellitus ; transplantation ; islets ; beta cells ; autoantibodies.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Islet allografts in insulin-dependent diabetic (IDDM) patients exhibit variable survival lengths and low rates of insulin-independence despite treatment with anti-T-cell antibodies and maintenance immunosuppression. Use of poorly characterized freshly isolated preparations makes it difficult to determine whether failures are caused by variations in donor tissue. This study assesses survival of standardized beta-cell allografts in C-peptide negative IDDM patients on maintenance immunosuppression following kidney transplantation and without receiving anti-T-cell antibodies or additional immunosuppression. Human islets were isolated from pancreatic segments after maximal 20 h cold-preservation. During culture, preparations were selected according to quality control tests and combined with grafts with standardized cell composition (≥ 50 % beta cells), viability ( ≥ 90 % ), total beta-cell number (1 to 2 · 106/kg body weight) and insulin-producing capacity (2 to 4 nmol · graft–1· h–1). Grafts were injected in a liver segment through the repermeabilized umbilical vein. After 2 weeks C-peptide positivity, four out of seven recipients became C-peptide negative; two of them were initially GAD65-antibody positive and exhibited a rise in titre during graft destruction. The other three patients remained C-peptide positive for more than 1 year, two of them becoming insulin-independent with near-normal fasting glycaemia and HbA1 c; they remained GAD65- and islet cell antibody negative. The three patients with surviving grafts presented a history of anti-thymocyte globulin therapy at kidney transplantation. Long-term surviving grafts increased C-peptide release following intravenous glucagon or oral glucose but not following intravenous glucose. Thus, cultured human beta-cells can survive for more than 1 year in IDDM patients on maintenance anti-rejection therapy for a prior kidney graft and without the need for an increased immunosuppression at the time of implantation. The use of functionally standardized beta-cell grafts helps to identify recipient and graft factors which influence their survival and metabolic effects. Insulin-independence can be achieved by injection of 1.5 million beta-cells per kg body weight in a liver segment. These beta-cell implants respond well to adenylcyclase activators but poorly to glucose. [Diabetologia (1998) 41: 452–459]
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  • 5
    ISSN: 1432-0428
    Keywords: Keywords Glucagon receptors ; GLP-1 receptors ; GIP receptors ; beta cells ; cyclic AMP ; insulin ; diabetes ; glucose competence
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Aims/hypothesis. Synergism between glucose and cAMP in the stimulation of insulin secretion has been suggested to regulate beta cells. This study assessed the importance of an interaction between glucose and cAMP in the stimulation of insulin secretion from human islet cells by investigating expression and functional activity of receptors recognising glucagon, glucagon-like peptide-1 (7–36)amide (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). Methods. Expression of the glucagon, GLP-1 and GIP receptors in human islets was investigated by northern blots and reverse transcription-polymerase chain reaction analysis. Functional activity of these receptors was assessed by the effects of peptides (agonists and antagonists) on glucose-induced insulin release. Results. Human islet cells express transcripts encoding glucagon, GLP-1 and GIP receptors. Glucose (10 mmol/l) stimulated insulin release 4.5 ± 0.6-fold over basal (2.5 mmol/l). This glucose effect was amplified by 10 nmol/l GLP-1, GIP or glucagon. It was reduced by 51 ± 6 % in the presence of 1 μmol/l of the glucagon-receptor antagonist des-His1-[Glu9]-glucagon-amide (n = 8; p 〈 0.05), indicating participation of endogenously released glucagon in the process of glucose-induced insulin release. The glucagon-receptor antagonist also suppressed the potentiation of glucose-induced insulin release by addition of 10 nmol/l glucagon. Conclusion/interpretation. These data suggest that human beta cells express functional glucagon receptors which can, similar to incretin hormone receptors, generate synergistic signals for glucose-induced insulin secretion. [Diabetologia (2000) 43: 1012–1019]
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  • 6
    ISSN: 1432-0428
    Keywords: Keywords Glucose-6-phosphatase ; insulin release ; glucose metabolism ; glucocorticoid sensitivity ; transgenic mice.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Glucose-6-phosphatase (G6Pase) activity and the rate of glucose cycling are increased in islets from animal models of Type II (non-insulin-dependent) diabetes mellitus. Glucocorticoid treatment further stimulates these processes and inhibits glucose-induced insulin release. To determine whether these effects result from a direct action of glucocorticoids on the beta-cells, we used isolated islets. The islets were from transgenic mice overexpressing the glucocorticoid receptor in their beta-cells to increase the cells' sensitivity to glucocorticoid. Islets from transgenic and non-transgenic control mice utilized and oxidized the same amount of glucose. In contrast, islet G6Pase activity was 70 % higher, glucose cycling was increased threefold and insulin release was 30 % lower in islets from transgenic mice. Hepatic G6Pase activity was the same in transgenic and control mice. Dexamethasone administration increased G6Pase activity and glucose cycling and decreased insulin release in both transgenic and control mouse islets. We conclude that glucocorticoids stimulate islet G6Pase activity and glucose cycling by acting directly on the beta-cell. That activity may be linked to the inhibition of insulin release. [Diabetologia (1998) 41: 634–639]
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  • 7
    ISSN: 1460-9568
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Vascular inflammation is well known for its ability to compromise the function of the blood–brain barrier (BBB). Whether inflammation on the parenchymal side of the barrier, such as that associated with Parkinson's-like dopamine (DA) neuron lesions, similarly disrupts BBB function, is unknown. We assessed BBB integrity by examining the leakage of FITC-labeled albumin or horseradish peroxidase from the vasculature into parenchyma in animals exposed to the DA neurotoxin 6-hydroxydopamine (6OHDA). Unilateral injections of 6OHDA into the striatum or the medial forebrain bundle produced increased leakage in the ipsilateral substantia nigra and striatum 10 and 34 days following 6OHDA. Microglia were markedly activated and DA neurons were reduced by the lesions. The areas of BBB leakage were associated with increased expression of P-glycoprotein and β3-integrin expression suggesting, respectively, a compensatory response to inflammation and possible angiogenesis. Behavioural studies revealed that domperidone, a DA antagonist that normally does not cross the BBB, attenuated apomorphine-induced stereotypic behaviour in animals with 6OHDA lesions. This suggests that drugs which normally have no effect in brain can enter following Parkinson-like lesions. These data suggest that the events associated with DA neuron loss compromise BBB function.
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  • 8
    ISSN: 1432-0800
    Source: Springer Online Journal Archives 1860-2000
    Topics: Energy, Environment Protection, Nuclear Power Engineering , Medicine
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1432-0428
    Keywords: Islets ; beta cells ; culture ; glucose ; growth hormone
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This study quantifies the survival of purified single rat beta cells under different culture conditions. Less than 10% of the cells survive 9 days of culture in Ham's F10 medium without supplements. Addition of fetal calf serum (5%) increases cell survival to 54% in the absence and to 78% in the presence of isobutylmethylxanthine (50 μmol/l). The effect of serum is explained, at least partly, by the presence of albumin and of low molecular weight constituents. In serum-free Ham's F10 with 50 μmol/l isobutylmethylxanthine, 75% of cells survive after the addition of bovine serum albumin (1%) and of ultroser (0.2%), a commercial serum substitute. Survival of at least 75% of cells is also maintained in Ham's F10 with isobutylmethylxanthine plus albumin, and supplemented by metabolizable nutrients or by the peptides glucagon (10−8 mol/l) or growth hormone (1 μg/ml) plus insulin like growth factor-I (50 ng/ml). d-Glucose increases beta-cell survival in a dosedependent manner up to 10 mmol/l; a beneficial effect is also observed with other metabolizable compounds (leucine and glutamine) but not with non-metabolizable monosaccharides. Glucose-induced survival of islet beta cells can be attributed to its dose-dependent recruitment of cells into metabolic activities; however, a 9-day exposure to excessively high nutrient concentrations (〉 20 mmol/l glucose) is deleterious to the cells. These results define culture media, with or without serum, wherein at least 75% of single rat islet beta cells can survive for a minimum of 9 days. This will allow for studies on beta-cell toxic conditions and potentially protective agents. The data also serve as basis for developing media with better survival of beta cells in cultured aggregates.
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  • 10
    ISSN: 1432-0428
    Keywords: Key words Islets, beta cells, culture, glucose, growth hormone.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary This study quantifies the survival of purified single rat beta cells under different culture conditions. Less than 10 % of the cells survive 9 days of culture in Ham's F10 medium without supplements. Addition of fetal calf serum (5 %) increases cell survival to 54 % in the absence and to 78 % in the presence of isobutylmethylxanthine (50 µmol/l). The effect of serum is explained, at least partly, by the presence of albumin and of low molecular weight constituents. In serum-free Ham's F10 with 50 µmol/l isobutylmethylxanthine, 75 % of cells survive after the addition of bovine serum albumin (1 %) and of ultroser (0.2 %), a commercial serum substitute. Survival of at least 75 % of cells is also maintained in Ham's F10 with isobutylmethylxanthine plus albumin, and supplemented by metabolizable nutrients or by the peptides glucagon (10–8 mol/l) or growth hormone (1 µg/ml) plus insulin like growth factor-I (50 ng/ml). D-Glucose increases beta-cell survival in a dose-dependent manner up to 10 mmol/l; a beneficial effect is also observed with other metabolizable compounds (leucine and glutamine) but not with non-metabolizable monosaccharides. Glucose-induced survival of islet beta cells can be attributed to its dose-dependent recruitment of cells into metabolic activities; however, a 9-day exposure to excessively high nutrient concentrations (〉20 mmol/l glucose) is deleterious to the cells. These results define culture media, with or without serum, wherein at least 75 % of single rat islet beta cells can survive for a minimum of 9 days. This will allow for studies on beta-cell toxic conditions and potentially protective agents. The data also serve as basis for developing media with better survival of beta cells in cultured aggregates. [Diabetologia (1994) 37: 15–21]
    Type of Medium: Electronic Resource
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