Carbachol stimulation of phospholipase A2 and insulin secretion in pancreatic islets.
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ABSTRACT:
SUBMITTER: Konrad RJ
PROVIDER: S-EPMC1133156 | biostudies-other | 1992 Oct
REPOSITORIES: biostudies-other
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Project description:BackgroundInsulin secreted by pancreatic islet ?-cells is the principal regulating hormone of glucose metabolism and plays a key role in controlling glucose level in blood. Impairment of the pancreatic islet function may cause glucose to accumulate in blood, and result in diabetes mellitus. Recent studies have shown that mitochondrial dysfunction has a strong negative effect on insulin secretion.MethodsIn order to study the cause of dysfunction of pancreatic islets, a multiple cell model containing healthy and unhealthy cells is proposed based on an existing single cell model. A parameter that represents the function of mitochondria is modified for unhealthy cells. A 3-D hexagonal lattice structure is used to model the spatial differences among ?-cells in a pancreatic islet. The ?-cells in the model are connected through direct electrical connections between neighboring ?-cells.ResultsThe simulation results show that the low ratio of total mitochondrial volume over cytoplasm volume per ?-cell is a main reason that causes some mitochondria to lose their function. The results also show that the overall insulin secretion will be seriously disrupted when more than 15% of the ?-cells in pancreatic islets become unhealthy.ConclusionAnalysis of the model shows that the insulin secretion can be reinstated by increasing the glucokinase level. This new discovery sheds light on antidiabetic medication.
| S-EPMC3981690 | biostudies-literature
Project description:Pancreatic islets play an essential role in regulating blood glucose levels. Age-dependent development of glucose intolerance and insulin resistance results in hyperglycemia, which in turn stimulates insulin synthesis and secretion from aged islets, to fulfill the increased demand for insulin. However, the mechanism underlying enhanced insulin secretion remains unknown. Glutamic acid decarboxylase 67 (GAD67) catalyzes the conversion of glutamate into γ-aminobutyric acid (GABA) and CO2. Both glutamate and GABA can affect islet function. Here, we investigated the role of GAD67 in insulin secretion in young (3 month old) and aged (24 month old) C57BL/6J male mice. Unlike young mice, aged mice displayed glucose-intolerance and insulin-resistance. However, aged mice secreted more insulin and showed lower fed blood glucose levels than young mice. GAD67 levels in primary islets increased with aging and in response to high glucose levels. Inhibition of GAD67 activity using a potent inhibitor of GAD, 3-mercaptopropionic acid, abrogated glucose-stimulated insulin secretion from a pancreatic β-cell line and from young and aged islets. Collectively, our results suggest that blood glucose levels regulate GAD67 expression, which contributes to β-cell responses to impaired glucose homeostasis caused by advanced aging.
| S-EPMC6548491 | biostudies-literature
Project description:A passively operated polydimethylsiloxane (PDMS) microfluidic device was designed for sampling of hormone secretions from eight individual murine pancreatic islets in parallel. Flow control was achieved using a single hand-held syringe and by exploiting inherent fluidic resistances of the microchannels (R(sampling) = 700 ± 20 kPa s mm(-3) at 37 °C). Basal (3 mM) or stimulatory (11 mM) glucose levels were applied to islets, with stimulation timing (t(stim)) minimized to 15 ± 2 s using modified reservoirs. Using enzyme-linked immunosorbent assays (ELISA) for postsampling analyses, we measured statistically equal levels of 1 h insulin secretion (1.26 ± 0.26 and 6.55 ± 1.00 pg islet(-1) min(-1), basal and stimulated; 62 islets) compared to standard, bulk sampling methods (1.01 ± 0.224 and 6.04 ± 1.53 pg islet(-1) min(-1), basal and stimulated; 200 islets). Importantly, the microfluidic platform revealed novel information on single-islet variability. Islet volume measurements with confocal reflectance microscopy revealed that insulin secretion had only limited correlation to islet volume, suggesting a more significant role for cellular architecture and paracrine signaling within the tissue. Compared to other methods using syringe pumps or electroosmotic flow control, this approach provides significant advantages in ease-of-use and device disposability, easing the burden on nonexperts.
| S-EPMC4980096 | biostudies-literature
Project description:Insulin secretion has only exceptionally been investigated in pancreatic islets from healthy young children. It remains unclear whether those islets behave like adult islets despite substantial differences in cellular composition and higher ?-cell replication rates. Islets were isolated from 5 infants/toddlers (11-36 month-old) and perifused to characterize their dynamics of insulin secretion when subjected to various stimuli and inhibitors. Their insulin responses were compared to those previously reported for similarly treated adult islets. Qualitatively, infant islets responded like adult islets to stimulation by glucose, tolbutamide, forskolin (to increase cAMP), arginine and the combination of leucine and glutamine, and to inhibition by diazoxide and CaCl2 omission. This similarity included the concentration-dependency and biphasic pattern of glucose-induced insulin secretion, the dynamics of the responses to non-glucose stimuli and metabolic amplification of these responses. The insulin content was not different, but fractional insulin secretion rates were lower in infant than adult islets irrespective of the stimulus. However, the stimulation index was similar because basal secretion rates were also lower in infant islets. In conclusion, human ?-cells are functionally mature by the age of one year, before expansion of their mass is complete. Their responsiveness (stimulation index) to all stimuli is not smaller than that of adult ?-cells. Yet, under basal and stimulated conditions, they secrete smaller proportions of their insulin stores in keeping with smaller in vivo insulin needs during infancy.
| S-EPMC5091846 | biostudies-literature
Project description:Lorcaserin is a serotonergic agonist specific to the 5-hydroxytryptamine 2c receptor (5-HT2CR) that is FDA approved for the long-term management of obesity with or without at least one weight-related comorbidity. Lorcaserin can restrain patients' appetite and improve insulin sensitivity and hyperinsulinemia mainly through activating 5-HT2CR in the hypothalamus. It is known that the mCPP, a kind of 5-HT2CR agonist, decreases plasma insulin concentration in mice and previous research in our laboratory found that mCPP inhibited glucose-stimulated insulin secretion (GSIS) by activating 5-HT2CR on the β cells. However, the effect of lorcaserin on GSIS of pancreatic β cell has not been studied so far. The present study found that 5-HT2CR was expressed in both mouse pancreatic β cells and β-cell-derived MIN6 cells. Dose-dependent activation of 5-HT2CR by lorcaserin suppressed GSIS and SB242084 or knockdown of 5-HT2CR abolished lorcaserin's effect in vitro. Additionally, lorcaserin also suppressed GSIS in high-fat diet (HFD)-fed mice in dose-dependent manner. Lorcaserin did not change insulin synthesis ATP content, but lorcaserin decrease cytosolic free calcium level [(Ca2+)i] in MIN6 cells stimulated with glucose and also inhibit insulin secretion and (Ca2+)i in MIN6 treated with potassium chloride. Furthermore, stimulation with the L-type channel agonist, Bay K8644 did not restore GSIS in MIN6 exposed to lorcaserin. Lorcaserin inhibits the cAMP generation of MIN6 cells and pretreatment with the Gα i/o inhibitor pertussis toxin (PTX), abolished lorcaserin-induced suppression of GSIS in β cells, while membrane-permeable cAMP analogue db-cAMP had same effect as PTX. These date indicated lorcaserin coupled to PTX-sensitive Gα i/o proteins in β cells reduced intracellular cAMP level and Ca2+ influx, thereby causing GSIS dysfunction of β cell. These results highlight a novel signaling mechanism of lorcaserin and provide valuable insights into the further investigation of 5-HT2CR functions in β-cell biology and it also provides guidance for the clinical application of lorcaserin.
| S-EPMC8602196 | biostudies-literature
Project description:Altered secretion of insulin as well as glucagon has been implicated in the pathogenesis of Type 2 diabetes (T2D), but the mechanisms controlling glucagon secretion from ?-cells largely remain unresolved. Therefore, we studied the regulation of glucagon secretion from ?TC1-6 (?TC1 clone 6) cells and compared it with insulin release from INS-1 832/13 cells. We found that INS-1 832/13 and ?TC1-6 cells respectively secreted insulin and glucagon concentration-dependently in response to glucose. In contrast, tight coupling of glycolytic and mitochondrial metabolism was observed only in INS-1 832/13 cells. Although glycolytic metabolism was similar in the two cell lines, TCA (tricarboxylic acid) cycle metabolism, respiration and ATP levels were less glucose-responsive in ?TC1-6 cells. Inhibition of the malate-aspartate shuttle, using phenyl succinate (PhS), abolished glucose-provoked ATP production and hormone secretion from ?TC1-6 but not INS-1 832/13 cells. Blocking the malate-aspartate shuttle increased levels of glycerol 3-phosphate only in INS-1 832/13 cells. Accordingly, relative expression of constituents in the glycerol phosphate shuttle compared with malate-aspartate shuttle was lower in ?TC1-6 cells. Our data suggest that the glycerol phosphate shuttle augments the malate-aspartate shuttle in INS-1 832/13 but not ?TC1-6 cells. These results were confirmed in mouse islets, where PhS abrogated secretion of glucagon but not insulin. Furthermore, expression of the rate-limiting enzyme of the glycerol phosphate shuttle was higher in sorted primary ?- than in ?-cells. Thus, suppressed glycerol phosphate shuttle activity in the ?-cell may prevent a high rate of glycolysis and consequently glucagon secretion in response to glucose. Accordingly, pyruvate- and lactate-elicited glucagon secretion remains unaffected since their signalling is independent of mitochondrial shuttles.
| S-EPMC7234840 | biostudies-literature
Project description:Increases in mitochondrial [Ca(2+)] ([Ca(2+)](m)) have recently been reported to cause long-term alterations in cellular ATP production [Jouaville, Bastianutto, Rutter and Rizzuto (1999) Proc. Natl. Acad. Sci. U.S.A. 96, 13807-13812]. We have determined the importance of this phenomenon for nutrient sensing in pancreatic islets and beta-cells by imaging adenovirally expressed Ca(2+) and ATP sensors (aequorin and firefly luciferase). [Ca(2+)](m) increases provoked by KCl or tolbutamide evoked an immediate increase in cytosolic and mitochondrial free ATP concentration ([ATP](c) and [ATP](m) respectively) at 3 mM glucose. Subsequent increases in [glucose] (to 16 or 30 mM) then caused a substantially larger increase in [ATP](c) and [ATP](m) than in naïve cells, and pre-stimulation with tolbutamide led to a larger secretory response in response to glucose. Whereas pre-challenge of islets with KCl altered the response to high [glucose] of [Ca(2+)](m) from periodic oscillations to a sustained elevation, oscillations in [ATP](c) were observed neither in naïve nor in stimulated islets. Hence, long-term potentiation of mitochondrial ATP synthesis is a central element in nutrient recognition by pancreatic islets.
| S-EPMC1221556 | biostudies-other
Project description:Epidemiologic evidence has linked chronic exposure to inorganic arsenic (iAs) with an increased prevalence of diabetes mellitus. Laboratory studies have identified several mechanisms by which iAs can impair glucose homeostasis. We have previously shown that micromolar concentrations of arsenite (iAs(III)) or its methylated trivalent metabolites, methylarsonite (MAs(III)) and dimethylarsinite (DMAs(III)), inhibit the insulin-activated signal transduction pathway, resulting in insulin resistance in adipocytes. Our present study examined effects of the trivalent arsenicals on insulin secretion by intact pancreatic islets isolated from C57BL/6 mice. We found that 48-hour exposures to low subtoxic concentrations of iAs(III), MAs(III) or DMAs(III) inhibited glucose-stimulated insulin secretion (GSIS), but not basal insulin secretion. MAs(III) and DMAs(III) were more potent than iAs(III) as GSIS inhibitors with estimated IC(50)?0.1 ?M. The exposures had little or no effects on insulin content of the islets or on insulin expression, suggesting that trivalent arsenicals interfere with mechanisms regulating packaging of the insulin transport vesicles or with translocation of these vesicles to the plasma membrane. Notably, the inhibition of GSIS by iAs(III), MAs(III) or DMAs(III) could be reversed by a 24-hour incubation of the islets in arsenic-free medium. These results suggest that the insulin producing pancreatic ?-cells are among the targets for iAs exposure and that the inhibition of GSIS by low concentrations of the methylated metabolites of iAs may be the key mechanism of iAs-induced diabetes.
| S-EPMC3670188 | biostudies-literature
Project description:Insulin is secreted from the pancreatic ?-cells in response to elevated glucose. In intact islets the capacity for insulin release is determined by a complex interplay between different cell types. This has made it difficult to specifically assess the role of ?-cell defects to the insulin secretory impairment in type 2 diabetes. Here we describe a new approach, based on optogenetics, that enables specific investigation of ?-cells in intact islets. We used transgenic mice expressing the light-sensitive cation channel Channelrhodopsin-2 (ChR2) under control of the insulin promoter. Glucose tolerance in vivo was assessed using intraperitoneal glucose tolerance tests, and glucose-induced insulin release was measured from static batch incubations. ChR2 localization was determined by fluorescence confocal microscopy. The effect of ChR2 stimulation with blue LED light was assessed using Ca(2+) imaging and static islet incubations. Light stimulation of islets from transgenic ChR2 mice triggered prompt increases in intracellular Ca(2+). Moreover, light stimulation enhanced insulin secretion in batch-incubated islets at low and intermediate but not at high glucose concentrations. Glucagon release was not affected. Beta-cells from mice rendered diabetic on a high-fat diet exhibited a 3.5-fold increase in light-induced Ca(2+) influx compared with mice on a control diet. Furthermore, light enhanced insulin release also at high glucose in these mice, suggesting that high-fat feeding leads to a compensatory potentiation of the Ca(2+) response in ?-cells. The results demonstrate the usefulness and versatility of optogenetics for studying mechanisms of perturbed hormone secretion in diabetes with high time-resolution and cell-specificity.
| S-EPMC4593566 | biostudies-literature
Project description:BACKGROUND: Because insulin is the main regulator of glucose homeostasis, quantitative models describing the dynamics of glucose-induced insulin secretion are of obvious interest. Here, a computational model is introduced that focuses not on organism-level concentrations, but on the quantitative modeling of local, cellular-level glucose-insulin dynamics by incorporating the detailed spatial distribution of the concentrations of interest within isolated avascular pancreatic islets. METHODS: All nutrient consumption and hormone release rates were assumed to follow Hill-type sigmoid dependences on local concentrations. Insulin secretion rates depend on both the glucose concentration and its time-gradient, resulting in second-and first-phase responses, respectively. Since hypoxia may also be an important limiting factor in avascular islets, oxygen and cell viability considerations were also built in by incorporating and extending our previous islet cell oxygen consumption model. A finite element method (FEM) framework is used to combine reactive rates with mass transport by convection and diffusion as well as fluid-mechanics. RESULTS: The model was calibrated using experimental results from dynamic glucose-stimulated insulin release (GSIR) perifusion studies with isolated islets. Further optimization is still needed, but calculated insulin responses to stepwise increments in the incoming glucose concentration are in good agreement with existing experimental insulin release data characterizing glucose and oxygen dependence. The model makes possible the detailed description of the intraislet spatial distributions of insulin, glucose, and oxygen levels. In agreement with recent observations, modeling also suggests that smaller islets perform better when transplanted and/or encapsulated. CONCLUSIONS: An insulin secretion model was implemented by coupling local consumption and release rates to calculations of the spatial distributions of all species of interest. The resulting glucose-insulin control system fits in the general framework of a sigmoid proportional-integral-derivative controller, a generalized PID controller, more suitable for biological systems, which are always nonlinear due to the maximum response being limited. Because of the general framework of the implementation, simulations can be carried out for arbitrary geometries including cultured, perifused, transplanted, and encapsulated islets.
| S-EPMC3138450 | biostudies-other