| 1. |
- Berts, Alf, et al.
(författare)
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Oscillatory Ca2+ signaling in somatostatin-producing cells from the human pancreas
- 1997
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Ingår i: Metabolism. - 0026-0495 .- 1532-8600. ; 46:4, s. 366-369
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Tidskriftsartikel (refereegranskat)abstract
- Oscillatory Ca2+ signaling was studied in human somatostatin-releasing pancreatic δ cells identified by immunostaining. A ratiometric fura-2 technique was used for measuring cytoplasmic concentrations of Ca2+ and Sr2+ in δ cells exposed to the respective cation. Rhythmic activity in terms of slow (frequency, 0.1 to 0.4 per minute) oscillations from close to the basal level was seen in the presence of 3 to 20 mmol/L glucose during superfusion with medium containing 2.6 to 5 mmol/L Ca2+ or 5 mmol/L Sr2. These oscillations could be transformed into a sustained increase by decreasing extracellular Ca2+ or adding 1 mmol/L tolbutamide or 20 nmol/L glucagon. Addition of glucagon to a medium containing 20 mmol/L glucose resulted in the generation of short (< 30 seconds) transients, which disappeared upon exposure to 100 nmol/L of the intracellular Ca2+-adenosine triphosphatase (ATPase) inhibitor thapsigargin. When analyzing small aggregates of islet cells, it became evident that oscillatory activity in δ cells can be synchronous with that in adjacent non—δ cells. It is concluded that secretion of pancreatic somatostatin in man involves Ca2+ signaling similar to that regulating the pulsatile release of insulin.
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| 2. |
- Berts, Alf, et al.
(författare)
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Suppression of Ca2+ oscillations in glucagon-producing alfa2-cells by insulin/glucose and amino acids
- 1996
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Ingår i: Biochimica et Biophysica Acta. - 0006-3002 .- 1878-2434. ; 1310:2, s. 212-216
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Tidskriftsartikel (refereegranskat)abstract
- The cytoplasmic Ca2+ concentration ([Ca2+]i) was continuously monitored in single glucagon-producing α2-cells isolated from the mouse pancreas and later identified by immunostaining. Up to 60% of the α2-cells exhibited spontaneous [Ca2+]i oscillations (frequency 0.1–0.3/min) in a medium containing 3 mM glucose. In originating from a basal level of 60–100 nM, reaching peak values of 300–400 nM and promptly disappearing after blocking voltage-dependent Ca2+ channels with methoxyverapamil, the oscillations resembled those in insulin-releasing β-cells stimulated by glucose. The oscillatory activity was suppressed when combining elevation of glucose to 20 mM with the addition of 2–2000 ng/ml insulin. Whereas 10 mM of l-arginine or l-glycine transformed the oscillations into sustained elevation of [Ca2+];, there was no response to 1 mM tolbutamide or 0.1–1 mM γ-aminobutyric acid. The observations that α2-cells differ from islet cells secreting insulin and somatostatin in responding to adrenaline with mobilisation of intracellular calcium can be used for their rapid identification. It is suggested that the oscillations reflect periodic entry of Ca2+ due to variations of the membrane potential.
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| 3. |
- Chow, R H, et al.
(författare)
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Coincidence of early glucose-induced depolarization with lowering of cytoplasmic Ca2+ in mouse pancreatic beta-cells
- 1995
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Ingår i: Journal of Physiology. - 0022-3751 .- 1469-7793. ; 485:3, s. 607-617
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Tidskriftsartikel (refereegranskat)abstract
- 1. The temporal relationship between the early glucose-induced changes of membrane potential and cytoplasmic Ca2+ concentration ([Ca2+]i) was studied in insulin-releasing pancreatic beta-cells. 2. The mean resting membrane potential and [Ca2+]i were about -70 mV and 60 nM, respectively, in 3 mM glucose. 3. Elevating the glucose concentration to 8-23 mM typically elicited a slow depolarization, which was paralleled by a lowering of [Ca2+]i. When the slow depolarization had reached a threshold of -55 to -40 mV, there was rapid further depolarization to a plateau with superimposed action potentials, and [Ca2+]i increased dramatically. 4. Imposing hyperpolarizations and depolarizations of 10 mV from a holding potential of -70 mV had no detectable effect on [Ca2+]i. Furthermore, glucose elevation elicited a decrease in [Ca2+]i even at a holding potential of -70 mV. 5. Step depolarizations induced [Ca2+]i transients, which decayed with time courses well fitted by double exponentials. The slower component became faster by a factor of about 4 upon elevation of glucose, suggesting involvement of ATP-dependent Ca2+ sequestration or extrusion of [Ca2+]i. 6. Glucose stimulation increased the size and accelerated the recovery of carbachol-triggered [Ca2+]i transients, and thapsigargin, an intracellular Ca(2+)-ATPase inhibitor, counteracted the glucose-induced lowering of [Ca2+]i, indicating that calcium transport into intracellular stores is involved in glucose-induced lowering of [Ca2+]i. 7. The results support the notion that in beta-cells, nutrient-induced elevation of ATP leads initially to ATP-dependent removal of Ca2+ from the cytoplasm, paralleled by a slow depolarization due to inhibition of ATP-sensitive K+ channels. Only after depolarization has reached a threshold do action potentials occur, inducing a sharp elevation in [Ca2+]i.
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| 7. |
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| 9. |
- Dezaki, Katsuya, et al.
(författare)
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Ghrelin Attenuates cAMP-PKA Signaling to Evoke Insulinostatic Cascade in Islet beta-Cells
- 2011
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 60:9, s. 2315-2324
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE-Ghrelin reportedly restricts insulin release in islet beta-cells via the G alpha(i2) subtype of G-proteins and thereby regulates glucose homeostasis. This study explored whether ghrelin regulates cAMP signaling and whether this regulation induces insulinostatic cascade in islet beta-cells. RESEARCH DESIGN AND METHODS-Insulin release was measured in rat perfused pancreas and isolated islets and cAMP production in isolated islets. Cytosolic cAMP concentrations ([cAMP](i)) were monitored in mouse MIN6 cells using evanescent-wave fluorescence imaging. In rat single beta-cells, cytosolic protein kinase-A activity ([PKA](i)) and Ca(2+) concentration ([Ca(2+)](i)) were measured by DR-II and fura-2 microfluorometry, respectively, and whole cell currents by patch-clamp technique. RESULTS-Ghrelin suppressed glucose (8.3 mmol/L)-induced insulin release in rat perfused pancreas and isolated islets, and these effects of ghrelin were blunted in the presence of cAMP analogs or adenylate cyclase inhibitor. Glucose-induced cAMP production in isolated islets was attenuated by ghrelin and enhanced by ghrelin receptor antagonist and anti-ghrelin antiserum, which counteract endogenous islet-derived ghrelin. Ghrelin inhibited the glucose-induced [cAMP](i) elevation and [PKA](i) activation in MIN6 and rat beta-cells, respectively. Furthermore, ghrelin potentiated voltage-dependent K(+) (Kv) channel currents without altering Ca(2+) channel currents and attenuated glucose-induced [Ca(2+)](i) increases in rat beta-cells in a PKA-dependent manner. CONCLUSIONS-Ghrelin directly interacts with islet beta-cells to attenuate glucose-induced cAMP production and PKA activation, which lead In activation of Kv channels and suppression of glucose-induced [Ca(2+)](i) increase and insulin release.
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| 10. |
- Dyachok, Oleg, 1965-, et al.
(författare)
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Glucose-induced cyclic AMP oscillations regulate pulsatile insulin secretion
- 2008
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Ingår i: Cell Metabolism. - : Cell Press. - 1550-4131 .- 1932-7420. ; 8:1, s. 26-37
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Tidskriftsartikel (refereegranskat)abstract
- Cyclic AMP (cAMP) and Ca2+ are key regulators of exocytosis in many cells, including insulin-secreting β-cells. Glucose-stimulated insulin secretion from β cells is pulsatile and involves oscillations of the cytoplasmic Ca2+ concentration ([Ca2+]i), but little is known about the detailed kinetics of cAMP signalling. Using evanescent-wave fluorescence imaging we found that glucose induces pronounced oscillations of cAMP in the sub-membrane space of single MIN6-cells and primary mouse β-cells. These oscillations were preceded and enhanced by elevations of [Ca2+]i. However, conditions raising cytoplasmic ATP could trigger cAMP elevations without accompanying [Ca2+]i rise, indicating that adenylyl cyclase activity may be controlled also by the substrate concentration. The cAMP oscillations correlated with pulsatile insulin release. Whereas elevation of cAMP enhanced secretion, inhibition of adenylyl cyclases suppressed both cAMP oscillations and pulsatile insulin release. We conclude that cell metabolism directly controls cAMP, and that glucose-induced cAMP oscillations regulate the magnitude and kinetics of insulin exocytosis.
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| 11. |
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| 12. |
- Hellman, Bo, 1930-, et al.
(författare)
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Glucose generates coincident insulin and somatostatin pulses and anti-synchronous glucagon pulses from human pancreatic islets
- 2009
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Ingår i: Endocrinology. - : The Endocrine Society. - 0013-7227 .- 1945-7170. ; 150:12, s. 5334-5340
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Tidskriftsartikel (refereegranskat)abstract
- The kinetics of insulin, glucagon and somatostatin release was studied in human pancreatic islets. Batches of 10-15 islets were perifused and the hormones measured with RIA in 30-sec fractions. Increase of glucose from 3 to 20 mM resulted in a brief pulse of glucagon coinciding with suppression of basal insulin and somatostatin release. There was a subsequent drop of glucagon release concomitant with the appearance of a pronounced pulse of insulin and a slightly delayed pulse of somatostatin. Continued exposure to 20 mM glucose generated pulsatile release of the three hormones with 7- to 8-min periods accounting for 60-70% of the secreted amounts. Glucose caused pronounced stimulation of average insulin and somatostatin release. However, the nadirs between the glucagon pulses were lower than the secretion at 3 mM glucose, resulting in 18% suppression of average release. The repetitive glucagon pulses were antisynchronous to coincident pulses of insulin and somatostatin. The resulting greater than 20-fold variations of the insulin to glucagon ratio might be essential for minute-to-minute regulation of the hepatic glucose production.
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| 13. |
- Lindholm, Cecilia K, et al.
(författare)
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Requirement of the Src homology 2 domain protein Shb for T cell receptor-dependent activation of the Interleukin-2 gene nuclear factor for activation of T cells element in Jurkat T cells
- 1999
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Ingår i: Journal of Biological Chemistry. - : Elsevier BV. - 0021-9258 .- 1083-351X. ; 274:39, s. 28050-28057
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Tidskriftsartikel (refereegranskat)abstract
- Stimulation of the T cell antigen receptor (TCR) induces tyrosine phosphorylation of numerous intracellular proteins. We have recently investigated the role of the adaptor protein Shb in the early events of T cell signaling and observed that Shb associates with Grb2, linker for activation of T cells (LAT) and the TCR zeta-chain in Jurkat cells. We now report that Shb also associates with phospholipase C-gamma1 (PLC-gamma1) in these cells. Overexpression of Src homology 2 domain defective Shb caused diminished phosphorylation of LAT and consequently the activation of mitogen-activated protein kinases was decreased upon TCR stimulation. In addition, the Shb mutant also blocked phosphorylation of PLC-gamma1 and the increase in cytoplasmic Ca(2+) following TCR stimulation. Nuclear factor for activation of T cells is a major target for Ras and calcium signaling pathways in T cells following TCR stimulation, and the overexpression of the mutant Shb prevented TCR-dependent activation of the nuclear factor for activation of T cells. Consequently, endogenous interleukin-2 production was decreased under these conditions. The results indicate a role for Shb as a link between the TCR and downstream signaling events involving LAT and PLC-gamma1 and resulting in the activation of transcription of the interleukin-2 gene.
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| 14. |
- Shuai, Hongyan
(författare)
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Studies of cAMP and Ca2+ signaling in pancreatic islet cells
- 2018
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The blood glucose-lowering and -elevating hormones insulin and glucagon are released from the pancreatic islet β- and α-cells, respectively. The intracellular messengers Ca2+ and cAMP have central roles in controlling the secretion of both hormones, but the underlying mechanisms are incompletely understood. A powerful approach to gain further insight is to study the messengers in individual cells within pancreatic islets, provided that each cell can be identified. To facilitate such studies, adenoviral vectors were generated for expression of fluorescent proteins controlled by the insulin and preproglucagon promoters, as well as the somatostatin and pancreatic polypeptide promoters that identify the other two major islet cell types, δ- and PP-cells. Recordings of cAMP and Ca2+ concentration changes with fluorescent reporters demonstrated that cells expressing identification markers responded as expected to well-known stimuli and modulators of the two messengers. Glucose-induced Ca2+ oscillations in β-cells were found to be synchronized with those in δ-cells, and two subpopulations of α-cells with different Ca2+ regulation by glucose were identified. Mouse and human β-cells responded to the insulinotropic hormones glucagon, GIP and GLP-1 with elevations of cAMP. Most α-cells reacted similarly to GIP, whereas only a subpopulation – larger among human than mouse α-cells - responded to glucagon and GLP-1. The GLP-1-receptor antagonist exendin-(9-39) suppressed both GLP-1- and glucagon-induced cAMP elevations in β-cells. Since exendin-(9-39) did not antagonize glucagon receptors, glucagon apparently activates GLP-1 receptors in β-cells. Even in the absence of glucagon/GLP-1, exendin-(9-39) reduced cAMP increases obtained by glucose stimulation or elevation of Ca2+. This effect was attributable to constitutive GLP-1-receptor activity rather than paracrine effects. Exendin-(9-39) also inhibited glucose-induced insulin release, highlighting the importance of cAMP formation in nutrient-stimulated secretion. Simultaneous recordings of cAMP and Ca2+ showed a complex and variable interrelationship between the messengers and the cAMP precursor ATP in β-cells. Depolarization-induced Ca2+ increases inhibited forskolin-, IBMX- and GLP-1-induced cAMP elevations. This cAMP lowering in part reflected suppression of the Ca2+-sensitive activity of adenylyl cyclases AC5 and 6, but also autocrine signaling induced by Ca2+-triggered exocytosis of insulin and adenine nucleotides, whose receptors activate phosphodiesterases and inhibit adenylyl cyclases, respectively.
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| 15. |
- Tengholm, Anders, 1971-, et al.
(författare)
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cAMP signalling in insulin and glucagon secretion
- 2017
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Ingår i: Diabetes, obesity and metabolism. - : Wiley. - 1462-8902 .- 1463-1326. ; 19, s. 42-53
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Forskningsöversikt (refereegranskat)abstract
- The second messenger archetype cAMP is one of the most important cellular signalling molecules with central functions including the regulation of insulin and glucagon secretion from the pancreatic - and -cells, respectively. cAMP is generally considered as an amplifier of insulin secretion triggered by Ca2+ elevation in the -cells. Both messengers are also positive modulators of glucagon release from -cells, but in this case cAMP may be the important regulator and Ca2+ have a more permissive role. The actions of cAMP are mediated by protein kinase A (PKA) and the guanine nucleotide exchange factor Epac. The present review focuses on how cAMP is regulated by nutrients, hormones and neural factors in - and -cells via adenylyl cyclase-catalysed generation and phosphodiesterase-mediated degradation. We will also discuss how PKA and Epac affect ion fluxes and the secretory machinery to transduce the stimulatory effects on insulin and glucagon secretion. Finally, we will briefly describe disturbances of the cAMP system associated with diabetes and how cAMP signalling can be targeted to normalize hypo- and hypersecretion of insulin and glucagon, respectively, in diabetic patients.
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| 16. |
- Tengholm, Anders, 1971-, et al.
(författare)
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Oscillatory control of insulin secretion
- 2009
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Ingår i: Molecular and Cellular Endocrinology. - : Elsevier BV. - 0303-7207 .- 1872-8057. ; 297:1-2, s. 58-72
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Forskningsöversikt (refereegranskat)abstract
- Pancreatic β-cells possess an inherent ability to generate oscillatory signals that trigger insulin release. Coordination of the secretory activity among β-cells results in pulsatile insulin secretion from the pancreas, which is considered important for the action of the hormone in the target tissues. This review focuses on the mechanisms underlying oscillatory control of insulin secretion at the level of the individual β-cell. Recent studies have demonstrated that oscillations of the cytoplasmic Ca2+ concentration are synchronized with oscillations in β-cell metabolism, intracellular cAMP concentration, phospholipase C activity and plasma membrane phosphoinositide lipid concentrations. There are complex interdependencies between the different messengers and signalling pathways that contribute to amplitude regulation and shaping of the insulin secretory response to nutrient stimuli and neurohormonal modulators. Several of these pathways may be important pharmacological targets for improving pulsatile insulin secretion in type 2 diabetes.
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| 17. |
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| 18. |
- Yang, Mingyu, et al.
(författare)
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Indicator-dependent differences in detection of local intracellular Ca2+release events evoked by voltage-gated Ca2+entry in pancreatic & beta;-cells
- 2023
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Ingår i: Cellular Signalling. - : Elsevier BV. - 0898-6568 .- 1873-3913. ; 109
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Tidskriftsartikel (refereegranskat)abstract
- Genetically encoded Ca2+ indicators have become widely used in cell signalling studies as they offer advantages over cell-loaded dye indicators in enabling specific cellular or subcellular targeting. Comparing responses from dye and protein-based indicators may provide information about indicator properties and cell physiology, but side-by-side recordings in cells are scarce. In this study, we compared cytoplasmic Ca2+ concentration ([Ca2+]i) changes in insulin-secreting & beta;-cells recorded with commonly used dyes and indicators based on circularly permuted fluorescent proteins. Total internal reflection fluorescence (TIRF) imaging of K+ depolarizationtriggered submembrane [Ca2+]i increases showed that the dyes Fluo-4 and Fluo-5F mainly reported stable [Ca2+]i elevations, whereas the proteins R-GECO1 and GCaMP5G more often reported distinct [Ca2+]i spikes from an elevated level. [Ca2+]i spiking occurred also in glucose-stimulated cells. The spikes reflected Ca2+ release from the endoplasmic reticulum, triggered by autocrine activation of purinergic receptors after exocytotic release of ATP and/or ADP, and the spikes were consequently prevented by SERCA inhibition or P2Y1-receptor antagonism. Widefield imaging, which monitors the entire cytoplasm, increased the spike detection by the Ca2+ dyes. The indicator-dependent response patterns were unrelated to Ca2+ binding affinity, buffering and mobility, and probably reflects the much slower dissociation kinetics of protein compared to dye indicators. Ca2+ dyes thus report signalling within the submembrane space excited by TIRF illumination, whereas the protein indicators also catch Ca2+ events originating outside this volume. The study highlights that voltage-dependent Ca2+ entry in & beta;-cells is tightly linked to local intracellular Ca2+ release mediated via an autocrine route that may be more important than previously reported direct Ca2+ effects on phospholipase C or on intracellular channels mediating calcium-induced calcium release.
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| 19. |
- Yu, Qian, et al.
(författare)
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Glucose controls glucagon secretion by directly modulating cAMP in alpha cells
- 2019
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Ingår i: Diabetologia. - : Springer Science and Business Media LLC. - 0012-186X .- 1432-0428. ; 62:7, s. 1212-1224
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Tidskriftsartikel (refereegranskat)abstract
- Aims/hypothesisGlucagon is critical for normal glucose homeostasis and aberrant secretion of the hormone aggravates dysregulated glucose control in diabetes. However, the mechanisms by which glucose controls glucagon secretion from pancreatic alpha cells remain elusive. The aim of this study was to investigate the role of the intracellular messenger cAMP in alpha-cell-intrinsic glucose regulation of glucagon release.MethodsSubplasmalemmal cAMP and Ca2+ concentrations were recorded in isolated and islet-located alpha cells using fluorescent reporters and total internal reflection microscopy. Glucagon secretion from mouse islets was measured using ELISA.ResultsGlucose induced Ca2+-independent alterations of the subplasmalemmal cAMP concentration in alpha cells that correlated with changes in glucagon release. Glucose-lowering-induced stimulation of glucagon secretion thus corresponded to an elevation in cAMP that was independent of paracrine signalling from insulin or somatostatin. Imposed cAMP elevations stimulated glucagon secretion and abolished inhibition by glucose elevation, while protein kinase A inhibition mimicked glucose suppression of glucagon release.Conclusions/interpretationGlucose concentrations in the hypoglycaemic range control glucagon secretion by directly modulating the cAMP concentration in alpha cells independently of paracrine influences. These findings define a novel mechanism for glucose regulation of glucagon release that underlies recovery from hypoglycaemia and may be disturbed in diabetes.
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