Regulated Exocytosis of GABA-containing Synaptic-like Microvesicles in Pancreatic β-cells

Braun, Matthias; Wendt, Anna; Birnir, Bryndis; Broman, Jonas; Eliasson, Lena; Galvanovskis, Juris; Gromada, Jesper; Mulder, Hindrik; Rorsman, Patrik

doi:10.1085/jgp.200308966

Cited by 121 publications

(172 citation statements)

References 58 publications

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“…1b). Consequently, it is unlikely that insulin or Zn 2+ co-secreted from the same beta cell granules or the similarly regulated release of GABA from beta cell microvesicles [36] contribute to inhibition of glucagon secretion by up to 7 mmol/l glucose. Although somatostatin secretion was dose-dependently stimulated by 4 to 20 mmol/l glucose (Fig.…”

Section: Resultsmentioning

confidence: 99%

Glucose inhibits glucagon secretion by a direct effect on mouse pancreatic alpha cells

2006

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Aims/hypothesis The mechanisms by which glucose regulates glucagon release are poorly understood. The present study aimed to clarify the direct effects of glucose on the glucagon-releasing alpha cells and those effects mediated by paracrine islet factors. Materials and methods Glucagon, insulin and somatostatin release were measured from incubated mouse pancreatic islets and the cytoplasmic Ca 2+ concentration ([Ca 2+ ] i ) recorded in isolated mouse alpha cells. Results Glucose inhibited glucagon release with maximal effect at 7 mmol/l. Since this concentration corresponded to threshold stimulation of insulin secretion, it is unlikely that inhibition of glucagon secretion is mediated by beta cell factors. Although somatostatin secretion data seemed consistent with a role of this hormone in glucose-inhibited glucagon release, a somatostatin receptor type 2 antagonist stimulated glucagon release without diminishing the inhibitory effect of glucose. In islets exposed to tolbutamide plus 8 mmol/l K + , glucose inhibited glucagon secretion without stimulating the release of insulin and somatostatin, indicating a direct inhibitory effect on the alpha cells that was independent of ATP-sensitive K + channels. Glucose lowered [Ca 2+ ] i of individual alpha cells independently of somatostatin and beta cell factors (insulin, Zn 2+ and γ-aminobutyric acid). Glucose suppression of glucagon release was prevented by inhibitors of the sarco(endo)plasmic reticulum Ca 2+ -ATPase, which abolished the [Ca 2+ ] i -lowering effect of glucose on isolated alpha cells. Conclusions/interpretation Beta cell factors or somatostatin do not seem to mediate glucose inhibition of glucagon secretion. We instead propose that glucose has a direct inhibitory effect on mouse alpha cells by suppressing a depolarising Ca 2+ store-operated current.

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Section: Resultsmentioning

confidence: 99%

Glucose inhibits glucagon secretion by a direct effect on mouse pancreatic alpha cells

2006

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“…There was only rare evidence for rapid internalization of granule-sized vesicles from the plasma membrane in MIN6 cells. Other types of smaller secretory vesicles (e.g., ␥-aminobutyric acid-containing) in beta cells could possibly use this distinct pathway (13,28).…”

Section: Discussionmentioning

confidence: 99%

Direct imaging shows that insulin granule exocytosis occurs by complete vesicle fusion

Bindokas

Kuznetsov

et al. 2004

Proc. Natl. Acad. Sci. U.S.A.

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Confocal imaging of GFP-tagged secretory granules combined with the use of impermeant extracellular dyes permits direct observation of insulin packaged in secretory granules, trafficking of these granules to the plasma membrane, exocytotic fusion of granules with the plasma membrane, and eventually the retrieval of membranes by endocytosis. Most such studies have been done in tumor cell lines, using either confocal methods or total internal reflectance microscopy. Here we compared these methods by using GFP-syncollin or PC3-GFP plus rhodamine dextrans to study insulin granule dynamics in insulinoma cells, normal mouse islets, and primary pancreatic beta cells. We found that most apparently docked granules did not fuse with the plasma membrane after stimulation. Granules that did fuse typically fused completely, but a few dextran-filled granules lingered at the membrane. Direct recycling of granules occurred only rarely. Similar results were obtained with both confocal and total internal reflection microscopy, although each technique had advantages for particular aspects of the granule life cycle. We conclude that insulin exocytosis involves a prolonged interaction of secretory granules with the plasma membrane, and that the majority of exocytotic events occur by full, not partial, fusion.

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“…5). We investigated the release of glycine from b-cells by adapting a patch-clamp-based assay that has previously been used to detect the exocytotic release of g-aminobutyric acid (GABA) and ATP (3,31,32). Isolated human islet cells were transfected with a plasmid vector overexpressing GlyRa1, leading to an approximate sevenfold increase of the glycine-evoked currents.…”

Section: Glycine Release From Human B-cellsmentioning

confidence: 99%

A Glycine-Insulin Autocrine Feedback Loop Enhances Insulin Secretion From Human β-Cells and Is Impaired in Type 2 Diabetes

et al. 2016

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The secretion of insulin from pancreatic islet β-cells is critical for glucose homeostasis. Disrupted insulin secretion underlies almost all forms of diabetes, including the most common form, type 2 diabetes (T2D). The control of insulin secretion is complex and affected by circulating nutrients, neuronal inputs, and local signaling. In the current study, we examined the contribution of glycine, an amino acid and neurotransmitter that activates ligand-gated Cl− currents, to insulin secretion from islets of human donors with and without T2D. We find that human islet β-cells express glycine receptors (GlyR), notably the GlyRα1 subunit, and the glycine transporter (GlyT) isoforms GlyT1 and GlyT2. β-Cells exhibit significant glycine-induced Cl− currents that promote membrane depolarization, Ca2+ entry, and insulin secretion from β-cells from donors without T2D. However, GlyRα1 expression and glycine-induced currents are reduced in β-cells from donors with T2D. Glycine is actively cleared by the GlyT expressed within β-cells, which store and release glycine that acts in an autocrine manner. Finally, a significant positive relationship exists between insulin and GlyR, because insulin enhances the glycine-activated current in a phosphoinositide 3-kinase–dependent manner, a positive feedback loop that we find is completely lost in β-cells from donors with T2D.

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Regulated Exocytosis of GABA-containing Synaptic-like Microvesicles in Pancreatic β-cells

Cited by 121 publications

References 58 publications

Glucose inhibits glucagon secretion by a direct effect on mouse pancreatic alpha cells

Glucose inhibits glucagon secretion by a direct effect on mouse pancreatic alpha cells

Direct imaging shows that insulin granule exocytosis occurs by complete vesicle fusion

A Glycine-Insulin Autocrine Feedback Loop Enhances Insulin Secretion From Human β-Cells and Is Impaired in Type 2 Diabetes

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