Inhibition of connexin 36 hemichannels by glucose contributes to the stimulation of insulin secretion

2014 ◽  
Vol 306 (12) ◽  
pp. E1354-E1366 ◽  
Author(s):  
Javier Pizarro-Delgado ◽  
Ilaria Fasciani ◽  
Ana Temperan ◽  
María Romero ◽  
Daniel González-Nieto ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Gap Junction ◽  
Atp Release ◽  
Sugar Metabolism ◽  
Atp Content ◽  
Wild Type ◽  
Β Cells ◽  
Gap Junction Channels ◽  
Connexin 36 ◽  
Stimulation Of

The existence of functional connexin36 ( Cx36) hemichannels in β-cells was investigated in pancreatic islets of rat and wild-type ( Cx36+/+), monoallelic ( Cx36+/−), and biallelic ( Cx36−/−) knockout mice. Hemichannel opening by KCl depolarization was studied by measuring ATP release and changes of intracellular ATP (ADP). Cx36+/+ islets lost ATP after depolarization with 70 mM KCl at 5 mM glucose; ATP loss was prevented by 8 and 20 mM glucose or 50 μM mefloquine (connexin inhibitor). ATP content was higher in Cx36−/− than Cx36+/+ islets and was not decreased by KCl depolarization; Cx36+/− islets showed values between that of control and homozygous islets. Five minimolar extracellular ATP increased ATP content and ATP/ADP ratio and induced a biphasic insulin secretion in depolarized Cx36+/+ and Cx36+/− but not Cx36−/− islets. Cx36 hemichannels expressed in oocytes opened upon depolarization of membrane potential, and their activation was inhibited by mefloquine and glucose (IC50 ∼8 mM). It is postulated that glucose-induced inhibition of Cx36 hemichannels in islet β-cells might avoid depolarization-induced ATP loss, allowing an optimum increase of the ATP/ADP ratio by sugar metabolism and a biphasic stimulation of insulin secretion. Gradual suppression of glucose-induced insulin release in Cx36+/− and Cx36−/− islets confirms that Cx36 gap junction channels are necessary for a full secretory stimulation and might account for the glucose intolerance observed in mice with defective Cx36 expression. Mefloquine targeting of Cx36 on both gap junctions and hemichannels also suppresses glucose-stimulated secretion. By contrast, glucose stimulation of insulin secretion requires Cx36 hemichannels' closure but keeping gap junction channels opened.

Slow intercellular Ca2+ signaling in wild-type and Cx43-null neonatal mouse cardiac myocytes

2000 ◽  
Vol 279 (6) ◽  
pp. H3076-H3088 ◽  
Author(s):  
Sylvia O. Suadicani ◽  
Monique J. Vink ◽  
David C. Spray
Keyword(s):  
Gap Junction ◽  
Cardiac Myocytes ◽  
Channel Blocker ◽  
Atp Release ◽  
Neonatal Mouse ◽  
Wild Type ◽  
Gap Junction Channels ◽  
Gap Junction Channel ◽  
Main Pathway ◽  
Stimulation Of

Focal mechanical stimulation of single neonatal mouse cardiac myocytes in culture induced intercellular Ca2+ waves that propagated with mean velocities of ∼14 μm/s, reaching ∼80% of the cells in the field. Deletion of connexin43 (Cx43), the main cardiac gap junction channel protein, did not prevent communication of mechanically induced Ca2+ waves, although the velocity and number of cells communicated by the Ca2+ signal were significantly reduced. Similar effects were observed in wild-type cardiac myocytes treated with heptanol, a gap junction channel blocker. Fewer cells were involved in intercellular Ca2+ signaling in both wild-type and Cx43-null cultures in the presence of suramin, a P2-receptor blocker; blockage was more effective in Cx43-null than in wild-type cells. Thus gap junction channels provide the main pathway for communication of slow intercellular Ca2+ signals in wild-type neonatal mouse cardiac myocytes. Activation of P2-receptors induced by ATP release contributes a secondary, extracellular pathway for transmission of Ca2+ signals. The importance of such ATP-mediated Ca2+ signaling would be expected to be enhanced under ischemic conditions, when release of ATP is increased and gap junction channels conductance is significantly reduced.

Potentiation of insulin secretion by phorbol esters is mediated by PKC-α and nPKC isoforms

2002 ◽  
Vol 283 (5) ◽  
pp. E880-E888 ◽  
Author(s):  
Gordon C. Yaney ◽  
Jamison M. Fairbanks ◽  
Jude T. Deeney ◽  
Helen M. Korchak ◽  
Keith Tornheim ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Membrane Potential ◽  
Phorbol Esters ◽  
Myristate Acetate ◽  
Β Cells ◽  
Kinase C ◽  
Pkc Isoforms ◽  
Enhanced Secretion ◽  
Intracellular Ca ◽  
Stimulation Of

Culturing clonal β-cells (HIT-T15) overnight in the presence of phorbol ester [phorbol myristate acetate (PMA)] enhanced insulin secretion while causing downregulation of some protein kinase C (PKC) isoforms and most PKC activity. We show here that this enhanced secretion required the retention of PMA in the cell. Hence, it could not be because of long-lived phosphorylation of cellular substrates by the isoforms that were downregulated, namely PKC-α, -βII, and -ε, but could be because of the continued activation of the two remaining diacylglycerol-sensitive isoforms δ and μ. The enhanced secretion did not involve changes in glucose metabolism, cell membrane potential, or intracellular Ca2+handling, suggesting a distal effect. PMA washout caused the loss of the enhanced response, but secretion was then stimulated by acute readdition of PMA or bombesin. The magnitude of this restimulation appeared dependent on the mass of PKC-α, which was rapidly resynthesized during PMA washout. Therefore, stimulation of insulin secretion by PMA, and presumably by endogenous diacylglycerol, involves the activation of PKC isoforms δ and/or μ, and also PKC-α.

Studies of the mechanism of amino acid-induced stimulation of insulin secretion from clonal pancreatic β-cells

2000 ◽  
Vol 28 (5) ◽  
pp. A196-A196
Author(s):  
A. Shine ◽  
N. H. Mc Clenaghan ◽  
P. Flatt ◽  
JPG Malthouse ◽  
C. Hewage ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Amino Acid ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Stimulation Of

Hexosamines regulate sensitivity of glucose-stimulated insulin secretion in β-cells

2006 ◽  
Vol 290 (2) ◽  
pp. E334-E340 ◽  
Author(s):  
Robert C. Cooksey ◽  
Sumitha Pusuluri ◽  
Mark Hazel ◽  
Donald A. McClain
Keyword(s):  
Insulin Secretion ◽  
Glucose Oxidation ◽  
Nutrient Sensing ◽  
Wild Type ◽  
Β Cells ◽  
Enhanced Sensitivity ◽  
Peripheral Insulin Resistance ◽  
Glucose Stimulated Insulin Secretion ◽  
Rate Limiting

Hexosamines serve a nutrient-sensing function through enzymatic O-glycosylation of proteins. We previously characterized transgenic (Tg) mice with overexpression of the rate-limiting enzyme in hexosamine production, glutamine:fructose-6-phosphate amidotransferase, in β-cells. Animals were hyperinsulinemic, resulting in peripheral insulin resistance. Glucose tolerance deteriorated with age, and males developed diabetes. We therefore examined islet function in these mice by perifusion in vitro. Young (2-mo-old) Tg animals had enhanced sensitivity to glucose of insulin secretion. Insulin secretion was maximal at 20 mM and half maximal at 9.9 ± 0.5 mM glucose in Tg islets compared with maximal at 30 mM and half maximal at 13.5 ± 0.7 mM glucose in wild type (WT; P < 0.005). Young Tg animals secreted more insulin in response to 20 mM glucose (Tg, 1,254 ± 311; WT, 425 ± 231 pg·islet−1·35 min−1; P < 0.01). Islets from older (8-mo-old) Tg mice became desensitized to glucose, with half-maximal secretion at 16.1 ± 0.8 mM glucose, compared with 11.8 ± 0.7 mM in WT ( P < 0.05). Older Tg mice secreted less insulin in response to 20 mM glucose (Tg, 2,256 ± 342; WT, 3,493 ± 367 pg·islet−1·35 min−1; P < 0.05). Secretion in response to carbachol was similar in WT and Tg at both ages. Glucose oxidation was blunted in older Tg islets. At 5 mM glucose, islet CO2 production was comparable between Tg and WT. However, WT mice increased islet CO2 production 2.7 ± 0.4-fold in 20 mM glucose, compared with only 1.4 ± 0.1-fold in Tg ( P < 0.02). Results demonstrate that hexosamines are involved in nutrient sensing for insulin secretion, acting at least in part by modulating glucose oxidation pathways. Prolonged excess hexosamine flux results in glucose desensitization and mimics glucose toxicity.

scholarly journals Chronic fructose renders pancreatic β-cells hyper-responsive to glucose-stimulated insulin secretion through extracellular ATP signaling

2019 ◽  
Vol 317 (1) ◽  
pp. E25-E41 ◽  
Author(s):  
Clarissa Bartley ◽  
Thierry Brun ◽  
Lucie Oberhauser ◽  
Mariagrazia Grimaldi ◽  
Filippo Molica ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Atp Release ◽  
Extracellular Atp ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Cellular Mechanisms ◽  
Kinase Activation ◽  
Glucose Stimulated Insulin Secretion ◽  
Insulinoma Cells ◽  
Atp Signaling

Fructose is widely used as a sweetener in processed food and is also associated with metabolic disorders, such as obesity. However, the underlying cellular mechanisms remain unclear, in particular, regarding the pancreatic β-cell. Here, we investigated the effects of chronic exposure to fructose on the function of insulinoma cells and isolated mouse and human pancreatic islets. Although fructose per se did not acutely stimulate insulin exocytosis, our data show that chronic fructose rendered rodent and human β-cells hyper-responsive to intermediate physiological glucose concentrations. Fructose exposure reduced intracellular ATP levels without affecting mitochondrial function, induced AMP-activated protein kinase activation, and favored ATP release from the β-cells upon acute glucose stimulation. The resulting increase in extracellular ATP, mediated by pannexin1 (Panx1) channels, activated the calcium-mobilizer P2Y purinergic receptors. Immunodetection revealed the presence of both Panx1 channels and P2Y1 receptors in β-cells. Addition of an ectonucleotidase inhibitor or P2Y1 agonists to naïve β-cells potentiated insulin secretion stimulated by intermediate glucose, mimicking the fructose treatment. Conversely, the P2Y1 antagonist and Panx1 inhibitor reversed the effects of fructose, as confirmed using Panx1-null islets and by the clearance of extracellular ATP by apyrase. These results reveal an important function of ATP signaling in pancreatic β-cells mediating fructose-induced hyper-responsiveness.

scholarly journals Direct Stimulation of Basal Insulin Secretion by Physiological Concentrations of Leptin in Pancreatic β Cells

Endocrinology ◽  
1997 ◽  
Vol 138 (10) ◽  
pp. 4513-4516 ◽  
Author(s):  
Yukio Tanizawa ◽  
Shigeru Okuya ◽  
Hisamitsu Ishihara ◽  
Tomoichiro Asano ◽  
Toshihiko Yada ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Basal Insulin ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Direct Stimulation ◽  
Basal Insulin Secretion ◽  
Stimulation Of

scholarly journals GPRC6A Mediates the Effects of l-Arginine on Insulin Secretion in Mouse Pancreatic Islets

Endocrinology ◽  
2012 ◽  
Vol 153 (10) ◽  
pp. 4608-4615 ◽  
Author(s):  
Min Pi ◽  
Yunpeng Wu ◽  
Nataliya I Lenchik ◽  
Ivan Gerling ◽  
L. Darryl Quarles
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Ex Vivo ◽  
Β Cells ◽  
Direct Role ◽  
Mouse Pancreatic Islets ◽  
Islet Size ◽  
G Protein Coupled ◽  
Stimulation Of

Abstract l-Arginine (l-Arg) is an insulin secretagogue, but the molecular mechanism whereby it stimulates insulin secretion from β-cells is not known. The possibility that l-Arg regulates insulin secretion through a G protein-coupled receptor (GPCR)-mediated mechanism is suggested by the high expression of the nutrient receptor GPCR family C group 6 member A (GPRC6A) in the pancreas and TC-6 β-cells and the finding that Gprc6a−/]minus] mice have abnormalities in glucose homeostasis. To test the direct role of GPRC6A in regulating insulin secretion, we evaluated the response of pancreatic islets derived from Gprc6a−/]minus] mice to l-Arg. We found that the islet size and insulin content were decreased in pancreatic islets from Gprac6a−/]minus] mice. These alterations were selective for β-cells, because there were no abnormalities in serum glucagon levels or glucagon content of islets derived from Gprac6a−/]minus] mice. Significant reduction was observed in both the pancreatic ERK response to l-Arg administration to Gprc6a−/]minus] mice in vivo and l-Arg-induced insulin secretion and production ex vivo in islets isolated from Gprc6a−/]minus] mice. l-Arg stimulation of cAMP accumulation in isolated islets isolated from Gprc6a−/]minus] mice was also diminished. These findings suggest that l-Arg stimulation of insulin secretion in β-cells is mediated, at least in part, through GPRC6A activation of cAMP pathways.

scholarly journals Glucose promotion of GABA metabolism contributes to the stimulation of insulin secretion in β-cells

2010 ◽  
Vol 431 (3) ◽  
pp. 381-390 ◽  
Author(s):  
Javier Pizarro-Delgado ◽  
Matthias Braun ◽  
Inés Hernández-Fisac ◽  
Rafael Martín-Del-Río ◽  
Jorge Tamarit-Rodriguez
Keyword(s):  
Insulin Secretion ◽  
Succinic Semialdehyde ◽  
Keto Acid ◽  
Β Cells ◽  
Action Potential Firing ◽  
Gaba Shunt ◽  
Gaba Transaminase ◽  
Gaba Metabolism ◽  
Potential Firing ◽  
Stimulation Of

We have demonstrated recently that branched-chain α-keto acid stimulation of insulin secretion is dependent on islet GABA (γ-aminobutyric acid) metabolism: GABA transamination to succinic semialdehyde is increased by 2-oxoglutarate, generated in α-keto acid transamination to its corresponding α-amino acid. The present work was aimed at investigating whether glucose also promotes islet GABA metabolism and whether the latter contributes to the stimulation of insulin secretion. Glucose (20 mM) decreased both the content and release of islet GABA. Gabaculine (1 mM), a GABA transaminase inhibitor, partially suppressed the secretory response of rat perifused islets to 20 mM glucose at different L-glutamine concentrations (0, 1 and 10 mM), as well as the glucose-induced decrease in islet GABA. The drug also reduced islet ATP content and the ATP/ADP ratio at 20 mM glucose. Exogenous succinic semialdehyde induced a dose-dependent increase in islet GABA content by reversal of GABA transamination and a biphasic insulin secretion in the absence of glucose. It depolarized isolated β-cells and triggered action potential firing, accompanied by a reduction of membrane currents through ATP-sensitive K+ channels. The gene expression and enzyme activity of GABA transaminase were severalfold higher than that of 2-oxoglutarate dehydrogenase in islet homogenates. We conclude that, at high glucose concentrations, there is an increased diversion of glucose metabolism from the citric acid cycle into the ‘GABA shunt’. Semialdehyde succinic acid is a cell-permeant ‘GABA-shunt’ metabolite that increases ATP and the ATP/ADP ratio, depolarizes β-cells and stimulates insulin secretion. In summary, an increased islet GABA metabolism may trigger insulin secretion.

Sign in / Sign up

Export Citation Format

Share Document