Involvement of stretch-activated cation channels in hypotonically induced insulin secretion in rat pancreatic β-cells

In isolated rat pancreatic β-cells, hypotonic stimulation elicited an increase in cytosolic Ca2+ concentration ([Ca2+]c) at 2.8 mM glucose. The hypotonically induced [Ca2+]c elevation was significantly suppressed by nicardipine, a voltage-dependent Ca2+ channel blocker, and by Gd3+, amiloride, 2-aminoethoxydiphenylborate, and ruthenium red, all cation channel blockers. In contrast, the [Ca2+]c elevation was not inhibited by suramin, a P2 purinoceptor antagonist. Whole cell patch-clamp analyses showed that hypotonic stimulation induced membrane depolarization of β-cells and produced outwardly rectifying cation currents; Gd3+ inhibited both responses. Hypotonic stimulation also increased insulin secretion from isolated rat islets, and Gd3+ significantly suppressed this secretion. Together, these results suggest that osmotic cell swelling activates cation channels in rat pancreatic β-cells, thereby causing membrane depolarization and subsequent activation of voltage-dependent Ca2+ channels and thus elevating insulin secretion.

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TRPV2 channels mediate insulin secretion induced by cell swelling in mouse pancreatic β-cells

AJP Cell Physiology ◽

10.1152/ajpcell.00210.2017 ◽

2019 ◽

Vol 316 (3) ◽

pp. C434-C443 ◽

Cited By ~ 7

Author(s):

Toshiaki Sawatani ◽

Yukiko K. Kaneko ◽

Isao Doutsu ◽

Ai Ogawa ◽

Tomohisa Ishikawa

Keyword(s):

Insulin Secretion ◽

Transient Receptor Potential ◽

Receptor Potential ◽

Ruthenium Red ◽

Cell Swelling ◽

Β Cells ◽

Β Cell ◽

Pancreatic Β Cells ◽

Min6 Cells ◽

Transient Receptor

β-Cell swelling induces membrane depolarization, which has been suggested to be caused at least partly by the activation of cation channels. Here, we show the identification of the cation channels. In isolated mouse pancreatic β-cells, the exposure to 30% hypotonic solution elicited an increase in cytosolic Ca2+ concentration ([Ca2+]c). The [Ca2+]c elevation was partially inhibited by ruthenium red, a blocker of several Ca2+-permeable channels including transient receptor potential vanilloid receptors [transient receptor potential cation channel subfamily V (TRPV)], and by nicardipine, but not by the depletion of intracellular Ca2+ stores with thapsigargin and caffeine. The hypotonic stimulation also increased insulin secretion from isolated mouse islets, which was significantly suppressed by ruthenium red. Expression of TRPV2 and TRPV4 was confirmed in mouse pancreatic islets and the MIN6 β-cell line by RT-PCR, Western blot, and immunohistochemical analyses. However, neither 4α-phorbol 12,13-didecanoate nor GSK1016790A, TRPV4 activators, showed any apparent effect on [Ca2+]c in isolated mouse β-cells or in MIN6 cells. In contrast, probenecid, a TRPV2 activator, induced an increase in [Ca2+]c in MIN6 cells, which was attenuated by ruthenium red. Moreover, the [Ca2+]c elevation induced by 30% hypotonic stimulation was significantly reduced by knockdown of TRPV2 with siRNA and by tranilast, a TRPV2 inhibitor. The knockdown of TRPV2 also decreased insulin secretion induced by the hypotonic stimulation. In addition, glucose-stimulated insulin secretion was also significantly reduced in the TRPV2-knockdown MIN6 cells. These results suggest that osmotic cell swelling activates TRPV2 in mouse β-cells, thereby causing membrane depolarization and subsequent activation of voltage-dependent Ca2+ channels and insulin secretion.

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Impaired Insulin Secretion by Diphenyleneiodium Associated with Perturbation of Cytosolic Ca2+ Dynamics in Pancreatic β-Cells

Endocrinology ◽

10.1210/en.2008-0186 ◽

2008 ◽

Vol 149 (11) ◽

pp. 5391-5400 ◽

Cited By ~ 22

Author(s):

Hirofumi Imoto ◽

Nobuhiro Sasaki ◽

Masanori Iwase ◽

Udai Nakamura ◽

Miwako Oku ◽

...

Keyword(s):

Insulin Secretion ◽

Nadph Oxidase ◽

Nicotinamide Adenine Dinucleotide Phosphate ◽

Mitochondrial Respiratory Chain ◽

Membrane Depolarization ◽

Oxidase Inhibitor ◽

Channel Blockers ◽

Β Cells ◽

Impaired Insulin Secretion ◽

Impaired Insulin

Pancreatic islets express the superoxide-producing nicotinamide adenine dinucleotide phosphate (NADPH) oxidase system, but its role remains unknown. To address this, we studied the mechanisms of impaired insulin secretion induced by diphenyleneiodium (DPI), an NADPH oxidase inhibitor. We investigated the effects of DPI on glucose- and nonfuel-stimulated insulin secretion, islet glucose metabolism, and intracellular Ca2+ concentration ([Ca2+]i) dynamics in rat islets and β-cell line RINm5F cells. DPI did not affect insulin secretion at 3.3 mm glucose but totally suppressed insulin secretion stimulated by 16.7 mm glucose (percentage of control, 9.2 ± 1.2%; P <0.001). DPI also inhibited insulin release by high K+-induced membrane depolarization (percentage of control, 36.0 ± 5.3%; P <0.01) and protein kinase C activation (percentage of control, 30.2 ± 10.6% in the presence of extracellular Ca2+, P <0.01; percentage of control, 42.0 ± 4.7% in the absence of extracellular Ca2+, P <0.01). However, DPI had no effect on mastoparan-induced insulin secretion at 3.3 and 16.7 mm glucose under Ca2+-free conditions. DPI significantly suppressed islet glucose oxidation and ATP content through its known inhibitory action on complex I in the mitochondrial respiratory chain. On the other hand, DPI altered [Ca2+]i dynamics in response to high glucose and membrane depolarization, and DPI per se dose-dependently increased [Ca2+]i. The DPI-induced [Ca2+]i rise was associated with a transient increase in insulin secretion and was attenuated by removal of extracellular Ca2+, by L-type voltage-dependent Ca2+ channel blockers, by mitochondrial inhibitors, or by addition of 0.1 or 1.0 μm H2O2 exogenously. Our results showed that DPI impairment of insulin secretion involved altered Ca2+ signaling, suggesting that NADPH oxidase may modulate Ca2+ signaling in β-cells.

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Protein Kinase CK2 Controls CaV2.1-Dependent Calcium Currents and Insulin Release in Pancreatic β-cells

International Journal of Molecular Sciences ◽

10.3390/ijms21134668 ◽

2020 ◽

Vol 21 (13) ◽

pp. 4668

Author(s):

Rebecca Scheuer ◽

Stephan Ernst Philipp ◽

Alexander Becker ◽

Lisa Nalbach ◽

Emmanuel Ampofo ◽

...

Keyword(s):

Insulin Secretion ◽

Calcium Currents ◽

Insulin Biosynthesis ◽

Β Cells ◽

Pancreatic Β Cells ◽

Voltage Dependent ◽

Regulatory Impact ◽

Kinase Ck2

The regulation of insulin biosynthesis and secretion in pancreatic β-cells is essential for glucose homeostasis in humans. Previous findings point to the highly conserved, ubiquitously expressed serine/threonine kinase CK2 as having a negative regulatory impact on this regulation. In the cell culture model of rat pancreatic β-cells INS-1, insulin secretion is enhanced after CK2 inhibition. This enhancement is preceded by a rise in the cytosolic Ca2+ concentration. Here, we identified the serine residues S2362 and S2364 of the voltage-dependent calcium channel CaV2.1 as targets of CK2 phosphorylation. Furthermore, co-immunoprecipitation experiments revealed that CaV2.1 binds to CK2 in vitro and in vivo. CaV2.1 knockdown experiments showed that the increase in the intracellular Ca2+ concentration, followed by an enhanced insulin secretion upon CK2 inhibition, is due to a Ca2+ influx through CaV2.1 channels. In summary, our results point to a modulating role of CK2 in the CaV2.1-mediated exocytosis of insulin.

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Propofol inhibits stromatoxin-1-sensitive voltage-dependent K+ channels in pancreatic β-cells and enhances insulin secretion

PeerJ ◽

10.7717/peerj.8157 ◽

2019 ◽

Vol 7 ◽

pp. e8157 ◽

Cited By ~ 1

Author(s):

Munenori Kusunoki ◽

Mikio Hayashi ◽

Tomohiro Shoji ◽

Takeo Uba ◽

Hiromasa Tanaka ◽

...

Keyword(s):

Insulin Secretion ◽

Energy Metabolism ◽

Glycemic Control ◽

Potassium Channels ◽

Β Cells ◽

Pancreatic Β Cells ◽

Kv Channels ◽

Voltage Dependent ◽

Cellular Oxygen ◽

Low Glucose

Background Proper glycemic control is an important goal of critical care medicine, including perioperative patient care that can influence patients’ prognosis. Insulin secretion from pancreatic β-cells is generally assumed to play a critical role in glycemic control in response to an elevated blood glucose concentration. Many animal and human studies have demonstrated that perioperative drugs, including volatile anesthetics, have an impact on glucose-stimulated insulin secretion (GSIS). However, the effects of the intravenous anesthetic propofol on glucose metabolism and insulin sensitivity are largely unknown at present. Methods The effect of propofol on insulin secretion under low glucose or high glucose was examined in mouse MIN6 cells, rat INS-1 cells, and mouse pancreatic β-cells/islets. Cellular oxygen or energy metabolism was measured by Extracellular Flux Analyzer. Expression of glucose transporter 2 (GLUT2), potassium channels, and insulin mRNA was assessed by qRT-PCR. Protein expression of voltage-dependent potassium channels (Kv2) was also assessed by immunoblot. Propofol’s effects on potassium channels including stromatoxin-1-sensitive Kv channels and cellular oxygen and energy metabolisms were also examined. Results We showed that propofol, at clinically relevant doses, facilitates insulin secretion under low glucose conditions and GSIS in MIN6, INS-1 cells, and pancreatic β-cells/islets. Propofol did not affect intracellular ATP or ADP concentrations and cellular oxygen or energy metabolism. The mRNA expression of GLUT2 and channels including the voltage-dependent calcium channels Cav1.2, Kir6.2, and SUR1 subunit of KATP, and Kv2 were not affected by glucose or propofol. Finally, we demonstrated that propofol specifically blocks Kv currents in β-cells, resulting in insulin secretion in the presence of glucose. Conclusions Our data support the hypothesis that glucose induces membrane depolarization at the distal site, leading to KATP channel closure, and that the closure of Kv channels by propofol depolarization in β-cells enhances Ca2+ entry, leading to insulin secretion. Because its activity is dependent on GSIS, propofol and its derivatives are potential compounds that enhance and initiate β-cell electrical activity.

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Peer Review #1 of "Propofol inhibits stromatoxin-1-sensitive voltage-dependent K+ channels in pancreatic β-cells and enhances insulin secretion (v0.1)"

10.7287/peerj.8157v0.1/reviews/1 ◽

2019 ◽

Keyword(s):

Insulin Secretion ◽

Peer Review ◽

Β Cells ◽

Pancreatic Β Cells ◽

K Channels ◽

Voltage Dependent

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Dual effect of nitric oxide on cytosolic Ca2+concentration and insulin secretion in rat pancreatic β-cells

AJP Cell Physiology ◽

10.1152/ajpcell.00223.2002 ◽

2003 ◽

Vol 284 (5) ◽

pp. C1215-C1222 ◽

Cited By ~ 38

Author(s):

Yukiko Kaneko ◽

Tomohisa Ishikawa ◽

Satoshi Amano ◽

Koichi Nakayama

Keyword(s):

Nitric Oxide ◽

Insulin Secretion ◽

Kinase Inhibitor ◽

Soluble Guanylate Cyclase ◽

Β Cells ◽

Pancreatic Β Cells ◽

Dual Effect ◽

Independent Manner ◽

No Donor ◽

Isolated Rat

In isolated rat pancreatic β-cells, the nitric oxide (NO) donor NOC-7 at 1 μM reduced the amplitude of the oscillations of cytosolic Ca2+ concentration ([Ca2+]c) induced by 11.1 mM glucose, and at 10 μM terminated them. In the presence of N G-nitro-l-arginine (l-NNA), however, NOC-7 at 0.5 and 1 μM increased the amplitude of the [Ca2+]c oscillations, although the NO donor at 10 μM still suppressed them. Aqueous NO solution also had a dual effect on the [Ca2+]c oscillations. The soluble guanylate cyclase inhibitor LY-83583 and the cGMP-dependent protein kinase inhibitor KT5823 inhibited the stimulatory effect of NO, and 8-bromo-cGMP increased the amplitude of the [Ca2+]c oscillations. Patch-clamp analyses in the perforated configuration showed that 8-bromo-cGMP inhibited whole cell ATP-sensitive K+ currents in the isolated rat pancreatic β-cells, suggesting that the inhibition by cGMP of ATP-sensitive K+ channels is, at least in part, responsible for the stimulatory effect of NO on the [Ca2+]c oscillations. In the presence ofl-NNA, the glucose-induced insulin secretion from isolated islets was facilitated by 0.5 μM NOC-7, whereas it was suppressed by 10 μM NOC-7. These results suggest that NO facilitates glucose-induced [Ca2+]c oscillations of β-cells and insulin secretion at low concentrations, which effects are mediated by cGMP, whereas NO inhibits them in a cGMP-independent manner at high concentrations.

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Linoleic acid induces Ca2+-induced inactivation of voltage-dependent Ca2+ currents in rat pancreatic β-cells

Journal of Endocrinology ◽

10.1677/joe-07-0426 ◽

2007 ◽

Vol 196 (2) ◽

pp. 377-384 ◽

Cited By ~ 10

Author(s):

Dan-Dan Feng ◽

Yu-Feng Zhao ◽

Zi-Qiang Luo ◽

Damien J Keating ◽

Chen Chen

Keyword(s):

Insulin Secretion ◽

Linoleic Acid ◽

Specific Protein ◽

Β Cells ◽

Pancreatic Β Cells ◽

Cell Dysfunction ◽

Cell Recording ◽

Voltage Dependent ◽

Intracellular Ca ◽

G Protein Coupled

Free fatty acids (FFAs) regulate insulin secretion in a complex pattern and induce pancreatic β-cell dysfunction in type 2 diabetes. Voltage-dependent Ca2+ channels (VDCC) in β-cells play a major role in regulating insulin secretion. The aim of present study is to clarify the action of the FFA, linoleic acid, on VDCC in β-cells. The VDCC current in primary cultured rat β-cells were recorded under nystatin-perforated whole-cell recording configuration. The VDCC was identified as high-voltage-gated Ca2+ channels due to there being no difference in current amplitude under holding potential between −70 and −40 mV. Linoleic acid (10 μM) significantly inhibited VDCC currents in β-cells, an effect which was fully reversible upon washout. Methyl-linoleic acid, which does not activate G protein coupled receptor (GPR)40, neither did alter VDCC current in rat β-cells nor did influence linoleic acid-induced inhibition of VDCC currents. Linoleic acid-induced inhibition of VDCC current was not blocked by preincubation of β-cells with either the specific protein kinase A (PKA) inhibitor, H89, or the PKC inhibitor, chelerythrine. However, pretreatment of β-cells with thapsigargin, which depletes intracellular Ca2+ stores, completely abolished linoleic acid-induced decrease in VDCC current. Measurement of intracellular Ca2+ concentration ([Ca2+]i) illustrated that linoleic acid induced an increase in [Ca2+]i and that thapsigargin pretreatment inhibited this increase. Methyl-linoleic acid neither did induce increase in [Ca2+]i nor did it block linoleic acid-induced increase in [Ca2+]i. These results suggest that linoleic acid stimulates Ca2+ release from intracellular Ca2+ stores and inhibits VDCC currents in rat pancreatic β-cells via Ca2+-induced inactivation of VDCC.

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Hv1 channel supports insulin secretion in pancreatic β cells through calcium entry, depolarization and intracellular pH regulation

10.1101/097816 ◽

2017 ◽

Cited By ~ 1

Author(s):

Huimin Pang ◽

Xudong Wang ◽

Wang Xi ◽

Qing Zhao ◽

Shangrong Zhang ◽

...

Keyword(s):

Insulin Secretion ◽

Regulatory Mechanism ◽

Ph Regulation ◽

Membrane Depolarization ◽

Calcium Entry ◽

Proton Channel ◽

Β Cells ◽

Pancreatic Β Cells ◽

Cytosolic Ph ◽

Deficient Mice

AbstractHere, we demonstrate that the voltage-gated proton channel Hv1 represents a regulatory mechanism for insulin secretion of pancreatic islet β cell. In vivo, Hv1-deficient mice display hyperglycemia and glucose intolerance due to reduced insulin secretion, but normal peripheral insulin sensitivity. In vitro, islets of Hv1-deficient and heterozygous mice, INS-1 (832/13) cells with siRNA-mediated knockdown of Hv1 exhibit a marked defect in glucose- and K+-induced insulin secretion. Hv1 deficiency decreases both insulin and proinsulin contents, and limits glucose-induced Ca2+ entry and membrane depolarization. Furthermore, loss of Hv1 increases insulin-containing granular pH and decreases cytosolic pH. In addition, histologic studies show a decrease in β cell mass in islets of Hv1-deficient mice. Collectively, our results indicate that Hv1 supports insulin secretion in the β cell by calcium entry, membrane depolarization and intracellular pH regulation.SIGNIFICANCE STATEMENTThe voltage-gated proton channel Hv1 is highly expressed in insulin-containing granules in pancreatic β cells. Hv1 supports insulin secretion in the β cell by calcium entry, membrane depolarization and regulation of intragranular and cytosolic pH, which represents a regulatory mechanism for insulin secretion of pancreatic islet β cell. Our research demonstrates that Hv1 expressed in β cell is required for insulin secretion and maintains glucose homeostasis, and reveals a significant role for the proton channel in the modulation of pancreatic β cell function.

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