scholarly journals Thiol oxidation by 2,2′-dithiodipyridine causes a reversible increase in cytoplasmic free Ca2+ concentration in pancreatic β-cells. Role for inositol 1,4,5-trisphosphate-sensitive Ca2+ stores

1997 ◽  
Vol 321 (2) ◽  
pp. 347-354 ◽  
Author(s):  
Md. Shahidul ISLAM ◽  
Henrik KINDMARK ◽  
Olof LARSSON ◽  
Per-Olof BERGGREN
Keyword(s):  
Ryanodine Receptors ◽  
Membrane Depolarization ◽  
Thiol Oxidation ◽  
High Concentration ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Patch Clamp Technique ◽  
Mitochondrial Inner Membrane ◽  
Patch Configuration ◽  
Ca2 Channels

2,2ƀ-Dithiodipyridine (2,2ƀ-DTDP), a reactive disulphide that mobilizes Ca2+ from ryanodine-sensitive Ca2+ stores in muscle, induced a biphasic increase in cytoplasmic free Ca2+ concentration ([Ca2+]i) in pancreatic α-cells loaded with fura 2. This increase consisted of an early transient followed by a second, slower, rise. The [Ca2+]i transient was dependent on extracellular Ca2+ and disappeared on treatment with nimodipine. The reactive disulphide caused plasma membrane depolarization, as studied by the perforated-patch configuration of the patch-clamp technique. Hence membrane depolarization and opening of the L-type voltage-gated Ca2+ channels were responsible for the first transient in [Ca2+]i. The second slower increase in [Ca2+]i was prolonged but readily reversed by the disulphide-reducing agent 1,4-dithiothreitol. This increase in [Ca2+]i was not decreased by nimodipine or by omission of extracellular Ca2+, but was eliminated when the Ins(1,4,5)P3-sensitive Ca2+ pool was first depleted by carbachol. Ryanodine or its α-alanyl analogue did not release Ca2+ from intracellular stores, and a high concentration of ryanodine did not inhibit Ca2+ release by 2,2ƀ-DTDP. The disulphide compound suppressed glucose metabolism and decreased the mitochondrial inner-membrane potential. We conclude that thiol oxidation by 2,2ƀ-DTDP affects Ca2+ homeostasis in α-cells by multiple mechanisms. However, unlike the situation in muscle, in α-cells 2,2ƀ-DTDP releases Ca2+ from intracellular pools by mechanisms that do not involve activation of ryanodine receptors. Instead, in these cells the Ins(1,4,5)P3-sensitive intracellular Ca2+ store comprises an alternative target for the Ca2+-mobilizing action of the reactive disulphide compound.

scholarly journals PIP2 in pancreatic β-cells regulates voltage-gated calcium channels by a voltage-independent pathway

2016 ◽  
Vol 311 (4) ◽  
pp. C630-C640 ◽  
Author(s):  
Lizbeth de la Cruz ◽  
Erika I. Puente ◽  
Arturo Reyes-Vaca ◽  
Isabel Arenas ◽  
Julieta Garduño ◽  
...  
Keyword(s):  
Ion Channels ◽  
Temporal Association ◽  
Membrane Phospholipids ◽  
High Concentration ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Patch Clamp Technique ◽  
Voltage Gated ◽  
Channel Inhibition ◽  
Insulin Secreting Cells

Phosphatidylinositol-4,5-bisphosphate (PIP2) is a membrane phosphoinositide that regulates the activity of many ion channels. Influx of calcium primarily through voltage-gated calcium (CaV) channels promotes insulin secretion in pancreatic β-cells. However, whether CaV channels are regulated by PIP2, as is the case for some non-insulin-secreting cells, is unknown. The purpose of this study was to investigate whether CaV channels are regulated by PIP2 depletion in pancreatic β-cells through activation of a muscarinic pathway induced by oxotremorine methiodide (Oxo-M). CaV channel currents were recorded by the patch-clamp technique. The CaV current amplitude was reduced by activation of the muscarinic receptor 1 (M1R) in the absence of kinetic changes. The Oxo-M-induced inhibition exhibited the hallmarks of voltage-independent regulation and did not involve PKC activation. A small fraction of the Oxo-M-induced CaV inhibition was diminished by a high concentration of Ca2+ chelator, whereas ≥50% of this inhibition was prevented by diC8-PIP2 dialysis. Localization of PIP2 in the plasma membrane was examined by transfecting INS-1 cells with PH-PLCδ1, which revealed a close temporal association between PIP2 hydrolysis and CaV channel inhibition. Furthermore, the depletion of PIP2 by a voltage-sensitive phosphatase reduced CaV currents in a way similar to that observed following M1R activation. These results indicate that activation of the M1R pathway inhibits the CaV channel via PIP2 depletion by a Ca2+-dependent mechanism in pancreatic β- and INS-1 cells and thereby support the hypothesis that membrane phospholipids regulate ion channel activity by interacting with ion channels.

scholarly journals Ca2+-induced Ca2+ Release via Inositol 1,4,5-trisphosphate Receptors Is Amplified by Protein Kinase A and Triggers Exocytosis in Pancreatic β-Cells

2004 ◽  
Vol 279 (44) ◽  
pp. 45455-45461 ◽  
Author(s):  
Oleg Dyachok ◽  
Erik Gylfe
Keyword(s):  
Protein Kinase ◽  
Protein Kinase A ◽  
Ryanodine Receptors ◽  
Nucleotide Exchange ◽  
High Concentration ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Inositol 1,4,5 Trisphosphate ◽  
Glucagon Like Peptide 1 ◽  
Kinase A

Hormones, such as glucagon and glucagon-like peptide-1, potently amplify nutrient stimulated insulin secretion by raising cAMP. We have studied how cAMP affects Ca2+-induced Ca2+release (CICR) in pancreatic β-cells from mice and rats and the role of CICR in secretion. CICR was observed as pronounced Ca2+spikes on top of glucose- or depolarization-dependent rise of the cytoplasmic Ca2+concentration ([Ca2+]i). cAMP-elevating agents strongly promoted CICR. This effect involved sensitization of the receptors underlying CICR, because many cells exhibited the characteristic Ca2+spiking at low or even in the absence of depolarization-dependent elevation of [Ca2+]i. The cAMP effect was mimicked by a specific activator of protein kinase A in cells unresponsive to activators of cAMP-regulated guanine nucleotide exchange factor. Ryanodine pretreatment, which abolishes CICR mediated by ryanodine receptors, did not prevent CICR. Moreover, a high concentration of caffeine, known to activate ryanodine receptors independently of Ca2+, failed to mobilize intracellular Ca2+. On the contrary, a high caffeine concentration abolished CICR by interfering with inositol 1,4,5-trisphosphate receptors (IP3Rs). Therefore, the cell-permeable IP3R antagonist 2-aminoethoxydiphenyl borate blocked the cAMP-promoted CICR. Individual CICR events in pancreatic β-cells were followed by [Ca2+]ispikes in neighboring human erythroleukemia cells, used to report secretory events in the β-cells. The results indicate that protein kinase A-mediated promotion of CICR via IP3Rs is part of the mechanism by which cAMP amplifies insulin release.

scholarly journals Metabolic inhibition impairs ATP-sensitive K+ channel block by sulfonylurea in pancreatic β-cells

1998 ◽  
Vol 274 (1) ◽  
pp. E38-E44 ◽  
Author(s):  
Eri Mukai ◽  
Hitoshi Ishida ◽  
Seika Kato ◽  
Yoshiyuki Tsuura ◽  
Shimpei Fujimoto ◽  
...  
Keyword(s):  
Metabolic Inhibition ◽  
K Channel ◽  
High Dose ◽  
Dependent Manner ◽  
Channel Activity ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Patch Clamp Technique ◽  
Channel Inhibition ◽  
Dose Dependent

The effect of metabolic inhibition on the blocking of β-cell ATP-sensitive K+ channels (KATP channels) by glibenclamide was investigated using a patch-clamp technique. Inhibition of KATP channels by glibenclamide was attenuated in the cell-attached mode under metabolic inhibition induced by 2,4-dinitrophenol. Under a low concentration (0.1 μM) of ATP applied in the inside-out mode, KATP channel activity was not fully abolished, even when a high dose of glibenclamide was applied, in contrast to the dose-dependent and complete KATP channel inhibition under 10 μM ATP. On the other hand, cibenzoline, a class Ia antiarrhythmic agent, inhibits KATP channel activity in a dose-dependent manner and completely blocks it, even under metabolic inhibition. In sulfonylurea receptor (SUR1)- and inward rectifier K+ channel (Kir6.2)-expressed proteins, cibenzoline binds directly to Kir6.2, unlike glibenclamide. Thus, KATPchannel inhibition by glibenclamide is impaired under the condition of decreased intracellular ATP in pancreatic β-cells, probably because of a defect in signal transmission between SUR1 and Kir6.2 downstream of the site of sulfonylurea binding to SUR1.

scholarly journals N-Type Ca2+-Channels in Murine Pancreatic β-Cells Are Inhibited by an Exclusive Coupling with Somatostatin Receptor Subtype 1

Endocrinology ◽  
2009 ◽  
Vol 150 (2) ◽  
pp. 741-748 ◽  
Author(s):  
Paul A. Smith
Keyword(s):  
Insulin Secretion ◽  
Somatostatin Receptor ◽  
Inhibitory Effect ◽  
Receptor Subtype ◽  
Receptor Subtypes ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Somatostatin Receptor Subtypes ◽  
Perforated Patch Clamp ◽  
Ca2 Channels

Somatostatin (SRIF) is a well-established inhibitor of insulin secretion, an effect in part mediated by a direct inhibition of voltage-operated Ca2+-channels. However, the identity of the somatostatin receptor subtypes (SSTRs) and voltage-operated Ca2+-channels involved in this process are unknown. Whole-cell perforated patch-clamp methods were applied to the murine pancreatic β-cell line, MIN6, to explore the molecular pharmacology of this problem. SRIF-14 inhibited voltage-gated Ca2+ currents (ICa2+) by 19 ± 3% (n=24) with a pEC50 = 9.05 (95% confidence limits 9–9.1). This action was mimicked solely by 100 nm CH-275, a selective agonist at the somatostatin type 1 receptor (SSTR1), but not by 100 nm BIM-23027, L-362855, or NNC-269100; agonists selective for the other four SSTRs known to exist in MIN6. The inhibition of ICa2+ produced by SRIF and CH-275 was insensitive to pertussis toxin but was reversed by a prepulse to +100 mV. The inhibition of ICa2+ by SRIF-14 was unaffected by 20 μm nifedipine, an inhibitor of L-type Ca2+ channels. Application of the specific N-type Ca2+ channel (Cav2.2) inhibitor ω-conotoxin GV1A at 100 nm mimicked, and as a consequence abolished, the inhibitory effect of SRIF-14 on ICa2+. SRIF selectively inhibits N-type Ca2+-channels in murine pancreatic β-cells via exclusive coupling with SSTR1. These findings help explain how SSTR1 activation can inhibit insulin secretion in pancreatic β-cells and suggest a possible new therapeutic lead for treatment of hyperinsulinemia. In pancreatic β-cells, somatostatin selectively inhibits N-type, but not other, Ca2+-channels via a direct and exclusive coupling with somatostatin receptor subtype 1.

scholarly journals Effect of caffeine and coffee diets on calcium signalling in rat hippocampal neurons

2021 ◽  
Vol 67 (4) ◽  
pp. 37-43
Author(s):  
V.M. Shkryl ◽  
◽  
T.G. Turytska ◽  
V.A. Yavorsky ◽  
V.P. Lyashenko ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Calcium Level ◽  
Hippocampal Neurons ◽  
Ryanodine Receptors ◽  
Calcium Signalling ◽  
Membrane Depolarization ◽  
Calcium Mobilization ◽  
High Concentration ◽  
Excitability Of Neurons

The effects of long-lasting high concentration coffee and caffeine diets on calcium mobilization in rat hippocampal neurons were studied. Changes in the basal calcium level in the hippocampal neurons of control and experimental rats kept on a coffee or caffeine diet were measured. We also recorded the changes in the Ca2+ transients’ amplitude evoked by membrane depolarization or emptying the Ca2+ depot of the endoplasmic reticulum (ER) induced by caffeine activator of the ryanodine receptors. In rats on a coffee or caffeine diet, the basal Ca2+ level was increased by 7.4% and 11%, respectively, compared to control animals. In these groups, the amplitude of Ca2+ transients increased by 70% and 90%, respectively, of the basal level in response to the membrane depolarization. In the same groups, the amount of Ca2+ released from the ER was increased by two and three times, respectively, compared to the control after activation of ryanodine receptors. We concluded that long-term coffee and caffeine diets in rats cause a significant disruption of the hippocampal neurons’ endoplasmic reticulum function. The diets evoke an increase in Ca2+ concentration in the neurons and an excessive release of Ca2+ in response to excitation. The latter can lead to increased excitability of neurons and their further death from excessive Ca2+ levels.

scholarly journals Intracellular ATP Signaling Contributes to FAM3A-Induced PDX1 Upregulation in Pancreatic Beta Cells

2021 ◽  
Author(s):  
Han Yan ◽  
Zhenzhen Chen ◽  
Haizeng Zhang ◽  
Weili Yang ◽  
Xiangyang Liu ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Pancreatic Beta Cells ◽  
Mitochondrial Protein ◽  
Extracellular Atp ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Intracellular Atp ◽  
Pdx1 Expression ◽  
Ca2 Channels

AbstractFAM3A is a recently identified mitochondrial protein that stimulates pancreatic-duodenal homeobox 1 (PDX1) and insulin expressions by promoting ATP release in islet β cells. In this study, the role of intracellular ATP in FAM3A-induced PDX1 expression in pancreatic β cells was further examined. Acute FAM3A inhibition using siRNA transfection in mouse pancreatic islets significantly reduced PDX1 expression, impaired insulin secretion, and caused glucose intolerance in normal mice. In vitro, FAM3A overexpression elevated both intracellular and extracellular ATP contents and promoted PDX1 expression and insulin secretion. FAM3A-induced increase in cellular calcium (Ca2+) levels, PDX1 expression, and insulin secretion, while these were significantly repressed by inhibitors of P2 receptors or the L-type Ca2+ channels. FAM3A-induced PDX1 expression was abolished by a calmodulin inhibitor. Likewise, FAM3A-induced β-cell proliferation was also inhibited by a P2 receptor inhibitor and an L-type Ca2+ channels inhibitor. Both intracellular and extracellular ATP contributed to FAM3A-induced PDX1 expression, insulin secretion, and proliferation of pancreatic β cells.

Expression of CFTR controls cAMP-dependent activation of epithelial K+ currents

1996 ◽  
Vol 271 (5) ◽  
pp. C1565-C1573 ◽  
Author(s):  
G. Loussouarn ◽  
S. Demolombe ◽  
R. Mohammad-Panah ◽  
D. Escande ◽  
I. Baro
Keyword(s):  
Cftr Gene ◽  
High Concentration ◽  
Patch Clamp Technique ◽  
Whole Cell ◽  
Transfected Cells ◽  
Cyclic Monophosphate ◽  
K Current ◽  
Patch Configuration ◽  
Camp Stimulation ◽  
K Currents

The perforated-patch configuration of the patch-clamp technique was used to record whole cell currents from human epithelial CFPAC-1 cells defective for functional cystic fibrosis transmembrane conductance regulator (CFTR). In CFPAC-1 cells, adenosine 3',5'-cyclic monophosphate (cAMP) stimulation with forskolin (10 microM) plus 8-(4-chlorophenylthio)adenosine 3',5'-cyclic monophosphate (400 microM) activated neither Cl- nor K+ currents. In the same cells transfected with wild-type CFTR gene, cAMP stimulation produced activation of both Cl- and K+ currents. In Cl(-)-depleted medium (gluconate as a substitute), cAMP stimulation evoked a K+ current in CFTR-transfected but not in untransfected CFPAC-1 cells. This cAMP-evoked K+ current was the sum of two components: 1) a time-independent inwardly rectifying component, and 2) a slowly relaxing component activated at positive voltages. Increasing intracellular Ca2+ with ionomycin (1 microM) activated K+ currents in either transfected or untransfected cells. In transfected cells, blocking the CFTR conductance with high-concentration glibenclamide (100 microM) reduced the K+ current when activated by cAMP but not when activated by Ca2+. Pretreating CFTR-transfected cells for 48 h with interferon-gamma downregulated CFTR gene expression and reduced cAMP but not Ca2+ activation of the whole cell K+ current. From these results, we conclude that functional membrane CFTR protein influences activation by cAMP of epithelial K+ currents.

Ryanodine receptors of pancreatic β‐cells mediate a distinct context‐dependent signal for insulin secretion

2002 ◽  
Vol 17 (2) ◽  
pp. 301-303 ◽  
Author(s):  
Joseph D. Bruton ◽  
Raf Lemmens ◽  
Chun‐Liang Shi ◽  
Solveig Persson‐Sjögren ◽  
Håkan Westerblad ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Ryanodine Receptors ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Dependent Signal ◽  
Context Dependent

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

2017 ◽  
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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