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Kostritskaia Y, Klüssendorf M, Pan YE, Hassani Nia F, Kostova S, Stauber T. Physiological Functions of the Volume-Regulated Anion Channel VRAC/LRRC8 and the Proton-Activated Chloride Channel ASOR/TMEM206. Handb Exp Pharmacol 2024; 283:181-218. [PMID: 37468723 DOI: 10.1007/164_2023_673] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/21/2023]
Abstract
Volume-regulated anion channels (VRACs) and the acid-sensitive outwardly rectifying anion channel (ASOR) mediate flux of chloride and small organic anions. Although known for a long time, they were only recently identified at the molecular level. VRACs are heteromers consisting of LRRC8 proteins A to E. Combining the essential LRRC8A with different LRRC8 paralogues changes key properties of VRAC such as conductance or substrate selectivity, which is how VRACs are involved in multiple physiological functions including regulatory volume decrease, cell proliferation and migration, cell death, purinergic signalling, fat and glucose metabolism, insulin signalling, and spermiogenesis. VRACs are also involved in pathological conditions, such as the neurotoxic release of glutamate and aspartate. Certain VRACs are also permeable to larger, organic anions, including antibiotics and anti-cancer drugs, making them an interesting therapeutic target. ASOR, also named proton-activated chloride channel (PAC), is formed by TMEM206 homotrimers on the plasma membrane and on endosomal compartments where it mediates chloride flux in response to extracytosolic acidification and plays a role in the shrinking and maturation of macropinosomes. ASOR has been shown to underlie neuronal swelling which causes cell death after stroke as well as promoting the metastasis of certain cancers, making them intriguing therapeutic targets as well.
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Affiliation(s)
- Yulia Kostritskaia
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Malte Klüssendorf
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Yingzhou Edward Pan
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Fatemeh Hassani Nia
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Simona Kostova
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany
| | - Tobias Stauber
- Institute for Molecular Medicine, MSH Medical School Hamburg, Hamburg, Germany.
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Chen L, König B, Liu T, Pervaiz S, Razzaque YS, Stauber T. More than just a pressure relief valve: physiological roles of volume-regulated LRRC8 anion channels. Biol Chem 2019; 400:1481-1496. [DOI: 10.1515/hsz-2019-0189] [Citation(s) in RCA: 31] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2019] [Accepted: 04/27/2019] [Indexed: 12/29/2022]
Abstract
Abstract
The volume-regulated anion channel (VRAC) is a key player in the volume regulation of vertebrate cells. This ubiquitously expressed channel opens upon osmotic cell swelling and potentially other cues and releases chloride and organic osmolytes, which contributes to regulatory volume decrease (RVD). A plethora of studies have proposed a wide range of physiological roles for VRAC beyond volume regulation including cell proliferation, differentiation and migration, apoptosis, intercellular communication by direct release of signaling molecules and by supporting the exocytosis of insulin. VRAC was additionally implicated in pathological states such as cancer therapy resistance and excitotoxicity under ischemic conditions. Following extensive investigations, 5 years ago leucine-rich repeat-containing family 8 (LRRC8) heteromers containing LRRC8A were identified as the pore-forming components of VRAC. Since then, molecular biological approaches have allowed further insight into the biophysical properties and structure of VRAC. Heterologous expression, siRNA-mediated downregulation and genome editing in cells, as well as the use of animal models have enabled the assessment of the proposed physiological roles, together with the identification of new functions including spermatogenesis and the uptake of antibiotics and platinum-based cancer drugs. This review discusses the recent molecular biological insights into the physiology of VRAC in relation to its previously proposed roles.
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Affiliation(s)
- Lingye Chen
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Benjamin König
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Tianbao Liu
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Sumaira Pervaiz
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Yasmin S. Razzaque
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
| | - Tobias Stauber
- Institut für Chemie und Biochemie , Freie Universität Berlin , Thielallee 63 , D-14195 Berlin , Germany
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Akita T, Okada Y. Characteristics and roles of the volume-sensitive outwardly rectifying (VSOR) anion channel in the central nervous system. Neuroscience 2014; 275:211-31. [DOI: 10.1016/j.neuroscience.2014.06.015] [Citation(s) in RCA: 72] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2014] [Revised: 06/06/2014] [Accepted: 06/07/2014] [Indexed: 01/05/2023]
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Langelueddecke C, Jakab M, Ketterl N, Lehner L, Hufnagl C, Schmidt S, Geibel JP, Fuerst J, Ritter M. Effect of the AMP-kinase modulators AICAR, metformin and compound C on insulin secretion of INS-1E rat insulinoma cells under standard cell culture conditions. Cell Physiol Biochem 2012; 29:75-86. [PMID: 22415077 DOI: 10.1159/000337589] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/19/2011] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND/AIMS The function of β-cells is regulated by nutrient uptake and metabolism. The cells' metabolic state can be expressed as concentration ratios of AMP, ADP and ATP. Relative changes in these ratios regulate insulin release. An increase in the intracellular ATP concentration causes closure of K(ATP) channels and cell membrane depolarization, which triggers stimulus-secretion coupling (SSC). In addition to K(ATP) channels, the AMP-dependent protein kinase (AMPK), a major cellular fuel sensor in a variety of cells and tissues, also affects insulin secretion and β-cell survival. In a previous study we found that the widely used AMPK inhibitor compound C retards proliferation and induces apoptosis in the rat β-cell line INS-1E. We therefore tested the effects of AMPK activators (AICAR and metformin), and compound C on AMPK phosphorylation, insulin secretion, K(ATP) channel currents, cell membrane potential, intracellular calcium concentration, apoptosis and cell cycle distribution of INS-1E cells under standard cell culture conditions (11 mM glucose). METHODS Western blotting, ELISA, patch-clamp, calcium imaging and flow cytometry. RESULTS We found that basal AMPK phosphorylation is enhanced by AICAR (1 mM) and metformin (1 mM) but remained unaffected by compound C (10 μM). Both AICAR and compound C stimulated basal insulin secretion whereas metformin had no effect. Pre-incubation with AICAR (1 mM) caused an inhibition of K(ATP) currents but did not significantly alter the average cell membrane potential (Vm) or the threshold potential of electrical activity. Acute administration of AICAR (300 μM) led to a depolarization of Vm, which was not due to an inhibition of the basal- or glucose-induced chloride conductance, and was not accompanied by elevations of intracellular calcium (Ca(i)). AICAR had no additive blocking effect on K(ATP) currents when applied together with tolbutamide. Compound C applied over 24 hours induced an increase in the percentage of cells positive for caspase activity, whereas AICAR (1 mM) applied for 48 hours was without effect. Medium glucose concentration <3 mM caused cell cycle arrest, caspase activation and an increase of cell granularity. CONCLUSION We conclude that under standard cell culture conditions the AMPK modulators AICAR and compound C, but not metformin, stimulate insulin secretion by AMPK-independent mechanisms.
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Drews G, Krippeit-Drews P, Düfer M. Electrophysiology of islet cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:115-63. [PMID: 20217497 DOI: 10.1007/978-90-481-3271-3_7] [Citation(s) in RCA: 100] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Stimulus-Secretion Coupling (SSC) of pancreatic islet cells comprises electrical activity. Changes of the membrane potential (V(m)) are regulated by metabolism-dependent alterations in ion channel activity. This coupling is best explored in beta-cells. The effect of glucose is directly linked to mitochondrial metabolism as the ATP/ADP ratio determines the open probability of ATP-sensitive K(+) channels (K(ATP) channels). Nucleotide sensitivity and concentration in the direct vicinity of the channels are controlled by several factors including phospholipids, fatty acids, and kinases, e.g., creatine and adenylate kinase. Closure of K(ATP) channels leads to depolarization of beta-cells via a yet unknown depolarizing current. Ca(2+) influx during action potentials (APs) results in an increase of the cytosolic Ca(2+) concentration ([Ca(2+)](c)) that triggers exocytosis. APs are elicited by the opening of voltage-dependent Na(+) and/or Ca(2+) channels and repolarized by voltage- and/or Ca(2+)-dependent K(+) channels. At a constant stimulatory glucose concentration APs are clustered in bursts that are interrupted by hyperpolarized interburst phases. Bursting electrical activity induces parallel fluctuations in [Ca(2+)](c) and insulin secretion. Bursts are terminated by I(Kslow) consisting of currents through Ca(2+)-dependent K(+) channels and K(ATP) channels. This review focuses on structure, characteristics, physiological function, and regulation of ion channels in beta-cells. Information about pharmacological drugs acting on K(ATP) channels, K(ATP) channelopathies, and influence of oxidative stress on K(ATP) channel function is provided. One focus is the outstanding significance of L-type Ca(2+) channels for insulin secretion. The role of less well characterized beta-cell channels including voltage-dependent Na(+) channels, volume sensitive anion channels (VSACs), transient receptor potential (TRP)-related channels, and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels is discussed. A model of beta-cell oscillations provides insight in the interplay of the different channels to induce and maintain electrical activity. Regulation of beta-cell electrical activity by hormones and the autonomous nervous system is discussed. alpha- and delta-cells are also equipped with K(ATP) channels, voltage-dependent Na(+), K(+), and Ca(2+) channels. Yet the SSC of these cells is less clear and is not necessarily dependent on K(ATP) channel closure. Different ion channels of alpha- and delta-cells are introduced and SSC in alpha-cells is described in special respect of paracrine effects of insulin and GABA secreted from beta-cells.
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Affiliation(s)
- Gisela Drews
- Institute of Pharmacy, Department of Pharmacology and Clinical Pharmacy, University of Tübingen, 72076 Tübingen, Germany.
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Merrins MJ, Stuenkel EL. Kinetics of Rab27a-dependent actions on vesicle docking and priming in pancreatic beta-cells. J Physiol 2008; 586:5367-81. [PMID: 18801842 PMCID: PMC2655366 DOI: 10.1113/jphysiol.2008.158477] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Accepted: 09/18/2008] [Indexed: 12/26/2022] Open
Abstract
The small GTPase Rab27a, along with the isoforms of Rab3, is present on insulin secretory granules and has been implicated in regulation of Ca(2+)-triggered exocytosis. We have used membrane capacitance measurements to define the role of Rab27a in regulating the size and refilling of distinct pools of insulin granules by comparison of evoked secretory responses from Rab27a-null ashen and strain-matched wild-type control pancreatic beta-cells. We find that ashen beta-cells display a kinetic defect in refilling of readily releasable and immediately releasable vesicle pools (RRP and IRP, respectively) in response to depolarization-evoked Ca(2+) influx. The deficit in IRP refilling was not observed in the presence of stimulatory glucose concentrations (16.7 mm), though incomplete refilling of the RRP persisted. Comparatively, beta-cells from Rab3a(-/-) mice exhibited complete refilling of the IRP and RRP, demonstrating that Rab27a and Rab3a exert distinct roles in the insulin granule secretory pathway. Further, depletion of the RRP in ashen beta-cells was twofold faster than that of control beta-cells. These deficits in refilling and exocytotic rate in ashen beta-cells were absent when cAMP-regulatory pathways were activated. Elevated cAMP increased the RRP pool size, and complete refilling of the RRP occurred in ashen beta-cells; responses were comparable to wild-type controls. These effects of cAMP were largely eliminated by Rp-cAMP inhibition of PKA, indicating that PKA acts on vesicle priming downstream or via pathways independent of Rab27a. In summary, Rab27a exerts dual roles in glucose-mediated insulin granule exocytosis, facilitating refilling of releasable granule pools while also limiting the rate of release from these pools.
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Affiliation(s)
- Matthew J Merrins
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109-0622, USA
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Best L, Elliott AC, Brown PD. Curcumin induces electrical activity in rat pancreatic beta-cells by activating the volume-regulated anion channel. Biochem Pharmacol 2007; 73:1768-75. [PMID: 17382910 DOI: 10.1016/j.bcp.2007.02.006] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2007] [Revised: 02/09/2007] [Accepted: 02/12/2007] [Indexed: 11/21/2022]
Abstract
Curcumin, the principal active component of turmeric, is reported to exert a number of therapeutic actions, including a hypoglycaemic/antidiabetic action. The underlying mechanisms to this action are essentially unknown. We have investigated the hypothesis that a direct stimulatory action on the pancreatic beta-cell could contribute towards the hypoglycaemic activity of this compound. Electrical and ion channel activity were recorded in rat beta-cells using the patch-clamp technique. beta-Cell volume was measured using a video-imaging technique. Insulin release was measured from intact islets by radioimmunoassay. Curcumin (2-10 microM) activated the volume-regulated anion channel in beta-cells. Single channel studies indicated that activation was the result of increased channel open probability. This effect was accompanied by depolarisation of the cell membrane potential, the generation of electrical activity and enhanced insulin release. Curcumin also decreased beta-cell volume, presumably reflecting loss of Cl(-) (and hence water) as a result of anion channel activation. These findings are consistent with the suggestion that Cl(-) fluxes play an important role in regulating beta-cell function. The stimulation of beta-cell function by curcumin could contribute to the hypoglycaemic actions of this compound, and these findings identify a novel potential therapeutic target for the treatment of type 2 diabetes mellitus.
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Affiliation(s)
- Leonard Best
- Department of Medicine, University of Manchester, Oxford Road, Manchester M13 9WL, UK.
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Davies SL, Brown PD, Best L. Glucose-induced swelling in rat pancreatic alpha-cells. Mol Cell Endocrinol 2007; 264:61-7. [PMID: 17112656 DOI: 10.1016/j.mce.2006.10.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/06/2006] [Revised: 07/31/2006] [Accepted: 10/05/2006] [Indexed: 11/23/2022]
Abstract
Pancreatic beta-cells increase in volume when exposed to elevated concentrations of extracellular glucose. This study has examined the effects of glucose on the volumes of pancreatic alpha-cells, which like beta-cells are regulated by glucose, and intestinal epithelial Caco-2 cells which are unresponsive to glucose. Cell volume changes were monitored by a video-imaging method. Increasing the extracellular glucose concentration caused a concentration-dependent increase in alpha-cell volume over the range 1-20mM. Glucose-induced swelling was not, however, observed in Caco-2 cells. The glucose-induced swelling in both alpha- and beta-cells was abolished by 0.5mM phloretin, an inhibitor of the GLUT proteins, indicating that GLUT mediated glucose transport is a pre-requisite for swelling. Glucose metabolism also appears to be essential, as islet cell swelling was not observed with 16 mM 3-O-methyl glucose. These data suggest that glucose-induced swelling may be a property exclusive to glucose-regulated cells.
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Affiliation(s)
- Sarah L Davies
- Faculty of Life Sciences, University of Manchester, 2nd Floor Core Technology Facility, 46 Grafton Street, Manchester M13 9NT, United Kingdom
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Hermoso M, Olivero P, Torres R, Riveros A, Quest AFG, Stutzin A. Cell volume regulation in response to hypotonicity is impaired in HeLa cells expressing a protein kinase Calpha mutant lacking kinase activity. J Biol Chem 2004; 279:17681-9. [PMID: 14960580 DOI: 10.1074/jbc.m304506200] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The chloride conductance (G(Cl,swell)) that participates in the regulatory volume decrease process triggered by osmotic swelling in HeLa cells was impaired by removal of extracellular Ca(2+), depletion of intracellular Ca(2+) stores with thapsigargin, or by preloading the cells with BAPTA-AM (1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid). Furthermore, overnight exposure to the phorbol ester tetradecanoyl phorbol acetate and acute incubation with inhibitors of the conventional protein kinase C (PKC) isoforms bisindolylmaleimide I and Gö6976 inhibited G(Cl,swell). Treatment of HeLa cells with U73122, a phospholipase C inhibitor, also prevented G(Cl,swell). Hypotonicity induced selective PKC alpha accumulation in the membrane/cytoskeleton fraction in fractionation experiments and translocation of a green fluorescent protein-PKC alpha fusion protein to the plasma membrane of transiently transfected HeLa cells. To further explore the role of PKCs in hypotonicity-induced G(Cl,swell), HeLa clones stably expressing either a kinase-dead dominant negative variant of the Ca(2+)-dependent PKC isoform alpha (PKC alpha K386R) or of the atypical PKC isoform zeta (PKCzeta K275W) were generated. G(Cl,swell) was significantly reduced in HeLa cells expressing the dominant negative PKC alpha mutant but remained unaltered in cells expressing dominant negative PKCzeta. These findings strongly implicate PKC alpha as a critical regulatory element that is required for efficient regulatory volume decrease in HeLa cells.
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Affiliation(s)
- Marcela Hermoso
- Instituto de Ciencias Biomédicas and Centro de Estudios Moleculares de la Célula Facultad de Medicina, Universidad de Chile, Santiago 6530499, Santiago, Chile
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Okada Y, Maeno E, Shimizu T, Dezaki K, Wang J, Morishima S. Receptor-mediated control of regulatory volume decrease (RVD) and apoptotic volume decrease (AVD). J Physiol 2001; 532:3-16. [PMID: 11283221 PMCID: PMC2278524 DOI: 10.1111/j.1469-7793.2001.0003g.x] [Citation(s) in RCA: 412] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2001] [Accepted: 01/30/2001] [Indexed: 01/31/2023] Open
Abstract
A fundamental property of animal cells is the ability to regulate their own cell volume. Even under hypotonic stress imposed by either decreased extracellular or increased intracellular osmolarity, the cells can re-adjust their volume after transient osmotic swelling by a mechanism known as regulatory volume decrease (RVD). In most cell types, RVD is accomplished mainly by KCl efflux induced by parallel activation of K+ and Cl- channels. We have studied the molecular mechanism of RVD in a human epithelial cell line (Intestine 407). Osmotic swelling results in a significant increase in the cytosolic Ca2+ concentration and thereby activates intermediate-conductance Ca2+-dependent K+ (IK) channels. Osmotic swelling also induces ATP release from the cells to the extracellular compartment. Released ATP stimulates purinergic ATP (P2Y2) receptors, thereby inducing phospholipase C-mediated Ca2+ mobilization. Thus, RVD is facilitated by stimulation of P2Y2 receptors due to augmentation of IK channels. In contrast, stimulation of another G protein-coupled Ca2+-sensing receptor (CaR) enhances the activity of volume-sensitive outwardly rectifying Cl- channels, thereby facilitating RVD. Therefore, it is possible that Ca2+ efflux stimulated by swelling-induced and P2Y2 receptor-mediated intracellular Ca2+ mobilization activates the CaR, thereby secondarily upregulating the volume-regulatory Cl- conductance. On the other hand, the initial process towards apoptotic cell death is coupled to normotonic cell shrinkage, called apoptotic volume decrease (AVD). Stimulation of death receptors, such as TNF receptor and Fas, induces AVD and thereafter biochemical apoptotic events in human lymphoid (U937), human epithelial (HeLa), mouse neuroblastoma x rat glioma hybrid (NG108-15) and rat phaeochromocytoma (PC12) cells. In those cells exhibiting AVD, facilitation of RVD is always observed. Both AVD induction and RVD facilitation as well as succeeding apoptotic events can be abolished by prior treatment with a blocker of volume-regulatory K+ or Cl- channels, suggesting that AVD is caused by normotonic activation of ion channels that are normally involved in RVD under hypotonic conditions. Therefore, it is likely that G protein-coupled receptors involved in RVD regulation and death receptors triggering AVD may share common downstream signals which should give us key clues to the detailed mechanisms of volume regulation and survival of animal cells. In this Topical Review, we look at the physiological ionic mechanisms of cell volume regulation and cell death-associated volume changes from the facet of receptor-mediated cellular processes.
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Affiliation(s)
- Y Okada
- Department of Cell Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan.
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Best L. Glucose-sensitive conductances in rat pancreatic beta-cells: contribution to electrical activity. BIOCHIMICA ET BIOPHYSICA ACTA 2000; 1468:311-9. [PMID: 11018675 DOI: 10.1016/s0005-2736(00)00272-8] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
The perforated patch technique was used to assess the relative contribution of K(ATP) channel activity, assessed from input conductance (G(input)), and volume-sensitive anion channel activity to the induction of electrical activity in single isolated rat pancreatic beta-cells by glucose, 2-ketoisocaproate and tolbutamide. In cells equilibrated in the absence of glucose, the membrane potential was -71 mV and G(input) 3.66 nS. Addition of 8 mM glucose resulted in depolarisation, electrical activity and a reduction in G(input), reflecting an inhibition of K(ATP) channels. Cells equilibrated in 4 mM glucose had a membrane potential of -59 mV and a G(input) of 0.88 nS. In this case, a rise in glucose concentration to 8-20 mM again resulted in depolarisation and electrical activity, but caused a small increase in G(input). 2-Ketoisocaproate also evoked electrical activity and an increase in G(input), whereas electrical activity elicited by addition of tolbutamide was accompanied by reduced G(input). Increasing the concentration of glucose from 4 to 8-20 mM generated a noisy inward current at -70 mV, reflecting activation of the volume-sensitive anion channel. The mean amplitude of this current was glucose-dependent within the range 4-20 mM. Addition of 2-ketoisocaproate or a 15% hypotonic solution elicited similar increases in inward current. In contrast, addition of tolbutamide failed to induce the inward current. It is concluded that K(ATP) channel activity is most sensitive to glucose within the range 0-4 mM. At higher glucose concentrations effective in generating electrical activity, activation of the volume-sensitive anion channel could contribute towards the nutrient-induced increase in G(input).
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Affiliation(s)
- L Best
- Department of Medicine, University of Manchester, Oxford Road, M13 9WL, Manchester, UK.
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Deleuze C, Duvoid A, Moos FC, Hussy N. Tyrosine phosphorylation modulates the osmosensitivity of volume-dependent taurine efflux from glial cells in the rat supraoptic nucleus. J Physiol 2000; 523 Pt 2:291-9. [PMID: 10699075 PMCID: PMC2269807 DOI: 10.1111/j.1469-7793.2000.t01-2-00291.x] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. In the supraoptic nucleus, taurine, selectively released in an osmodependent manner by glial cells through volume-sensitive anion channels, is likely to inhibit neuronal activity as part of the osmoregulation of vasopressin release. We investigated the involvement of various kinases in the activation of taurine efflux by measuring [3H]taurine release from rat acutely isolated supraoptic nuclei. 2. The protein tyrosine kinase inhibitors genistein and tyrphostin B44 specifically reduced, but did not suppress, both the basal release of taurine and that evoked by a hypotonic stimulus. Inhibition of tyrosine phosphatase by orthovanadate had the opposite effect. 3. The tyrosine kinase and phosphatase inhibitors shifted the relationship between taurine release and medium osmolarity in opposite directions, suggesting that tyrosine phosphorylation modulates the osmosensitivity of taurine release, but is not necessary for its activation. 4. Genistein also increased the amplitude of the decay of the release observed during prolonged hypotonic stimulation. Potentiation of taurine release by tyrosine kinases could serve to maintain a high level of taurine release in spite of cell volume regulation. 5. Taurine release was unaffected by inhibitors and/or activators of PKA, PKC, MEK and Rho kinase. 6. Our results demonstrate a unique regulation by protein tyrosine kinase of the osmosensitivity of taurine efflux in supraoptic astrocytes. This points to the presence of specific volume-dependent anion channels in these cells, or to a specific activation mechanism or regulatory properties. This may relate to the particular role of the osmodependent release of taurine in this structure in the osmoregulation of neuronal activity.
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Affiliation(s)
- C Deleuze
- Biologie des Neurones Endocrines, CNRS-UPR 9055, CCIPE, 141 rue de la Cardonille, 34094 Montpellier Cedex 5, France
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