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Abstract
Beta cells of the pancreatic islet express many different types of ion channels. These channels reside in the β-cell plasma membrane as well as subcellular organelles and their coordinated activity and sensitivity to metabolism regulate glucose-dependent insulin secretion. Here, we review the molecular nature, expression patterns, and functional roles of many β-cell channels, with an eye toward explaining the ionic basis of glucose-induced insulin secretion. Our primary focus is on KATP and voltage-gated Ca2+ channels as these primarily regulate insulin secretion; other channels in our view primarily help to sculpt the electrical patterns generated by activated β-cells or indirectly regulate metabolism. Lastly, we discuss why understanding the physiological roles played by ion channels is important for understanding the secretory defects that occur in type 2 diabetes. © 2021 American Physiological Society. Compr Physiol 11:1-21, 2021.
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Affiliation(s)
- Benjamin Thompson
- Department of Pharmacology, University of Michigan Medical School, Ann Arbor, Michigan, USA
- Brehm Diabetes Research Center, University of Michigan Medical School, Ann Arbor, Michigan, USA
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2
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Selvaraj C, Selvaraj G, Kaliamurthi S, Cho WC, Wei DQ, Singh SK. Ion Channels as Therapeutic Targets for Type 1 Diabetes Mellitus. Curr Drug Targets 2020; 21:132-147. [PMID: 31538892 DOI: 10.2174/1389450119666190920152249] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 08/06/2019] [Accepted: 08/07/2019] [Indexed: 02/07/2023]
Abstract
Ion channels are integral proteins expressed in almost all living cells and are involved in muscle contraction and nutrient transport. They play a critical role in the normal functioning of the excitable tissues of the nervous system and regulate the action potential and contraction events. Dysfunction of genes encodes ion channel proteins, which disrupt the channel function and lead to a number of diseases, among which is type 1 diabetes mellitus (T1DM). Therefore, understanding the complex mechanism of ion channel receptors is necessary to facilitate the diagnosis and management of treatment. In this review, we summarize the mechanism of important ion channels and their potential role in the regulation of insulin secretion along with the limitations of ion channels as therapeutic targets. Furthermore, we discuss the recent investigations of the mechanism regulating the ion channels in pancreatic beta cells, which suggest that ion channels are active participants in the regulation of insulin secretion.
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Affiliation(s)
- Chandrabose Selvaraj
- Department of Bioinformatics, Computer-Aided Drug Design, and Molecular Modeling Lab, Science Block, Alagappa University, Karaikudi, Tamil Nadu, 630004, India
| | - Gurudeeban Selvaraj
- Center of Interdisciplinary Sciences-Computational Life Sciences, College of Food Science and Engineering, Henan University of Technology, Zhengzhou, 450001, China
- Peng Cheng Laboratory, Vanke Cloud City Phase I Building 8, Xili Street, Nanshan District, Shenzhen, Guangdong, 518055, China
| | - Satyavani Kaliamurthi
- Center of Interdisciplinary Sciences-Computational Life Sciences, College of Food Science and Engineering, Henan University of Technology, Zhengzhou, 450001, China
- Peng Cheng Laboratory, Vanke Cloud City Phase I Building 8, Xili Street, Nanshan District, Shenzhen, Guangdong, 518055, China
| | - William C Cho
- Department of Clinical Oncology, Queen Elizabeth Hospital, Kowloon, Hong Kong
| | - Dong-Qing Wei
- Center of Interdisciplinary Sciences-Computational Life Sciences, College of Food Science and Engineering, Henan University of Technology, Zhengzhou, 450001, China
- Peng Cheng Laboratory, Vanke Cloud City Phase I Building 8, Xili Street, Nanshan District, Shenzhen, Guangdong, 518055, China
- Department of Bioinformatics, The State Key Laboratory of Microbial Metabolism, College of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai, 200240, China
| | - Sanjeev Kumar Singh
- Department of Bioinformatics, Computer-Aided Drug Design, and Molecular Modeling Lab, Science Block, Alagappa University, Karaikudi, Tamil Nadu, 630004, India
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3
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Rorsman P, Ashcroft FM. Pancreatic β-Cell Electrical Activity and Insulin Secretion: Of Mice and Men. Physiol Rev 2018; 98:117-214. [PMID: 29212789 PMCID: PMC5866358 DOI: 10.1152/physrev.00008.2017] [Citation(s) in RCA: 446] [Impact Index Per Article: 74.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Revised: 05/30/2017] [Accepted: 06/18/2017] [Indexed: 12/14/2022] Open
Abstract
The pancreatic β-cell plays a key role in glucose homeostasis by secreting insulin, the only hormone capable of lowering the blood glucose concentration. Impaired insulin secretion results in the chronic hyperglycemia that characterizes type 2 diabetes (T2DM), which currently afflicts >450 million people worldwide. The healthy β-cell acts as a glucose sensor matching its output to the circulating glucose concentration. It does so via metabolically induced changes in electrical activity, which culminate in an increase in the cytoplasmic Ca2+ concentration and initiation of Ca2+-dependent exocytosis of insulin-containing secretory granules. Here, we review recent advances in our understanding of the β-cell transcriptome, electrical activity, and insulin exocytosis. We highlight salient differences between mouse and human β-cells, provide models of how the different ion channels contribute to their electrical activity and insulin secretion, and conclude by discussing how these processes become perturbed in T2DM.
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Affiliation(s)
- Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
| | - Frances M Ashcroft
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, United Kingdom; Department of Neuroscience and Physiology, Metabolic Research Unit, Göteborg, Sweden; and Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford, United Kingdom
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4
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Skelin Klemen M, Dolenšek J, Slak Rupnik M, Stožer A. The triggering pathway to insulin secretion: Functional similarities and differences between the human and the mouse β cells and their translational relevance. Islets 2017; 9:109-139. [PMID: 28662366 PMCID: PMC5710702 DOI: 10.1080/19382014.2017.1342022] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
In β cells, stimulation by metabolic, hormonal, neuronal, and pharmacological factors is coupled to secretion of insulin through different intracellular signaling pathways. Our knowledge about the molecular machinery supporting these pathways and the patterns of signals it generates comes mostly from rodent models, especially the laboratory mouse. The increased availability of human islets for research during the last few decades has yielded new insights into the specifics in signaling pathways leading to insulin secretion in humans. In this review, we follow the most central triggering pathway to insulin secretion from its very beginning when glucose enters the β cell to the calcium oscillations it produces to trigger fusion of insulin containing granules with the plasma membrane. Along the way, we describe the crucial building blocks that contribute to the flow of information and focus on their functional role in mice and humans and on their translational implications.
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Affiliation(s)
- Maša Skelin Klemen
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Jurij Dolenšek
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
| | - Marjan Slak Rupnik
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
- Institute of Physiology; Center for Physiology and Pharmacology; Medical University of Vienna; Vienna, Austria
| | - Andraž Stožer
- Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia
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Nguyen TTN, Folch B, Létourneau M, Truong NH, Doucet N, Fournier A, Chatenet D. Design of a truncated cardiotoxin-I analogue with potent insulinotropic activity. J Med Chem 2014; 57:2623-33. [PMID: 24552570 DOI: 10.1021/jm401904q] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Insulin secretion by pancreatic β-cells in response to glucose or other secretagogues is tightly coupled to membrane potential. Various studies have highlighted the prospect of enhancing insulin secretion in a glucose-dependent manner by blocking voltage-gated potassium channels (K(v)) and calcium-activated potassium channels (K(Ca)). Such strategy is expected to present a lower risk for hypoglycemic events compared to KATP channel blockers. Our group recently reported the discovery of a new insulinotropic agent, cardiotoxin-I (CTX-I), from the Naja kaouthia snake venom. In the present study, we report the design and synthesis of [Lys(52)]CTX-I(41-60) via structure-guided modification, a truncated, equipotent analogue of CTX-I, and demonstrate, using various pharmacological inhibitors, that this derivative probably exerts its action through Kv channels. This new analogue could represent a useful pharmacological tool to study β-cell physiology or even open a new therapeutic avenue for the treatment of type 2 diabetes.
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Affiliation(s)
- Thi Tuyet Nhung Nguyen
- INRS-Institut Armand-Frappier , Université du Québec , 531 Boulevard des Prairies Ville de Laval, Québec H7 V 1B7, Québec Canada
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6
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Abstract
Mathematical modeling of the electrical activity of the pancreatic β-cell has been extremely important for understanding the cellular mechanisms involved in glucose-stimulated insulin secretion. Several models have been proposed over the last 30 y, growing in complexity as experimental evidence of the cellular mechanisms involved has become available. Almost all the models have been developed based on experimental data from rodents. However, given the many important differences between species, models of human β-cells have recently been developed. This review summarizes how modeling of β-cells has evolved, highlighting the proposed physiological mechanisms underlying β-cell electrical activity.
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Key Words
- ADP, adenosine diphosphate
- ATP, adenosine triphosphate
- CK, Chay-Keizer
- CRAC, calcium release-activated current
- Ca2+, calcium ions
- DOM, dual oscillator model
- ER, endoplasmic reticulum
- F6P, fructose-6-phosphate
- FBP, fructose-1,6-bisphosphate
- GLUT, glucose transporter
- GSIS, glucose-stimulated insulin secretion
- HERG, human eter à-go-go related gene
- IP3R, inositol-1,4,5-trisphosphate receptors
- KATP, ATP-sensitive K+ channels
- KCa, Ca2+-dependent K+ channels
- Kv, voltage-dependent K+ channels
- MCU, mitochondrial Ca2+ uniporter
- NCX, Na+/Ca2+ exchanger
- PFK, phosphofructokinase
- PMCA, plasma membrane Ca2+-ATPase
- ROS, reactive oxygen species
- RyR, ryanodine receptors
- SERCA, sarco-endoplasmic reticulum Ca2+-ATPase
- T2D, Type 2 Diabetes
- TCA, trycarboxylic acid cycle
- TRP, transient receptor potential
- VDCC, voltage-dependent Ca2+ channels
- Vm, membrane potential
- [ATP]i, cytosolic ATP
- [Ca2+]i, intracellular calcium concentration
- [Ca2+]m, mitochondrial calcium
- [Na+], Na+ concentration
- action potentials
- bursting
- cAMP, cyclic AMP
- calcium
- electrical activity
- ion channels
- mNCX, mitochondrial Na+/Ca2+ exchanger
- mathematical model
- β-cell
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Affiliation(s)
- Gerardo J Félix-Martínez
- Department of Electrical Engineering; Universidad
Autónoma Metropolitana-Iztapalapa; México, DF,
México
- Correspondence to: Gerardo J
Félix-Martínez;
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7
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Andres MA. Glucose-sensitivity of the afterhyperpolarization potential: role of SK1 channel in insulin-secreting cells. Gen Comp Endocrinol 2012; 178:459-62. [PMID: 22809667 DOI: 10.1016/j.ygcen.2012.07.005] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/14/2012] [Accepted: 07/08/2012] [Indexed: 11/19/2022]
Abstract
The role of the small-conductance, calcium-activated SK potassium channel in regulating pancreatic β cell function remains controversial with conflicting pharmacological results. In this study, we used current clamp recordings to further characterize the function of SK channels in INS-1 cell line. We compared afterhyperpolarization potential (AHP) responses of SK1-downregulated cells with those of control INS-1 cells. They were tested with and without the presence of glucose. We found that cells in which SK1 channel subunit expression had been downregulated exhibited AHPs in the presence of 20mM glucose while control INS-1 cells had AHPs only in the absence of glucose. Our findings show that the glucose-dependence of the AHP in the rat INS-1 cell line depends only on SK1 channel subunit expression.
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Affiliation(s)
- Marilou A Andres
- Pacific Biosciences Research Center, University of Hawaii, Honolulu, HI 96822, USA.
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Rorsman P, Eliasson L, Kanno T, Zhang Q, Gopel S. Electrophysiology of pancreatic β-cells in intact mouse islets of Langerhans. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2011; 107:224-35. [PMID: 21762719 DOI: 10.1016/j.pbiomolbio.2011.06.009] [Citation(s) in RCA: 82] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Accepted: 06/21/2011] [Indexed: 10/18/2022]
Abstract
When exposed to intermediate glucose concentrations (6-16 mol/l), pancreatic β-cells in intact islets generate bursts of action potentials (superimposed on depolarised plateaux) separated by repolarised electrically silent intervals. First described more than 40 years ago, these oscillations have continued to intrigue β-cell electrophysiologists. To date, most studies of β-cell ion channels have been performed on isolated cells maintained in tissue culture (that do not burst). Here we will review the electrophysiological properties of β-cells in intact, freshly isolated, mouse pancreatic islets. We will consider the role of ATP-regulated K⁺-channels (K(ATP)-channels), small-conductance Ca²⁺-activated K⁺-channels and voltage-gated Ca²⁺-channels in the generation of the bursts. Our data indicate that K(ATP)-channels not only constitute the glucose-regulated resting conductance in the β-cell but also provide a variable K⁺-conductance that influence the duration of the bursts of action potentials and the silent intervals. We show that inactivation of the voltage-gated Ca²⁺-current is negligible at voltages corresponding to the plateau potential and consequently unlikely to play a major role in the termination of the burst. Finally, we propose a model for glucose-induced β-cell electrical activity based on observations made in intact pancreatic islets.
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Affiliation(s)
- Patrik Rorsman
- Oxford Centre for Diabetes, Endocrinology and Metabolism, University of Oxford, Oxford OX37LJ, UK.
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Cha CY, Nakamura Y, Himeno Y, Wang J, Fujimoto S, Inagaki N, Earm YE, Noma A. Ionic mechanisms and Ca2+ dynamics underlying the glucose response of pancreatic β cells: a simulation study. ACTA ACUST UNITED AC 2011; 138:21-37. [PMID: 21708953 PMCID: PMC3135323 DOI: 10.1085/jgp.201110611] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
To clarify the mechanisms underlying the pancreatic β-cell response to varying glucose concentrations ([G]), electrophysiological findings were integrated into a mathematical cell model. The Ca2+ dynamics of the endoplasmic reticulum (ER) were also improved. The model was validated by demonstrating quiescent potential, burst–interburst electrical events accompanied by Ca2+ transients, and continuous firing of action potentials over [G] ranges of 0–6, 7–18, and >19 mM, respectively. These responses to glucose were completely reversible. The action potential, input impedance, and Ca2+ transients were in good agreement with experimental measurements. The ionic mechanisms underlying the burst–interburst rhythm were investigated by lead potential analysis, which quantified the contributions of individual current components. This analysis demonstrated that slow potential changes during the interburst period were attributable to modifications of ion channels or transporters by intracellular ions and/or metabolites to different degrees depending on [G]. The predominant role of adenosine triphosphate–sensitive K+ current in switching on and off the repetitive firing of action potentials at 8 mM [G] was taken over at a higher [G] by Ca2+- or Na+-dependent currents, which were generated by the plasma membrane Ca2+ pump, Na+/K+ pump, Na+/Ca2+ exchanger, and TRPM channel. Accumulation and release of Ca2+ by the ER also had a strong influence on the slow electrical rhythm. We conclude that the present mathematical model is useful for quantifying the role of individual functional components in the whole cell responses based on experimental findings.
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Affiliation(s)
- Chae Young Cha
- Biosimulation Project, Ritsumeikan University, Kusatsu, Shiga, Japan
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10
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Düfer M, Neye Y, Hörth K, Krippeit-Drews P, Hennige A, Widmer H, McClafferty H, Shipston MJ, Häring HU, Ruth P, Drews G. BK channels affect glucose homeostasis and cell viability of murine pancreatic beta cells. Diabetologia 2011; 54:423-32. [PMID: 20981405 PMCID: PMC4005923 DOI: 10.1007/s00125-010-1936-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2010] [Accepted: 09/08/2010] [Indexed: 01/04/2023]
Abstract
AIMS/HYPOTHESIS Evidence is accumulating that Ca(2+)-regulated K(+) (K(Ca)) channels are important for beta cell function. We used BK channel knockout (BK-KO) mice to examine the role of these K(Ca) channels for glucose homeostasis, beta cell function and viability. METHODS Glucose and insulin tolerance were tested with male wild-type and BK-KO mice. BK channels were detected by single-cell RT-PCR, cytosolic Ca(2+) concentration ([Ca(2+)](c)) by fura-2 fluorescence, and insulin secretion by radioimmunoassay. Electrophysiology was performed with the patch-clamp technique. Apoptosis was detected via caspase 3 or TUNEL assay. RESULTS BK channels were expressed in murine pancreatic beta cells. BK-KO mice were normoglycaemic but displayed markedly impaired glucose tolerance. Genetic or pharmacological deletion of the BK channel reduced glucose-induced insulin secretion from isolated islets. BK-KO and BK channel inhibition (with iberiotoxin, 100 nmol/l) broadened action potentials and abolished the after-hyperpolarisation in glucose-stimulated beta cells. However, BK-KO did not affect action potential frequency, the plateau potential at which action potentials start or glucose-induced elevation of [Ca(2+)](c). BK-KO had no direct influence on exocytosis. Importantly, in BK-KO islet cells the fraction of apoptotic cells and the rate of cell death induced by oxidative stress (H(2)O(2), 10-100 μmol/l) were significantly increased compared with wild-type controls. Similar effects were obtained with iberiotoxin. Determination of H(2)O(2)-induced K(+) currents revealed that BK channels contribute to the hyperpolarising K(+) current activated under conditions of oxidative stress. CONCLUSIONS/INTERPRETATION Ablation or inhibition of BK channels impairs glucose homeostasis and insulin secretion by interfering with beta cell stimulus-secretion coupling. In addition, BK channels are part of a defence mechanism against apoptosis and oxidative stress.
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Affiliation(s)
- M Düfer
- Department of Pharmacology and Toxicology, Institute of Pharmacy, University of Tübingen, Auf der Morgenstelle 8, 72076 Tübingen, Germany
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11
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Houamed KM, Sweet IR, Satin LS. BK channels mediate a novel ionic mechanism that regulates glucose-dependent electrical activity and insulin secretion in mouse pancreatic β-cells. J Physiol 2010; 588:3511-23. [PMID: 20643769 DOI: 10.1113/jphysiol.2009.184341] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
BK channels are large unitary conductance K(+) channels cooperatively activated by intracellular calcium and membrane depolarisation. We show that BK channels regulate electrical activity in β-cells of mouse pancreatic islets exposed to elevated glucose. In 11.1 mM glucose, the non-peptidyl BK channel blocker paxilline increased the height of β-cell action potentials (APs) by 21 mV without affecting burst- or silent-period durations. In isolated β-cells, paxilline increased AP height by 16 mV without affecting resting membrane potential. In voltage clamp, paxilline blocked a transient component of outward current activated by a short depolarisation, which accounted for at least 90% of the initial outward K(+) current. This BK current (I(BK)) was blocked by the Ca(2+) channel blockers Cd(2+) (200 μM) or nimodipine (1 μM), and potentiated by FPL-64176 (1 μM). I(BK) was also 56% blocked by the BK channel blocker iberiotoxin (100 nM). I(BK) activated more than 10-fold faster than the delayed rectifier I(Kv) over the physiological voltage range, and partially inactivated. An AP-like command revealed that I(BK) activated and deactivated faster than I(Kv) and accounted for 86% of peak I(K), explaining why I(BK) block increased AP height. A higher amplitude AP-like command, patterned on an AP recorded in 11.1 mM glucose plus paxilline, activated 4-fold more I(Kv) and significantly increased Ca(2+) entry. Paxilline increased insulin secretion in islets exposed to 11.1 mM glucose by 67%, but did not affect basal secretion in 2.8 mM glucose. These data suggest a modified model of β-cell AP generation where I(BK) and I(Kv) coordinate the AP repolarisation.
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Affiliation(s)
- Khaled M Houamed
- Department of Pharmacology and Brehm Diabetes Center, University of Michigan Medical School, Ann Arbor, MI 48105, USA
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12
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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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13
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Düfer M, Gier B, Wolpers D, Krippeit-Drews P, Ruth P, Drews G. Enhanced glucose tolerance by SK4 channel inhibition in pancreatic beta-cells. Diabetes 2009; 58:1835-43. [PMID: 19401418 PMCID: PMC2712794 DOI: 10.2337/db08-1324] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/26/2008] [Accepted: 04/22/2009] [Indexed: 11/13/2022]
Abstract
OBJECTIVE Ca(2+)-regulated K(+) channels are involved in numerous Ca(2+)-dependent signaling pathways. In this study, we investigated whether the Ca(2+)-activated K(+) channel of intermediate conductance SK4 (KCa3.1, IK1) plays a physiological role in pancreatic beta-cell function. RESEARCH DESIGN AND METHODS Glucose tolerance and insulin sensitivity were determined in wild-type (WT) or SK4 knockout (SK4-KO) mice. Electrophysiological experiments were performed with the patch-clamp technique. The cytosolic Ca(2+) concentration ([Ca(2+)](c)) was determined by fura-2 fluorescence. Insulin release was assessed by radioimmunoassay, and SK4 protein was detected by Western blot analysis. RESULTS SK4-KO mice showed improved glucose tolerance, whereas insulin sensitivity was not altered. The animals were not hypoglycemic. Isolated SK4-KO beta-cells stimulated with 15 mmol/l glucose had an increased Ca(2+) action potential frequency, and single-action potentials were broadened. These alterations were coupled to increased [Ca(2+)](c). In addition, glucose responsiveness of membrane potential, [Ca(2+)](c), and insulin secretion were shifted to lower glucose concentrations. SK4 protein was expressed in WT islets. An increase in K(+) currents and concomitant membrane hyperpolarization could be evoked in WT beta-cells by the SK4 channel opener DCEBIO (100 micromol/l). Accordingly, the SK4 channel blocker TRAM-34 (1 micromol/l) partly inhibited K(Ca) currents and induced electrical activity at a threshold glucose concentration. In stimulated WT beta-cells, TRAM-34 further increased [Ca(2+)](c) and broadened action potentials similar to those seen in SK4-KO beta-cells. SK4 channels were found to substantially contribute to K(slow) (slowly activating K(+) current). CONCLUSIONS SK4 channels are involved in beta-cell stimulus-secretion coupling. Deficiency of SK4 current induces elevated beta-cell responsiveness and coincides with improved glucose tolerance in vivo. Therefore, pharmacologic modulation of these channels might provide an interesting approach for the development of novel insulinotropic drugs.
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Affiliation(s)
- Martina Düfer
- From the Institute of Pharmacy, the Department of Pharmacology, University of Tübingen, Tübingen, Germany
| | - Belinda Gier
- From the Institute of Pharmacy, the Department of Pharmacology, University of Tübingen, Tübingen, Germany
| | - Daniela Wolpers
- From the Institute of Pharmacy, the Department of Pharmacology, University of Tübingen, Tübingen, Germany
| | - Peter Krippeit-Drews
- From the Institute of Pharmacy, the Department of Pharmacology, University of Tübingen, Tübingen, Germany
| | - Peter Ruth
- From the Institute of Pharmacy, the Department of Pharmacology, University of Tübingen, Tübingen, Germany
| | - Gisela Drews
- From the Institute of Pharmacy, the Department of Pharmacology, University of Tübingen, Tübingen, Germany
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14
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Andres MA, Baptista NC, Efird JT, Ogata KK, Bellinger FP, Zeyda T. Depletion of SK1 channel subunits leads to constitutive insulin secretion. FEBS Lett 2008; 583:369-76. [PMID: 19101546 DOI: 10.1016/j.febslet.2008.12.024] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2008] [Revised: 12/08/2008] [Accepted: 12/09/2008] [Indexed: 11/28/2022]
Abstract
In the pancreas, the role of the small-conductance, calcium-activated SK channels remains controversial. Here, we show that three SK subtypes are expressed in the rat insulinoma cells. Our findings demonstrate that rat SK1 (rSK1) channels ensure appropriate insulin secretion by establishing the cell's negative resting membrane potential and shortening the duration of the action potential. We also found that the depletion of rSK1 transcripts generated a condition in which beta cells constitutively secrete insulin, even in the absence of a stimulating molecule (such as glucose). Together, these results implicate SK1 subunits as key regulators of excitability and endocrine function in beta cells.
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Affiliation(s)
- Marilou A Andres
- Pacific Biosciences Research Center, University of Hawaii, 1993 East-West Road, Honolulu, HI 96822, United States.
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15
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Rosário LM, Barbosa RM, Antunes CM, Baldeiras IE, Silva AM, Tomé AR, Santos RM. Regulation by glucose of oscillatory electrical activity and 5-HT/insulin release from single mouse pancreatic islets in absence of functional K(ATP) channels. Endocr J 2008; 55:639-50. [PMID: 18493109 DOI: 10.1507/endocrj.k07e-131] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The glucose sensitivity of bursting electrical activity and pulsatile insulin release from pancreatic islets was determined in absence of functional K(ATP) channels. Membrane potential, [Ca(2+)](i) and 5-HT/insulin release were measured by intracellular recording, fura-2 fluorescence and 5-HT amperometry, respectively. Single mouse islets, bathed in tolbutamide or glibenclamide and high extracellular Ca(2+) (Ca(2+)(o)), displayed bursting activity and concomitant fast [Ca(2+)](i) and 5-HT/insulin oscillations. Sulphonylurea block of K(ATP) channel current was unaffected by raising Ca(2+)(o). Raising glucose or alpha-ketoisocaproic acid (KIC) concentration from 3 to 30 mM increased spiking activity and burst plateau duration. Staurosporine did not impair glucose potentiation of electrical activity, ruling out the involvement of serine/threonine kinases. Glucose enhanced both [Ca(2+)](i) and 5-HT/insulin oscillatory activity, causing a approximately 3-fold increase in overall 5-HT release rate. Cells lacking bursting activity in high Ca(2+)(o) and low glucose (or KIC) developed a pattern of intensified spiking in response to 11 mM glucose. It is concluded that beta-cells exhibit graded oscillatory electrical and secretory responses to glucose in absence of functional K(ATP) channels. This suggests that, under physiological conditions, early glucose sensing may involve other channels besides the K(ATP) channel.
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Affiliation(s)
- Luís M Rosário
- Center for Neurosciences and Cell Biology, University of Coimbra, Portugal
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16
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Braun M, Ramracheya R, Bengtsson M, Zhang Q, Karanauskaite J, Partridge C, Johnson PR, Rorsman P. Voltage-gated ion channels in human pancreatic beta-cells: electrophysiological characterization and role in insulin secretion. Diabetes 2008; 57:1618-28. [PMID: 18390794 DOI: 10.2337/db07-0991] [Citation(s) in RCA: 313] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
OBJECTIVE To characterize the voltage-gated ion channels in human beta-cells from nondiabetic donors and their role in glucose-stimulated insulin release. RESEARCH DESIGN AND METHODS Insulin release was measured from intact islets. Whole-cell patch-clamp experiments and measurements of cell capacitance were performed on isolated beta-cells. The ion channel complement was determined by quantitative PCR. RESULTS Human beta-cells express two types of voltage-gated K(+) currents that flow through delayed rectifying (K(V)2.1/2.2) and large-conductance Ca(2+)-activated K(+) (BK) channels. Blockade of BK channels (using iberiotoxin) increased action potential amplitude and enhanced insulin secretion by 70%, whereas inhibition of K(V)2.1/2.2 (with stromatoxin) was without stimulatory effect on electrical activity and secretion. Voltage-gated tetrodotoxin (TTX)-sensitive Na(+) currents (Na(V)1.6/1.7) contribute to the upstroke of action potentials. Inhibition of Na(+) currents with TTX reduced glucose-stimulated (6-20 mmol/l) insulin secretion by 55-70%. Human beta-cells are equipped with L- (Ca(V)1.3), P/Q- (Ca(V)2.1), and T- (Ca(V)3.2), but not N- or R-type Ca(2+) channels. Blockade of L-type channels abolished glucose-stimulated insulin release, while inhibition of T- and P/Q-type Ca(2+) channels reduced glucose-induced (6 mmol/l) secretion by 60-70%. Membrane potential recordings suggest that L- and T-type Ca(2+) channels participate in action potential generation. Blockade of P/Q-type Ca(2+) channels suppressed exocytosis (measured as an increase in cell capacitance) by >80%, whereas inhibition of L-type Ca(2+) channels only had a minor effect. CONCLUSIONS Voltage-gated T-type and L-type Ca(2+) channels as well as Na(+) channels participate in glucose-stimulated electrical activity and insulin secretion. Ca(2+)-activated BK channels are required for rapid membrane repolarization. Exocytosis of insulin-containing granules is principally triggered by Ca(2+) influx through P/Q-type Ca(2+) channels.
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Affiliation(s)
- Matthias Braun
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford, UK.
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17
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Abstract
Coordinated electrical activity allows pancreatic beta-cells to respond to secretagogues with calcium entry followed by insulin secretion. Metabolism of glucose affects multiple membrane proteins including ion channels, transporters and pumps that collaborate in a cascade of electrical activity resulting in insulin release. Glucose induces beta-cell depolarization resulting in the firing of action potentials (APs), which are the primary electrical signal of the beta-cell. They are shaped by orchestrated activation of ion channels. Here we give an overview of the voltage-gated potassium (Kv) channels of the beta-cell, which are responsible in part for the falling phase of the AP, and how their regulation affects insulin secretion. beta cells contain several Kv channels allowing dynamic integration of multiple signals on repolarization of glucose-stimulated APs. Recent studies on Kv channel regulation by cAMP and arachidonic acid and on the Kv2.1 null mouse have greatly increased our understanding of beta-cell excitation-secretion coupling.
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Affiliation(s)
- D A Jacobson
- Department of Medicine, The University of Chicago, Chicago, IL 60637, USA
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18
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Jacobson DA, Kuznetsov A, Lopez JP, Kash S, Ämmälä CE, Philipson LH. Kv2.1 ablation alters glucose-induced islet electrical activity, enhancing insulin secretion. Cell Metab 2007; 6:229-35. [PMID: 17767909 PMCID: PMC2699758 DOI: 10.1016/j.cmet.2007.07.010] [Citation(s) in RCA: 138] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/04/2007] [Revised: 07/10/2007] [Accepted: 07/30/2007] [Indexed: 11/18/2022]
Abstract
Voltage-gated potassium currents (Kv), primarily due to Kv2.1 channels, are activated by glucose-stimulated pancreatic beta cell depolarization, but the exact role (or roles) of this channel in regulating insulin secretion remains uncertain. Here we report that, compared with controls, Kv2.1 null mice have reduced fasting blood glucose levels and elevated serum insulin levels. Glucose tolerance is improved and insulin secretion is enhanced compared to control animals, with similar results in isolated islets in vitro. Isolated Kv2.1(-/-) beta cells have residual Kv currents, which are decreased by 83% at +50 mV compared with control cells. The glucose-induced action potential (AP) duration is increased while the firing frequency is diminished, similar to the effect of specific toxins on control cells but substantially different from the effect of the less specific blocker tetraethylammonium. These results reveal the specific role of Kv2.1 in modulating glucose-stimulated APs of beta cells, exposing additional important currents involved in regulating physiological insulin secretion.
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Affiliation(s)
- David A. Jacobson
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
- Correspondence: (D.A.J.), (L.H.P.)
| | - Andrey Kuznetsov
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
| | - James P. Lopez
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
| | - Shera Kash
- Deltagen Inc., San Mateo, California 94403, USA
| | - Carina E. Ämmälä
- Department of Metabolic Diseases, GlaxoSmithKline, Research Triangle Park, North Carolina 27709, USA
| | - Louis H. Philipson
- Department of Medicine, The University of Chicago, Chicago, Illinois 60637, USA
- Correspondence: (D.A.J.), (L.H.P.)
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19
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Meyer-Hermann ME. The electrophysiology of the beta-cell based on single transmembrane protein characteristics. Biophys J 2007; 93:2952-68. [PMID: 17573431 PMCID: PMC1989707 DOI: 10.1529/biophysj.107.106096] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The electrophysiology of beta-cells is at the origin of insulin secretion. beta-Cells exhibit a complex behavior upon stimulation with glucose including repeated bursts and continuous spiking. Mathematical modeling is most suitable to improve knowledge about the function of various transmembrane currents provided the model is based on reliable data. This is the first attempt to build a mathematical model for the beta-cell electrophysiology in a bottom-up approach that relies on single protein conductance data. The results of previous whole-cell-based models are reconsidered. The full simulation including all prominent transmembrane proteins in beta-cells is used to provide a functional interpretation of their role in beta-cell bursting and an updated vantage point of beta-cell electrophysiology. As a result of a number of in silico knock-out and block experiments the novel model makes some unexpected predictions: single-channel conductance data imply that large-conductance calcium-gated potassium currents acquire the potential of driving oscillations at supralarge glucose levels. A more complex burst interruption model is presented. It also turns out that, depending on the species, sodium currents may be more relevant than considered so far. Experiments are proposed to verify these predictions.
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20
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Chen WP, Chi TC, Chuang LM, Su MJ. Resveratrol enhances insulin secretion by blocking K(ATP) and K(V) channels of beta cells. Eur J Pharmacol 2007; 568:269-77. [PMID: 17573071 DOI: 10.1016/j.ejphar.2007.04.062] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2006] [Revised: 04/21/2007] [Accepted: 04/24/2007] [Indexed: 02/06/2023]
Abstract
The present study investigated the effect of resveratrol on the electrophysiology and insulin secretion of pancreatic beta cells, and examined resveratrol-induced alterations in insulin levels and plasma glucose of normal and streptozotocin-induced diabetic rats. Whole-cell voltage clamp study in the MIN6 cell, a mouse beta cell line, revealed that resveratrol significantly inhibited ATP-sensitive K(+) current at 3 micromol/l, and voltage-gated K(+) currents at 30 micromol/l. Ca(2+)-activated K(+) current was activated by resveratrol at 100 micromol/l. In MIN6 cells stained with membrane potential dye DiBAC(4)(5), resveratrol markedly depolarized membrane potential at the concentrations of 3-100 micromol/l. Insulin secretion was increased in the presence of resveratrol in MIN6, Hit-T15, and RIN-m5F cells. Resveratrol (3 mg/kg, i.p.) increased insulin secretion associated with a lowering in plasma glucose in normal rats, but not in streptozotocin-diabetic rats within the initial 60 min. In conclusion, resveratrol can act as an insulin-secretagogue through I(KATP) and I(KV) inhibition which can contribute to plasma glucose lowering effect in normal rats.
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Affiliation(s)
- Wen-Pin Chen
- Institute of Pharmacology, National Taiwan University Medical College, Taipei, Taiwan
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21
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Zhang M, Houamed K, Kupershmidt S, Roden D, Satin LS. Pharmacological properties and functional role of Kslow current in mouse pancreatic beta-cells: SK channels contribute to Kslow tail current and modulate insulin secretion. ACTA ACUST UNITED AC 2005; 126:353-63. [PMID: 16186562 PMCID: PMC2266621 DOI: 10.1085/jgp.200509312] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The pharmacological properties of slow Ca2+-activated K+ current (Kslow) were investigated in mouse pancreatic β-cells and islets to understand how Kslow contributes to the control of islet bursting, [Ca2+]i oscillations, and insulin secretion. Kslow was insensitive to apamin or the KATP channel inhibitor tolbutamide, but UCL 1684, a potent and selective nonpeptide SK channel blocker reduced the amplitude of Kslow tail current in voltage-clamped mouse β-cells. Kslow was also selectively and reversibly inhibited by the class III antiarrythmic agent azimilide (AZ). In isolated β-cells or islets, pharmacologic inhibition of Kslow by UCL 1684 or AZ depolarized β-cell silent phase potential, increased action potential firing, raised [Ca2+]i, and enhanced glucose-dependent insulin secretion. AZ inhibition of Kslow also supported mediation by SK, rather than cardiac-like slow delayed rectifier channels since bath application of AZ to HEK 293 cells expressing SK3 cDNA reduced SK current. Further, AZ-sensitive Kslow current was extant in β-cells from KCNQ1 or KCNE1 null mice lacking cardiac slow delayed rectifier currents. These results strongly support a functional role for SK channel-mediated Kslow current in β-cells, and suggest that drugs that target SK channels may represent a new approach for increasing glucose-dependent insulin secretion. The apamin insensitivity of β-cell SK current suggests that β-cells express a unique SK splice variant or a novel heteromultimer consisting of different SK subunits.
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Affiliation(s)
- Min Zhang
- Department of Pharmacology and Toxicology, School of Medicine, Virginia Commonwealth University Medical Center, Richmond, VA 23264, USA
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22
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Ullrich S, Su J, Ranta F, Wittekindt OH, Ris F, Rösler M, Gerlach U, Heitzmann D, Warth R, Lang F. Effects of I(Ks) channel inhibitors in insulin-secreting INS-1 cells. Pflugers Arch 2005; 451:428-36. [PMID: 16133261 DOI: 10.1007/s00424-005-1479-2] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2005] [Accepted: 06/06/2005] [Indexed: 12/18/2022]
Abstract
Potassium channels regulate insulin secretion. The closure of K(ATP) channels leads to membrane depolarisation, which triggers Ca(2+) influx and stimulates insulin secretion. The subsequent activation of K(+) channels terminates secretion. We examined whether KCNQ1 channels are expressed in pancreatic beta-cells and analysed their functional role. Using RT/PCR cellular mRNA of KCNQ1 but not of KCNE1 channels was detected in INS-1 cells. Effects of two sulfonamide analogues, 293B and HMR1556, inhibitors of KCNQ1 channels, were examined on voltage-activated outwardly rectifying K(+) currents using the patch-clamp method. It was found that 293B inhibited 60% of whole-cell outward currents induced by voltage pulses from -70 to +50 mV with a concentration for half-maximal inhibition (IC(50)) of 37 microM. The other sulfonamide analogue HMR1556 inhibited 48% of the outward current with an IC(50) of 7 microM. The chromanol 293B had no effect on tolbutamide-sensitive K(ATP) channels. Action potentials induced by current injections were broadened and after-repolarisation was attenuated by 293B. Insulin secretion in the presence but not in the absence of tolbutamide was significantly increased by 293B. These results suggest that 293B- and HMR1556-sensitive channels, probably in concert with other voltage-activated K(+) channels, influence action potential duration and frequency and thus insulin secretion.
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Affiliation(s)
- Susanne Ullrich
- Institute of Neurophysiology, University of Köln, Robert Koch Strasse 39, 50931 Cologne, Germany.
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23
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Kang D, Choe C, Kim D. Functional expression of TREK-2 in insulin-secreting MIN6 cells. Biochem Biophys Res Commun 2004; 323:323-31. [PMID: 15351740 DOI: 10.1016/j.bbrc.2004.08.089] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2004] [Indexed: 11/26/2022]
Abstract
Insulin secretion from pancreatic beta cells is partly regulated by cell membrane potential. Background K+ channels that stabilize the resting membrane potential would suppress excitability and insulin secretion. Recent studies show that members of the two-pore domain K+ (K2P) channel family behave as background K+ channels in many excitable cells. Therefore, the expression of K2P channels was studied in insulin-secreting MIN6 cells. Reverse transcriptase PCR showed that, among nine K2P channels tested, TASK-1, TASK-2, TASK-3, TREK-2, and TRESK-2 were expressed in MIN6 cells. Cell-attached recordings on MIN6 cells revealed five types of K+ channels that were open at rest. Two were ATP-sensitive and Ca2+-activated K+ channels, as judged by their sensitivity to ATP and Ca2+, respectively, and single-channel conductance. Among five K2P channels, only TREK-2 could be clearly identified in MIN6 cells. The molecular identity of two other K+ channels is not yet known. TREK-2 in MIN6 cells was activated by arachidonic acid, membrane stretch, and low pH solution (pH 5.8). Arachidonic acid increased Ba2+-sensitive whole-cell current in MIN6 cell. These results suggest that TREK-2 contributes to the background K+ conductance in MIN6 cells, and may regulate depolarization-induced secretion of insulin.
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Affiliation(s)
- Dawon Kang
- Department of Physiology and Biophysics, Rosalind Franklin University of Medicine and Science/The Chicago Medical School, 3333 Green Bay Road, North Chicago, IL 60064, USA
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24
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Yan L, Figueroa DJ, Austin CP, Liu Y, Bugianesi RM, Slaughter RS, Kaczorowski GJ, Kohler MG. Expression of voltage-gated potassium channels in human and rhesus pancreatic islets. Diabetes 2004; 53:597-607. [PMID: 14988243 DOI: 10.2337/diabetes.53.3.597] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Voltage-gated potassium channels (Kv channels) are involved in repolarization of excitable cells. In pancreatic beta-cells, prolongation of the action potential by block of delayed rectifier potassium channels would be expected to increase intracellular free calcium and to promote insulin release in a glucose-dependent manner. However, the specific Kv channel subtypes responsible for repolarization in beta-cells, most importantly in humans, are not completely resolved. In this study, we have investigated the expression of 26 subtypes from Kv subfamilies in human islet mRNA. The results of the RT-PCR analysis were extended by in situ hybridization and/or immunohistochemical analysis on sections from human or Rhesus pancreas. Cell-specific markers were used to show that Kv2.1, Kv3.2, Kv6.2, and Kv9.3 are expressed in beta-cells, that Kv3.1 and Kv6.1 are expressed in alpha-cells, and that Kv2.2 is expressed in delta-cells. This study suggests that more than one Kv channel subtype might contribute to the beta-cell delayed rectifier current and that this current could be formed by heterotetramers of active and silent subunits.
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Affiliation(s)
- Lizhen Yan
- Department of Ion Channels, Merck Research Laboratories, Rahway, New Jersey, USA.
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25
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Tamarina NA, Wang Y, Mariotto L, Kuznetsov A, Bond C, Adelman J, Philipson LH. Small-conductance calcium-activated K+ channels are expressed in pancreatic islets and regulate glucose responses. Diabetes 2003; 52:2000-6. [PMID: 12882916 DOI: 10.2337/diabetes.52.8.2000] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Glucose-stimulated insulin secretion is associated with transients of intracellular Ca(2+) concentration [Ca(2+)](i) in the pancreatic beta-cell. We identified the expression and function of specific small-conductance Ca(2+)-activated K(+) (SK) channel genes in insulin-secreting cells. The presence of mRNA for SK1, -2, -3, and -4 (intermediate-conductance Ca(2+)-activated K(+) 1 [IK1]) channels was demonstrated by RT-PCR in rodent islets and insulinoma cells. SK2 and -3 proteins in mouse islets were detected by immunoblot and immunocytochemistry. In the tTA-SK3 tet-off mouse, a normal amount of SK3 protein was present in islets, but it became undetectable after exposure to doxycycline (DOX), which inhibits the transcription of the tTA-SK3 gene. The SK/IK channel-blockers apamin, dequalinium, and charybdotoxin caused increases in average [Ca(2+)](i) levels and in frequency of [Ca(2+)](i) oscillations in wild-type mouse islets. In SK3-tTA tet-off mice, the addition of apamin with glucose and tetraethylammonium (TEA) caused a similar elevation in [Ca(2+)](i), which was greatly diminished after DOX suppression of SK3 expression. We conclude that SK1, -2, -3, and IK1 (SK4) are expressed in islet cells and insulin-secreting cells and are able to influence glucose-induced calcium responses, thereby regulating insulin secretion.
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26
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MacDonald PE, Wheeler MB. Voltage-dependent K(+) channels in pancreatic beta cells: role, regulation and potential as therapeutic targets. Diabetologia 2003; 46:1046-62. [PMID: 12830383 DOI: 10.1007/s00125-003-1159-8] [Citation(s) in RCA: 182] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2003] [Revised: 05/23/2003] [Indexed: 01/11/2023]
Abstract
Insulin secretion from pancreatic islet beta cells is acutely regulated by a complex interplay of metabolic and electrogenic events. The electrogenic mechanism regulating insulin secretion from beta cells is commonly referred to as the ATP-sensitive K(+) (K(ATP)) channel dependent pathway. Briefly, an increase in ATP and, perhaps more importantly, a decrease in ADP stimulated by glucose metabolism depolarises the beta cell by closing K(ATP) channels. Membrane depolarisation results in the opening of voltage-dependent Ca(2+) channels, and influx of Ca(2+) is the main trigger for insulin secretion. Repolarisation of pancreatic beta cell action potential is mediated by the activation of voltage-dependent K(+) (Kv) channels. Various Kv channel homologues have been detected in insulin secreting cells, and recent studies have shown a role for specific Kv channels as modulators of insulin secretion. Here we review the evidence supporting a role for Kv channels in the regulation of insulin secretion and discuss the potential and the limitations for beta-cell Kv channels as therapeutic targets. Furthermore, we review recent investigations of mechanisms regulating Kv channels in beta cells, which suggest that Kv channels are active participants in the regulation of beta-cell electrical activity and insulin secretion.
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Affiliation(s)
- P E MacDonald
- Department of Physiology, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
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27
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Fridlyand LE, Tamarina N, Philipson LH. Modeling of Ca2+ flux in pancreatic beta-cells: role of the plasma membrane and intracellular stores. Am J Physiol Endocrinol Metab 2003; 285:E138-54. [PMID: 12644446 DOI: 10.1152/ajpendo.00194.2002] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
We have developed a detailed mathematical model of ionic flux in beta-cells that includes the most essential channels and pumps in the plasma membrane. This model is coupled to equations describing Ca2+, inositol 1,4,5-trisphosphate (IP3), ATP, and Na+ homeostasis, including the uptake and release of Ca2+ by the endoplasmic reticulum (ER). In our model, metabolically derived ATP activates inward Ca2+ flux by regulation of ATP-sensitive K+ channels and depolarization of the plasma membrane. Results from the simulations support the hypothesis that intracellular Na+ and Ca2+ in the ER can be the main variables driving both fast (2-7 osc/min) and slow intracellular Ca2+ concentration oscillations (0.3-0.9 osc/min) and that the effect of IP3 on Ca2+ leak from the ER contributes to the pattern of slow calcium oscillations. Simulations also show that filling the ER Ca2+ stores leads to faster electrical bursting and Ca2+ oscillations. Specific Ca2+ oscillations in isolated beta-cell lines can also be simulated.
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28
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Goforth PB, Bertram R, Khan FA, Zhang M, Sherman A, Satin LS. Calcium-activated K+ channels of mouse beta-cells are controlled by both store and cytoplasmic Ca2+: experimental and theoretical studies. J Gen Physiol 2002; 120:307-22. [PMID: 12198088 PMCID: PMC2229522 DOI: 10.1085/jgp.20028581] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2002] [Revised: 05/24/2002] [Accepted: 06/05/2002] [Indexed: 02/05/2023] Open
Abstract
A novel calcium-dependent potassium current (K(slow)) that slowly activates in response to a simulated islet burst was identified recently in mouse pancreatic beta-cells (Göpel, S.O., T. Kanno, S. Barg, L. Eliasson, J. Galvanovskis, E. Renström, and P. Rorsman. 1999. J. Gen. Physiol. 114:759-769). K(slow) activation may help terminate the cyclic bursts of Ca(2+)-dependent action potentials that drive Ca(2+) influx and insulin secretion in beta-cells. Here, we report that when [Ca(2+)](i) handling was disrupted by blocking Ca(2+) uptake into the ER with two separate agents reported to block the sarco/endoplasmic calcium ATPase (SERCA), thapsigargin (1-5 microM) or insulin (200 nM), K(slow) was transiently potentiated and then inhibited. K(slow) amplitude could also be inhibited by increasing extracellular glucose concentration from 5 to 10 mM. The biphasic modulation of K(slow) by SERCA blockers could not be explained by a minimal mathematical model in which [Ca(2+)](i) is divided between two compartments, the cytosol and the ER, and K(slow) activation mirrors changes in cytosolic calcium induced by the burst protocol. However, the experimental findings were reproduced by a model in which K(slow) activation is mediated by a localized pool of [Ca(2+)] in a subspace located between the ER and the plasma membrane. In this model, the subspace [Ca(2+)] follows changes in cytosolic [Ca(2+)] but with a gradient that reflects Ca(2+) efflux from the ER. Slow modulation of this gradient as the ER empties and fills may enhance the role of K(slow) and [Ca(2+)] handling in influencing beta-cell electrical activity and insulin secretion.
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Affiliation(s)
- P B Goforth
- Department of Pharmacology and Toxicology, Medical College of Virginia at Virginia Commonwealth University, Richmond, VA 2398, USA
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29
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Rolland JF, Henquin JC, Gilon P. Feedback control of the ATP-sensitive K(+) current by cytosolic Ca(2+) contributes to oscillations of the membrane potential in pancreatic beta-cells. Diabetes 2002; 51:376-84. [PMID: 11812744 DOI: 10.2337/diabetes.51.2.376] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
During glucose stimulation, pancreatic beta-cells display membrane potential oscillations that correspond to intermittent Ca(2+) influx, leading to oscillations of the cytosolic free calcium concentration ([Ca(2+)](c)) and insulin secretion. The role of ATP-sensitive K(+) (K(+)-ATP) channels in the control of these oscillations was investigated by measuring the K(+)-ATP current (I(KATP)) with the perforated mode of the patch-clamp technique. No oscillations of I(KATP) were observed when glucose-stimulated beta-cells were kept hyperpolarized, thus with low and stable [Ca(2+)](c). However, increasing [Ca(2+)](c) by Ca(2+) influx (depolarizing pulses) or Ca(2+) mobilization (acetylcholine) transiently augmented I(KATP). This effect was abolished by tolbutamide, attenuated by increasing the glucose concentration in the medium, and prevented by abrogation of the [Ca(2+)](c) rise, which demonstrates that the current is really I(KATP) and that its increase is Ca(2+)-dependent. Injection of a current of a similar amplitude to that of the Ca(2+)-induced increase in I(KATP) was sufficient to repolarize glucose-stimulated beta-cells. These results suggest that, in the absence of [Ca(2+)](c) oscillations, no metabolic oscillations affect I(KATP) in pancreatic beta-cells. In contrast, [Ca(2+)](c) oscillations evoke I(KATP) oscillations. This mechanism may constitute the feedback loop controlling the glucose-induced oscillating electrical activity in beta-cells.
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30
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Dunne MJ, Ämmälä C, Straub SG, Sharp GWG. Electrophysiology of the β Cell and Mechanisms of Inhibition of Insulin Release. Compr Physiol 2001. [DOI: 10.1002/cphy.cp070204] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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31
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Gall D, Susa I. Effect of Na/Ca exchange on plateau fraction and [Ca]i in models for bursting in pancreatic beta-cells. Biophys J 1999; 77:45-53. [PMID: 10388739 PMCID: PMC1300311 DOI: 10.1016/s0006-3495(99)76871-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
Abstract
In the presence of an insulinotropic glucose concentration, beta-cells, in intact pancreatic islets, exhibit periodic bursting electrical activity consisting of an alternation of active and silent phases. The fraction of time spent in the active phase over a period is called the plateau fraction and is correlated with the rate of insulin release. However, the mechanisms that regulate the plateau fraction remain unclear. In this paper we investigate the possible role of the plasma membrane Na+/Ca2+ exchange of the beta-cell in controlling the plateau fraction. We have extended different single-cell models to incorporate this Ca2+-activated electrogenic Ca2+ transporter. We find that the Na+/Ca2+ exchange can provide a physiological mechanism to increase the plateau fraction as the glucose concentration is raised. In addition, we show theoretically that the Na+/Ca2+ exchanger is a key regulator of the cytoplasmic calcium concentration in clusters of heterogeneous cells with gap-junctional electrical coupling.
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Affiliation(s)
- D Gall
- Laboratoire de Pharmacodynamie et Thérapeutique (CP617), Faculté de Médecine, Université Libre de Bruxelles, B-1070 Bruxelles, Belgium
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Li ZW, Ding JP, Kalyanaraman V, Lingle CJ. RINm5f cells express inactivating BK channels whereas HIT cells express noninactivating BK channels. J Neurophysiol 1999; 81:611-24. [PMID: 10036264 DOI: 10.1152/jn.1999.81.2.611] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Large-conductance Ca2+- and voltage-activated BK-type K+ channels are expressed abundantly in normal rat pancreatic islet cells and in the clonal rat insulinoma tumor (RINm5f) and hamster insulinoma tumor (HIT) beta cell lines. Previous work has suggested that the Ca2+ sensitivity of BK channels in RIN cells is substantially less than that in HIT cells, perhaps contributing to differences between the cell lines in responsiveness to glucose in mediating insulin secretion. In both RIN cells and normal pancreatic beta cells, BK channels are thought to play a limited role in responses of beta cells to secretagogues and in the electrical activity of beta cells. Here we examine in detail the properties of BK channels in RIN and HIT cells using inside-out patches and whole cell recordings. BK channels in RIN cells exhibit rapid inactivation that results in an anomalous steady-state Ca2+ dependence of activation. In contrast, BK channels in HIT cells exhibit the more usual noninactivating behavior. When BK inactivation is taken into account, the Ca2+ and voltage dependence of activation of BK channels in RIN and HIT cells is essentially indistinguishable. The properties of BK channel inactivation in RIN cells are similar to those of inactivating BK channels (termed BKi channels) previously identified in rat chromaffin cells. Inactivation involves multiple, trypsin-sensitive cytosolic domains and exhibits a dependence on Ca2+ and voltage that appears to arise from coupling to channel activation. In addition, the rates of inactivation onset and recovery are similar to that of BKi channels in chromaffin cells. The charybdotoxin (CTX) sensitivity of BKi currents is somewhat less than that of the noninactivating BK variant. Action potential voltage-clamp waveforms indicate that BK current is activated only weakly by Ca2+ influx in RIN cells but more strongly activated in HIT cells even when Ca2+ current magnitude is comparable. Concentrations of CTX sufficient to block BKi current in RIN cells have no effect on action potential activity initiated by glucose or DC injection. Despite its abundant expression in RIN cells, BKi current appears to play little role in action potential activity initiated by glucose or DC injection in RIN cells, but BK current may play an important role in action potential repolarization in HIT cells.
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Affiliation(s)
- Z W Li
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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33
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Kozak JA, Misler S, Logothetis DE. Characterization of a Ca2+-activated K+ current in insulin-secreting murine betaTC-3 cells. J Physiol 1998; 509 ( Pt 2):355-70. [PMID: 9575286 PMCID: PMC2230977 DOI: 10.1111/j.1469-7793.1998.355bn.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. The whole-cell perforated-patch recording mode was used to record a Ca2+-dependent K+ current (IK(Ca)) in mouse betaTC-3 insulin-secreting cells. 2. Depolarizing voltage steps (to potentials where Ca2+ currents are activated) evoked a slowly activating, outward current, which exhibited a slow deactivation (in seconds) upon subsequent hyperpolarization. 3. This current was shown to increase with progressively longer depolarizing voltage steps. It could be reversibly abolished by the removal of Ca2+ from the external medium or by application of Ca2+ channel blockers, such as Cd2+ and nifedipine. It was concluded that the depolarization-evoked current was activated by Ca2+. 4. Variations in external K+ concentration led to shifts in the reversal potential of the Ca2+-dependent current as predicted by the Nernst equation for a K+-selective current. 5. The Ca2+-activated K+ current was insensitive to external TEA (10 mM), a concentration sufficient to block the large-conductance Ca2+-dependent (maxi-KCa) channel in beta-cells. It was also insensitive to apamin, tubocurarine and scyllatoxin (leiurotoxin I), specific blockers of small-conductance KCa channels. 6. The current was blocked by quinine, a non-specific KCa channel blocker and, surprisingly, by charybdotoxin (ChTX; 100 nM) but not iberiotoxin, a charybdotoxin analogue, which blocks the maxi-KCa channel. It was sensitive to block by clotrimazole and could be potently and reversibly potentiated by micromolar concentrations of niflumic acid. Thus, the current exhibited unique pharmacological characteristics, not conforming to the known KCa channel classes. 7. The ChTX-sensitive KCa channel was permeable to Tl+, K+, Rb+ and NH4+ but not Cs+ ions. 8. The ChTX-sensitive IK(Ca) could be activated by the muscarinic agonists in the presence or absence of external Ca2+, presumably by releasing Ca2+ from internal stores. 9. Acutely isolated porcine islet cells also exhibited a slow IK(Ca) resembling that described in betaTC-3 cells in kinetic properties, insensitivity to TEA (5 mM) and sensitivity to quinidine, an analogue of quinine. The porcine IK(Ca), however, was not sensitive to block by 100-200 nM ChTX. It is likely, that species differences account for pharmacological differences between the mouse and porcine slow IK(Ca).
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Affiliation(s)
- J A Kozak
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, NY 10029, USA.
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34
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Sherman A. Contributions of modeling to understanding stimulus-secretion coupling in pancreatic beta-cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1996; 271:E362-72. [PMID: 8770032 DOI: 10.1152/ajpendo.1996.271.2.e362] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Mechanisms of ionic control of insulin secretion in beta-cells of the pancreatic islets of Langerhans are reviewed. The focus is on aspects that have been treated by mathematical models, especially those related to bursting electrical activity. The study of these mechanisms is difficult because of the need to consider ionic fluxes, calcium handling, metabolism, and electrical coupling with other cells in the islet. The data come either from islets, where experimental maneuvers tend to have multiple effects, or from isolated cells, which have degraded electrical activity and secretory sensitivity. Modeling aids in the process by integrating data on individual components such as channels and calcium handling and testing hypotheses for coherence and quantitative plausibility. The study of a variety of models has led to some general mathematical results that have yielded qualitative model-independent insights.
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Affiliation(s)
- A Sherman
- National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, Maryland 20892-2690, USA
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35
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Ferrer J, Wasson J, Salkoff L, Permutt MA. Cloning of human pancreatic islet large conductance Ca(2+)-activated K+ channel (hSlo) cDNAs: evidence for high levels of expression in pancreatic islets and identification of a flanking genetic marker. Diabetologia 1996; 39:891-8. [PMID: 8858210 DOI: 10.1007/bf00403907] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Insulin secretion from pancreatic beta cells is dependent on membrane potential changes that result from the concerted regulation of multiple ion channels. Among the distinct K+ channels known to be expressed in beta cells, large conductance Ca(2+)-activated K+ channels have been suggested to play an important role in stimulus-secretion coupling. In the course of a strategy to identify transcripts that are enriched in human pancreatic islet cells, we isolated a partial cDNA encoding a human large conductance Ca(2+)-activated K+ channel mRNA (hSlo). Northern analysis of mRNA showed that among a panel of human tissues hSlo is expressed at its highest levels in pancreatic islets. Screening of human insulinoma and islet cDNA libraries with the partial cDNA resulted in the isolation of 19 hSlo cDNAs. These comprised three splice variants: one shared the common underlying structure of previously reported Slo cDNAs, another variant encoded a novel 60-amino acid insertion in the putative Ca(2+)-sensing domain of hSlo, while the third group of clones had an alternate exon encoding eight amino acids in the predicted COOH-terminal end. Analysis of somatic-cell hybrids containing different portions of chromosome 10 indicated that hSlo maps to chromosome 10q22.2-q23.1. Furthermore, high resolution localization was obtained by analysis of genome-wide radiation hybrids and the CEPH "B" mega-YAC library, both of which identified for the first time a highly polymorphic genetic marker (D10S195) linked to hSlo. These studies provide tools with which to explore the physiological role of Ca(2+)-activated K+ channel proteins in pancreatic islets, and also to investigate the contribution of this locus to the inherited susceptibility to non-insulin-dependent diabetes mellitus.
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Affiliation(s)
- J Ferrer
- Division of Endocrinology, Diabetes, and Metabolism, Washington University School of Medicine, St. Louis, MO 63110, USA
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36
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Ding WG, He LP, Omatsu-Kanbe M, Kitasato H. A possible role of the ATP-sensitive potassium ion channel in determining the duration of spike-bursts in mouse pancreatic beta-cells. BIOCHIMICA ET BIOPHYSICA ACTA 1996; 1279:219-26. [PMID: 8603090 DOI: 10.1016/0005-2736(95)00249-9] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The pancreatic beta-cell displays an electrical activity consisting of spike bursts and silent phases at glucose concentrations of about 10 mM. The mechanism of initial depolarization induced by glucose is well defined. However, the mechanism inducing the silent phase has not been fully elucidated. In the present study, the possibility of involvement of ATP-sensitive K+ channels in repolarization was examined using the patch-clamp technique in the cell-attached recording configuration. Ouabain (0.1 mM), an inhibitor of Na+/K+-ATPase, caused a complete suppression of ATP-sensitive K+ channel activity followed by typical biphasic current deflections, which were due to action potentials. The channel activity was also inhibited by removal of K+ from a perifusion solution. Furthermore, the activity of ATP-sensitive K+ channels was markedly inhibited either by replacement of external NaCl with LiCl or by addition of amiloride (0.2 mM), a blocker of Na+/H+ antiport. Addition of L-type Ca2+ channel blockers such as Nifedipine for Mn2+ induced the complete suppression of K+ channel activity. These findings strongly suggest that a fall in ATP consumption results in sustained depolarization, and that the repolarizations interposed between spike-bursts under normal ionic conditions are due to the periodical fall of ATP concentration brought about by periodical acceleration of ATP consumption at Na+/K+-pumps. It is concluded that the elevation of intracellular Na+ concentration as a consequence of accelerated Na+/Ca2+-countertransport during the period of spike-burst enhances ATP consumption, leading to a fall in ATP concentration which is responsible for termination of spike-burst and initiation of repolarization.
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Affiliation(s)
- W G Ding
- Department of Physiology, Shiga University of Medical Science, Ohtsu, Japan
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37
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Mears D, Sheppard NF, Atwater I, Rojas E. Magnitude and modulation of pancreatic beta-cell gap junction electrical conductance in situ. J Membr Biol 1995; 146:163-76. [PMID: 7473686 DOI: 10.1007/bf00238006] [Citation(s) in RCA: 77] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The parallel gap junction electrical conductance between a beta-cell and its nearest neighbors was measured by using an intracellular microelectrode to clamp the voltage of a beta-cell within a bursting islet of Langerhans. The holding current records consisted of bursts of inward current due to the synchronized oscillations in membrane potential of the surrounding cells. The membrane potential record of the impaled cell, obtained in current clamp mode, was used to estimate the behavior of the surrounding cells during voltage clamp, and the coupling conductance was calculated by dividing the magnitude of the current bursts by that of the voltage bursts. The histogram of coupling conductance magnitude from 26 cells was bimodal with peaks at 2.5 and 3.5 nS, indicating heterogeneity in extent of electrical communication within the islet of Langerhans. Gap junction conductance reversibly decreased when the temperature was lowered from 37 to 30 degrees C and when the extracellular calcium concentration was raised from 2.56 to 7.56 mM. The coupling conductance decreased slightly during the active phase of the burst. Activation of adenylate cyclase with forskolin (10 microM) resulted in an increase in cell-to-cell electrical coupling. We conclude that beta-cell gap junction conductance can be measured in situ under near physiological conditions. Furthermore, the magnitude and physiological regulation of beta-cell gap junction conductance suggest that intercellular electrical communication plays an important role in the function of the endocrine pancreas.
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Affiliation(s)
- D Mears
- Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, MD 21218, USA
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38
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Bertram R, Smolen P, Sherman A, Mears D, Atwater I, Martin F, Soria B. A role for calcium release-activated current (CRAC) in cholinergic modulation of electrical activity in pancreatic beta-cells. Biophys J 1995; 68:2323-32. [PMID: 7647236 PMCID: PMC1282142 DOI: 10.1016/s0006-3495(95)80414-5] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
S. Bordin and colleagues have proposed that the depolarizing effects of acetylcholine and other muscarinic agonists on pancreatic beta-cells are mediated by a calcium release-activated current (CRAC). We support this hypothesis with additional data, and present a theoretical model which accounts for most known data on muscarinic effects. Additional phenomena, such as the biphasic responses of beta-cells to changes in glucose concentration and the depolarizing effects of the sarco-endoplasmic reticulum calcium ATPase pump poison thapsigargin, are also accounted for by our model. The ability of this single hypothesis, that CRAC is present in beta-cells, to explain so many phenomena motivates a more complete characterization of this current.
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Affiliation(s)
- R Bertram
- Mathematical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA
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39
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Marangoni S, Toyama MH, Arantes EC, Giglio JR, da Silva CA, Carneiro EM, Gonçalves AA, Oliveira B. Amino acid sequence of TsTX-V, an alpha-toxin from Tityus serrulatus scorpion venom, and its effect on K+ permeability of beta-cells from isolated rat islets of Langerhans. BIOCHIMICA ET BIOPHYSICA ACTA 1995; 1243:309-14. [PMID: 7727504 DOI: 10.1016/0304-4165(94)00142-k] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
Highly purified Tityustoxin V (TsTX-V), an alpha-toxin isolated from the venom of the Brazilian scorpion Tityus serrulatus, was obtained by ion exchange chromatography on carboxymethylcellulose-52. It was shown to be homogeneous by reverse phase high performance liquid chromatography, N-terminal sequencing (first 39 residues) of the reduced and alkylated protein and by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate and tricine. Following enzymatic digestion, the complete amino acid sequence (64 residues) was determined. The sequence showed higher homology with the toxins from the venoms of the North African than with those of the North and South American scorpions. Using the rate of 86Rb+ release from depolarized rat pancreatic beta-cells as a measure of K+ permeability changes, TsTX-V (5.6 micrograms/ml) was found to increase by 2.0-2.4-fold the rate of marker outflow in the presence of 8.3 mM glucose. This effect was persistent and slowly reversible, showing similarity to that induced by 100 microM veratridine, an agent that increases the open period of Na+ channels, delaying their inactivation. It is suggested that, by extending the depolarized period, TsTX-V indirectly affects beta-cell voltage-dependent K+ channels, thus increasing K+ permeability.
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Affiliation(s)
- S Marangoni
- Departamento de Bioquímica, Universidade Estadual de Campinas, SP, Brazil
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40
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Fournier L, Whitfield J, Schwartz J, Bégin-Heick N. Cyclic AMP triggers large [Ca2+]i oscillations in glucose-stimulated beta-cells from ob/ob mice. J Biol Chem 1994. [DOI: 10.1016/s0021-9258(17)42229-0] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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41
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Etcheberrigaray R, Ito E, Oka K, Tofel-Grehl B, Gibson GE, Alkon DL. Potassium channel dysfunction in fibroblasts identifies patients with Alzheimer disease. Proc Natl Acad Sci U S A 1993; 90:8209-13. [PMID: 8367484 PMCID: PMC47318 DOI: 10.1073/pnas.90.17.8209] [Citation(s) in RCA: 95] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Since memory loss is characteristic of Alzheimer disease (AD), and since K+ channels change during acquisition of memory in both molluscs and mammals, we investigated K+ channel function as a possible site of AD pathology and, therefore, as a possible diagnostic index as well. A 113-pS tetraethylammonium (TEA)-sensitive K+ channel was consistently absent from AD fibroblasts, while it was often present in young and aged control fibroblasts. A second (166-pS) K+ channel was present in all three groups. Elevated external potassium raised intracellular Ca2+ in all cases. TEA depolarized and caused intracellular Ca2+ elevation in young and aged control fibroblasts but not AD fibroblasts. The invariable absence of a 113-pS TEA-sensitive K+ channel and TEA-induced Ca2+ signal indicate K+ channel dysfunction in AD fibroblasts. These results suggest the possibility of a laboratory method that would diagnostically distinguish AD patients, with or without a family history of AD, from normal age-matched controls and also from patients with non-AD neurological and psychiatric disorders.
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Affiliation(s)
- R Etcheberrigaray
- National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
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42
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Rosário LM, Barbosa RM, Antunes CM, Silva AM, Abrunhosa AJ, Santos RM. Bursting electrical activity in pancreatic beta-cells: evidence that the channel underlying the burst is sensitive to Ca2+ influx through L-type Ca2+ channels. Pflugers Arch 1993; 424:439-47. [PMID: 7504808 DOI: 10.1007/bf00374906] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
In glucose-stimulated pancreatic beta-cells, the membrane potential alternates between a hyperpolarized silent phase and a depolarized phase with Ca2+ action potentials. The molecular and ionic mechanisms underlying these bursts of electrical activity remain unknown. We have observed that 10.2-12.8 mM Ca2+, 1 microM Bay K 8644 and 2 mM tetraethylammonium (TEA) trigger bursts of electrical activity and oscillations of intracellular free Ca2+ concentration ([Ca2+]i) in the presence of 100 microM tolbutamide. The [Ca2+]i was monitored from single islets of Langerhans using fura-2 microfluorescence techniques. Both the high-Ca(2+)- and Bay-K-8644-evoked [Ca2+]i oscillations overshot the [Ca2+]i recorded in tolbutamide. Nifedipine (10-20 microM) caused an immediate membrane hyperpolarization, which was followed by a slow depolarization to a level close to the burst active phase potential. The latter depolarization was accompanied by suppression of spiking activity. Exposure to high Ca2+ in the presence of nifedipine caused a steady depolarization of approximately 8 mV. Ionomycin (10 microM) caused membrane hyperpolarization in the presence of 7.7 mM Ca2+, which was not abolished by nifedipine. Charybdotoxin (CTX, 40-80 nM), TEA (2 mM) and quinine (200 microM) did not suppress the high-Ca(2+)-evoked bursts. It is concluded that: (1) the channel underlying the burst is sensitive to [Ca2+]i rises mediated by Ca2+ influx through L-type Ca2+ channels, (2) both the ATP-dependent K+ channel and the CTX- and TEA-sensitive Ca(2+)-dependent K+ channel are highly unlikely to provide the pacemaker current underlying the burst.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- L M Rosário
- Departamento de Bioquímica, Faculdade de Ciências e Tecnologia da Universidade de Coimbra, Portugal
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43
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Stokes CL, Rinzel J. Diffusion of extracellular K+ can synchronize bursting oscillations in a model islet of Langerhans. Biophys J 1993; 65:597-607. [PMID: 8218890 PMCID: PMC1225762 DOI: 10.1016/s0006-3495(93)81092-0] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Electrical bursting oscillations of mammalian pancreatic beta-cells are synchronous among cells within an islet. While electrical coupling among cells via gap junctions has been demonstrated, its extent and topology are unclear. The beta-cells also share an extracellular compartment in which oscillations of K+ concentration have been measured (Perez-Armendariz and Atwater, 1985). These oscillations (1-2 mM) are synchronous with the burst pattern, and apparently are caused by the oscillating voltage-dependent membrane currents: Extracellular K+ concentration (Ke) rises during the depolarized active (spiking) phase and falls during the hyperpolarized silent phase. Because raising Ke depolarizes the cell membrane by increasing the potassium reversal potential (VK), any cell in the active phase should recruit nonspiking cells into the active phase. The opposite is predicted for the silent phase. This positive feedback system might couple the cells' electrical activity and synchronize bursting. We have explored this possibility using a theoretical model for bursting of beta-cells (Sherman et al., 1988) and K+ diffusion in the extracellular space of an islet. Computer simulations demonstrate that the bursts synchronize very quickly (within one burst) without gap junctional coupling among the cells. The shape and amplitude of computed Ke oscillations resemble those seen in experiments for certain parameter ranges. The model cells synchronize with exterior cells leading, though incorporating heterogeneous cell properties can allow interior cells to lead. The model islet can also be forced to oscillate at both faster and slower frequencies using periodic pulses of higher K+ in the medium surrounding the islet. Phase plane analysis was used to understand the synchronization mechanism. The results of our model suggest that diffusion of extracellular K+ may contribute to coupling and synchronization of electrical oscillations in beta-cells within an islet.
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Affiliation(s)
- C L Stokes
- Mathematical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
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44
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Fournier L, Whitfield JF, Xiang H, Schwartz JL, Bégin-Heick N. K+ channel and alpha 2-adrenergic effects on glucose-induced Ca2+i surges: aberrant behavior in ob/ob mice. THE AMERICAN JOURNAL OF PHYSIOLOGY 1993; 264:C1458-65. [PMID: 8392795 DOI: 10.1152/ajpcell.1993.264.6.c1458] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Glucose-induced shifts in intracellular free Ca2+ concentration ([Ca2+]i) were quantitatively and temporally the same in ob/ob and +/+ beta-cells. In both, epinephrine promptly and protractedly inhibited the glucose-induced [Ca2+]i surge via a pertussis toxin-sensitive alpha 2-adrenergic mechanism that was reversible by potassium depolarization. When added before glucose, epinephrine blocked completely in the ob/ob beta-cells, but in the +/+ beta-cells it produced a delayed, reduced, and transient intracellular Ca2+ (Ca2+i) surge. Neither the ATP-sensitive K+ channel blocker tolbutamide nor the large-conductance Ca(2+)-activated K+ channel (Kmaxi) blocker charybdotoxin reversed the effect of epinephrine. Tetraethylammonium (TEA), a blocker of both the Kmaxi and the delayed-rectifier K+ channel, and forskolin attenuated the effect of epinephrine in +/+ but not in the ob/ob beta-cells. The data show that 1) alpha 2-adrenoreceptor activation decreases the glucose-stimulated Ca2+i surge in +/+ beta-cells primarily by activating a tolbutamide- and charybdotoxin-insensitive, TEA- and forskolin-sensitive K+ channel; 2) the hypersecretion of insulin in ob/ob beta-cells is not due to enhanced glucose-induced Ca2+ influx; and 3) the ob/ob beta-cells are aberrant with regard to alpha 2-adrenergic modulation.
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Affiliation(s)
- L Fournier
- Department of Biochemistry, University of Ottawa, Ontario, Canada
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45
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Smolen P, Rinzel J, Sherman A. Why pancreatic islets burst but single beta cells do not. The heterogeneity hypothesis. Biophys J 1993; 64:1668-80. [PMID: 8369400 PMCID: PMC1262502 DOI: 10.1016/s0006-3495(93)81539-x] [Citation(s) in RCA: 118] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Previous mathematical modeling of beta cell electrical activity has involved single cells or, recently, clusters of identical cells. Here we model clusters of heterogeneous cells that differ in size, channel density, and other parameters. We use gap-junctional electrical coupling, with conductances determined by an experimental histogram. We find that, for reasonable parameter distributions, only a small proportion of isolated beta cells will burst when uncoupled, at any given value of a glucose-sensing parameter. However, a coupled, heterogeneous cluster of such cells, if sufficiently large (approximately 125 cells), will burst synchronously. Small clusters of such cells will burst only with low probability. In large clusters, the dynamics of intracellular calcium compare well with experiments. Also, these clusters possess a dose-response curve of increasing average electrical activity with respect to a glucose-sensing parameter that is sharp when the cluster is coupled, but shallow when the cluster is decoupled into individual cells. This is in agreement with comparative experiments on cells in suspension and islets.
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Affiliation(s)
- P Smolen
- Mathematical Research Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892
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46
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Ammälä C, Bokvist K, Larsson O, Berggren PO, Rorsman P. Demonstration of a novel apamin-insensitive calcium-activated K+ channel in mouse pancreatic B cells. Pflugers Arch 1993; 422:443-8. [PMID: 8474849 DOI: 10.1007/bf00375069] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The whole-cell configuration of the patch-clamp technique was used to characterize the biophysical and pharmacological properties of an oscillating K(+)-current that can be induced by intracellular application of GTP[gamma S] in mouse pancreatic B cells (Ammälä et al. 1991). These K+ conductance changes are evoked by periodic increases in the cytoplasmic Ca2+ concentration ([Ca2+]i) and transiently repolarize the B cell, thus inhibiting action-potential firing and giving rise to a bursting pattern. GTP[gamma S]-evoked oscillations in K+ conductance were reversibly suppressed by a high (300 microM) concentration of carbamylcholine. By contrast, alpha 2-adrenoreceptor stimulation by 20 microM clonidine did not interfere with the oscillatory behaviour but evoked a small sustained outward current. At 0 mV membrane potential, the oscillating K(+)-current elicited by GTP[gamma S] was highly sensitive to extracellular tetraethylammonium (TEA; 70% block by 1 mM). The TEA-resistant component, which carried approximately 80% of the current at -40 mV, was affected neither by apamin (1 microM) nor by tolbutamide (500 microM). The current evoked by internal GTP[gamma S] was highly selective for K+, as demonstrated by a 51-mV change in the reversal potential for a sevenfold change in [K+]o. Stationary fluctuation analysis indicated a unitary conductance of 0.5 pS when measured with symmetric (approximately 140 mM) KCl solutions. The estimated single-channel conductance with physiological ionic gradients is 0.1 pS. The results indicate the existence of a novel Ca(2+)-gated K+ conductance in pancreatic B cells. Activation of this K+ current may contribute to the generation of the oscillatory electrical activity characterizing the B cell at intermediate glucose concentrations.
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Affiliation(s)
- C Ammälä
- Department of Medical Biophysics, Göteborgs Universitet, Sweden
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Oosawa Y, Ashcroft SJ, Ashcroft FM. Ca(2+)-activated K+ channels from an insulin-secreting cell line incorporated into planar lipid bilayers. Diabetologia 1992; 35:619-23. [PMID: 1379561 DOI: 10.1007/bf00400252] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
This study evaluates the use of the planar lipid bilayer as a functional assay of Ca(2+)-activated K+ channel activity for use in purification of the channel protein. Ca(2+)-activated K+ channels from the plasma membrane of an insulin-secreting hamster Beta-cell line (HIT T15) were incorporated into planar lipid bilayers. The single channel conductance was 233 picoSiemens (pS) in symmetrical 140 mmol/l KCl and the channel was strongly K(+)-selective (PCl/PK = 0.046; PNa/PK = 0.027). Channels incorporated into the bilayer with two orientations. In 65% of cases, the probability of the channel being open was increased by raising calcium on the cis side of the bilayer (to which the membrane vesicles were added) or by making the cis side potential more positive. At a membrane potential of + 20 mV, which is close to the peak of the Beta-cell action potential, channel activity was half-maximal at a Ca2+ concentration of about 15 mumol/l. Charybdotoxin greatly reduced the probability of the channel being open when added to the side opposite to that at which Ca2+ activated the channel. These results resemble those found for Ca(2+)-activated K+ channels in native Beta cell membranes and indicate that the channel properties are not significantly altered by incorporation in a planar lipid bilayer.
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Affiliation(s)
- Y Oosawa
- University Laboratory of Physiology, University of Oxford, UK
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48
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Abstract
Ionic and electrical events play a central role in the stimulus-secretion coupling of the pancreatic B cell. Potassium permeability is critically involved in the regulation of B cell membrane potential and insulin secretion. In the absence of glucose, membrane potential remains stable, around -65 mV. This resting potential is mainly determined by the high potassium conductance of the membrane. The ATP generated by glucose metabolism in B cells blocks the K+(ATP) channels controlling resting membrane potential. Thus, glucose metabolism leads to closure of the ATP-dependent potassium channels; the resulting decrease in K+ permeability induces depolarization and opening of voltage-activated Ca-channels. The subsequent increase in Ca2+ influx raises the cytoplasmic concentration of free Ca2+, which in turn triggers exocytosis of secretory granules. Other types of K+ channels have also been identified in the B cell, such as voltage- and Ca(2+)-dependent K+ channels, which are not a target for the action of glucose, but may play a role in the repolarization of spikes. The modulation of insulin release by some hormones and neurotransmitters involves, among other mechanisms, an interference with the plasma membrane K+ conductance. Thus, galanine, somatostatin and adrenaline, which inhibit insulin release, increase K+ conductance by a G protein-dependent mechanism; both peptides were reported to open ATP-sensitive K+ channels in insulin-secreting cell line RINm5F. It was also observed that extracellular purine nucleotides could interfere with K+ channels. Among the various drugs interfering with insulin secretion, sulfonylureas, such as tolbutamide and glibenclamide, directly inhibit ATP-dependent K+ channels in the B cell membrane and thereby initiate insulin release. In contrast, potassium channel openers such as diazoxide, antagonize the effects of glucose by increasing K+ permeability of the B cell membrane. Furthermore, other classes of drugs have recently been shown to interact with K+ (ATP) channels. Thus, K+ channels of the pancreatic B cell, particularly ATP-dependent ones, play a crucial role in the electrophysiology of insulin secretion; they are an important target for pharmacological agents designed to modulate this secretion.
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Affiliation(s)
- P Petit
- Laboratoire de Pharmacologie, URA 599 du CNRS, Faculté de Médecine, Montpellier, France
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Ammälä C, Larsson O, Berggren PO, Bokvist K, Juntti-Berggren L, Kindmark H, Rorsman P. Inositol trisphosphate-dependent periodic activation of a Ca(2+)-activated K+ conductance in glucose-stimulated pancreatic beta-cells. Nature 1991; 353:849-52. [PMID: 1719424 DOI: 10.1038/353849a0] [Citation(s) in RCA: 110] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Glucose-stimulated insulin secretion is associated with the appearance of electrical activity in the pancreatic beta-cell. At intermediate glucose concentrations, beta-cell electrical activity follows a characteristic pattern of slow oscillations in membrane potential on which bursts of action potentials are superimposed. The electrophysiological background of the bursting pattern remains unestablished. Activation of Ca(2+)-activated large-conductance K+ channels (KCa channel) has been implicated in this process but seems unlikely in view of recent evidence demonstrating that the beta-cell electrical activity is unaffected by the specific KCa channel blocker charybdotoxin. Another hypothesis postulates that the bursting arises as a consequence of two components of Ca(2+)-current inactivation. Here we show that activation of a novel Ca(2+)-dependent K+ current in glucose-stimulated beta-cells produces a transient membrane repolarization. This interrupts action potential firing so that action potentials appear in bursts. Spontaneous activity of this current was seen only rarely but could be induced by addition of compounds functionally related to hormones and neurotransmitters present in the intact pancreatic islet. K+ currents of the same type could be evoked by intracellular application of GTP, the effect of which was mediated by mobilization of Ca2+ from inositol 1,4,5-trisphosphate (InsP3)-sensitive intracellular Ca2+ stores. These observations suggest that oscillatory glucose-stimulated electrical activity, which is correlated with pulsatile release of insulin, results from the interaction between the beta-cell and intraislet hormones and neurotransmitters. Our data also provide evidence for a close interplay between ion channels in the plasma membrane and InsP3-induced mobilization of intracellular Ca2+ in an excitable cell.
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Affiliation(s)
- C Ammälä
- Department of Medical Physics, Gothenburg University, Sweden
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Abstract
Insulin secretogogues have long been known to stimulate and modulate bursting electrical activity in pancreatic islet B cells and thereby supply extracellular Ca2+ for the exocytosis of insulin. Recent results have ruled out a long-held hypothesis for the mechanism of burst formation that postulated key roles for intracellular Ca2+ accumulation and activation of Ca(2+)-activated K+ channels. Here, we present an alternative hypotheses based on a persistent Ca2+ conductance and, possibly, phasic activation of ATP-sensitive K+ channels. These hypotheses are compared with mechanisms of bursting proposed for invertebrate and mammalian neurons.
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Affiliation(s)
- D L Cook
- Division of Metabolism, Seattle VA Medical Center, WA 98108
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