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Nakhe AY, Dadi PK, Kim J, Dickerson MT, Behera S, Dobson JR, Shrestha S, Cartailler JP, Sampson L, Magnuson MA, Jacobson DA. The MODY-associated KCNK16 L114P mutation increases islet glucagon secretion and limits insulin secretion resulting in transient neonatal diabetes and glucose dyshomeostasis in adults. eLife 2024; 12:RP89967. [PMID: 38700926 PMCID: PMC11068355 DOI: 10.7554/elife.89967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/05/2024] Open
Abstract
The gain-of-function mutation in the TALK-1 K+ channel (p.L114P) is associated with maturity-onset diabetes of the young (MODY). TALK-1 is a key regulator of β-cell electrical activity and glucose-stimulated insulin secretion. The KCNK16 gene encoding TALK-1 is the most abundant and β-cell-restricted K+ channel transcript. To investigate the impact of KCNK16 L114P on glucose homeostasis and confirm its association with MODY, a mouse model containing the Kcnk16 L114P mutation was generated. Heterozygous and homozygous Kcnk16 L114P mice exhibit increased neonatal lethality in the C57BL/6J and the CD-1 (ICR) genetic background, respectively. Lethality is likely a result of severe hyperglycemia observed in the homozygous Kcnk16 L114P neonates due to lack of glucose-stimulated insulin secretion and can be reduced with insulin treatment. Kcnk16 L114P increased whole-cell β-cell K+ currents resulting in blunted glucose-stimulated Ca2+ entry and loss of glucose-induced Ca2+ oscillations. Thus, adult Kcnk16 L114P mice have reduced glucose-stimulated insulin secretion and plasma insulin levels, which significantly impairs glucose homeostasis. Taken together, this study shows that the MODY-associated Kcnk16 L114P mutation disrupts glucose homeostasis in adult mice resembling a MODY phenotype and causes neonatal lethality by inhibiting islet insulin secretion during development. These data suggest that TALK-1 is an islet-restricted target for the treatment for diabetes.
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Affiliation(s)
- Arya Y Nakhe
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
| | - Jinsun Kim
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
- Department of Chemistry, Vanderbilt UniversityNashvilleUnited States
| | - Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
| | - Soma Behera
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
| | - Jordyn R Dobson
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
| | - Shristi Shrestha
- Center for Stem Cell Biology, Vanderbilt UniversityNashvilleUnited States
| | | | - Leesa Sampson
- Center for Stem Cell Biology, Vanderbilt UniversityNashvilleUnited States
| | - Mark A Magnuson
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
- Center for Stem Cell Biology, Vanderbilt UniversityNashvilleUnited States
- Department of Cell and Developmental Biology, Vanderbilt UniversityNashvilleUnited States
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt UniversityNashvilleUnited States
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Nakhe AY, Dadi PK, Kim J, Dickerson MT, Behera S, Dobson JR, Shrestha S, Cartailler JP, Sampson L, Magnuson MA, Jacobson DA. The MODY-associated KCNK16 L114P mutation increases islet glucagon secretion and limits insulin secretion resulting in transient neonatal diabetes and glucose dyshomeostasis in adults. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2023.06.20.545631. [PMID: 37546831 PMCID: PMC10401960 DOI: 10.1101/2023.06.20.545631] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/08/2023]
Abstract
The gain-of-function mutation in the TALK-1 K + channel (p.L114P) is associated with maturity-onset diabetes of the young (MODY). TALK-1 is a key regulator of β-cell electrical activity and glucose-stimulated insulin secretion (GSIS). The KCNK16 gene encoding TALK-1, is the most abundant and β-cell-restricted K + channel transcript. To investigate the impact of KCNK16 L114P on glucose homeostasis and confirm its association with MODY, a mouse model containing the Kcnk16 L114P mutation was generated. Heterozygous and homozygous Kcnk16 L114P mice exhibit increased neonatal lethality in the C57BL/6J and the mixed C57BL/6J:CD-1(ICR) genetic background, respectively. Lethality is likely a result of severe hyperglycemia observed in the homozygous Kcnk16 L114P neonates due to lack of glucose-stimulated insulin secretion and can be reduced with insulin treatment. Kcnk16 L114P increased whole-cell β-cell K + currents resulting in blunted glucose-stimulated Ca 2+ entry and loss of glucose-induced Ca 2+ oscillations. Thus, adult Kcnk16 L114P mice have reduced glucose-stimulated insulin secretion and plasma insulin levels, which significantly impaired glucose homeostasis. Taken together, this study shows that the MODY-associated Kcnk16 L114P mutation disrupts glucose homeostasis in adult mice resembling a MODY phenotype and causes neonatal lethality by inhibiting islet hormone secretion during development. These data strongly suggest that TALK-1 is an islet-restricted target for the treatment of diabetes.
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Mourtzi N, Sertedaki A, Markou A, Piaditis GP, Katsanis N, Traeger-Synodinos J, Tsigos C, Charmandari E. Genetic screening of hypertensive patients with aldosterone hypersecretion under conditions of stress. Hormones (Athens) 2022; 21:525-536. [PMID: 36044182 DOI: 10.1007/s42000-022-00394-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/27/2022] [Accepted: 08/03/2022] [Indexed: 02/01/2023]
Abstract
PURPOSE Although ACTH is considered a secondary regulator of aldosterone production, patients with apparent essential hypertension have been treated with mineralocorticoid receptor antagonists (MRAs). In this study, we aimed to identify potentially damaging variants that might be implicated in the phenotype of a well-characterized cohort of 21 hypertensive patients without PA but with stress-induced aldosterone hypersecretion. The patients' blood pressure was normalized though MRA administration. METHODS Genetic screening was performed through whole-exome sequencing (WES), and variants in PA-associated or in ion-channels of aldosterone-regulating genes were prioritized. Variants with population frequency < 0.01, predicted to alter protein structure and classified as likely pathogenic by in silico tools, were retained. RESULTS Qualifying variants were identified in nine of the 21 patients screened. Seven patients were carriers of six potentially damaging variants in six genes associated with PA (KCNK9, KCNK5, ATP13A3, SLC26A2, CACNA1H, and CACNA1D). A novel variant in the KCNK9 gene (p.V221M) is reported. Our analysis revealed two variants in two novel susceptibility genes for aldosterone hypersecretion, namely, KCNK16 (p.P255H) and CACNA2D3 (p.V557I). CONCLUSION WES revealed potentially damaging germline variants in genes participating in aldosterone synthesis/regulating pathways in 9/21 patients of our cohort. The variants identified might play a role in aldosterone hypersecretion under conditions of stress. The potential pathogenicity of these variants should be examined in future functional studies.
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Affiliation(s)
- Niki Mourtzi
- Division of Endocrinology, Metabolism and Diabetes, First Department of Pediatrics, National and Kapodistrian University of Athens Medical School, Aghia Sophia' Children's Hospital, 11527, Athens, Greece
| | - Amalia Sertedaki
- Division of Endocrinology, Metabolism and Diabetes, First Department of Pediatrics, National and Kapodistrian University of Athens Medical School, Aghia Sophia' Children's Hospital, 11527, Athens, Greece.
| | - Athina Markou
- Department of Endocrinology and Diabetes Center, G. Gennimatas General Hospital, 11527, Athens, Greece
| | - George P Piaditis
- Department of Endocrinology and Diabetes Center, G. Gennimatas General Hospital, 11527, Athens, Greece
| | - Nicholas Katsanis
- Department of Cell Biology and Pediatrics, School of Medicine and Rescindo Therapeutics, Northwestern University, Chicago, USA
| | - Joanne Traeger-Synodinos
- Laboratory of Medical Genetics, Choremeio Research Laboratory, National and Kapodistrian University of Athens, 'Aghia Sophia' Children's Hospital, 11527, Athens, Greece
| | - Constantine Tsigos
- Department of Nutrition and Dietetics, School of Health Science and Education, Harokopio University, 17671, Athens, Greece
| | - Evangelia Charmandari
- Division of Endocrinology, Metabolism and Diabetes, First Department of Pediatrics, National and Kapodistrian University of Athens Medical School, Aghia Sophia' Children's Hospital, 11527, Athens, Greece
- Division of Endocrinology and Metabolism, Center of Clinical, Biomedical Research Foundation, Experimental Surgery and Translational Research, Academy of Athens, 11527, Athens, Greece
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Khoubza L, Gilbert N, Kim EJ, Chatelain FC, Feliciangeli S, Abelanet S, Kang D, Lesage F, Bichet D. Alkaline-sensitive two-pore domain potassium channels form functional heteromers in pancreatic β-cells. J Biol Chem 2022; 298:102447. [PMID: 36063992 PMCID: PMC9520024 DOI: 10.1016/j.jbc.2022.102447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2021] [Revised: 08/26/2022] [Accepted: 08/29/2022] [Indexed: 11/15/2022] Open
Abstract
Two-pore domain K+ channels (K2P channels), active as dimers, produce inhibitory currents regulated by a variety of stimuli. Among them, TWIK1-related alkalinization-activated K+ channel 1 (TALK1), TWIK1-related alkalinization-activated K+ channel 2 (TALK2), and TWIK1-related acid-sensitive K+ channel 2 (TASK2) form a subfamily of structurally related K2P channels stimulated by extracellular alkalosis. The human genes encoding these proteins are clustered at chromosomal region 6p21 and coexpressed in multiple tissues, including the pancreas. The question whether these channels form functional heteromers remained open. By analyzing single-cell transcriptomic data, we show that these channels are coexpressed in insulin-secreting pancreatic β-cells. Using in situ proximity ligation assay and electrophysiology, we show that they form functional heterodimers both upon heterologous expression and under native conditions in human pancreatic β-cells. We demonstrate that heteromerization of TALK2 with TALK1 or with TASK2 endows TALK2 with sensitivity to extracellular alkalosis in the physiological range. We further show that the association of TASK2 with TALK1 and TALK2 increases their unitary conductance. These results provide a new example of heteromerization in the K2P channel family expanding the range of the potential physiological and pathophysiological roles of TALK1/TALK2/TASK2 channels, not only in insulin-secreting cells but also in the many other tissues in which they are coexpressed.
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Affiliation(s)
- Lamyaa Khoubza
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, Valbonne, France
| | - Nicolas Gilbert
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, Valbonne, France
| | - Eun-Jin Kim
- Department of Physiology, College of Medicine and Institute of Health Sciences, Gyeongsang National University, Jinju, South Korea
| | - Franck C Chatelain
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, Valbonne, France
| | - Sylvain Feliciangeli
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, Valbonne, France; Inserm, Paris, France
| | - Sophie Abelanet
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, Valbonne, France
| | - Dawon Kang
- Department of Physiology, College of Medicine and Institute of Health Sciences, Gyeongsang National University, Jinju, South Korea
| | - Florian Lesage
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, Valbonne, France; Inserm, Paris, France.
| | - Delphine Bichet
- Université côte d'Azur, IPMC CNRS UMR7275, Laboratory of Excellence ICST, Valbonne, France
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5
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Tsai WH, Grauffel C, Huang MY, Postić S, Rupnik MS, Lim C, Yang SB. Allosteric coupling between transmembrane segment 4 and the selectivity filter of TALK1 potassium channels regulates their gating by extracellular pH. J Biol Chem 2022; 298:101998. [PMID: 35500647 PMCID: PMC9168622 DOI: 10.1016/j.jbc.2022.101998] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2021] [Revised: 04/19/2022] [Accepted: 04/27/2022] [Indexed: 11/28/2022] Open
Abstract
Opening of two-pore domain K+ channels (K2Ps) is regulated by various external cues, such as pH, membrane tension, or temperature, which allosterically modulate the selectivity filter (SF) gate. However, how these cues cause conformational changes in the SF of some K2P channels remains unclear. Herein, we investigate the mechanisms by which extracellular pH affects gating in an alkaline-activated K2P channel, TALK1, using electrophysiology and molecular dynamics (MD) simulations. We show that R233, located at the N-terminal end of transmembrane segment 4, is the primary pHo sensor. This residue distally regulates the orientation of the carbonyl group at the S1 potassium-binding site through an interacting network composed of residues on transmembrane segment 4, the pore helix domain 1, and the SF. Moreover, in the presence of divalent cations, we found the acidic pH-activated R233E mutant recapitulates the network interactions of protonated R233. Intriguingly, our data further suggested stochastic coupling between R233 and the SF gate, which can be described by an allosteric gating model. We propose that this allosteric model could predict the hybrid pH sensitivity in heterodimeric channels with alkaline-activated and acidic-activated K2P subunits.
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Affiliation(s)
- Wen-Hao Tsai
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan; Taiwan International Graduate Program in Molecular Medicine, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan
| | - Cédric Grauffel
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Ming-Yueh Huang
- Institute of Statistical Science, Academia Sinica, Taipei, Taiwan
| | - Sandra Postić
- Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria
| | - Marjan Slak Rupnik
- Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria; Institute of Physiology, Faculty of Medicine, University of Maribor, Maribor, Slovenia; Alma Mater Europaea - European Center Maribor, Maribor, Slovenia
| | - Carmay Lim
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Shi-Bing Yang
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan; Taiwan International Graduate Program in Molecular Medicine, National Yang Ming Chiao Tung University and Academia Sinica, Taipei, Taiwan.
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6
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Two-Pore-Domain Potassium (K 2P-) Channels: Cardiac Expression Patterns and Disease-Specific Remodelling Processes. Cells 2021; 10:cells10112914. [PMID: 34831137 PMCID: PMC8616229 DOI: 10.3390/cells10112914] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2021] [Revised: 10/18/2021] [Accepted: 10/22/2021] [Indexed: 12/23/2022] Open
Abstract
Two-pore-domain potassium (K2P-) channels conduct outward K+ currents that maintain the resting membrane potential and modulate action potential repolarization. Members of the K2P channel family are widely expressed among different human cell types and organs where they were shown to regulate important physiological processes. Their functional activity is controlled by a broad variety of different stimuli, like pH level, temperature, and mechanical stress but also by the presence of lipids or pharmacological agents. In patients suffering from cardiovascular diseases, alterations in K2P-channel expression and function have been observed, suggesting functional significance and a potential therapeutic role of these ion channels. For example, upregulation of atrial specific K2P3.1 (TASK-1) currents in atrial fibrillation (AF) patients was shown to contribute to atrial action potential duration shortening, a key feature of AF-associated atrial electrical remodelling. Therefore, targeting K2P3.1 (TASK-1) channels might constitute an intriguing strategy for AF treatment. Further, mechanoactive K2P2.1 (TREK-1) currents have been implicated in the development of cardiac hypertrophy, cardiac fibrosis and heart failure. Cardiovascular expression of other K2P channels has been described, functional evidence in cardiac tissue however remains sparse. In the present review, expression, function, and regulation of cardiovascular K2P channels are summarized and compared among different species. Remodelling patterns, observed in disease models are discussed and compared to findings from clinical patients to assess the therapeutic potential of K2P channels.
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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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8
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Graff SM, Johnson SR, Leo PJ, Dadi PK, Dickerson MT, Nakhe AY, McInerney-Leo AM, Marshall M, Zaborska KE, Schaub CM, Brown MA, Jacobson DA, Duncan EL. A KCNK16 mutation causing TALK-1 gain of function is associated with maturity-onset diabetes of the young. JCI Insight 2021; 6:138057. [PMID: 34032641 PMCID: PMC8410089 DOI: 10.1172/jci.insight.138057] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2020] [Accepted: 05/12/2021] [Indexed: 11/17/2022] Open
Abstract
Maturity-onset diabetes of the young (MODY) is a heterogeneous group of monogenic disorders of impaired pancreatic β cell function. The mechanisms underlying MODY include β cell KATP channel dysfunction (e.g., KCNJ11 [MODY13] or ABCC8 [MODY12] mutations); however, no other β cell channelopathies have been associated with MODY to date. Here, we have identified a nonsynonymous coding variant in KCNK16 (NM_001135105: c.341T>C, p.Leu114Pro) segregating with MODY. KCNK16 is the most abundant and β cell-restricted K+ channel transcript, encoding the two-pore-domain K+ channel TALK-1. Whole-cell K+ currents demonstrated a large gain of function with TALK-1 Leu114Pro compared with TALK-1 WT, due to greater single-channel activity. Glucose-stimulated membrane potential depolarization and Ca2+ influx were inhibited in mouse islets expressing TALK-1 Leu114Pro with less endoplasmic reticulum Ca2+ storage. TALK-1 Leu114Pro significantly blunted glucose-stimulated insulin secretion compared with TALK-1 WT in mouse and human islets. These data suggest that KCNK16 is a previously unreported gene for MODY.
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Affiliation(s)
- Sarah M. Graff
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Stephanie R. Johnson
- Department of Endocrinology, Queensland Children’s Hospital, South Brisbane, Queensland, Australia
- Translational Genomics Group, Institute of Health and Biomedical Innovation, Faculty of Health, Queensland University of Technology, Translational Research Institute, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
- Faculty of Medicine, University of Queensland, Herston, Queensland, Australia
| | - Paul J. Leo
- Translational Genomics Group, Institute of Health and Biomedical Innovation, Faculty of Health, Queensland University of Technology, Translational Research Institute, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
| | - Prasanna K. Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Matthew T. Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Arya Y. Nakhe
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Aideen M. McInerney-Leo
- Dermatology Research Centre, Dermatology Research Centre, The University of Queensland Diamantina Institute, Brisbane, Queensland, Australia
| | - Mhairi Marshall
- Translational Genomics Group, Institute of Health and Biomedical Innovation, Faculty of Health, Queensland University of Technology, Translational Research Institute, Princess Alexandra Hospital, Woolloongabba, Queensland, Australia
| | - Karolina E. Zaborska
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Charles M. Schaub
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Matthew A. Brown
- Guy’s and St Thomas’ NHS Foundation Trust and King’s College London NIHR Biomedical Research Centre, King’s College London, London, United Kingdom
| | - David A. Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, USA
| | - Emma L. Duncan
- Faculty of Medicine, University of Queensland, Herston, Queensland, Australia
- Department of Twin Research & Genetic Epidemiology, School of Life Course Sciences, Faculty of Life Sciences and Medicine, King’s College London, London, United Kingdom
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9
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Herrera-Pérez S, Campos-Ríos A, Rueda-Ruzafa L, Lamas JA. Contribution of K2P Potassium Channels to Cardiac Physiology and Pathophysiology. Int J Mol Sci 2021; 22:ijms22126635. [PMID: 34205717 PMCID: PMC8234311 DOI: 10.3390/ijms22126635] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 06/08/2021] [Accepted: 06/18/2021] [Indexed: 12/28/2022] Open
Abstract
Years before the first two-pore domain potassium channel (K2P) was cloned, certain ion channels had already been demonstrated to be present in the heart with characteristics and properties usually attributed to the TREK channels (a subfamily of K2P channels). K2P channels were later detected in cardiac tissue by RT-PCR, although the distribution of the different K2P subfamilies in the heart seems to depend on the species analyzed. In order to collect relevant information in this regard, we focus here on the TWIK, TASK and TREK cardiac channels, their putative roles in cardiac physiology and their implication in coronary pathologies. Most of the RNA expression data and electrophysiological recordings available to date support the presence of these different K2P subfamilies in distinct cardiac cells. Likewise, we show how these channels may be involved in certain pathologies, such as atrial fibrillation, long QT syndrome and Brugada syndrome.
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10
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Recovery of Human Embryonic Stem Cells-Derived Neural Progenitors Exposed to Hypoxic-Ischemic-Reperfusion Injury by Indirect Exposure to Wharton’s Jelly Mesenchymal Stem Cells Through Phosphatidyl-inositol-3-Kinase Pathway. Cell Mol Neurobiol 2020; 42:1167-1188. [DOI: 10.1007/s10571-020-01007-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2020] [Accepted: 11/11/2020] [Indexed: 12/13/2022]
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11
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Structural basis for pH gating of the two-pore domain K+ channel TASK2. Nature 2020; 586:457-462. [DOI: 10.1038/s41586-020-2770-2] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2020] [Accepted: 07/06/2020] [Indexed: 12/31/2022]
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12
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Pattison LA, Callejo G, St John Smith E. Evolution of acid nociception: ion channels and receptors for detecting acid. Philos Trans R Soc Lond B Biol Sci 2019; 374:20190291. [PMID: 31544616 PMCID: PMC6790391 DOI: 10.1098/rstb.2019.0291] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/27/2019] [Indexed: 12/13/2022] Open
Abstract
Nociceptors, i.e. sensory neurons tuned to detect noxious stimuli, are found in numerous phyla of the Animalia kingdom and are often polymodal, responding to a variety of stimuli, e.g. heat, cold, pressure and chemicals, such as acid. Owing to the ability of protons to have a profound effect on ionic homeostasis and damage macromolecular structures, it is no wonder that the ability to detect acid is conserved across many species. To detect changes in pH, nociceptors are equipped with an assortment of different acid sensors, some of which can detect mild changes in pH, such as the acid-sensing ion channels, proton-sensing G protein-coupled receptors and several two-pore potassium channels, whereas others, such as the transient receptor potential vanilloid 1 ion channel, require larger shifts in pH. This review will discuss the evolution of acid sensation and the different mechanisms by which nociceptors can detect acid. This article is part of the Theo Murphy meeting issue 'Evolution of mechanisms and behaviour important for pain'.
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Affiliation(s)
| | | | - Ewan St John Smith
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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13
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Gupta MK, Sarojamma V, Vadde R. Diabetes and Pancreatic Cancer: A Bidirectional Relationship Perspective. EXPLORING PANCREATIC METABOLISM AND MALIGNANCY 2019:35-51. [DOI: 10.1007/978-981-32-9393-9_3] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 09/06/2023]
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14
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Cardiovascular pharmacology of K 2P17.1 (TASK-4, TALK-2) two-pore-domain K + channels. Naunyn Schmiedebergs Arch Pharmacol 2018; 391:1119-1131. [PMID: 30008082 DOI: 10.1007/s00210-018-1535-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2018] [Accepted: 07/06/2018] [Indexed: 10/28/2022]
Abstract
K2P17.1 (TASK-4, TALK-2) potassium channels are expressed in the heart and represent potential targets for pharmacological management of atrial and ventricular arrhythmias. Reduced K2P17.1 expression was found in atria and ventricles of heart failure (HF) patients. Modulation of K2P17.1 currents by antiarrhythmic compounds has not been comprehensively studied to date. The objective of this study was to investigate acute effects of clinically relevant antiarrhythmic drugs on human K2P17.1 channels to provide a more complete picture of K2P17.1 electropharmacology. Whole-cell patch clamp and two-electrode voltage clamp electrophysiology was employed to study human K2P17.1 channel pharmacology. K2P17.1 channels expressed in Xenopus laevis oocytes were screened for sensitivity to antiarrhythmic drugs, revealing significant activation by propafenone (+ 296%; 100 μM), quinidine (+ 58%; 100 μM), mexiletine (+ 21%; 100 μM), propranolol (+ 139%; 100 μM), and metoprolol (+ 17%; 100 μM) within 60 min. In addition, the currents were inhibited by amiodarone (- 13%; 100 μM), sotalol (- 10%; 100 μM), verapamil (- 21%; 100 μM), and ranolazine (- 8%; 100 μM). K2P17.1 channels were not significantly affected by ajmaline and carvedilol. Concentration-dependent K2P17.1 activation by propafenone was characterized in more detail. The onset of activation was fast, and current-voltage relationships were not modulated by propafenone. K2P17.1 activation was confirmed in mammalian Chinese hamster ovary cells, revealing 7.8-fold current increase by 100 μM propafenone. Human K2P17.1 channels were sensitive to multiple antiarrhythmic drugs. Differential pharmacological regulation of repolarizing K2P17.1 background K+ channels may be employed for personalized antiarrhythmic therapy.
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15
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Inoue M, Matsuoka H, Lesage F, Harada K. Lack of p11 expression facilitates acidity‐sensing function of TASK1 channels in mouse adrenal medullary cells. FASEB J 2018; 33:455-468. [DOI: 10.1096/fj.201800407rr] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Masumi Inoue
- Department of Cell and Systems PhysiologySchool of MedicineUniversity of Occupational and Environmental Health Kitakyushu Japan
| | - Hidetada Matsuoka
- Department of Cell and Systems PhysiologySchool of MedicineUniversity of Occupational and Environmental Health Kitakyushu Japan
| | - Florian Lesage
- Université Côte d'AzurINSERMCentre National de la Recherche Scientifique (CNRS)Institut de Pharmacologie Moléculaire et CellulaireLaboratory of Excellence in Ion Channel Science and Therapeutics (LabEx ICST) Valbonne France
| | - Keita Harada
- Department of Cell and Systems PhysiologySchool of MedicineUniversity of Occupational and Environmental Health Kitakyushu Japan
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16
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Staudacher I, Illg C, Gierten J, Seehausen S, Schweizer PA, Katus HA, Thomas D. Identification and functional characterization of zebrafish K 2P 17.1 (TASK-4, TALK-2) two-pore-domain K + channels. Eur J Pharmacol 2018; 831:94-102. [DOI: 10.1016/j.ejphar.2018.05.007] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2018] [Revised: 05/04/2018] [Accepted: 05/08/2018] [Indexed: 12/12/2022]
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17
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Dickerson MT, Bogart AM, Altman MK, Milian SC, Jordan KL, Dadi PK, Jacobson DA. Cytokine-mediated changes in K + channel activity promotes an adaptive Ca 2+ response that sustains β-cell insulin secretion during inflammation. Sci Rep 2018; 8:1158. [PMID: 29348619 PMCID: PMC5773563 DOI: 10.1038/s41598-018-19600-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Accepted: 01/04/2018] [Indexed: 12/13/2022] Open
Abstract
Cytokines present during low-grade inflammation contribute to β-cell dysfunction and diabetes. Cytokine signaling disrupts β-cell glucose-stimulated Ca2+ influx (GSCI) and endoplasmic reticulum (ER) Ca2+ ([Ca2+]ER) handling, leading to diminished glucose-stimulated insulin secretion (GSIS). However, cytokine-mediated changes in ion channel activity that alter β-cell Ca2+ handling remain unknown. Here we investigated the role of K+ currents in cytokine-mediated β-cell dysfunction. Kslow currents, which control the termination of intracellular Ca2+ ([Ca2+]i) oscillations, were reduced following cytokine exposure. As a consequence, [Ca2+]i and electrical oscillations were accelerated. Cytokine exposure also increased basal islet [Ca2+]i and decreased GSCI. The effect of cytokines on TALK-1 K+ currents were also examined as TALK-1 mediates Kslow by facilitating [Ca2+]ER release. Cytokine exposure decreased KCNK16 transcript abundance and associated TALK-1 protein expression, increasing [Ca2+]ER storage while maintaining 2nd phase GSCI and GSIS. This adaptive Ca2+ response was absent in TALK-1 KO islets, which exhibited decreased 2nd phase GSCI and diminished GSIS. These findings suggest that Kslow and TALK-1 currents play important roles in altered β-cell Ca2+ handling and electrical activity during low-grade inflammation. These results also reveal that a cytokine-mediated reduction in TALK-1 serves an acute protective role in β-cells by facilitating increased Ca2+ content to maintain GSIS.
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Affiliation(s)
- Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Avery M Bogart
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
- Department of Biological Sciences, Ohio University, Athens, OH, USA
| | - Molly K Altman
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Sarah C Milian
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA.
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18
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Breton JD, Stuart GJ. GABA B receptors in neocortical and hippocampal pyramidal neurons are coupled to different potassium channels. Eur J Neurosci 2017; 46:2859-2866. [PMID: 29131436 DOI: 10.1111/ejn.13777] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2017] [Revised: 11/07/2017] [Accepted: 11/07/2017] [Indexed: 02/05/2023]
Abstract
Classically, GABAB receptors are thought to regulate neuronal excitability via G-protein-coupled inwardly rectifying potassium (GIRK) channels. Recent data, however, indicate that GABAB receptors can also activate two-pore domain potassium channels. Here, we investigate which potassium channels are coupled to GABAB receptors in rat neocortical layer 5 and hippocampal CA1 pyramidal neurons. Bath application of the non-specific GIRK channel blocker barium (200 μm) abolished outward currents evoked by GABAB receptors in CA1 pyramidal, but only partially blocked GABAB responses in layer 5 neurons. Layer 5 and CA1 pyramidal neurons also showed differential sensitivity to tertiapin-Q, a specific GIRK channel blocker. Tertiapin-Q partially blocked GABAB responses in CA1 pyramidal neurons, but was ineffective in blocking GABAB responses in neocortical layer 5 neurons. Consistent with the idea that GABAB receptors are coupled to two-pore domain potassium channels, the non-specific blockers quinidine and bupivacaine partially blocked GABAB responses in both layer 5 and CA1 neurons. Finally, we show that lowering external pH, as occurs in hypoxia, blocks the component of GABAB responses mediated by two-pore domain potassium channels in neocortical layer 5 pyramidal neurons, while at the same time revealing a GIRK channel component. These data indicate that GABAB receptors in neocortical layer 5 and hippocampal CA1 pyramidal neurons are coupled to different channels, with this coupling pH dependent on neocortical layer 5 pyramidal neurons. This pH dependency may act to maintain constant levels of GABAB inhibition during hypoxia by enhancing GIRK channel function following a reduction in two-pore domain potassium channel activity.
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Affiliation(s)
- Jean-Didier Breton
- Eccles Institute of Neuroscience and Australian Research Council Centre of Excellence for Integrative Brain Function, John Curtin School of Medical Research, Australian National University, Canberra, ACT, 2601, Australia
| | - Greg J Stuart
- Eccles Institute of Neuroscience and Australian Research Council Centre of Excellence for Integrative Brain Function, John Curtin School of Medical Research, Australian National University, Canberra, ACT, 2601, Australia
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19
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Heterodimerization of two pore domain K+ channel TASK1 and TALK2 in living heterologous expression systems. PLoS One 2017; 12:e0186252. [PMID: 29016681 PMCID: PMC5634629 DOI: 10.1371/journal.pone.0186252] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2017] [Accepted: 09/27/2017] [Indexed: 11/19/2022] Open
Abstract
Two-pore-domain K+ (K2P) channels sense a wide variety of stimuli such as mechanical stress, inhalational anesthetics, and changes in extracellular pH or temperature. The K2P channel activity forms a background K+ current and, thereby, contributes to resting membrane potentials. Six subfamilies including fifteen subtypes of K2P channels have been identified. Each K2P channel molecule with two pores consists of a homodimer of each subtype. In addition, a few heterodimers mainly within the same subfamilies have been found recently. In the present study, the possibility of heterodimerization between TASK1 (TWIK-Related Acid-Sensitive K+ channel) and TALK2 (TWIK-Related Alkaline pH-Activated K+ channel) was examined. These channels belong to separate subfamilies and show extremely different channel properties. Surprisingly, single molecular imaging analyses in this study using a total internal reflection microscope suggested the heterodimerization of TASK1 and TALK2 in a pancreatic cell line, QGP-1. This heterodimer was also detected using a bimolecular fluorescence complementation assay in a HEK293 heterologous expression system. Fluorescence resonance energy transfer analyses showed that the affinity between TASK1 and TALK2 appeared to be close to those of homodimers. Whole-cell patch-clamp recordings revealed that TASK1 currents in HEK293 cells were significantly attenuated by co-expression of a dominant-negative form of TALK2 in comparison with that of wild-type TALK2. The sensitivities of TASK1-TALK2 tandem constructs to extracellular pH and halothane were characterized as a unique hybrid of TASK1 and TALK2. These results suggested that heterodimerization of TASK1 and TALK2 provides cells with the ability to make multiple responses to a variety of physiological and pharmacological stimuli.
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20
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Dickerson MT, Vierra NC, Milian SC, Dadi PK, Jacobson DA. Osteopontin activates the diabetes-associated potassium channel TALK-1 in pancreatic β-cells. PLoS One 2017; 12:e0175069. [PMID: 28403169 PMCID: PMC5389796 DOI: 10.1371/journal.pone.0175069] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2016] [Accepted: 03/20/2017] [Indexed: 12/17/2022] Open
Abstract
Glucose-stimulated insulin secretion (GSIS) relies on β-cell Ca2+ influx, which is modulated by the two-pore-domain K+ (K2P) channel, TALK-1. A gain-of-function polymorphism in KCNK16, the gene encoding TALK-1, increases risk for developing type-2 diabetes. While TALK-1 serves an important role in modulating GSIS, the regulatory mechanism(s) that control β-cell TALK-1 channels are unknown. Therefore, we employed a membrane-specific yeast two-hybrid (MYTH) assay to identify TALK-1-interacting proteins in human islets, which will assist in determining signaling modalities that modulate TALK-1 function. Twenty-one proteins from a human islet cDNA library interacted with TALK-1. Some of these interactions increased TALK-1 activity, including intracellular osteopontin (iOPN). Intracellular OPN is highly expressed in β-cells and is upregulated under pre-diabetic conditions to help maintain normal β-cell function; however, the functional role of iOPN in β-cells is poorly understood. We found that iOPN colocalized with TALK-1 in pancreatic sections and coimmunoprecipitated with human islet TALK-1 channels. As human β-cells express two K+ channel-forming variants of TALK-1, regulation of these TALK-1 variants by iOPN was assessed. At physiological voltages iOPN activated TALK-1 transcript variant 3 channels but not TALK-1 transcript variant 2 channels. Activation of TALK-1 channels by iOPN also hyperpolarized resting membrane potential (Vm) in HEK293 cells and in primary mouse β-cells. Intracellular OPN was also knocked down in β-cells to test its effect on β-cell TALK-1 channel activity. Reducing β-cell iOPN significantly decreased TALK-1 K+ currents and increased glucose-stimulated Ca2+ influx. Importantly, iOPN did not affect the function of other K2P channels or alter Ca2+ influx into TALK-1 deficient β-cells. These results reveal the first protein interactions with the TALK-1 channel and found that an interaction with iOPN increased β-cell TALK-1 K+ currents. The TALK-1/iOPN complex caused Vm hyperpolarization and reduced β-cell glucose-stimulated Ca2+ influx, which is predicted to inhibit GSIS.
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Affiliation(s)
- Matthew T. Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Nicholas C. Vierra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Sarah C. Milian
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America
| | - Prasanna K. Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America
| | - David A. Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee, United States of America
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21
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Chai S, Wan X, Nassal DM, Liu H, Moravec CS, Ramirez-Navarro A, Deschênes I. Contribution of two-pore K + channels to cardiac ventricular action potential revealed using human iPSC-derived cardiomyocytes. Am J Physiol Heart Circ Physiol 2017; 312:H1144-H1153. [PMID: 28341634 DOI: 10.1152/ajpheart.00107.2017] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/15/2017] [Revised: 03/16/2017] [Accepted: 03/22/2017] [Indexed: 01/12/2023]
Abstract
Two-pore K+ (K2p) channels have been described in modulating background conductance as leak channels in different physiological systems. In the heart, the expression of K2p channels is heterogeneous with equivocation regarding their functional role. Our objective was to determine the K2p expression profile and their physiological and pathophysiological contribution to cardiac electrophysiology. Induced pluripotent stem cells (iPSCs) generated from humans were differentiated into cardiomyocytes (iPSC-CMs). mRNA was isolated from these cells, commercial iPSC-CM (iCells), control human heart ventricular tissue (cHVT), and ischemic (iHF) and nonischemic heart failure tissues (niHF). We detected 10 K2p channels in the heart. Comparing quantitative PCR expression of K2p channels between human heart tissue and iPSC-CMs revealed K2p1.1, K2p2.1, K2p5.1, and K2p17.1 to be higher expressed in cHVT, whereas K2p3.1 and K2p13.1 were higher in iPSC-CMs. Notably, K2p17.1 was significantly lower in niHF tissues compared with cHVT. Action potential recordings in iCells after K2p small interfering RNA knockdown revealed prolongations in action potential depolarization at 90% repolarization for K2p2.1, K2p3.1, K2p6.1, and K2p17.1. Here, we report the expression level of 10 human K2p channels in iPSC-CMs and how they compared with cHVT. Importantly, our functional electrophysiological data in human iPSC-CMs revealed a prominent role in cardiac ventricular repolarization for four of these channels. Finally, we also identified K2p17.1 as significantly reduced in niHF tissues and K2p4.1 as reduced in niHF compared with iHF. Thus, we advance the notion that K2p channels are emerging as novel players in cardiac ventricular electrophysiology that could also be remodeled in cardiac pathology and therefore contribute to arrhythmias.NEW & NOTEWORTHY Two-pore K+ (K2p) channels are traditionally regarded as merely background leak channels in myriad physiological systems. Here, we describe the expression profile of K2p channels in human-induced pluripotent stem cell-derived cardiomyocytes and outline a salient role in cardiac repolarization and pathology for multiple K2p channels.
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Affiliation(s)
- Sam Chai
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio.,Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio; and
| | - Xiaoping Wan
- Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio; and
| | - Drew M Nassal
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio.,Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio; and
| | - Haiyan Liu
- Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio; and
| | | | - Angelina Ramirez-Navarro
- Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio; and
| | - Isabelle Deschênes
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio; .,Heart and Vascular Research Center, Department of Medicine, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio; and
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22
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Ryoo K, Park JY. Two-pore Domain Potassium Channels in Astrocytes. Exp Neurobiol 2016; 25:222-232. [PMID: 27790056 PMCID: PMC5081468 DOI: 10.5607/en.2016.25.5.222] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2016] [Revised: 09/01/2016] [Accepted: 09/15/2016] [Indexed: 12/23/2022] Open
Abstract
Two-pore domain potassium (K2P) channels have a distinct structure and channel properties, and are involved in a background K+ current. The 15 members of the K2P channels are identified and classified into six subfamilies on the basis of their sequence similarities. The activity of the channels is dynamically regulated by various physical, chemical, and biological effectors. The channels are expressed in a wide variety of tissues in mammals in an isoform specific manner, and play various roles in many physiological and pathophysiological conditions. To function as channels, the K2P channels form dimers, and some isoforms form heterodimers that provide diversity in channel properties. In the brain, TWIK1, TREK1, TREK2, TRAAK, TASK1, and TASK3 are predominantly expressed in various regions, including the cerebral cortex, dentate gyrus, CA1-CA3, and granular layer of the cerebellum. TWIK1, TREK1, and TASK1 are highly expressed in astrocytes, where they play specific cellular roles. Astrocytes keep leak K+ conductance, called the passive conductance, which mainly involves TWIK1-TREK1 heterodimeric channel. TWIK1 and TREK1 also mediate glutamate release from astrocytes in an exocytosis-independent manner. The expression of TREK1 and TREK2 in astrocytes increases under ischemic conditions, that enhance neuroprotection from ischemia. Accumulated evidence has indicated that astrocytes, together with neurons, are involved in brain function, with the K2P channels playing critical role in these astrocytes.
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Affiliation(s)
- Kanghyun Ryoo
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul 02841, Korea
| | - Jae-Yong Park
- School of Biosystem and Biomedical Science, College of Health Science, Korea University, Seoul 02841, Korea
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23
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Vierra NC, Dadi PK, Jeong I, Dickerson M, Powell DR, Jacobson DA. Type 2 Diabetes-Associated K+ Channel TALK-1 Modulates β-Cell Electrical Excitability, Second-Phase Insulin Secretion, and Glucose Homeostasis. Diabetes 2015; 64:3818-28. [PMID: 26239056 PMCID: PMC4613978 DOI: 10.2337/db15-0280] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Accepted: 07/22/2015] [Indexed: 12/11/2022]
Abstract
Two-pore domain K+ (K2P) channels play an important role in tuning β-cell glucose-stimulated insulin secretion (GSIS). The K2P channel TWIK-related alkaline pH-activated K2P (TALK)-1 is linked to type 2 diabetes risk through a coding sequence polymorphism (rs1535500); however, its physiological function has remained elusive. Here, we show that TALK-1 channels are expressed in mouse and human β-cells, where they serve as key regulators of electrical excitability and GSIS. We find that the rs1535500 polymorphism, which results in an alanine-to-glutamate substitution in the C-terminus of human TALK-1, increases channel activity. Genetic ablation of TALK-1 results in β-cell membrane potential depolarization, increased islet Ca2+ influx, and enhanced second-phase GSIS. Moreover, mice lacking TALK-1 channels are resistant to high-fat diet-induced elevations in fasting glycemia. These findings reveal TALK-1 channels as important modulators of second-phase insulin secretion and suggest a clinically relevant mechanism for rs1535500, which may increase type 2 diabetes risk by limiting GSIS.
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Affiliation(s)
- Nicholas C Vierra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN
| | - Imju Jeong
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN
| | - Matthew Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN
| | | | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN
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24
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Murayama T, Maruyama IN. Alkaline pH sensor molecules. J Neurosci Res 2015; 93:1623-30. [PMID: 26154399 DOI: 10.1002/jnr.23621] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2015] [Revised: 06/12/2015] [Accepted: 06/26/2015] [Indexed: 12/22/2022]
Abstract
Animals can survive only within a narrow pH range. This requires continual monitoring of environmental and body-fluid pH. Although a variety of acidic pH sensor molecules have been reported, alkaline pH sensor function is not well understood. This Review describes neuronal alkaline pH sensors, grouped according to whether they monitor extracellular or intracellular alkaline pH. Extracellular sensors include the receptor-type guanylyl cyclase, the insulin receptor-related receptor, ligand-gated Cl- channels, connexin hemichannels, two-pore-domain K+ channels, and transient receptor potential (TRP) channels. Intracellular sensors include TRP channels and gap junction channels. Identification of molecular mechanisms underlying alkaline pH sensing is crucial for understanding how animals respond to environmental alkaline pH and how body-fluid pH is maintained within a narrow range.
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Affiliation(s)
- Takashi Murayama
- Information Processing Biology Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
| | - Ichiro N Maruyama
- Information Processing Biology Unit, Okinawa Institute of Science and Technology Graduate University, Okinawa, Japan
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25
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Kumar NN, Velic A, Soliz J, Shi Y, Li K, Wang S, Weaver JL, Sen J, Abbott SBG, Lazarenko RM, Ludwig MG, Perez-Reyes E, Mohebbi N, Bettoni C, Gassmann M, Suply T, Seuwen K, Guyenet PG, Wagner CA, Bayliss DA. PHYSIOLOGY. Regulation of breathing by CO₂ requires the proton-activated receptor GPR4 in retrotrapezoid nucleus neurons. Science 2015; 348:1255-60. [PMID: 26068853 DOI: 10.1126/science.aaa0922] [Citation(s) in RCA: 169] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 05/06/2015] [Indexed: 12/12/2022]
Abstract
Blood gas and tissue pH regulation depend on the ability of the brain to sense CO2 and/or H(+) and alter breathing appropriately, a homeostatic process called central respiratory chemosensitivity. We show that selective expression of the proton-activated receptor GPR4 in chemosensory neurons of the mouse retrotrapezoid nucleus (RTN) is required for CO2-stimulated breathing. Genetic deletion of GPR4 disrupted acidosis-dependent activation of RTN neurons, increased apnea frequency, and blunted ventilatory responses to CO2. Reintroduction of GPR4 into RTN neurons restored CO2-dependent RTN neuronal activation and rescued the ventilatory phenotype. Additional elimination of TASK-2 (K(2P)5), a pH-sensitive K(+) channel expressed in RTN neurons, essentially abolished the ventilatory response to CO2. The data identify GPR4 and TASK-2 as distinct, parallel, and essential central mediators of respiratory chemosensitivity.
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Affiliation(s)
- Natasha N Kumar
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Ana Velic
- Institute of Physiology, University of Zurich, Zurich, CH-8057, Switzerland
| | - Jorge Soliz
- Institute of Veterinary Physiology, University of Zurich, Zurich, CH-8057, Switzerland. Centre de Recherche du CHU de Québec, Département de Pédiatrie, Faculté de Médecine, Université Laval, Québec, QC, Canada
| | - Yingtang Shi
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Keyong Li
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Sheng Wang
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA. Department of Physiology, Hebei Medical University, Shijiazhuang, Hebei, 050017, China
| | - Janelle L Weaver
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Josh Sen
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Stephen B G Abbott
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA. School of Medical Sciences, University of New South Wales, New South Wales 2052, Australia. Department of Neurology, Harvard Medical School and Beth Israel Deaconess Medical Center, Boston, MA, USA
| | - Roman M Lazarenko
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | | | - Edward Perez-Reyes
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Nilufar Mohebbi
- Institute of Physiology, University of Zurich, Zurich, CH-8057, Switzerland
| | - Carla Bettoni
- Institute of Physiology, University of Zurich, Zurich, CH-8057, Switzerland
| | - Max Gassmann
- Institute of Veterinary Physiology, University of Zurich, Zurich, CH-8057, Switzerland
| | - Thomas Suply
- Novartis Institutes for Biomedical Research, Basel, CH-4002, Switzerland
| | - Klaus Seuwen
- Novartis Institutes for Biomedical Research, Basel, CH-4002, Switzerland
| | - Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA
| | - Carsten A Wagner
- Institute of Physiology, University of Zurich, Zurich, CH-8057, Switzerland.
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA.
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26
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Renigunta V, Schlichthörl G, Daut J. Much more than a leak: structure and function of K₂p-channels. Pflugers Arch 2015; 467:867-94. [PMID: 25791628 DOI: 10.1007/s00424-015-1703-7] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2015] [Accepted: 03/09/2015] [Indexed: 11/27/2022]
Abstract
Over the last decade, we have seen an enormous increase in the number of experimental studies on two-pore-domain potassium channels (K2P-channels). The collection of reviews and original articles compiled for this special issue of Pflügers Archiv aims to give an up-to-date summary of what is known about the physiology and pathophysiology of K2P-channels. This introductory overview briefly describes the structure of K2P-channels and their function in different organs. Its main aim is to provide some background information for the 19 reviews and original articles of this special issue of Pflügers Archiv. It is not intended to be a comprehensive review; instead, this introductory overview focuses on some unresolved questions and controversial issues, such as: Do K2P-channels display voltage-dependent gating? Do K2P-channels contribute to the generation of action potentials? What is the functional role of alternative translation initiation? Do K2P-channels have one or two or more gates? We come to the conclusion that we are just beginning to understand the extremely complex regulation of these fascinating channels, which are often inadequately described as 'leak channels'.
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Affiliation(s)
- Vijay Renigunta
- Institute of Physiology and Pathophysiology, Marburg University, 35037, Marburg, Germany
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27
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Bouhadfane M, Kaszás A, Rózsa B, Harris-Warrick RM, Vinay L, Brocard F. Sensitization of neonatal rat lumbar motoneuron by the inflammatory pain mediator bradykinin. eLife 2015; 4:e06195. [PMID: 25781633 PMCID: PMC4410746 DOI: 10.7554/elife.06195] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2014] [Accepted: 03/16/2015] [Indexed: 11/27/2022] Open
Abstract
Bradykinin (Bk) is a potent inflammatory mediator that causes hyperalgesia. The action of Bk on the sensory system is well documented but its effects on motoneurons, the final pathway of the motor system, are unknown. By a combination of patch-clamp recordings and two-photon calcium imaging, we found that Bk strongly sensitizes spinal motoneurons. Sensitization was characterized by an increased ability to generate self-sustained spiking in response to excitatory inputs. Our pharmacological study described a dual ionic mechanism to sensitize motoneurons, including inhibition of a barium-sensitive resting K+ conductance and activation of a nonselective cationic conductance primarily mediated by Na+. Examination of the upstream signaling pathways provided evidence for postsynaptic activation of B2 receptors, G protein activation of phospholipase C, InsP3 synthesis, and calmodulin activation. This study questions the influence of motoneurons in the assessment of hyperalgesia since the withdrawal motor reflex is commonly used as a surrogate pain model. DOI:http://dx.doi.org/10.7554/eLife.06195.001 When we accidentally place our hand on a hot stove, we normally experience a painful sensation that starts with the sensory nerves under our skin. These nerves respond by transmitting electrical impulses to our brain, where the painful sensation is then processed. At the same time, these impulses are also transmitted to the motor nerves that control the muscles in our hand to trigger an immediate reflex to withdraw the hand from the hot stove. Pain therefore has a useful role as it can reduce how bad an injury is. People with a condition called hyperalgesia have an increased sensitivity to pain. This condition can result from a chemical called bradykinin ‘sensitizing’ the sensory nerves, causing them to transmit more electrical impulses in response to pain than normal. This makes the injury feel much more painful, and can make the pain last for longer than is beneficial. It was less clear whether bradykinin also affects motor nerves and so triggers a withdrawal reflex. By recording the electrical activity of motor nerve cells taken from the spinal cords of newborn rats, Bouhadfane et al. now show that these motor nerves become more active when exposed to bradykinin. Nerve cells generate electrical signals when ions—such as potassium, sodium, and calcium ions—move through channels in the membranes of the cell. Therefore, to investigate how bradykinin influences the electrical activity of motor nerves, Bouhadfane et al. exposed the cells to drugs that inhibit particular ion channels. This revealed that bradykinin sensitizes the motor nerves by blocking a type of potassium ion channel and activating another ion channel that mainly transports sodium ions. Furthermore, Bouhadfane et al. were able to identify the signaling pathways that allow bradykinin to affect the motor nerve cells. The study implies that the neuronal circuitry for pain does not rely exclusively on sensory nerve cells but should also integrate motor nerve cells. A future challenge remains in developing a protocol to resolve the contribution of motor nerve cells to hyperalgesia assessed by reflex withdrawal. DOI:http://dx.doi.org/10.7554/eLife.06195.002
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Affiliation(s)
- Mouloud Bouhadfane
- Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France
| | - Attila Kaszás
- Institut de Neuroscience des Systèmes (UMR1106), Aix Marseille Université and INSERM, Marseille, France
| | - Balázs Rózsa
- Two-Photon Imaging Center, Institute of Experimental Medicine, Hungarian Academy of Sciences, Budapest, Hungary
| | | | - Laurent Vinay
- Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France
| | - Frédéric Brocard
- Institut de Neurosciences de la Timone (UMR7289), Aix-Marseille Université and CNRS, Marseille, France
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Sepúlveda FV, Pablo Cid L, Teulon J, Niemeyer MI. Molecular aspects of structure, gating, and physiology of pH-sensitive background K2P and Kir K+-transport channels. Physiol Rev 2015; 95:179-217. [PMID: 25540142 DOI: 10.1152/physrev.00016.2014] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
K(+) channels fulfill roles spanning from the control of excitability to the regulation of transepithelial transport. Here we review two groups of K(+) channels, pH-regulated K2P channels and the transport group of Kir channels. After considering advances in the molecular aspects of their gating based on structural and functional studies, we examine their participation in certain chosen physiological and pathophysiological scenarios. Crystal structures of K2P and Kir channels reveal rather unique features with important consequences for the gating mechanisms. Important tasks of these channels are discussed in kidney physiology and disease, K(+) homeostasis in the brain by Kir channel-equipped glia, and central functions in the hearing mechanism in the inner ear and in acid secretion by parietal cells in the stomach. K2P channels fulfill a crucial part in central chemoreception probably by virtue of their pH sensitivity and are central to adrenal secretion of aldosterone. Finally, some unorthodox behaviors of the selectivity filters of K2P channels might explain their normal and pathological functions. Although a great deal has been learned about structure, molecular details of gating, and physiological functions of K2P and Kir K(+)-transport channels, this has been only scratching at the surface. More molecular and animal studies are clearly needed to deepen our knowledge.
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Affiliation(s)
- Francisco V Sepúlveda
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - L Pablo Cid
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - Jacques Teulon
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - María Isabel Niemeyer
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
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29
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Feliciangeli S, Chatelain FC, Bichet D, Lesage F. The family of K2P channels: salient structural and functional properties. J Physiol 2015; 593:2587-603. [PMID: 25530075 DOI: 10.1113/jphysiol.2014.287268] [Citation(s) in RCA: 148] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Accepted: 12/10/2014] [Indexed: 12/11/2022] Open
Abstract
Potassium channels participate in many biological functions, from ion homeostasis to generation and modulation of the electrical membrane potential. They are involved in a large variety of diseases. In the human genome, 15 genes code for K(+) channels with two pore domains (K2P ). These channels form dimers of pore-forming subunits that produce background conductances finely regulated by a range of natural and chemical effectors, including signalling lipids, temperature, pressure, pH, antidepressants and volatile anaesthetics. Since the cloning of TWIK1, the prototypical member of this family, a lot of work has been carried out on their structure and biology. These studies are still in progress, but data gathered so far show that K2P channels are central players in many processes, including ion homeostasis, hormone secretion, cell development and excitability. A growing number of studies underline their implication in physiopathological mechanisms, such as vascular and pulmonary hypertension, cardiac arrhythmias, nociception, neuroprotection and depression. This review gives a synthetic view of the most noticeable features of these channels.
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Affiliation(s)
- Sylvain Feliciangeli
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Frank C Chatelain
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Delphine Bichet
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Florian Lesage
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
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30
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López-Cayuqueo KI, Peña-Münzenmayer G, Niemeyer MI, Sepúlveda FV, Cid LP. TASK-2 K₂p K⁺ channel: thoughts about gating and its fitness to physiological function. Pflugers Arch 2014; 467:1043-53. [PMID: 25315981 DOI: 10.1007/s00424-014-1627-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2014] [Revised: 10/02/2014] [Accepted: 10/03/2014] [Indexed: 01/08/2023]
Abstract
TASK-2 (K2P5) was one of the earliest members of the K2P two-pore, four transmembrane domain K(+) channels to be identified. TASK-2 gating is controlled by changes in both extra- and intracellular pH through separate sensors: arginine 224 and lysine 245, located at the extra- and intracellular ends of transmembrane domain 4. TASK-2 is inhibited by a direct effect of CO2 and is regulated by and interacts with G protein subunits. TASK-2 takes part in regulatory adjustments and is a mediator in the chemoreception process in neurons of the retrotrapezoid nucleus where its pHi sensitivity could be important in regulating excitability and therefore signalling of the O2/CO2 status. Extracellular pH increases brought about by HCO3 (-) efflux from proximal tubule epithelial cells have been proposed to couple to TASK-2 activation to maintain electrochemical gradients favourable to HCO3 (-) reabsorption. We demonstrate that, as suspected previously, TASK-2 is expressed at the basolateral membrane of the same proximal tubule cells that express apical membrane Na(+)-H(+)-exchanger NHE-3 and basolateral membrane Na(+)-HCO3 (-) cotransporter NBCe1-A, the main components of the HCO3 (-) transport machinery. We also discuss critically the mechanism by which TASK-2 is modulated and impacts the process of HCO3 (-) reclaim by the proximal tubule epithelium, concluding that more than a mere shift in extracellular pH is probably involved.
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Affiliation(s)
- Karen I López-Cayuqueo
- Centro de Estudios Científicos (CECs), Avenida Arturo Prat 514, 5110466, Valdivia, Chile
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31
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Venglovecz V, Rakonczay Z, Gray MA, Hegyi P. Potassium channels in pancreatic duct epithelial cells: their role, function and pathophysiological relevance. Pflugers Arch 2014; 467:625-40. [PMID: 25074489 DOI: 10.1007/s00424-014-1585-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 07/09/2014] [Accepted: 07/18/2014] [Indexed: 12/14/2022]
Abstract
Pancreatic ductal epithelial cells play a fundamental role in HCO3 (-) secretion, a process which is essential for maintaining the integrity of the pancreas. Although several studies have implicated impaired HCO3 (-) and fluid secretion as a triggering factor in the development of pancreatitis, the mechanism and regulation of HCO3 (-) secretion is still not completely understood. To date, most studies on the ion transporters that orchestrate ductal HCO3 (-) secretion have focussed on the role of Cl(-)/HCO3 (-) exchangers and Cl(-) channels, whereas much less is known about the role of K(+) channels. However, there is growing evidence that many types of K(+) channels are present in ductal cells where they have an essential role in establishing and maintaining the electrochemical driving force for anion secretion. For this reason, strategies that increase K(+) channel function may help to restore impaired HCO3 (-) and fluid secretion, such as in pancreatitis, and therefore provide novel directions for future pancreatic therapy. In this review, our aims are to summarize the types of K(+) channels found in pancreatic ductal cells and to discuss their individual roles in ductal HCO3 (-) secretion. We will also describe how K(+) channels are involved in pathophysiological conditions and discuss how they could act as new molecular targets for the development of therapeutic approaches to treat pancreatic diseases.
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Affiliation(s)
- Viktória Venglovecz
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Szeged, Hungary,
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32
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Cid LP, Roa-Rojas HA, Niemeyer MI, González W, Araki M, Araki K, Sepúlveda FV. TASK-2: a K2P K(+) channel with complex regulation and diverse physiological functions. Front Physiol 2013; 4:198. [PMID: 23908634 PMCID: PMC3725403 DOI: 10.3389/fphys.2013.00198] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 07/10/2013] [Indexed: 11/13/2022] Open
Abstract
TASK-2 (K2P5.1) is a two-pore domain K(+) channel belonging to the TALK subgroup of the K2P family of proteins. TASK-2 has been shown to be activated by extra- and intracellular alkalinization. Extra- and intracellular pH-sensors reside at arginine 224 and lysine 245 and might affect separate selectivity filter and inner gates respectively. TASK-2 is modulated by changes in cell volume and a regulation by direct G-protein interaction has also been proposed. Activation by extracellular alkalinization has been associated with a role of TASK-2 in kidney proximal tubule bicarbonate reabsorption, whilst intracellular pH-sensitivity might be the mechanism for its participation in central chemosensitive neurons. In addition to these functions TASK-2 has been proposed to play a part in apoptotic volume decrease in kidney cells and in volume regulation of glial cells and T-lymphocytes. TASK-2 is present in chondrocytes of hyaline cartilage, where it is proposed to play a central role in stabilizing the membrane potential. Additional sites of expression are dorsal root ganglion neurons, endocrine and exocrine pancreas and intestinal smooth muscle cells. TASK-2 has been associated with the regulation of proliferation of breast cancer cells and could become target for breast cancer therapeutics. Further work in native tissues and cells together with genetic modification will no doubt reveal the details of TASK-2 functions that we are only starting to suspect.
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Affiliation(s)
- L Pablo Cid
- Centro de Estudios Científicos Valdivia, Chile
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33
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Toczyłowska-Mamińska R, Dołowy K. Ion transporting proteins of human bronchial epithelium. J Cell Biochem 2012; 113:426-32. [PMID: 21975871 DOI: 10.1002/jcb.23393] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The electrolyte transport system across human airway epithelium followed by water movement is essential for the normal mucociliary clearance that allows the maintenance of the aseptic condition of the respiratory tract. The function of epithelial cells is to control and regulate ionic composition and volume of fluids in the airways. Various types of proteins taking part in assuring effective ions and water transport in apical and basolateral membranes of the airway epithelium have been found (e.g., CFTR, ENaC, CaCC, ORCC, potassium channels, NaKATPase, aquaporins). The paper reviews the current state of the art in the field of ion channels, transporters, and other signaling proteins identified in the human bronchial epithelium.
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Affiliation(s)
- Renata Toczyłowska-Mamińska
- Department of Biophysics, Warsaw University of Life Sciences (SGGW), 159 Nowoursynowska St, 0-776 Warsaw, Poland.
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34
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Sandoval M, Burgos J, Sepúlveda FV, Cid LP. Extracellular pH in restricted domains as a gating signal for ion channels involved in transepithelial transport. Biol Pharm Bull 2011; 34:803-9. [PMID: 21628875 DOI: 10.1248/bpb.34.803] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The importance of intracellular pH (pH(i)) in the regulation of diverse cellular activities ranging from cell proliferation and differentiation to cell cycle, migration and apoptosis has long been recognised. More recently, extracellular pH (pH₀), in particular that of relatively inaccessible compartments or domains that occur between cells in tissues, has begun to be acknowledged as a relevant signal in cell regulation. This should not be surprising given the abundant reports highlighting the pH₀-dependence of the activity of membrane proteins facing the extracellular space such as receptors, transporters, ion channels and enzymes. Changes in pH affect the ionisation state of proteins through the effect on their titratable groups. There are proteins, however, which respond to pH shifts with conformational changes that are crucial for catalysis or transport activity. In such cases protons act as signalling molecules capable of eliciting fast and localised responses. We provide examples of ion channels that appear fastidiously designed to respond to extracellular pH in a manner that suggests specific functions in transporting epithelia. We shall also present ideas as to how these channels participate in complex transepithelial transport processes and provide preliminary experiments illustrating a new way to gauge pH₀ in confined spaces of native epithelial tissue.
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35
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Nam JH, Shin DH, Zheng H, Lee DS, Park SJ, Park KS, Kim SJ. Expression of TASK-2 and its upregulation by B cell receptor stimulation in WEHI-231 mouse immature B cells. Am J Physiol Cell Physiol 2011; 300:C1013-22. [DOI: 10.1152/ajpcell.00475.2010] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Stimulation of B cell receptors (BCR ligation) induces apoptosis of immature B cells, which is critical to the elimination of self-reactive clones. In the mouse immature B cell line WEHI-231, the authors previously reported two types of background K+ channels with large (∼300 pS, LKbg) and medium (∼100 pS, MKbg) conductance in divalent cation-free conditions. While the authors have recently identified LKbg as TREK-2, the molecular nature of MKbg is unknown yet. In the present study, the authors found that BCR ligation markedly increased the background K+ conductance of WEHI-231. A single-channel study revealed that MKbg activity is increased by BCR ligation and that the biophysical properties (unitary conductance and pH sensitivity) of MKbg are consistent with those of TWIK-related acid-sensitive K+ channel 2 (TASK-2). The expression of TASK-2 and its upregulation by BCR ligation were confirmed by RT-PCR and immunoblot assays in WEHI-231. The BCR ligation-induced increase of K+ current was prevented by calcineurin inhibitors (cyclosporine A or FK506), and also by TASK-2-specific small interfering RNA (siRNA) transfection (si-TASK-2). Furthermore, si-TASK-2 attenuated the apoptosis of WEHI-231 caused by BCR ligation. TASK-2 activity and its mRNA were also confirmed in the primary splenic B cells of mouse. Summarizing, the authors report for the first time the expression of TASK-2 in B cells and surmise that the upregulation of TASK-2 by BCR ligation is associated with the apoptosis of immature B cells.
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Affiliation(s)
- Joo Hyun Nam
- Department of Physiology and
- Department of Physiology, Dongguk University College of Medicine; and
| | | | | | - Dong-Sup Lee
- Department of Anatomy, Seoul National University College of Medicine
| | | | - Kyung Sun Park
- Department of Physiology and
- Ischemia/Hypoxia Disease Institute, Medical Research Center, Seoul National University, Seoul, Korea
| | - Sung Joon Kim
- Department of Physiology and
- Ischemia/Hypoxia Disease Institute, Medical Research Center, Seoul National University, Seoul, Korea
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36
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Zúñiga L, Márquez V, González-Nilo FD, Chipot C, Cid LP, Sepúlveda FV, Niemeyer MI. Gating of a pH-sensitive K(2P) potassium channel by an electrostatic effect of basic sensor residues on the selectivity filter. PLoS One 2011; 6:e16141. [PMID: 21283586 PMCID: PMC3026807 DOI: 10.1371/journal.pone.0016141] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2010] [Accepted: 12/06/2010] [Indexed: 01/13/2023] Open
Abstract
K+ channels share common selectivity characteristics but exhibit a wide diversity in how they are gated open. Leak K2P K+ channels TASK-2, TALK-1 and TALK-2 are gated open by extracellular alkalinization. The mechanism for this alkalinization-dependent gating has been proposed to be the neutralization of the side chain of a single arginine (lysine in TALK-2) residue near the pore of TASK-2, which occurs with the unusual pKa of 8.0. We now corroborate this hypothesis by transplanting the TASK-2 extracellular pH (pHo) sensor in the background of a pHo-insensitive TASK-3 channel, which leads to the restitution of pHo-gating. Using a concatenated channel approach, we also demonstrate that for TASK-2 to open, pHo sensors must be neutralized in each of the two subunits forming these dimeric channels with no apparent cross-talk between the sensors. These results are consistent with adaptive biasing force analysis of K+ permeation using a model selectivity filter in wild-type and mutated channels. The underlying free-energy profiles confirm that either a doubly or a singly charged pHo sensor is sufficient to abolish ion flow. Atomic detail of the associated mechanism reveals that, rather than a collapse of the pore, as proposed for other K2P channels gated at the selectivity filter, an increased height of the energetic barriers for ion translocation accounts for channel blockade at acid pHo. Our data, therefore, strongly suggest that a cycle of protonation/deprotonation of pHo-sensing arginine 224 side chain gates the TASK-2 channel by electrostatically tuning the conformational stability of its selectivity filter.
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Affiliation(s)
| | - Valeria Márquez
- Centro de Bioinformática y Simulación Molecular, Universidad de Talca, Talca, Chile
| | | | - Christophe Chipot
- Beckman Institute, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States of America
- Équipe de Dynamique des Assemblages Membranaires, Unité Mixte de Recherche CNRS/UHP 7565, Université de Nancy, Vandoeuvre-lès-Nancy, France
| | - L. Pablo Cid
- Centro de Estudios Científicos (CECS), Valdivia, Chile
| | - Francisco V. Sepúlveda
- Centro de Estudios Científicos (CECS), Valdivia, Chile
- Centro de Ingeniería de la Innovación del CECS (CIN), Valdivia, Chile
- * E-mail:
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37
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Enyedi P, Czirják G. Molecular background of leak K+ currents: two-pore domain potassium channels. Physiol Rev 2010; 90:559-605. [PMID: 20393194 DOI: 10.1152/physrev.00029.2009] [Citation(s) in RCA: 620] [Impact Index Per Article: 44.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Two-pore domain K(+) (K(2P)) channels give rise to leak (also called background) K(+) currents. The well-known role of background K(+) currents is to stabilize the negative resting membrane potential and counterbalance depolarization. However, it has become apparent in the past decade (during the detailed examination of the cloned and corresponding native K(2P) channel types) that this primary hyperpolarizing action is not performed passively. The K(2P) channels are regulated by a wide variety of voltage-independent factors. Basic physicochemical parameters (e.g., pH, temperature, membrane stretch) and also several intracellular signaling pathways substantially and specifically modulate the different members of the six K(2P) channel subfamilies (TWIK, TREK, TASK, TALK, THIK, and TRESK). The deep implication in diverse physiological processes, the circumscribed expression pattern of the different channels, and the interesting pharmacological profile brought the K(2P) channel family into the spotlight. In this review, we focus on the physiological roles of K(2P) channels in the most extensively investigated cell types, with special emphasis on the molecular mechanisms of channel regulation.
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Affiliation(s)
- Péter Enyedi
- Department of Physiology, Semmelweis University, Budapest, Hungary.
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38
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Niemeyer MI, Cid LP, Peña-Münzenmayer G, Sepúlveda FV. Separate gating mechanisms mediate the regulation of K2P potassium channel TASK-2 by intra- and extracellular pH. J Biol Chem 2010; 285:16467-75. [PMID: 20351106 DOI: 10.1074/jbc.m110.107060] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
TASK-2 (KCNK5 or K(2P)5.1) is a background K(+) channel that is opened by extracellular alkalinization and plays a role in renal bicarbonate reabsorption and central chemoreception. Here, we demonstrate that in addition to its regulation by extracellular protons (pH(o)) TASK-2 is gated open by intracellular alkalinization. The following pieces of evidence suggest that the gating process controlled by intracellular pH (pH(i)) is independent from that under the command of pH(o). It was not possible to overcome closure by extracellular acidification by means of intracellular alkalinization. The mutant TASK-2-R224A that lacks sensitivity to pH(o) had normal pH(i)-dependent gating. Increasing extracellular K(+) concentration acid shifts pH(o) activity curve of TASK-2 yet did not affect pH(i) gating of TASK-2. pH(o) modulation of TASK-2 is voltage-dependent, whereas pH(i) gating was not altered by membrane potential. These results suggest that pH(o), which controls a selectivity filter external gate, and pH(i) act at different gating processes to open and close TASK-2 channels. We speculate that pH(i) regulates an inner gate. We demonstrate that neutralization of a lysine residue (Lys(245)) located at the C-terminal end of transmembrane domain 4 by mutation to alanine abolishes gating by pH(i). We postulate that this lysine acts as an intracellular pH sensor as its mutation to histidine acid-shifts the pH(i)-dependence curve of TASK-2 as expected from its lower pK(a). We conclude that intracellular pH, together with pH(o), is a critical determinant of TASK-2 activity and therefore of its physiological function.
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Differential effects of temperature on acid-activated currents mediated by TRPV1 and ASIC channels in rat dorsal root ganglion neurons. Brain Res 2010; 1329:55-66. [PMID: 20206612 DOI: 10.1016/j.brainres.2010.02.064] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2009] [Revised: 01/28/2010] [Accepted: 02/21/2010] [Indexed: 11/23/2022]
Abstract
Elevated temperature and decreased extracellular pH are hallmarks of inflammatory pain states. Dorsal root ganglia (DRG) neurons are integral in transferring painful stimuli from the periphery to central sites. This study investigated the effect of elevated temperatures on the response of DRG neurons to acute application of acidic solutions. At room temperature (22 degrees C), in response to pH 5.5, there were a variety of kinetic responses consistent with differential expression of TRPV1 and ASIC channels. Increasing the temperature resulted in a significant increase in the peak and total current mediated by TRPV1 in response to an acidic solution. In contrast, the amplitude of a fast activating, rapidly inactivating ASIC1-like current was not affected by increasing the temperature but did result in an increased rate of desensitization that reduced the total current level. This effect on the rate of desensitization was temperature-dependent and could be reversed by returning to 22 degrees C. Likewise, cells exhibiting slowly inactivating ASIC2-like responses also had temperature-dependent increase in the rate of desensitization. The ASIC2-like responses and the TRPV1 responses tended to decrease in amplitude with repetitive application of pH 5.5 even at 22 degrees C. The rate of desensitization of ASIC-like currents activated by less acidic solutions (pH 6.8) was also increased in a temperature-dependent manner. Finally, acidic pH reduced threshold to trigger action potentials, however, the pattern of action potential firing was shaped by the distribution of ASIC and TRPV1 channels. These results indicate that the ambient temperature at which acidosis occurs has a profound effect on the contribution of ASIC and TRPV1 channels, therefore, altering the neuronal excitability.
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40
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Kim D, Cavanaugh EJ, Kim I, Carroll JL. Heteromeric TASK-1/TASK-3 is the major oxygen-sensitive background K+ channel in rat carotid body glomus cells. J Physiol 2009; 587:2963-75. [PMID: 19403596 DOI: 10.1113/jphysiol.2009.171181] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Carotid body (CB) glomus cells from rat express a TASK-like background K+ channel that is believed to play a critical role in the regulation of excitability and hypoxia-induced increase in respiration. Here we studied the kinetic behaviour of single channel openings from rat CB cells to determine the molecular identity of the 'TASK-like' K+ channels. In outside-out patches, the TASK-like background K+ channel in CB cells was inhibited >90% by a reduction of pH(o) from 7.3 to 5.8. In cell-attached patches with 140 mM KCl and 1 mM Mg2+ in the bath and pipette solutions, two main open levels with conductance levels of approximately 14 pS and approximately 32 pS were recorded at a membrane potential of -60 mV. The K+ channels showed kinetic properties similar to TASK-1 (approximately 14 pS), TASK-3 (approximately 32 pS) and TASK-1/3 heteromer (approximately 32 pS). The presence of three TASK isoforms was tested by reducing [Mg2+](o) to approximately 0 mM, which had no effect on the conductance of TASK-1, but increased those of TASK-1/3 and TASK-3 to 42 pS and 74 pS, respectively. In CB cells, the reduction of [Mg2+](o) to approximately 0 mM also caused the appearance of approximately 42 pS (TASK-1/3-like) and approximately 74 pS (TASK-3-like) channels, in addition to the approximately 14 pS (TASK-1-like) channel. The 42 pS channel was the most abundant, contributing approximately 75% of the current produced by TASK-like channels. Ruthenium red (5 microM) had no effect on TASK-1 and TASK-1/3, but inhibited TASK-3 by 87%. In CB cells, ruthenium red caused approximately 12% inhibition of TASK-like activity. Methanandamide reduced the activity of all three TASKs by 80-90%, and that of TASK-like channels in CB cell also by approximately 80%. In CB cells, hypoxia caused inhibition of TASK-like channels, including TASK-1/3-like channels. These results show that TASK-1, TASK-1/3 and TASK-3 are all functionally expressed in isolated CB cells, and that the TASK-1/3 heteromer provides the major part of the oxygen-sensitive TASK-like background K+ conductance.
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Affiliation(s)
- Donghee Kim
- 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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Gating the pore of potassium leak channels. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2009; 39:61-73. [PMID: 19404634 DOI: 10.1007/s00249-009-0457-6] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/13/2009] [Revised: 04/02/2009] [Accepted: 04/07/2009] [Indexed: 11/27/2022]
Abstract
A key feature of potassium channel function is the ability to switch between conducting and non-conducting states by undergoing conformational changes in response to cellular or extracellular signals. Such switching is facilitated by the mechanical coupling of gating domain movements to pore opening and closing. Two-pore domain potassium channels (K(2P)) conduct leak or background potassium-selective currents that are mostly time- and voltage-independent. These channels play a significant role in setting the cell resting membrane potential and, therefore modulate cell responsiveness and excitability. Thus, K(2P) channels are key players in numerous physiological processes and were recently shown to also be involved in human pathologies. It is well established that K(2P) channel conductance, open probability and cell surface expression are significantly modulated by various physical and chemical stimuli. However, in understanding how such signals are translated into conformational changes that open or close the channels gate, there remain more open questions than answers. A growing line of evidence suggests that the outer pore area assumes a critical role in gating K(2P) channels, in a manner reminiscent of C-type inactivation of voltage-gated potassium channels. In some K(2P) channels, this gating mechanism is facilitated in response to external pH levels. Recently, it was suggested that K(2P) channels also possess a lower activation gate that is positively coupled to the outer pore gate. The purpose of this review is to present an up-to-date summary of research describing the conformational changes and gating events that take place at the K(2P) channel ion-conducting pathway during the channel regulation.
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42
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Kim JE, Kwak SE, Kang TC. Upregulated TWIK-related acid-sensitive K+ channel-2 in neurons and perivascular astrocytes in the hippocampus of experimental temporal lobe epilepsy. Epilepsia 2009; 50:654-63. [PMID: 19220408 DOI: 10.1111/j.1528-1167.2008.01957.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
PURPOSE To identify the modulation of Tandem of P-domains in a weak inwardly rectifying K(+) channel (TWIK)-related acid-sensitive K(+) (TASK)-2 channel expressions in epilepsy, we conducted a comparative analysis of TASK-2 channel immunoreactivity in the hippocampus of a pilocarpine-induced rat epilepsy model. METHODS We performed and immunohistochemical study for TASK-2 and double immunofluorescent staining for TASK-2 and glial fibrillary acidic protein (GFAP) in the rat hippocampus of pilocarpine-induced epilepsy models. RESULTS In control animals, TASK-2 immunoreactivity was strongly detected in CA1-3 pyramidal layers and dentate granule cell layer. After status epilepticus (SE), TASK-2 immunoreactivity was increased in dentate granule cell layer and CA3 pyramidal cell layer, whereas its immunoreactivity was reduced in CA1 pyramidal cell layer. In addition, TASK-2 immunoreactivity is gradually increased in perivascular regions following SE. Double immunofluorescent study revealed that the enhancement of TASK-2 immunoreactivity in perivascular regions is caused by increase in the number of TASK-2 immunoreactive endfeet of perivascular astrocytes. DISCUSSION Our findings suggest that elevated TASK-2 immunoreactivity in neurons may contribute to rapid adaptive responses (presumably for extracellular alkalinization), which result in hyperpolarization and regulate seizure activity. In contrast, upregulated TASK-2 immunoreactivity in perivascular regions may be involved in abnormalities of blood flow regulation or brain-blood barrier impairment. These changes may contribute to acquisition of the properties of the epileptic hippocampus.
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Affiliation(s)
- Ji-Eun Kim
- Department of Anatomy and Neurobiology and Institute of Epilepsy Research, College of Medicine, Hallym University, Chunchon, South Korea
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43
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Abstract
Acidosis is a noxious condition associated with inflammation, ischaemia or defective acid containment. As a consequence, acid sensing has evolved as an important property of afferent neurons with unmyelinated and thinly myelinated nerve fibres. Protons evoke multiple currents in primary afferent neurons, which are carried by several acid-sensitive ion channels. Among these, acid-sensing ion channels (ASICs) and transient receptor potential (TRP) vanilloid-1 (TRPV1) ion channels have been most thoroughly studied. ASICs survey moderate decreases in extracellular pH, whereas TRPV1 is activated only by severe acidosis resulting in pH values below 6. Two-pore-domain K(+) (K(2P)) channels are differentially regulated by small deviations of extra- or intracellular pH from physiological levels. Other acid-sensitive channels include TRPV4, TRPC4, TRPC5, TRPP2 (PKD2L1), ionotropic purinoceptors (P2X), inward rectifier K(+) channels, voltage-activated K(+) channels, L-type Ca(2+) channels, hyperpolarization-activated cyclic nucleotide gated channels, gap junction channels, and Cl(-) channels. In addition, acid-sensitive G protein coupled receptors have also been identified. Most of these molecular acid sensors are expressed by primary sensory neurons, although to different degrees and in various combinations. Emerging evidence indicates that many of the acid-sensitive ion channels and receptors play a role in acid sensing, acid-induced pain and acid-evoked feedback regulation of homeostatic reactions. The existence and apparent redundancy of multiple pH surveillance systems attests to the concept that acid-base regulation is a vital issue for cell and tissue homeostasis. Since upregulation and overactivity of acid sensors appear to contribute to various forms of chronic pain, acid-sensitive ion channels and receptors are considered as targets for novel analgesic drugs. This approach will only be successful if the pathological implications of acid sensors can be differentiated pharmacologically from their physiological function.
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Affiliation(s)
- Peter Holzer
- Research Unit of Translational Neurogastroenterology, Institute of Experimental and Clinical Pharmacology, Medical University of Graz, Universitätsplatz 4, 8010, Graz, Austria.
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Jang I, La JH, Kim GT, Lee JS, Kim EJ, Lee ES, Kim SJ, Seo JM, Ahn SH, Park JY, Hong SG, Kang D, Han J. Single-Channel Recording of TASK-3-like K Channel and Up-Regulation of TASK-3 mRNA Expression after Spinal Cord Injury in Rat Dorsal Root Ganglion Neurons. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2008; 12:245-51. [PMID: 19967063 DOI: 10.4196/kjpp.2008.12.5.245] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Single-channel recordings of TASK-1 and TASK-3, members of two-pore domain K(+) channel family, have not yet been reported in dorsal root ganglion (DRG) neurons, even though their mRNA and activity in whole-cell currents have been detected in these neurons. Here, we report single-channel kinetics of the TASK-3-like K(+) channel in DRG neurons and up-regulation of TASK-3 mRNA expression in tissues isolated from animals with spinal cord injury (SCI). In DRG neurons, the single-channel conductance of TASK-3-like K(+) channel was 33.0+/-0.1 pS at -60 mV, and TASK-3 activity fell by 65+/-5% when the extracellular pH was changed from 7.3 to 6.3, indicating that the DRG K(+) channel is similar to cloned TASK-3 channel. TASK-3 mRNA and protein levels in brain, spinal cord, and DRG were significantly higher in injured animals than in sham-operated ones. These results indicate that TASK-3 channels are expressed and functional in DRG neurons and the expression level is up-regulated following SCI, and suggest that TASK-3 channel could act as a potential background K(+) channel under SCI-induced acidic condition.
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Affiliation(s)
- Inseok Jang
- Department of Thoracic Surgery, College of Medicine and Institute of Health Sciences, Gyeongsang National University, Jinju 660-751, Korea
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45
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Weber M, Schmitt A, Wischmeyer E, Döring F. Excitability of pontine startle processing neurones is regulated by the two-pore-domain K+channel TASK-3 coupled to 5-HT2Creceptors. Eur J Neurosci 2008; 28:931-40. [DOI: 10.1111/j.1460-9568.2008.06400.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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46
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Heitzmann D, Warth R. Physiology and pathophysiology of potassium channels in gastrointestinal epithelia. Physiol Rev 2008; 88:1119-82. [PMID: 18626068 DOI: 10.1152/physrev.00020.2007] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Epithelial cells of the gastrointestinal tract are an important barrier between the "milieu interne" and the luminal content of the gut. They perform transport of nutrients, salts, and water, which is essential for the maintenance of body homeostasis. In these epithelia, a variety of K(+) channels are expressed, allowing adaptation to different needs. This review provides an overview of the current literature that has led to a better understanding of the multifaceted function of gastrointestinal K(+) channels, thereby shedding light on pathophysiological implications of impaired channel function. For instance, in gastric mucosa, K(+) channel function is a prerequisite for acid secretion of parietal cells. In epithelial cells of small intestine, K(+) channels provide the driving force for electrogenic transport processes across the plasma membrane, and they are involved in cell volume regulation. Fine tuning of salt and water transport and of K(+) homeostasis occurs in colonic epithelia cells, where K(+) channels are involved in secretory and reabsorptive processes. Furthermore, there is growing evidence for changes in epithelial K(+) channel expression during cell proliferation, differentiation, apoptosis, and, under pathological conditions, carcinogenesis. In the future, integrative approaches using functional and postgenomic/proteomic techniques will help us to gain comprehensive insights into the role of K(+) channels of the gastrointestinal tract.
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Affiliation(s)
- Dirk Heitzmann
- Institute of Physiology and Clinic and Policlinic for Internal Medicine II, Regensburg, Germany
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47
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Role of Nox2 in elimination of microorganisms. Semin Immunopathol 2008; 30:237-53. [PMID: 18574584 DOI: 10.1007/s00281-008-0126-3] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2008] [Accepted: 05/23/2008] [Indexed: 12/16/2022]
Abstract
NADPH oxidase of the phagocytic cells (Nox2) transfers electrons from cytosolic NADPH to molecular oxygen in the extracellular or intraphagosomal space. The produced superoxide anion (O*2) provides the source for formation of all toxic oxygen derivatives, but continuous O*2 generation depends on adequate charge compensation. The vital role of Nox2 in efficient elimination of microorganisms is clearly indicated by human pathology as insufficient activity of the enzyme results in severe, recurrent bacterial infections, the typical symptoms of chronic granulomatous disease. The goals of this contribution are to provide critical review of the Nox2-dependent cellular processes that potentially contribute to bacterial killing and degradation and to indicate possible targets of pharmacological interventions.
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48
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Beckett EAH, Han I, Baker SA, Han J, Britton FC, Koh SD. Functional and molecular identification of pH-sensitive K+ channels in murine urinary bladder smooth muscle. BJU Int 2008; 102:113-24. [PMID: 18394011 DOI: 10.1111/j.1464-410x.2008.07541.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
OBJECTIVE To examine the role of pH-sensitive K(+) channels in setting the resting membrane potential in murine bladder smooth muscle, as bladder contractility is influenced by the resting membrane potential, which is mainly regulated by background K(+) conductances. MATERIALS AND METHODS Using conventional microelectrode recordings, isometric tension measurements, patch-clamp recordings, reverse transcription-polymerase chain reaction (RT-PCR), Western blotting and immunohistochemistry, we assessed bladder smooth muscle cells and tissues. RESULTS Acidic pH (pH 6.5) depolarized the resting membrane potential of murine bladder smooth muscles and increased muscle tone and contractility. The pH-induced changes were not abolished by neuronal blockers or classical K(+)-channel antagonists. Lidocaine (1 mM) and bupivacaine (100 microm) mimicked the effects of acidifying the external solution, and in the presence of lidocaine no further increase in contractility was induced by reducing the pH to 6.5. Voltage-clamp experiments on freshly dispersed bladder myocytes showed that pH 6.5 decreased the outward current. Pre-treatment of bladder myocytes with the classical K(+) antagonists tetraethylammonium (10 mm), 4-aminopyridine (5 mM), glibenclamide (10 microm) or apamin (300 nM) did not inhibit the effects of low pH on outward current. However, treatment with lidocaine (1 mM) abolished the effects of acidic pH on outward current. RT-PCR showed the expression of the acid-sensitive K(+) channel (TASK)-1 and TASK-2 gene transcripts in murine bladder, and immunohistochemistry and Western blot analysis showed TASK-1 and TASK-2 channel expression and distribution in smooth muscle tissues and cells. CONCLUSION TASK channels are expressed in bladder smooth muscle and contribute to the basal K(+) conductances responsible for resting membrane potential.
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Affiliation(s)
- Elizabeth A H Beckett
- Department of Physiology and Cell Biology, University of Nevada Reno, School of Medicine, Reno, NV 89557, USA
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Lotshaw DP. Biophysical, pharmacological, and functional characteristics of cloned and native mammalian two-pore domain K+ channels. Cell Biochem Biophys 2007; 47:209-56. [PMID: 17652773 DOI: 10.1007/s12013-007-0007-8] [Citation(s) in RCA: 149] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/1999] [Revised: 11/30/1999] [Accepted: 11/30/1999] [Indexed: 12/12/2022]
Abstract
The mammalian family of two-pore domain K+ (K2P) channel proteins are encoded by 15 KCNK genes and subdivided into six subfamilies on the basis of sequence similarities: TWIK, TREK, TASK, TALK, THIK, and TRESK. K2P channels are expressed in cells throughout the body and have been implicated in diverse cellular functions including maintenance of the resting potential and regulation of excitability, sensory transduction, ion transport, and cell volume regulation, as well as metabolic regulation and apoptosis. In recent years K2P channel isoforms have been identified as important targets of several widely employed drugs, including: general anesthetics, local anesthetics, neuroprotectants, and anti-depressants. An important goal of future studies will be to identify the basis of drug actions and channel isoform selectivity. This goal will be facilitated by characterization of native K2P channel isoforms, their pharmacological properties and tissue-specific expression patterns. To this end the present review examines the biophysical, pharmacological, and functional characteristics of cloned mammalian K2P channels and compares this information with the limited data available for native K2P channels in order to determine criteria which may be useful in identifying ionic currents mediated by native channel isoforms and investigating their pharmacological and functional characteristics.
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Affiliation(s)
- David P Lotshaw
- Department of Biological Sciences, Northern Illinois University, DeKalb, IL 60115, USA.
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50
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Niemeyer MI, González-Nilo FD, Zúñiga L, González W, Cid LP, Sepúlveda FV. Neutralization of a single arginine residue gates open a two-pore domain, alkali-activated K+ channel. Proc Natl Acad Sci U S A 2007; 104:666-71. [PMID: 17197424 PMCID: PMC1766441 DOI: 10.1073/pnas.0606173104] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2006] [Indexed: 12/19/2022] Open
Abstract
Potassium channels share a common selectivity filter that determines the conduction characteristics of the pore. Diversity in K+ channels is given by how they are gated open. TASK-2, TALK-1, and TALK-2 are two-pore region (2P) KCNK K+ channels gated open by extracellular alkalinization. We have explored the mechanism for this alkalinization-dependent gating using molecular simulation and site-directed mutagenesis followed by functional assay. We show that the side chain of a single arginine residue (R224) near the pore senses pH in TASK-2 with an unusual pKa of 8.0, a shift likely due to its hydrophobic environment. R224 would block the channel through an electrostatic effect on the pore, a situation relieved by its deprotonation by alkalinization. A lysine residue in TALK-2 fulfills the same role but with a largely unchanged pKa, which correlates with an environment that stabilizes its positive charge. In addition to suggesting unified alkaline pH-gating mechanisms within the TALK subfamily of channels, our results illustrate in a physiological context the principle that hydrophobic environment can drastically modulate the pKa of charged amino acids within a protein.
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Affiliation(s)
| | - Fernando D. González-Nilo
- Centro de Bioinformática y Simulación Molecular, Universidad de Talca, 2 Norte 685, Talca 346-0000, Chile; and
| | - Leandro Zúñiga
- *Centro de Estudios Científicos, Avenida Arturo Prat 514, Valdivia 509-9100, Chile
- Universidad Austral de Chile, Valdivia 509-9200, Chile
| | - Wendy González
- Centro de Bioinformática y Simulación Molecular, Universidad de Talca, 2 Norte 685, Talca 346-0000, Chile; and
| | - L. Pablo Cid
- *Centro de Estudios Científicos, Avenida Arturo Prat 514, Valdivia 509-9100, Chile
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