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Li E, van der Heyden MAG. The network of cardiac K IR2.1: its function, cellular regulation, electrical signaling, diseases and new drug avenues. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 2024:10.1007/s00210-024-03116-5. [PMID: 38683369 DOI: 10.1007/s00210-024-03116-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2024] [Accepted: 04/19/2024] [Indexed: 05/01/2024]
Abstract
The functioning of the human heart relies on complex electrical and communication systems that coordinate cardiac contractions and sustain rhythmicity. One of the key players contributing to this intricate system is the KIR2.1 potassium ion channel, which is encoded by the KCNJ2 gene. KIR2.1 channels exhibit abundant expression in both ventricular myocytes and Purkinje fibers, exerting an important role in maintaining the balance of intracellular potassium ion levels within the heart. And by stabilizing the resting membrane potential and contributing to action potential repolarization, these channels have an important role in cardiac excitability also. Either gain- or loss-of-function mutations, but also acquired impairments of their function, are implicated in the pathogenesis of diverse types of cardiac arrhythmias. In this review, we aim to elucidate the system functions of KIR2.1 channels related to cellular electrical signaling, communication, and their contributions to cardiovascular disease. Based on this knowledge, we will discuss existing and new pharmacological avenues to modulate their function.
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Affiliation(s)
- Encan Li
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, Yalelaan 50, 3584 CM, Utrecht, Netherlands
| | - Marcel A G van der Heyden
- Department of Medical Physiology, Division Heart & Lungs, University Medical Center Utrecht, Yalelaan 50, 3584 CM, Utrecht, Netherlands.
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Hegyi B, Chen-Izu Y, Izu LT, Bányász T. Altered K + current profiles underlie cardiac action potential shortening in hyperkalemia and β-adrenergic stimulation. Can J Physiol Pharmacol 2019; 97:773-780. [PMID: 31091413 DOI: 10.1139/cjpp-2019-0056] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Hyperkalemia is known to develop in various conditions including vigorous physical exercise. In the heart, hyperkalemia is associated with action potential (AP) shortening that was attributed to altered gating of K+ channels. However, it remains unknown how hyperkalemia changes the profiles of each K+ current under a cardiac AP. Therefore, we recorded the major K+ currents (inward rectifier K+ current, IK1; rapid and slow delayed rectifier K+ currents, IKr and IKs, respectively) using AP-clamp in rabbit ventricular myocytes. As K+ may accumulate at rapid heart rates during sympathetic stimulation, we also examined the effect of isoproterenol on these K+ currents. We found that IK1 was significantly increased in hyperkalemia, whereas the reduction of driving force for K+ efflux dominated over the altered channel gating in case of IKr and IKs. Overall, the markedly increased IK1 in hyperkalemia overcame the relative decreases of IKr and IKs during AP, resulting in an increased net repolarizing current during AP phase 3. β-Adrenergic stimulation of IKs also provided further repolarizing power during sympathetic activation, although hyperkalemia limited IKs upregulation. These results indicate that facilitation of IK1 in hyperkalemia and β-adrenergic stimulation of IKs represent important compensatory mechanisms against AP prolongation and arrhythmia susceptibility.
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Affiliation(s)
- Bence Hegyi
- a Department of Pharmacology, University of California, Davis, CA 95616, USA
| | - Ye Chen-Izu
- a Department of Pharmacology, University of California, Davis, CA 95616, USA.,b Department of Biomedical Engineering, University of California, Davis, CA 95616, USA.,c Department of Internal Medicine/Cardiology, University of California, Davis, CA 95616, USA
| | - Leighton T Izu
- a Department of Pharmacology, University of California, Davis, CA 95616, USA
| | - Tamás Bányász
- a Department of Pharmacology, University of California, Davis, CA 95616, USA.,d Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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3
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Sigg DM, Chang HK, Shieh RC. Linkage analysis reveals allosteric coupling in Kir2.1 channels. J Gen Physiol 2018; 150:1541-1553. [PMID: 30327330 PMCID: PMC6219689 DOI: 10.1085/jgp.201812127] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 09/28/2018] [Indexed: 12/04/2022] Open
Abstract
Inwardly rectifying potassium (Kir) channels experience strong (blocking) and weak (intrinsic) rectification. Linkage analysis in the form of a conductance Hill plot is a sensitive method of resolving allosteric interactions between the pore and mediators of the Kir gating process. Potassium-selective inward rectifier (Kir) channels are a class of membrane proteins necessary for maintaining stable resting membrane potentials, controlling excitability, and shaping the final repolarization of action potentials in excitable cells. In addition to the strong inward rectification of the ionic current caused by intracellular blockers, Kir2.1 channels possess “weak” inward rectification observed in inside-out patches after prolonged washout of intracellular blockers. The mechanisms underlying strong inward rectification have been attributed to voltage-dependent block by intracellular Mg2+ and polyamines; however, the mechanism responsible for weak rectification remains elusive. Hypotheses include weak voltage-dependent block and intrinsic voltage-dependent gating. Here, we performed a conductance Hill analysis of currents recorded with a double-ramp protocol to evaluate different mechanisms proposed for weak inward rectification of Kir2.1 channels. Linkage analysis in the form of a Hill plot revealed that the ramp currents could be best explained by allosteric coupling between a mildly voltage-dependent pore gate (gating charge ∼0.18 eo) and a voltage sensor (gating charge ∼1.7 eo). The proposed voltage sensor stabilized the closing of the pore gate (coupling factor ∼31). We anticipate that the use of linkage analysis will broaden understanding of functional coupling in ion channels and proteins in general.
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Affiliation(s)
| | - Hsueh-Kai Chang
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
| | - Ru-Chi Shieh
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
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Salomonsson M, Brasen JC, Sorensen CM. Role of renal vascular potassium channels in physiology and pathophysiology. Acta Physiol (Oxf) 2017; 221:14-31. [PMID: 28371470 DOI: 10.1111/apha.12882] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2016] [Revised: 05/10/2016] [Accepted: 03/22/2017] [Indexed: 12/31/2022]
Abstract
The control of renal vascular tone is important for the regulation of salt and water balance, blood pressure and the protection against damaging elevated glomerular pressure. The K+ conductance is a major factor in the regulation of the membrane potential (Vm ) in vascular smooth muscle (VSMC) and endothelial cells (EC). The vascular tone is controlled by Vm via its effect on the opening probability of voltage-operated Ca2+ channels (VOCC) in VSMC. When K+ conductance increases Vm becomes more negative and vasodilation follows, while deactivation of K+ channels leads to depolarization and vasoconstriction. K+ channels in EC indirectly participate in the control of vascular tone by endothelium-derived vasodilation. Therefore, by regulating the tone of renal resistance vessels, K+ channels have a potential role in the control of fluid homoeostasis and blood pressure as well as in the protection of the renal parenchyma. The main classes of K+ channels (calcium activated (KCa ), inward rectifier (Kir ), voltage activated (Kv ) and ATP sensitive (KATP )) have been found in the renal vessels. In this review, we summarize results available in the literature and our own studies in the field. We compare the ambiguous in vitro and in vivo results. We discuss the role of single types of K+ channels and the integrated function of several classes. We also deal with the possible role of renal vascular K+ channels in the pathophysiology of hypertension, diabetes mellitus and sepsis.
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Affiliation(s)
| | - J. C. Brasen
- Department of Electrical Engineering; Technical University of Denmark; Kgs. Lyngby Denmark
| | - C. M. Sorensen
- Department of Biomedical Sciences; Division of Renal and Vascular Physiology; University of Copenhagen; Copenhagen Denmark
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Cervera J, Meseguer S, Mafe S. MicroRNA Intercellular Transfer and Bioelectrical Regulation of Model Multicellular Ensembles by the Gap Junction Connectivity. J Phys Chem B 2017; 121:7602-7613. [DOI: 10.1021/acs.jpcb.7b04774] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Affiliation(s)
- Javier Cervera
- Dept.
de Termodinàmica, Facultat de Física, Universitat de València, E-46100 Burjassot, Spain
| | - Salvador Meseguer
- Laboratory
of RNA Modification and Mitochondrial Diseases, Centro de Investigación Príncipe Felipe, Valencia 46012, Spain
| | - Salvador Mafe
- Dept.
de Termodinàmica, Facultat de Física, Universitat de València, E-46100 Burjassot, Spain
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6
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Kostyunina DS, Shvetsova AA, Gaynullina DK, Tarasova OS. The role of inwardly rectifying potassium channels in the relaxation of rat hind-limb arteries. Biophysics (Nagoya-shi) 2016. [DOI: 10.1134/s0006350916050146] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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Cervera J, Alcaraz A, Mafe S. Bioelectrical Signals and Ion Channels in the Modeling of Multicellular Patterns and Cancer Biophysics. Sci Rep 2016; 6:20403. [PMID: 26841954 PMCID: PMC4740742 DOI: 10.1038/srep20403] [Citation(s) in RCA: 39] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 01/06/2016] [Indexed: 01/08/2023] Open
Abstract
Bioelectrical signals and ion channels are central to spatial patterns in cell ensembles, a problem of fundamental interest in positional information and cancer processes. We propose a model for electrically connected cells based on simple biological concepts: i) the membrane potential of a single cell characterizes its electrical state; ii) the long-range electrical coupling of the multicellular ensemble is realized by a network of gap junction channels between neighboring cells; and iii) the spatial distribution of an external biochemical agent can modify the conductances of the ion channels in a cell membrane and the multicellular electrical state. We focus on electrical effects in small multicellular ensembles, ignoring slow diffusional processes. The spatio-temporal patterns obtained for the local map of cell electric potentials illustrate the normalization of regions with abnormal cell electrical states. The effects of intercellular coupling and blocking of specific channels on the electrical patterns are described. These patterns can regulate the electrically-induced redistribution of charged nanoparticles over small regions of a model tissue. The inclusion of bioelectrical signals provides new insights for the modeling of cancer biophysics because collective multicellular states show electrical coupling mechanisms that are not readily deduced from biochemical descriptions at the individual cell level.
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Affiliation(s)
- Javier Cervera
- Dept. de Termodinàmica, Facultat de Física, Universitat de València, E-46100 Burjassot, Spain
| | - Antonio Alcaraz
- Dept. de Física, Laboratori de Biofísica Molecular, Universitat “Jaume I”, E-12080 Castelló, Spain
| | - Salvador Mafe
- Dept. de Termodinàmica, Facultat de Física, Universitat de València, E-46100 Burjassot, Spain
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Riz M, Braun M, Wu X, Pedersen MG. Inwardly rectifying Kir2.1 currents in human β-cells control electrical activity: Characterisation and mathematical modelling. Biochem Biophys Res Commun 2015; 459:284-287. [DOI: 10.1016/j.bbrc.2015.02.099] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2015] [Accepted: 02/18/2015] [Indexed: 11/26/2022]
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Cheng CJ, Sung CC, Huang CL, Lin SH. Inward-rectifying potassium channelopathies: new insights into disorders of sodium and potassium homeostasis. Pediatr Nephrol 2015; 30:373-83. [PMID: 24899236 DOI: 10.1007/s00467-014-2764-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/29/2013] [Revised: 12/11/2013] [Accepted: 01/10/2014] [Indexed: 11/30/2022]
Abstract
Inward-rectifying potassium (Kir) channels allow more inward than outward potassium flux when channels are open in mammalian cells. At physiological resting membrane potentials, however, they predominantly mediate outward potassium flux and play important roles in regulating the resting membrane potential in diverse cell types and potassium secretion in the kidneys. Mutations of Kir channels cause human hereditary diseases collectively called Kir channelopathies, many of which are characterized by disorders of sodium and potassium homeostasis. Studies on these genetic Kir channelopathies have shed light on novel pathophysiological mechanisms, including renal sodium and potassium handling, potassium shifting in skeletal muscles, and aldosterone production in the adrenal glands. Here, we review several recent advances in Kir channels and their clinical implications in sodium and potassium homeostasis.
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Affiliation(s)
- Chih-Jen Cheng
- Department of Medicine, Division of Nephrology, Tri-Service General Hospital, National Defense Medical Center, No. 325, Section 2, Cheng-Kung Road, Neihu 114, Taipei, Taiwan
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Li J, Xie X, Liu J, Yu H, Zhang S, Zhan Y, Zhang H, Logothetis DE, An H. Lack of negatively charged residues at the external mouth of Kir2.2 channels enable the voltage-dependent block by external Mg2+. PLoS One 2014; 9:e111372. [PMID: 25350118 PMCID: PMC4211740 DOI: 10.1371/journal.pone.0111372] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2014] [Accepted: 10/01/2014] [Indexed: 11/18/2022] Open
Abstract
Kir channels display voltage-dependent block by cytosolic cations such as Mg2+ and polyamines that causes inward rectification. In fact, cations can regulate K channel activity from both the extracellular and intracellular sides. Previous studies have provided insight into the up-regulation of Kir channel activity by extracellular K+ concentration. In contrast, extracellular Mg2+ has been found to reduce the amplitude of the single-channel current at milimolar concentrations. However, little is known about the molecular mechanism of Kir channel blockade by external Mg2+ and the relationship between the Mg2+ blockade and activity potentiation by permeant K+ ions. In this study, we applied an interactive approach between theory and experiment. Electrophysiological recordings on Kir2.2 and its mutants were performed by heterologous expression in Xenopus laevis oocytes. Our results confirmed that extracellular Mg2+ could reduce heterologously expressed WT Kir2.2 currents in a voltage dependent manner. The kinetics of inhibition and recovery of Mg2+ exhibit a 3∼4s time constant. Molecular dynamics simulation results revealed a Mg2+ binding site located at the extracellular mouth of Kir2.2 that showed voltage-dependent Mg2+ binding. The mutants, G119D, Q126E and H128D, increased the number of permeant K+ ions and reduced the voltage-dependent blockade of Kir2.2 by extracellular Mg2+.
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Affiliation(s)
- Junwei Li
- Institute of Biophysics, Hebei University of Technology, Tianjin, China
| | - Xiaoxiao Xie
- Institute of Biophysics, Hebei University of Technology, Tianjin, China
| | - Jun Liu
- Institute of Biophysics, Hebei University of Technology, Tianjin, China
| | - Hui Yu
- Institute of Biophysics, Hebei University of Technology, Tianjin, China
| | - Suhua Zhang
- Institute of Biophysics, Hebei University of Technology, Tianjin, China
| | - Yong Zhan
- Institute of Biophysics, Hebei University of Technology, Tianjin, China
- * E-mail: (HA); (YZ)
| | - Hailin Zhang
- Key Laboratory of Neural and Vascular Biology, Ministry of Education, Key Laboratory of Pharmacology and Toxicology for New Drug, Hebei Province, Department of Pharmacology, Hebei Medical University, Shijiazhuang, Hebei Province, China
| | - Diomedes E. Logothetis
- Department of Physiology and Biophysics, School of Medicine, Virginia Commonwealth University, Richmond, VA, United States of America
| | - Hailong An
- Institute of Biophysics, Hebei University of Technology, Tianjin, China
- * E-mail: (HA); (YZ)
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Cheng CJ, Kuo E, Huang CL. Extracellular potassium homeostasis: insights from hypokalemic periodic paralysis. Semin Nephrol 2014; 33:237-47. [PMID: 23953801 DOI: 10.1016/j.semnephrol.2013.04.004] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Extracellular potassium makes up only about 2% of the total body's potassium store. The majority of the body potassium is distributed in the intracellular space, of which about 80% is in skeletal muscle. Movement of potassium in and out of skeletal muscle thus plays a pivotal role in extracellular potassium homeostasis. The exchange of potassium between the extracellular space and skeletal muscle is mediated by specific membrane transporters. These include potassium uptake by Na(+), K(+)-adenosine triphosphatase and release by inward-rectifier K(+) channels. These processes are regulated by circulating hormones, peptides, ions, and by physical activity of muscle as well as dietary potassium intake. Pharmaceutical agents, poisons, and disease conditions also affect the exchange and alter extracellular potassium concentration. Here, we review extracellular potassium homeostasis, focusing on factors and conditions that influence the balance of potassium movement in skeletal muscle. Recent findings that mutations of a skeletal muscle-specific inward-rectifier K(+) channel cause hypokalemic periodic paralysis provide interesting insights into the role of skeletal muscle in extracellular potassium homeostasis. These recent findings are reviewed.
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Affiliation(s)
- Chih-Jen Cheng
- Department of Medicine, Division of Nephrology, University of Texas Southwestern Medical Center, Dallas, TX 75390-8859, USA
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12
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Wang CL, Tsai ML, Wu SN. Evidence for mitoxantrone-induced block of inwardly rectifying K(+) channels expressed in the osteoclast precursor RAW 264.7 cells differentiated with lipopolysaccharide. Cell Physiol Biochem 2012; 30:687-701. [PMID: 22854649 DOI: 10.1159/000341449] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/19/2012] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND/AIMS Mitoxanthrone (MX) is an anthracenedione antineoplastic agent. Whether this drug and other related compounds have any effects on ion currents in osteoclasts remains largely unclear. METHODS In this study, the effects of MX and other related compounds on inwardly rectifying K(+) current (I(K(IR))) were investigated in RAW 264.7 osteoclast precursor cells treated with lipopolysaccharide. RESULTS The I(K(IR))in these cells are blocked by BaCl(2) (1 mM). MX (1-100 µM) decreased the amplitude of I(K(IR)) in a concentration-dependent manner with an IC(50) value of 6.4 µM. MX also slowed the time course of I(K(IR)) inactivation elicited by large hyperpolarization. Doxorubicin (10 µM), 17β-estradiol (10 µM) and tertiapin (1 µM) decreased the I(K(IR)) amplitude in these cells. In bafilomycin A(1)-treated cells, MX-mediated block of I(K(IR)) still existed. In cell-attached configuration, when the electrode was filled with MX (10 µM), the activity of inwardly rectifying K(+) (Kir) channels was decreased with no change in single-channel conductance. MX-mediated reduction of channel activity is accompanied by a shortening of mean open time. Under current-clamp conditions, addition of MX resulted in membrane depolarization. Therefore, MX can interact with the Kir channels to decrease the I(K(IR)) amplitude and to depolarize the membrane in these cells. CONCLUSION The block by this drug of Kir2.1 channels appears to be one of the important mechanisms underlying its actions on the resorptive activity of osteoclasts, if similar results occur in vivo. Targeting at Kir channels may be clinically useful as an adjunctive regimen to anti-cancer drugs (e.g., MX or doxorubicin) in influencing the resorptive activity of osteoclasts.
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Affiliation(s)
- Chung-Lin Wang
- Department of Nursing, Chung Jen College of Nursing, Health Sciences and Management, Chiayi city, Taiwan
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Sackin H, Nanazashvili M, Li H, Palmer LG, Yang L. Residues at the outer mouth of Kir1.1 determine K-dependent gating. Biophys J 2012; 102:2742-50. [PMID: 22735524 DOI: 10.1016/j.bpj.2012.05.018] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2012] [Revised: 05/09/2012] [Accepted: 05/10/2012] [Indexed: 10/28/2022] Open
Abstract
Three residues (E132, F127, and R128) at the outer mouth of Kir1.1b directly affected inward rectifier gating by external K, independent of pH gating. Each of the individual mutations E132Q, F127V, F127D, and R128Y changed the normal K dependence of macroscopic conductance from hyperbolic (Km = 6 ± 2 mM) to linear, up to 500 mM, without changing the hyperbolic K dependence of single-channel conductance. This suggests that E132, F127, and R128 are responsible for maximal Kir1.1b activation by external K. In addition, these same residues were also essential for recovery of Kir1.1b activity after complete removal of external K by 18-Crown-6 polyether. In contrast, charge-altering mutations at neighboring residues (E92A, E104A, D97V, or Q133E) near the outer mouth of the channel did not affect Kir1.1b recovery after chelation of external K. The collective role of E132, R128, and F127 in preventing Kir1.1b inactivation by either cytoplasmic acidification or external K removal implies that pH inactivation and the external K sensor share a common mechanism, whereby E132, R128, and F127 stabilize the Kir1.1b selectivity filter gate in an open conformation, allowing rapid recovery of channel activity after a period of external K depletion.
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Affiliation(s)
- Henry Sackin
- Department of Physiology, The Chicago Medical School, Rosalind Franklin University, North Chicago, Illinois, USA.
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Cheng CJ, Lin SH, Lo YF, Yang SS, Hsu YJ, Cannon SC, Huang CL. Identification and functional characterization of Kir2.6 mutations associated with non-familial hypokalemic periodic paralysis. J Biol Chem 2011; 286:27425-35. [PMID: 21665951 DOI: 10.1074/jbc.m111.249656] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Hypokalemic periodic paralysis (hypoKPP) is characterized by episodic flaccid paralysis of muscle and acute hypokalemia during attacks. Familial forms of hypoKPP are predominantly caused by mutations of either voltage-gated Ca(2+) or Na(+) channels. The pathogenic gene mutation in non-familial hypoKPP, consisting mainly of thyrotoxic periodic paralysis (TPP) and sporadic periodic paralysis (SPP), is largely unknown. Recently, mutations in KCNJ18, which encodes a skeletal muscle-specific inwardly rectifying K(+) channel Kir2.6, were reported in some TPP patients. Whether mutations of Kir2.6 occur in other patients with non-familial hypoKPP and how mutations of the channel predispose patients to paralysis are unknown. Here, we report one conserved heterozygous mutation in KCNJ18 in two TPP patients and two separate heterozygous mutations in two SPP patients. These mutations result in V168M, R43C, and A200P amino acid substitution of Kir2.6, respectively. Compared with the wild type channel, whole-cell currents of R43C and V168M mutants were reduced by ∼78 and 43%, respectively. No current was detected for the A200P mutant. Single channel conductance and open probability were reduced for R43C and V168M, respectively. Biotinylation assays showed reduced cell surface abundance for R43C and A200P. All three mutants exerted dominant negative inhibition on wild type Kir2.6 as well as wild type Kir2.1, another Kir channel expressed in the skeletal muscle. Thus, mutations of Kir2.6 are associated with SPP as well as TPP. We suggest that decreased outward K(+) current from hypofunction of Kir2.6 predisposes the sarcolemma to hypokalemia-induced paradoxical depolarization during attacks, which in turn leads to Na(+) channel inactivation and inexcitability of muscles.
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Affiliation(s)
- Chih-Jen Cheng
- Department of Medicine, Division of Nephrology, University of Texas, Southwestern Medical Center, Dallas, Texas 75390-8856, USA
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