1
|
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.
Collapse
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.
| |
Collapse
|
2
|
Maksaev G, Bründl-Jirout M, Stary-Weinzinger A, Zangerl-Plessl EM, Lee SJ, Nichols CG. Subunit gating resulting from individual protonation events in Kir2 channels. Nat Commun 2023; 14:4538. [PMID: 37507406 PMCID: PMC10382558 DOI: 10.1038/s41467-023-40058-7] [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] [Received: 04/07/2023] [Accepted: 07/10/2023] [Indexed: 07/30/2023] Open
Abstract
Inwardly rectifying potassium (Kir) channels open at the 'helix bundle crossing' (HBC), formed by the M2 helices at the cytoplasmic end of the transmembrane pore. Introduced negative charges at the HBC (G178D) in Kir2.2 channels forces opening, allowing pore wetting and free movement of permeant ions between the cytoplasm and the inner cavity. Single-channel recordings reveal striking, pH-dependent, subconductance behaviors in G178D (or G178E and equivalent Kir2.1[G177E]) mutant channels, with well-resolved non-cooperative subconductance levels. Decreasing cytoplasmic pH shifts the probability towards lower conductance levels. Molecular dynamics simulations show how protonation of Kir2.2[G178D], or the D173 pore-lining residues, changes solvation, K+ ion occupancy, and K+ conductance. Ion channel gating and conductance are classically understood as separate processes. The present data reveal how individual protonation events change the electrostatic microenvironment of the pore, resulting in step-wise alterations of ion pooling, and hence conductance, that appear as 'gated' substates.
Collapse
Affiliation(s)
- Grigory Maksaev
- Department of Cell Biology and Physiology, and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Michael Bründl-Jirout
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Anna Stary-Weinzinger
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Eva-Maria Zangerl-Plessl
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria.
| | - Sun-Joo Lee
- Department of Cell Biology and Physiology, and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Colin G Nichols
- Department of Cell Biology and Physiology, and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA.
| |
Collapse
|
3
|
Maksaev G, Bründl-Jirout M, Stary-Weinzinger A, Zangerl-Plessl EM, Lee SJ, Nichols CG. Subunit gating resulting from individual protonation events in Kir2 channels. RESEARCH SQUARE 2023:rs.3.rs-2640647. [PMID: 36993294 PMCID: PMC10055540 DOI: 10.21203/rs.3.rs-2640647/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Inwardly rectifying potassium (Kir) channels play a critical role in stabilizing the membrane potential, thus controlling numerous physiological phenomena in multiple tissues. Channel conductance is activated by cytoplasmic modulators that open the channel at the 'helix bundle crossing' (HBC), formed by the coming together of the M2 helices from each of the four subunits, at the cytoplasmic end of the transmembrane pore. We introduced a negative charge at the bundle crossing region (G178D) in classical inward rectifier Kir2.2 channel subunits that forces channel opening, allowing pore wetting and free movement of permeant ions between the cytoplasm and the inner cavity. Single-channel recordings reveal a striking pH-dependent subconductance behavior in G178D (or G178E and equivalent Kir2.1[G177E]) mutant channels that reflects individual subunit events. These subconductance levels are well resolved temporally and occur independently, with no evidence of cooperativity. Decreasing cytoplasmic pH shifts the probability towards lower conductance levels, and molecular dynamics simulations show how protonation of Kir2.2[G178D] and, additionally, the rectification controller (D173) pore-lining residues leads to changes in pore solvation, K+ ion occupancy, and ultimately K+ conductance. While subconductance gating has long been discussed, resolution and explanation have been lacking. The present data reveals how individual protonation events change the electrostatic microenvironment of the pore, resulting in distinct, uncoordinated, and relatively long-lasting conductance states, which depend on levels of ion pooling in the pore and the maintenance of pore wetting. Gating and conductance are classically understood as separate processes in ion channels. The remarkable sub-state gating behavior of these channels reveals how intimately connected 'gating' and 'conductance' are in reality.
Collapse
Affiliation(s)
- Grigory Maksaev
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Michael Bründl-Jirout
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Anna Stary-Weinzinger
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Eva-Maria Zangerl-Plessl
- Department of Pharmaceutical Sciences, Division of Pharmacology and Toxicology, University of Vienna, Vienna, Austria
| | - Sun-Joo Lee
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| | - Colin G. Nichols
- Department of Cell Biology and Physiology and the Center for Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, USA
| |
Collapse
|
4
|
Iijima A, Švecová O, Hošek J, Kula R, Bébarová M. Sildenafil affects the human Kir2.1 and Kir2.2 channels at clinically relevant concentrations: Inhibition potentiated by low Ba 2. Front Pharmacol 2023; 14:1136272. [PMID: 36817146 PMCID: PMC9932908 DOI: 10.3389/fphar.2023.1136272] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2023] [Accepted: 01/23/2023] [Indexed: 02/05/2023] Open
Abstract
Sildenafil (Viagra), the first approved and widely used oral drug for the treatment of erectile dysfunction, was occasionally associated with life-threatening ventricular arrhythmias in patients. Since inward rectifier potassium current (I K1) may considerably contribute to this arrhythmogenesis, we investigated the effect of sildenafil on the human Kir2.1 and Kir2.2, the prevailing subunits forming the ventricular I K1 channels. Experiments were performed by the whole-cell patch clamp technique at 37°C using Chinese hamster ovary cells transiently expressing the human Kir2.1 and Kir2.2 channels. Changes of both the inward and outward current components (at -110 and -50 mV, respectively) were tested to be able to consider the physiological relevance of the sildenafil effect (changes at -110 and -50 mV did not significantly differ, results at -50 mV are listed below). A significant Kir2.1 inhibition was observed at all applied sildenafil concentrations (16.1% ± 3.7%, 20.0% ± 2.6%, and 15.0% ± 3.0% at 0.1, 1, and 10 μM, respectively). The inhibitory effect of 0.1 μM sildenafil was potentiated by the presence of a low concentration of Ba2+ (0.1 μM) which induced only a slight Kir2.1 inhibition by 5.95% ± 0.75% alone (the combined effect was 35.5% ± 3.4%). The subtherapeutic and therapeutic sildenafil concentrations (0.1 and 1 μM) caused a dual effect on Kir2.2 channels whereas a significant Kir2.2 activation was observed at the supratherapeutic sildenafil concentration (10 μM: 34.1% ± 5.6%). All effects were fully reversible. This is the first study demonstrating that sildenafil at clinically relevant concentrations inhibits both the inward and outward current components of the main human ventricular I K1 subunit Kir2.1. This inhibitory effect was significantly potentiated by a low concentration of environmental contaminant Ba2+ in agreement with recently reported data on rat ventricular I K1 which additionally showed a significant repolarization delay. Considering the similar subunit composition of the human and rat ventricular I K1 channels, the observed effects might contribute to sildenafil-associated arrhythmogenesis in clinical practice.
Collapse
Affiliation(s)
- Akimasa Iijima
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Olga Švecová
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Jan Hošek
- Department of Molecular Pharmacy, Faculty of Pharmacy, Masaryk University, Brno, Czech Republic
| | - Roman Kula
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic
| | - Markéta Bébarová
- Department of Physiology, Faculty of Medicine, Masaryk University, Brno, Czech Republic,*Correspondence: Markéta Bébarová,
| |
Collapse
|
5
|
Jogini V, Jensen MØ, Shaw DE. Gating and modulation of an inward-rectifier potassium channel. J Gen Physiol 2022; 155:213765. [PMID: 36524993 PMCID: PMC9764021 DOI: 10.1085/jgp.202213085] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Accepted: 11/28/2022] [Indexed: 12/23/2022] Open
Abstract
Inward-rectifier potassium channels (Kirs) are lipid-gated ion channels that differ from other K+ channels in that they allow K+ ions to flow more easily into, rather than out of, the cell. Inward rectification is known to result from endogenous magnesium ions or polyamines (e.g., spermine) binding to Kirs, resulting in a block of outward potassium currents, but questions remain regarding the structural and dynamic basis of the rectification process and lipid-dependent channel activation. Here, we present the results of long-timescale molecular dynamics simulations starting from a crystal structure of phosphatidylinositol 4,5-bisphosphate (PIP2)-bound chicken Kir2.2 with a non-conducting pore. After introducing a mutation (G178R) that is known to increase the open probability of a homologous channel, we were able to observe transitions to a stably open, ion-conducting pore, during which key conformational changes occurred in the main activation gate and the cytoplasmic domain. PIP2 binding appeared to increase stability of the pore in its open and conducting state, as PIP2 removal resulted in pore closure, with a median closure time about half of that with PIP2 present. To investigate structural details of inward rectification, we simulated spermine binding to and unbinding from the open pore conformation at positive and negative voltages, respectively, and identified a spermine-binding site located near a previously hypothesized site between the pore cavity and the selectivity filter. We also studied the effects of long-range electrostatics on conduction and spermine binding by mutating charged residues in the cytoplasmic domain and found that a finely tuned charge density, arising from basic and acidic residues within the cytoplasmic domain, modulated conduction and rectification.
Collapse
Affiliation(s)
| | | | - David E. Shaw
- D. E. Shaw Research, New York, NY, USA,Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA
| |
Collapse
|
6
|
Coyote-Maestas W, Nedrud D, He Y, Schmidt D. Determinants of trafficking, conduction, and disease within a K + channel revealed through multiparametric deep mutational scanning. eLife 2022; 11:e76903. [PMID: 35639599 PMCID: PMC9273215 DOI: 10.7554/elife.76903] [Citation(s) in RCA: 18] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2022] [Accepted: 05/27/2022] [Indexed: 01/04/2023] Open
Abstract
A long-standing goal in protein science and clinical genetics is to develop quantitative models of sequence, structure, and function relationships to understand how mutations cause disease. Deep mutational scanning (DMS) is a promising strategy to map how amino acids contribute to protein structure and function and to advance clinical variant interpretation. Here, we introduce 7429 single-residue missense mutations into the inward rectifier K+ channel Kir2.1 and determine how this affects folding, assembly, and trafficking, as well as regulation by allosteric ligands and ion conduction. Our data provide high-resolution information on a cotranslationally folded biogenic unit, trafficking and quality control signals, and segregated roles of different structural elements in fold stability and function. We show that Kir2.1 surface trafficking mutants are underrepresented in variant effect databases, which has implications for clinical practice. By comparing fitness scores with expert-reviewed variant effects, we can predict the pathogenicity of 'variants of unknown significance' and disease mechanisms of known pathogenic mutations. Our study in Kir2.1 provides a blueprint for how multiparametric DMS can help us understand the mechanistic basis of genetic disorders and the structure-function relationships of proteins.
Collapse
Affiliation(s)
- Willow Coyote-Maestas
- Department of Biochemistry, Molecular Biology and Biophysics, University of MinnesotaMinneapolisUnited States
| | - David Nedrud
- Department of Biochemistry, Molecular Biology and Biophysics, University of MinnesotaMinneapolisUnited States
| | - Yungui He
- Department of Genetics, Cell Biology and Development, University of MinnesotaMinneapolisUnited States
| | - Daniel Schmidt
- Department of Genetics, Cell Biology and Development, University of MinnesotaMinneapolisUnited States
| |
Collapse
|
7
|
Cheng P, Qiu Z, Du Y. Potassium channels and autism spectrum disorder: An overview. Int J Dev Neurosci 2021; 81:479-491. [PMID: 34008235 DOI: 10.1002/jdn.10123] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2021] [Revised: 05/08/2021] [Accepted: 05/11/2021] [Indexed: 11/07/2022] Open
Abstract
Autism spectrum disorder (ASD) comprises a group of neurodevelopmental disorders characterized by impaired social interaction and communication, and restricted, repetitive patterns of behaviors, interests, or activities. It had been demonstrated that potassium channels played a key role in regulating neuronal excitability, which was closely associated with neurological diseases including epilepsy, ataxia, myoclonus, and psychiatric disorders. In recent years, a growing body of evidence from whole-genome sequencing and whole-exome sequencing had identified several ASD susceptibility genes of potassium channels in ASD subjects. Genetically dysfunction of potassium channels may be involved in altered neuronal excitability and abnormal brain function in the pathogenesis of ASD. This review summarizes current findings on the features of ASD-risk genes (KCND2, KCNQ2, KCNQ3, KCNH5, KCNJ2, KCNJ10, and KCNMA1) and further expatiate their potential role in the pathogenicity of ASD.
Collapse
Affiliation(s)
- Peipei Cheng
- Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Zilong Qiu
- Institute of Neuroscience, State Key Laboratory of Neuroscience, Key Laboratory of Primate Neurobiology, Center for Excellence in Brain Science and Intelligence Technology, Chinese Academy of Sciences, Shanghai, China.,Shanghai Center for Brain Science and Brain-Inspired Intelligence Technology, Shanghai, China
| | - Yasong Du
- Shanghai Mental Health Center, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| |
Collapse
|
8
|
Kir2.2 p.Thr140Met: a genetic susceptibility to sporadic periodic paralysis. ACTA MYOLOGICA : MYOPATHIES AND CARDIOMYOPATHIES : OFFICIAL JOURNAL OF THE MEDITERRANEAN SOCIETY OF MYOLOGY 2018; 37:193-203. [PMID: 30838349 PMCID: PMC6390110] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
INTRODUCTION Periodic paralyses (PP) are recurrent episodes of flaccid limb muscle weakness. Next to autosomal dominant forms, sporadic PP (SPP) cases are known but their genetics are unclear. METHODS In a patient with hypokalemic SPP, we performed exome sequencing to identify a candidate gene. We sequenced this gene in 263 unrelated PP patients without any known causative mutations. Then we performed functional analysis of all variants found and molecular modelling for interpretation. RESULTS Exome sequencing in the proband yielded three heterozygous variants predicted to be linked to disease. These encoded p.Thr140Met in the Kir2.2 potassium channel, p.Asp229Asn in protein kinase C theta, and p.Thr15943Ile in titin. Since all hitherto known causative PP genes code for ion channels, we studied the Kir2.2-encoding gene, KCNJ12, for involvement in PP pathogenesis. KCNJ12 screening in 263 PP patients revealed three further variants, each in a single individual and coding for p.Gly419Ser, p.Cys75Tyr, and p.Ile283Val. All four Kir2.2 variants were functionally expressed. Only p.Thr140Met displayed relevant functional alterations, i.e. homo-tetrameric channels produced almost no current, and hetero-tetrameric channels suppressed co-expressed wildtype Kir2.1 in a dominant-negative manner. Molecular modelling showed Kir2.2 p.Thr140Met to reduce movement of potassium ions towards binding sites in the hetero-tetramer pore compatible with a reduced maximal current. MD simulations revealed loss of hydrogen bonding with the p.Thr140Met substitution. DISCUSSION The electrophysiological findings of p.Thr140Met are similar to those found in thyrotoxic PP caused by Kir2.6 mutations. Also, the homologous Thr140 residue is mutated in Kir2.6. This supports the idea that Kir2.2 p.Thr140Met conveys susceptibility to SPP and should be included in genetic screening.
Collapse
|
9
|
Goversen B, van der Heyden MAG, van Veen TAB, de Boer TP. The immature electrophysiological phenotype of iPSC-CMs still hampers in vitro drug screening: Special focus on I K1. Pharmacol Ther 2017; 183:127-136. [PMID: 28986101 DOI: 10.1016/j.pharmthera.2017.10.001] [Citation(s) in RCA: 103] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/09/2023]
Abstract
Preclinical drug screens are not based on human physiology, possibly complicating predictions on cardiotoxicity. Drug screening can be humanised with in vitro assays using human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). However, in contrast to adult ventricular cardiomyocytes, iPSC-CMs beat spontaneously due to presence of the pacemaking current If and reduced densities of the hyperpolarising current IK1. In adult cardiomyocytes, IK1 finalises repolarisation by stabilising the resting membrane potential while also maintaining excitability. The reduced IK1 density contributes to proarrhythmic traits in iPSC-CMs, which leads to an electrophysiological phenotype that might bias drug responses. The proarrhythmic traits can be suppressed by increasing IK1 in a balanced manner. We systematically evaluated all studies that report strategies to mature iPSC-CMs and found that only few studies report IK1 current densities. Furthermore, these studies did not succeed in establishing sufficient IK1 levels as they either added too little or too much IK1. We conclude that reduced densities of IK1 remain a major flaw in iPSC-CMs, which hampers their use for in vitro drug screening.
Collapse
Affiliation(s)
- Birgit Goversen
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Yalelaan 50, 3584 CM, Utrecht, The Netherlands
| | - Marcel A G van der Heyden
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Yalelaan 50, 3584 CM, Utrecht, The Netherlands
| | - Toon A B van Veen
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Yalelaan 50, 3584 CM, Utrecht, The Netherlands
| | - Teun P de Boer
- Department of Medical Physiology, Division of Heart & Lungs, University Medical Center Utrecht, Yalelaan 50, 3584 CM, Utrecht, The Netherlands.
| |
Collapse
|
10
|
Cordeiro JM, Zeina T, Goodrow R, Kaplan AD, Thomas LM, Nesterenko VV, Treat JA, Hawel L, Byus C, Bett GC, Rasmusson RL, Panama BK. Regional variation of the inwardly rectifying potassium current in the canine heart and the contributions to differences in action potential repolarization. J Mol Cell Cardiol 2015; 84:52-60. [PMID: 25889894 DOI: 10.1016/j.yjmcc.2015.04.010] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Revised: 03/09/2015] [Accepted: 04/08/2015] [Indexed: 10/23/2022]
Abstract
The inward rectifier potassium current, IK1, contributes to the terminal phase of repolarization of the action potential (AP), as well as the value and stability of the resting membrane potential. Regional variation in IK1 has been noted in the canine heart, but the biophysical properties have not been directly compared. We examined the properties and functional contribution of IK1 in isolated myocytes from ventricular, atrial and Purkinje tissue. APs were recorded from canine left ventricular midmyocardium, left atrial and Purkinje tissue. The terminal rate of repolarization of the AP in ventricle, but not in Purkinje, depended on changes in external K(+) ([K(+)]o). Isolated ventricular myocytes had the greatest density of IK1 while atrial myocytes had the lowest. Furthermore, the outward component of IK1 in ventricular cells exhibited a prominent outward component and steep negative slope conductance, which was also enhanced in 10 mM [K(+)]o. In contrast, both Purkinje and atrial cells exhibited little outward IK1, even in the presence of 10 mM [K(+)]o, and both cell types showed more persistent current at positive potentials. Expression of Kir2.1 in the ventricle was 76.9-fold higher than that of atria and 5.8-fold higher than that of Purkinje, whereas the expression of Kir2.2 and Kir2.3 subunits was more evenly distributed in Purkinje and atria. Finally, AP clamp data showed distinct contributions of IK1 for each cell type. IK1 and Kir2 subunit expression varies dramatically in regions of the canine heart and these regional differences in Kir2 expression likely underlie regional distinctions in IK1 characteristics, contributing to variations in repolarization in response to in [K(+)]o changes.
Collapse
Affiliation(s)
- Jonathan M Cordeiro
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Tanya Zeina
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Robert Goodrow
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Aaron D Kaplan
- Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States
| | - Lini M Thomas
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Vladislav V Nesterenko
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Jacqueline A Treat
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States
| | - Leo Hawel
- Division of Biomedical Sciences, School of Medicine, University of California, Riverside, Riverside, CA, United States
| | - Craig Byus
- Division of Biomedical Sciences, School of Medicine, University of California, Riverside, Riverside, CA, United States
| | - Glenna C Bett
- Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States; Department of Obstetrics and Gynecology, State University of New York, University of Buffalo, Buffalo, NY, United States
| | - Randall L Rasmusson
- Department of Physiology and Biophysics, State University of New York, University of Buffalo, Buffalo, NY, United States
| | - Brian K Panama
- Department of Experimental Cardiology, Masonic Medical Research Laboratory, Utica, NY, United States.
| |
Collapse
|
11
|
Masia R, Krause DS, Yellen G. The inward rectifier potassium channel Kir2.1 is expressed in mouse neutrophils from bone marrow and liver. Am J Physiol Cell Physiol 2014; 308:C264-76. [PMID: 25472961 DOI: 10.1152/ajpcell.00176.2014] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Neutrophils are phagocytic cells that play a critical role in innate immunity by destroying bacterial pathogens. Channels belonging to the inward rectifier potassium channel subfamily 2 (Kir2 channels) have been described in other phagocytes (monocytes/macrophages and eosinophils) and in hematopoietic precursors of phagocytes. Their physiological function in these cells remains unclear, but some evidence suggests a role in growth factor-dependent proliferation and development. Expression of functional Kir2 channels has not been definitively demonstrated in mammalian neutrophils. Here, we show by RT-PCR that neutrophils from mouse bone marrow and liver express mRNA for the Kir2 subunit Kir2.1 but not for other subunits (Kir2.2, Kir2.3, and Kir2.4). In electrophysiological experiments, resting (unstimulated) neutrophils from mouse bone marrow and liver exhibit a constitutively active, external K(+)-dependent, strong inwardly rectifying current that constitutes the dominant current. The reversal potential is dependent on the external K(+) concentration in a Nernstian fashion, as expected for a K(+)-selective current. The current is not altered by changes in external or internal pH, and it is blocked by Ba(2+), Cs(+), and the Kir2-selective inhibitor ML133. The single-channel conductance is in agreement with previously reported values for Kir2.1 channels. These properties are characteristic of homomeric Kir2.1 channels. Current density in short-term cultures of bone marrow neutrophils is decreased in the absence of growth factors that are important for neutrophil proliferation [granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF)]. These results demonstrate that mouse neutrophils express functional Kir2.1 channels and suggest that these channels may be important for neutrophil function, possibly in a growth factor-dependent manner.
Collapse
Affiliation(s)
- Ricard Masia
- Department of Pathology and Laboratory Medicine, Massachusetts General Hospital, Boston, Massachusetts; and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts
| | - Daniela S Krause
- Department of Pathology and Laboratory Medicine, Massachusetts General Hospital, Boston, Massachusetts; and
| | - Gary Yellen
- Department of Neurobiology, Harvard Medical School, Boston, Massachusetts
| |
Collapse
|
12
|
Insights in KIR2.1 channel structure and function by an evolutionary approach; cloning and functional characterization of the first reptilian inward rectifier channel KIR2.1, derived from the California kingsnake (Lampropeltis getula californiae). Biochem Biophys Res Commun 2014; 452:992-7. [DOI: 10.1016/j.bbrc.2014.09.031] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 09/08/2014] [Indexed: 11/21/2022]
|
13
|
Mustroph J, Maier LS, Wagner S. CaMKII regulation of cardiac K channels. Front Pharmacol 2014; 5:20. [PMID: 24600393 PMCID: PMC3930912 DOI: 10.3389/fphar.2014.00020] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 01/31/2014] [Indexed: 11/23/2022] Open
Abstract
Cardiac K channels are critical determinants of cardiac excitability. In hypertrophied and failing myocardium, alterations in the expression and activity of voltage-gated K channels are frequently observed and contribute to the increased propensity for life-threatening arrhythmias. Thus, understanding the mechanisms of disturbed K channel regulation in heart failure (HF) is of critical importance. Amongst others, Ca/calmodulin-dependent protein kinase II (CaMKII) has been identified as an important regulator of K channel activity. In human HF but also various animal models, increased CaMKII expression and activity has been linked to deteriorated contractile function and arrhythmias. This review will discuss the current knowledge about CaMKII regulation of several K channels, its influence on action potential properties, dispersion of repolarization, and arrhythmias with special focus on HF.
Collapse
Affiliation(s)
- Julian Mustroph
- Department of Cardiology, University Medical Center Göttingen Göttingen, Germany
| | - Lars S Maier
- Department of Cardiology, University Medical Center Göttingen Göttingen, Germany
| | - Stefan Wagner
- Department of Cardiology, University Medical Center Göttingen Göttingen, Germany
| |
Collapse
|
14
|
Kamikawa A, Ishikawa T. Functional expression of a Kir2.1-like inwardly rectifying potassium channel in mouse mammary secretory cells. Am J Physiol Cell Physiol 2013; 306:C230-40. [PMID: 24259419 DOI: 10.1152/ajpcell.00219.2013] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
K(+) channels in mammary secretory (MS) cells are believed to play a role in transcellular electrolyte transport and thus determining ionic composition of the aqueous phase of milk. However, direct evidence for specific K(+) channel activity in native MS cells is lacking at the single-cell level. Here, we show for the first time that an inwardly rectifying K(+) (Kir) channel is functionally expressed in fully differentiated MS cells that were freshly isolated from the mammary gland of lactating mice. Using the standard whole cell patch-clamp technique, we found that mouse MS cells consistently displayed a K(+) current, whose electrophysiological properties are similar to those previously reported for Kir2.x channels, particularly Kir2.1: 1) current-voltage relationship with strong inward rectification, 2) slope conductance approximately proportional to the square root of external K(+) concentration, 3) voltage- and time-dependent and high-affinity block by external Ba(2+), and 4) voltage-dependent inhibition by external Cs(+). Accordingly, RT-PCR analysis revealed the gene expression of Kir2.1, but not Kir2.2, Kir2.3, and Kir2.4, in lactating mouse mammary gland, and immunohistochemical staining showed Kir2.1 protein expression in the secretory cells. Cell-attached patch recordings from MS cells revealed that a 31-pS K(+) channel with strong inward rectification was likely active at the resting membrane potential. Collectively, the present work demonstrates that a functional Kir2.1-like channel is expressed in lactating mouse MS cells. We propose that the channel might be involved, at least in part, in secretion and/or preservation of ionic components of milk stored into the lumen of these cells.
Collapse
Affiliation(s)
- Akihiro Kamikawa
- Department of Basic Veterinary Medicine, Obihiro University of Agriculture and Veterinary Medicine, Obihiro, Japan
| | | |
Collapse
|
15
|
Levin ME, Holt JR. The function and molecular identity of inward rectifier channels in vestibular hair cells of the mouse inner ear. J Neurophysiol 2012; 108:175-86. [PMID: 22496522 DOI: 10.1152/jn.00098.2012] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Inner ear hair cells respond to mechanical stimuli with graded receptor potentials. These graded responses are modulated by a host of voltage-dependent currents that flow across the basolateral membrane. Here, we examine the molecular identity and the function of a class of voltage-dependent ion channels that carries the potassium-selective inward rectifier current known as I(K1). I(K1) has been identified in vestibular hair cells of various species, but its molecular composition and functional contributions remain obscure. We used quantitative RT-PCR to show that the inward rectifier gene, Kir2.1, is highly expressed in mouse utricle between embryonic day 15 and adulthood. We confirmed Kir2.1 protein expression in hair cells by immunolocalization. To examine the molecular composition of I(K1), we recorded voltage-dependent currents from type II hair cells in response to 50-ms steps from -124 to -54 in 10-mV increments. Wild-type cells had rapidly activating inward currents with reversal potentials close to the K(+) equilibrium potential and a whole-cell conductance of 4.8 ± 1.5 nS (n = 46). In utricle hair cells from Kir2.1-deficient (Kir2.1(-/-)) mice, I(K1) was absent at all stages examined. To identify the functional contribution of Kir2.1, we recorded membrane responses in current-clamp mode. Hair cells from Kir2.1(-/-) mice had significantly (P < 0.001) more depolarized resting potentials and larger, slower membrane responses than those of wild-type cells. These data suggest that Kir2.1 is required for I(K1) in type II utricle hair cells and contributes to hyperpolarized resting potentials and fast, small amplitude receptor potentials in response to current inputs, such as those evoked by hair bundle deflections.
Collapse
Affiliation(s)
- Michaela E Levin
- Department of Neuroscience, University of Virginia School of Medicine, Charlottesville, Virginia, USA
| | | |
Collapse
|
16
|
Self-directed assembly and clustering of the cytoplasmic domains of inwardly rectifying Kir2.1 potassium channels on association with PSD-95. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1808:2374-89. [DOI: 10.1016/j.bbamem.2011.06.021] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2011] [Revised: 06/22/2011] [Accepted: 06/28/2011] [Indexed: 12/21/2022]
|
17
|
Dassau L, Conti LR, Radeke CM, Ptáček LJ, Vandenberg CA. Kir2.6 regulates the surface expression of Kir2.x inward rectifier potassium channels. J Biol Chem 2011; 286:9526-41. [PMID: 21209095 DOI: 10.1074/jbc.m110.170597] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Precise trafficking, localization, and activity of inward rectifier potassium Kir2 channels are important for shaping the electrical response of skeletal muscle. However, how coordinated trafficking occurs to target sites remains unclear. Kir2 channels are tetrameric assemblies of Kir2.x subunits. By immunocytochemistry we show that endogenous Kir2.1 and Kir2.2 are localized at the plasma membrane and T-tubules in rodent skeletal muscle. Recently, a new subunit, Kir2.6, present in human skeletal muscle, was identified as a gene in which mutations confer susceptibility to thyrotoxic hypokalemic periodic paralysis. Here we characterize the trafficking and interaction of wild type Kir2.6 with other Kir2.x in COS-1 cells and skeletal muscle in vivo. Immunocytochemical and electrophysiological data demonstrate that Kir2.6 is largely retained in the endoplasmic reticulum, despite high sequence identity with Kir2.2 and conserved endoplasmic reticulum and Golgi trafficking motifs shared with Kir2.1 and Kir2.2. We identify amino acids responsible for the trafficking differences of Kir2.6. Significantly, we show that Kir2.6 subunits can coassemble with Kir2.1 and Kir2.2 in vitro and in vivo. Notably, this interaction limits the surface expression of both Kir2.1 and Kir2.2. We provide evidence that Kir2.6 functions as a dominant negative, in which incorporation of Kir2.6 as a subunit in a Kir2 channel heterotetramer reduces the abundance of Kir2 channels on the plasma membrane.
Collapse
Affiliation(s)
- Lior Dassau
- Department of Molecular, Cellular, and Developmental Biology and the Neuroscience Research Institute, University of California, Santa Barbara, California 93106, USA
| | | | | | | | | |
Collapse
|