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Gaballah M, Penttinen K, Kreutzer J, Mäki AJ, Kallio P, Aalto-Setälä K. Cardiac Ischemia On-a-Chip: Antiarrhythmic Effect of Levosimendan on Ischemic Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes. Cells 2022; 11:cells11061045. [PMID: 35326497 PMCID: PMC8947267 DOI: 10.3390/cells11061045] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Revised: 03/15/2022] [Accepted: 03/17/2022] [Indexed: 02/05/2023] Open
Abstract
Ischemic heart disease (IHD) is one of the leading causes of mortality worldwide. Preserving functionality and preventing arrhythmias of the heart are key principles in the management of patients with IHD. Levosimendan, a unique calcium (Ca2+) enhancer with inotropic activity, has been introduced into clinical usage for heart failure treatment. Human-induced pluripotent cell-derived cardiomyocytes (hiPSC-CMs) offer an opportunity to better understand the pathophysiological mechanisms of the disease as well as to serve as a platform for drug screening. Here, we developed an in vitro IHD model using hiPSC-CMs in hypoxic conditions and defined the effects of the subsequent hypoxic stress on CMs functionality. Furthermore, the effect of levosimendan on hiPSC-CMs functionality was evaluated during and after hypoxic stress. The morphology, contractile, Ca2+-handling, and gene expression properties of hiPSC-CMs were investigated in response to hypoxia. Hypoxia resulted in significant cardiac arrhythmia and decreased Ca2+ transient amplitude. In addition, disorganization of sarcomere structure was observed after hypoxia induction. Interestingly, levosimendan presented significant antiarrhythmic properties, as the arrhythmia was abolished or markedly reduced with levosimendan treatment either during or after the hypoxic stress. Moreover, levosimendan presented significant protection from the sarcomere alterations induced by hypoxia. In conclusion, this chip model appears to be a suitable preclinical representation of IHD. With this hypoxia platform, detailed knowledge of the disease pathophysiology can be obtained. The antiarrhythmic effect of levosimendan was clearly observed, suggesting a possible new clinical use for the drug.
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Affiliation(s)
- Mahmoud Gaballah
- Heart Group, Faculty of Medicine and Health Technology, Tampere University, 33520 Tampere, Finland; (K.P.); (K.A.-S.)
- Department of Forensic Medicine and Toxicology, Faculty of Veterinary Medicine, University of Sadat City, Menoufia 32897, Egypt
- Correspondence: ; Tel.: +358-402574148
| | - Kirsi Penttinen
- Heart Group, Faculty of Medicine and Health Technology, Tampere University, 33520 Tampere, Finland; (K.P.); (K.A.-S.)
| | - Joose Kreutzer
- Micro- and Nanosystems Research Group, Faculty of Medicine and Health Technology, Tampere University, 33520 Tampere, Finland; (J.K.); (A.-J.M.); (P.K.)
| | - Antti-Juhana Mäki
- Micro- and Nanosystems Research Group, Faculty of Medicine and Health Technology, Tampere University, 33520 Tampere, Finland; (J.K.); (A.-J.M.); (P.K.)
| | - Pasi Kallio
- Micro- and Nanosystems Research Group, Faculty of Medicine and Health Technology, Tampere University, 33520 Tampere, Finland; (J.K.); (A.-J.M.); (P.K.)
| | - Katriina Aalto-Setälä
- Heart Group, Faculty of Medicine and Health Technology, Tampere University, 33520 Tampere, Finland; (K.P.); (K.A.-S.)
- Heart Hospital, Tampere University Hospital, 33520 Tampere, Finland
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2
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Korotkov SM, Sobol KV, Shemarova IV, Nesterov VP. Effect of Sodium Ions on Calcium-Loaded Rat Heart Mitochondria and Frog Myocardium. J EVOL BIOCHEM PHYS+ 2021. [DOI: 10.1134/s0022093021060041] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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3
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Ferreira JJ, Amazu C, Puga-Molina LC, Ma X, England SK, Santi CM. SLO2.1/NALCN a sodium signaling complex that regulates uterine activity. iScience 2021; 24:103210. [PMID: 34746693 PMCID: PMC8551532 DOI: 10.1016/j.isci.2021.103210] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2021] [Revised: 07/29/2021] [Accepted: 09/29/2021] [Indexed: 01/05/2023] Open
Abstract
Depolarization of the myometrial smooth muscle cell (MSMC) resting membrane potential is necessary for the uterus to transition from a quiescent state to a contractile state. The molecular mechanisms involved in this transition are not completely understood. Here, we report that a coupled system between the Na+-activated K+ channel (SLO2.1) and the non-selective Na+ leak channel (NALCN) determines the MSMC membrane potential. Our data indicate that Na+ entering through NALCN acts as an intracellular signaling molecule that activates SLO2.1. Potassium efflux through SLO2.1 hyperpolarizes the membrane. A decrease in SLO2.1/NALCN activity induces membrane depolarization, triggering Ca2+ entry through voltage-dependent Ca2+ channels and promoting contraction. Consistent with functional coupling, our data show that NALCN and SLO2.1 are in close proximity in human MSMCs. We propose that these arrangements of SLO2.1 and NALCN permit these channels to functionally regulate MSMC membrane potential and cell excitability and modulate uterine contractility.
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Affiliation(s)
- Juan J. Ferreira
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO 63110, USA
| | - Chinwendu Amazu
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Lis C. Puga-Molina
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Xiaofeng Ma
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Sarah K. England
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
| | - Celia M. Santi
- Department of Obstetrics and Gynecology, Center for Reproductive Health Sciences, Washington University in St. Louis, School of Medicine, 425 S. Euclid Avenue, CB 8064, St. Louis, MO 63110, USA
- Department of Neuroscience, Washington University in St. Louis, School of Medicine, St. Louis, MO 63110, USA
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Li P, Halabi CM, Stewart R, Butler A, Brown B, Xia X, Santi C, England S, Ferreira J, Mecham RP, Salkoff L. Sodium-activated potassium channels moderate excitability in vascular smooth muscle. J Physiol 2019; 597:5093-5108. [PMID: 31444905 PMCID: PMC6800802 DOI: 10.1113/jp278279] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2019] [Accepted: 08/19/2019] [Indexed: 12/12/2022] Open
Abstract
KEY POINTS We report that a sodium-activated potassium current, IKNa , has been inadvertently overlooked in both conduit and resistance arterial smooth muscle cells. IKNa is a major K+ resting conductance and is absent in cells of IKNa knockout (KO) mice. The phenotype of the IKNa KO is mild hypertension, although KO mice react more strongly than wild-type with raised blood pressure when challenged with vasoconstrictive agents. IKNa is negatively regulated by angiotensin II acting through Gαq protein-coupled receptors. In current clamp, KO arterial smooth muscle cells have easily evoked Ca2+ -dependent action potentials. ABSTRACT Although several potassium currents have been reported to play a role in arterial smooth muscle (ASM), we find that one of the largest contributors to membrane conductance in both conduit and resistance ASMs has been inadvertently overlooked. In the present study, we show that IKNa , a sodium-activated potassium current, contributes a major portion of macroscopic outward current in a critical physiological voltage range that determines intrinsic cell excitability; IKNa is the largest contributor to ASM cell resting conductance. A genetic knockout (KO) mouse strain lacking KNa channels (KCNT1 and KCNT2) shows only a modest hypertensive phenotype. However, acute administration of vasoconstrictive agents such as angiotensin II (Ang II) and phenylephrine results in an abnormally large increase in blood pressure in the KO animals. In wild-type animals Ang II acting through Gαq protein-coupled receptors down-regulates IKNa , which increases the excitability of the ASMs. The complete genetic removal of IKNa in KO mice makes the mutant animal more vulnerable to vasoconstrictive agents, thus producing a paroxysmal-hypertensive phenotype. This may result from the lowering of cell resting K+ conductance allowing the cells to depolarize more readily to a variety of excitable stimuli. Thus, the sodium-activated potassium current may serve to moderate blood pressure in instances of heightened stress. IKNa may represent a new therapeutic target for hypertension and stroke.
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Affiliation(s)
- Ping Li
- Dept. of Neuroscience, Washington University School of Medicine, Saint Louis. MO 63110
- Equal contributors
| | - Carmen M. Halabi
- Dept. of Pediatrics, Washington University School of Medicine, Saint Louis. MO 63110
- Equal contributors
| | - Richard Stewart
- Dept. of Neuroscience, Washington University School of Medicine, Saint Louis. MO 63110
| | - Alice Butler
- Dept. of Neuroscience, Washington University School of Medicine, Saint Louis. MO 63110
| | - Bobbie Brown
- Dept. of Neuroscience, Washington University School of Medicine, Saint Louis. MO 63110
| | - Xiaoming Xia
- Dept. of Anesthesiology, Washington University School of Medicine, Saint Louis. MO 63110
| | - Celia Santi
- Dept. of Neuroscience, Washington University School of Medicine, Saint Louis. MO 63110
- Dept. of OBGYN, Washington University School of Medicine, Saint Louis. MO 63110
| | - Sarah England
- Dept. of OBGYN, Washington University School of Medicine, Saint Louis. MO 63110
| | - Juan Ferreira
- Dept. of Neuroscience, Washington University School of Medicine, Saint Louis. MO 63110
- Dept. of OBGYN, Washington University School of Medicine, Saint Louis. MO 63110
| | - Robert P. Mecham
- Dept. of Cell Biology, Washington University School of Medicine, Saint Louis. MO 63110
| | - Lawrence Salkoff
- Dept. of Neuroscience, Washington University School of Medicine, Saint Louis. MO 63110
- Dept. of Genetics, Washington University School of Medicine, Saint Louis. MO 63110
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5
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Verkhratsky A, Untiet V, Rose CR. Ionic signalling in astroglia beyond calcium. J Physiol 2019; 598:1655-1670. [PMID: 30734296 DOI: 10.1113/jp277478] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2018] [Accepted: 01/15/2019] [Indexed: 12/18/2022] Open
Abstract
Astrocytes are homeostatic and protective cells of the central nervous system. Astroglial homeostatic responses are tightly coordinated with neuronal activity. Astrocytes maintain neuronal excitability through regulation of extracellular ion concentrations, as well as assisting and modulating synaptic transmission by uptake and catabolism of major neurotransmitters. Moreover, they support neuronal metabolism and detoxify ammonium and reactive oxygen species. Astroglial homeostatic actions are initiated and controlled by intercellular signalling of ions, including Ca2+ , Na+ , Cl- , H+ and possibly K+ . This review summarises current knowledge on ionic signals mediated by the major monovalent ions, which occur in microdomains, as global events, or as propagating intercellular waves and thereby represent the substrate for astroglial excitability.
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Affiliation(s)
- Alexei Verkhratsky
- Faculty of Biology, Medicine and Health, The University of Manchester, M13 9PT, Manchester, UK.,Centre for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark.,Achucarro Centre for Neuroscience, IKERBASQUE, Basque Foundation for Science, 48011, Bilbao, Spain
| | - Verena Untiet
- Centre for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, 2200, Copenhagen, Denmark
| | - Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, Universitätsstrasse 1, D-40225, Düsseldorf, Germany
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Skogestad J, Lines GT, Louch WE, Sejersted OM, Sjaastad I, Aronsen JM. Evidence for heterogeneous subsarcolemmal Na + levels in rat ventricular myocytes. Am J Physiol Heart Circ Physiol 2019; 316:H941-H957. [PMID: 30657726 DOI: 10.1152/ajpheart.00637.2018] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The intracellular Na+ concentration ([Na+]) regulates cardiac contractility. Previous studies have suggested that subsarcolemmal [Na+] is higher than cytosolic [Na+] in cardiac myocytes, but this concept remains controversial. Here, we used electrophysiological experiments and mathematical modeling to test whether there are subsarcolemmal pools with different [Na+] and dynamics compared with the bulk cytosol in rat ventricular myocytes. A Na+ dependency curve for Na+-K+-ATPase (NKA) current was recorded with symmetrical Na+ solutions, i.e., the same [Na+] in the superfusate and internal solution. This curve was used to estimate [Na+] sensed by NKA in other experiments. Three experimental observations suggested that [Na+] is higher near NKA than in the bulk cytosol: 1) when extracellular [Na+] was high, [Na+] sensed by NKA was ~6 mM higher than the internal solution in quiescent cells; 2) long trains of Na+ channel activation almost doubled this gradient; compared with an even intracellular distribution of Na+, the increase of [Na+] sensed by NKA was 10 times higher than expected, suggesting a local Na+ domain; and 3) accumulation of Na+ near NKA after trains of Na+ channel activation dissipated very slowly. Finally, mathematical models assuming heterogeneity of [Na+] between NKA and the Na+ channel better reproduced experimental data than the homogeneous model. In conclusion, our data suggest that NKA-sensed [Na+] is higher than [Na+] in the bulk cytosol and that there are differential Na+ pools in the subsarcolemmal space, which could be important for cardiac contractility and arrhythmogenesis. NEW & NOTEWORTHY Our data suggest that the Na+-K+-ATPase-sensed Na+ concentration is higher than the Na+ concentration in the bulk cytosol and that there are differential Na+ pools in the subsarcolemmal space, which could be important for cardiac contractility and arrhythmogenesis. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/heterogeneous-sodium-in-ventricular-myocytes/ .
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Affiliation(s)
- J Skogestad
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway
| | - G T Lines
- Simula Research Laboratory, Center for Cardiological Innovation , Oslo , Norway
| | - W E Louch
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway.,K. G. Jebsen Center for Cardiac Research, University of Oslo , Oslo , Norway
| | - O M Sejersted
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway
| | - I Sjaastad
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway.,K. G. Jebsen Center for Cardiac Research, University of Oslo , Oslo , Norway
| | - J M Aronsen
- Institute for Experimental Medical Research, Oslo University Hospital Ullevål and University of Oslo , Oslo , Norway.,Bjørknes College , Oslo , Norway
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7
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Chi L, Belardinelli L, Zeng A, Hirakawa R, Rajamani S, Ling H, Dhalla AK. Inhibition of late Na+ current, a novel target to improve diastolic function and electrical abnormalities in Dahl salt-sensitive rats. Am J Physiol Heart Circ Physiol 2016; 310:H1313-20. [PMID: 26993228 DOI: 10.1152/ajpheart.00863.2015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 03/11/2016] [Indexed: 12/19/2022]
Abstract
Late Na(+) current (INaL) is enhanced in myocytes of animals with chronic heart failure and patients with hypertrophic cardiomyopathy. To define the role of INaL in diastolic heart failure, the effects of GS-458967 (GS-967), a potent INaL inhibitor on mechanical and electrical abnormalities, were determined in an animal model of diastolic dysfunction. Dahl salt-sensitive (DSS) rats fed a high-salt (HS) diet for 8 wk, compared with a normal salt (NS) diet, had increased left ventricular (LV) mass (1,257 ± 96 vs. 891 ± 34 mg) and diastolic dysfunction [isovolumic relaxation time (IVRT): 26.8 ± 0.5 vs. 18.9 ± 0.2 ms; early transmitral flow velocity/early mitral annulus velocity (E/E') ratio: 25.5 ± 1.9 vs. 14.9 ± 0.9]. INaL in LV myocytes from HS rats was significantly increased to 0.41 ± 0.02 from 0.14 ± 0.02 pA/pF in NS rats. The action potential duration (APD) was prolonged to 136 ± 12 from 68 ± 9 ms in NS rats. QTc intervals were longer in HS vs. NS rats (267 ± 8 vs. 212 ± 2 ms). Acute and chronic treatment with GS-967 decreased the enhanced INaL to 0.24 ± 0.01 and 0.17 ± 0.02 pA/pF, respectively, vs. 0.41 ± 0.02 pA/pF in the HS group. Chronic treatment with GS-967 dose-dependently reduced LV mass, the increases in E/E' ratio, and the prolongation of IVRT by 27, 27, and 20%, respectively, at the 1.0 mg·kg(-1)·day(-1) dose without affecting blood pressure or LV systolic function. The prolonged APDs in myocytes and QTc of HS rats were significantly reduced with GS-967 treatment. These results indicate that INaL is a significant contributor to the LV diastolic dysfunction, hypertrophy, and repolarization abnormalities and thus, inhibition of this current is a promising therapeutic target for diastolic heart failure.
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Affiliation(s)
- Liguo Chi
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Luiz Belardinelli
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Aliya Zeng
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Ryoko Hirakawa
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Sridharan Rajamani
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Haiyun Ling
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Arvinder K Dhalla
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
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8
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Garcia A, Liu CC, Cornelius F, Clarke RJ, Rasmussen HH. Glutathionylation-Dependence of Na(+)-K(+)-Pump Currents Can Mimic Reduced Subsarcolemmal Na(+) Diffusion. Biophys J 2016; 110:1099-109. [PMID: 26958887 DOI: 10.1016/j.bpj.2016.01.014] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2015] [Revised: 12/18/2015] [Accepted: 01/12/2016] [Indexed: 01/03/2023] Open
Abstract
The existence of a subsarcolemmal space with restricted diffusion for Na(+) in cardiac myocytes has been inferred from a transient peak electrogenic Na(+)-K(+) pump current beyond steady state on reexposure of myocytes to K(+) after a period of exposure to K(+)-free extracellular solution. The transient peak current is attributed to enhanced electrogenic pumping of Na(+) that accumulated in the diffusion-restricted space during pump inhibition in K(+)-free extracellular solution. However, there are no known physical barriers that account for such restricted Na(+) diffusion, and we examined if changes of activity of the Na(+)-K(+) pump itself cause the transient peak current. Reexposure to K(+) reproduced a transient current beyond steady state in voltage-clamped ventricular myocytes as reported by others. Persistence of it when the Na(+) concentration in patch pipette solutions perfusing the intracellular compartment was high and elimination of it with K(+)-free pipette solution could not be reconciled with restricted subsarcolemmal Na(+) diffusion. The pattern of the transient current early after pump activation was dependent on transmembrane Na(+)- and K(+) concentration gradients suggesting the currents were related to the conformational poise imposed on the pump. We examined if the currents might be accounted for by changes in glutathionylation of the β1 Na(+)-K(+) pump subunit, a reversible oxidative modification that inhibits the pump. Susceptibility of the β1 subunit to glutathionylation depends on the conformational poise of the Na(+)-K(+) pump, and glutathionylation with the pump stabilized in conformations equivalent to those expected to be imposed on voltage-clamped myocytes supported this hypothesis. So did elimination of the transient K(+)-induced peak Na(+)-K(+) pump current when we included glutaredoxin 1 in patch pipette solutions to reverse glutathionylation. We conclude that transient K(+)-induced peak Na(+)-K(+) pump current reflects the effect of conformation-dependent β1 pump subunit glutathionylation, not restricted subsarcolemmal diffusion of Na(+).
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Affiliation(s)
- Alvaro Garcia
- North Shore Heart Research Group, Kolling Institute, University of Sydney, Sydney, Australia; School of Chemistry, University of Sydney, Sydney, Australia
| | - Chia-Chi Liu
- North Shore Heart Research Group, Kolling Institute, University of Sydney, Sydney, Australia
| | | | - Ronald J Clarke
- School of Chemistry, University of Sydney, Sydney, Australia
| | - Helge H Rasmussen
- North Shore Heart Research Group, Kolling Institute, University of Sydney, Sydney, Australia.
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9
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Rose CR, Verkhratsky A. Principles of sodium homeostasis and sodium signalling in astroglia. Glia 2016; 64:1611-27. [DOI: 10.1002/glia.22964] [Citation(s) in RCA: 88] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 12/21/2015] [Indexed: 12/22/2022]
Affiliation(s)
- Christine R. Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences; Heinrich Heine University Düsseldorf; Düsseldorf Germany
| | - Alexei Verkhratsky
- Faculty of Life Sciences; the University of Manchester; Manchester United Kingdom
- Achucarro Center for Neuroscience, IKERBASQUE, Basque Foundation for Science, Bilbao, Spain
- Department of Neurosciences; University of the Basque Country UPV/EHU and CIBERNED; Leioa Spain
- University of Nizhny Novgorod; Nizhny Novgorod Russia
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10
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Shryock JC, Song Y, Rajamani S, Antzelevitch C, Belardinelli L. The arrhythmogenic consequences of increasing late INa in the cardiomyocyte. Cardiovasc Res 2013; 99:600-11. [PMID: 23752976 DOI: 10.1093/cvr/cvt145] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
This review presents the roles of cardiac sodium channel NaV1.5 late current (late INa) in generation of arrhythmic activity. The assumption of the authors is that proper Na(+) channel function is necessary to the maintenance of the transmembrane electrochemical gradient of Na(+) and regulation of cardiac electrical activity. Myocyte Na(+) channels' openings during the brief action potential upstroke contribute to peak INa and initiate excitation-contraction coupling. Openings of Na(+) channels outside the upstroke contribute to late INa, a depolarizing current that persists throughout the action potential plateau. The small, physiological late INa does not appear to be critical for normal electrical or contractile function in the heart. Late INa does, however, reduce the net repolarizing current, prolongs action potential duration, and increases cellular Na(+) loading. An increase of late INa, due to acquired conditions (e.g. heart failure) or inherited Na(+) channelopathies, facilitates the formation of early and delayed afterpolarizations and triggered arrhythmias, spontaneous diastolic depolarization, and cellular Ca(2+) loading. These in turn increase the spatial and temporal dispersion of repolarization time and may lead to reentrant arrhythmias.
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Affiliation(s)
- John C Shryock
- Department of Biology, Cardiovascular Therapeutic Area, Gilead Sciences, Foster City, CA, USA
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11
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Ginsburg KS, Weber CR, Bers DM. Cardiac Na+-Ca2+ exchanger: dynamics of Ca2+-dependent activation and deactivation in intact myocytes. J Physiol 2013; 591:2067-86. [PMID: 23401616 PMCID: PMC3634520 DOI: 10.1113/jphysiol.2013.252080] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Accepted: 02/10/2013] [Indexed: 01/05/2023] Open
Abstract
Cardiac Na(+)-Ca(2+) exchange (NCX) activity is regulated by [Ca(2+)]i. The physiological role and dynamics of this process in intact cardiomyocytes are largely unknown. We examined NCX Ca(2+) activation in intact rabbit and mouse cardiomyocytes at 37°C. Sarcoplasmic reticulum (SR) function was blocked, and cells were bathed in 2 mm Ca(2+). We probed Ca(2+) activation without voltage clamp by applying Na(+)-free (0 Na(+)) solution for 5 s bouts, repeated each 10 s, which should evoke [Ca(2+)]i transients due to Ca(2+) influx via NCX. In rested rabbit myocytes, Ca(2+) influx was undetectable even after 0 Na(+) applications were repeated for 2-5 min or more, suggesting that NCX was inactive. After external electric field stimulation pulses were applied, to admit Ca(2+) via L-type Ca(2+) channels, 0 Na(+) bouts activated Ca(2+) influx efficaciously, indicating that NCX had become active. Calcium activation increased with more field pulses, reaching a maximum typically after 15-20 pulses (1 Hz). At rest, NCX deactivated with a time constant typically of 20-40 s. An increase in [Na(+)]i, either in rabbit cardiomyocytes as a result of inhibition of Na(+)-K(+) pumping, or in mouse cardiomyocytes where normal [Na(+)]i is higher vs. rabbit, sensitized NCX to self-activation by 0 Na(+) bouts. In experiments with the SR functional but initially empty, the activation time course was slowed. It is possible that the SR initially accumulated Ca(2+) that would otherwise cause activation. We modelled Ca(2+) activation as a fourth-order highly co-operative process ([Ca]i required for half-activation K0.5act = 375 nm), with dynamics severalfold slower than the cardiac cycle. We incorporated this NCX model into an established ventricular myocyte model, which allowed us to predict responses to twitch stimulation in physiological conditions with the SR intact. Model NCX fractional activation increased from 0.1 to 1.0 as the frequency was increased from 0.2 to 2 Hz. By adjusting Ca(2+) activation on a multibeat time scale, NCX might better maintain a stable long-term Ca(2+) balance while contributing to the ability of myocytes to produce Ca(2+) transients over a wide range of intensity.
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Affiliation(s)
- Kenneth S Ginsburg
- Department of Pharmacology, University of California Davis, Davis, CA 95616, USA
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12
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Sodium-activated potassium channels are functionally coupled to persistent sodium currents. J Neurosci 2012; 32:2714-21. [PMID: 22357855 DOI: 10.1523/jneurosci.5088-11.2012] [Citation(s) in RCA: 58] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We report a novel coupled system of sodium-activated potassium currents (I(KNa)) and persistent sodium currents (I(NaP)), the components of which are widely distributed throughout the brain. Its existence and importance has not been previously recognized. Although I(KNa) was known to exist in many cell types, the source of Na(+) which activates I(KNa) remained a mystery. We now show in single membrane patches generated from the somas of rat neurons that sodium influx through I(NaP) is sufficient for activation of K(Na) channels, without substantial contribution from the transient sodium current or bulk [Na(+)](i). I(NaP) was found to be active at cell membrane resting potentials, a finding that may explain why I(KNa) can be evoked from negative holding potentials. These results show an unanticipated role for I(NaP) in activating a negative feedback system countering the excitable effects I(NaP); the interrelatedness of I(NaP) and I(KNa) suggests new ways neurons can tune their excitability.
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13
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To establish a pharmacological experimental platform for the study of cardiac hypoxia using the microelectrode array. J Pharmacol Toxicol Methods 2009; 59:146-52. [DOI: 10.1016/j.vascn.2009.02.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2009] [Accepted: 02/17/2009] [Indexed: 11/19/2022]
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Moshal KS, Tipparaju SM, Vacek TP, Kumar M, Singh M, Frank IE, Patibandla PK, Tyagi N, Rai J, Metreveli N, Rodriguez WE, Tseng MT, Tyagi SC. Mitochondrial matrix metalloproteinase activation decreases myocyte contractility in hyperhomocysteinemia. Am J Physiol Heart Circ Physiol 2008; 295:H890-7. [PMID: 18567713 DOI: 10.1152/ajpheart.00099.2008] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Cardiomyocyte N-methyl-d-aspartate receptor-1 (NMDA-R1) activation induces mitochondrial dysfunction. Matrix metalloproteinase protease (MMP) induction is a negative regulator of mitochondrial function. Elevated levels of homocysteine [hyperhomocysteinemia (HHCY)] activate latent MMPs and causes myocardial contractile abnormalities. HHCY is associated with mitochondrial dysfunction. We tested the hypothesis that HHCY activates myocyte mitochondrial MMP (mtMMP), induces mitochondrial permeability transition (MPT), and causes contractile dysfunction by agonizing NMDA-R1. The C57BL/6J mice were administered homocystinemia (1.8 g/l) in drinking water to induce HHCY. NMDA-R1 expression was detected by Western blot and confocal microscopy. Localization of MMP-9 in the mitochondria was determined using confocal microscopy. Ultrastructural analysis of the isolated myocyte was determined by electron microscopy. Mitochondrial permeability was measured by a decrease in light absorbance at 540 nm using the spectrophotometer. The effect of MK-801 (NMDA-R1 inhibitor), GM-6001 (MMP inhibitor), and cyclosporine A (MPT inhibitor) on myocyte contractility and calcium transients was evaluated using the IonOptix video edge track detection system and fura 2-AM. Our results demonstrate that HHCY activated the mtMMP-9 and caused MPT by agonizing NMDA-R1. A significant decrease in percent cell shortening, maximal rate of contraction (-dL/dt), and maximal rate of relaxation (+dL/dt) was observed in HHCY. The decay of calcium transient amplitude was faster in the wild type compared with HHCY. Furthermore, the HHCY-induced decrease in percent cell shortening, -dL/dt, and +dL/dt was attenuated in the mice treated with MK-801, GM-6001, and cyclosporin A. We conclude that HHCY activates mtMMP-9 and induces MPT, leading to myocyte mechanical dysfunction by agonizing NMDA-R1.
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Affiliation(s)
- Karni S Moshal
- Department of Physiology and Biophysics, Potentia Pharmaceuticals, Louisville, KY, USA
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Murphy E, Steenbergen C. Ion transport and energetics during cell death and protection. Physiology (Bethesda) 2008; 23:115-23. [PMID: 18400694 DOI: 10.1152/physiol.00044.2007] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
During ischemia, ATP and phosphocreatine (PCr) decline, whereas intracellular hydrogen ion, intracellular sodium (Na(+)), calcium (Ca(2+)), and magnesium (Mg(2+)) concentrations all rise. If the ischemia is relatively short and there is little irreversible injury (cell death), PCr, pH, Na(+), Mg(2+), and Ca(2+) all recovery quickly on reperfusion. ATP recovery can take up to 24 h because of loss of adenine base from the cell and the need for de novo synthesis. There are correlative data showing that a sustained rise in Ca(2+) during ischemia and/or lack of recovery during reperfusion is associated with irreversible cell injury. Interventions that reduce the rise in Ca(2+) during ischemia and reperfusion have been shown to reduce cell death. Therefore, a better understanding of the mechanisms responsible for the rise in Ca(2+) during ischemia and early reperfusion could have important therapeutic implications. This review will discuss mechanisms involved in alterations in ions and high energy phosphate metabolites in perfused or intact heart during ischemia and reperfusion.
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Affiliation(s)
- Elizabeth Murphy
- National Heart, Lung, and Blood Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA.
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Ranolazine Inhibits An Oxidative Stress-induced Increase in Myocyte Sodium and Calcium Loading During Simulated-demand Ischemia. J Cardiovasc Pharmacol 2008; 51:443-9. [DOI: 10.1097/fjc.0b013e318168e711] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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The role of the Na+/Ca2+ exchangers in Ca2+ dynamics in ventricular myocytes. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 96:377-98. [DOI: 10.1016/j.pbiomolbio.2007.07.018] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
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Bers DM, Ginsburg KS. Na:Ca Stoichiometry and Cytosolic Ca-Dependent Activation of NCX in Intact Cardiomyocytes. Ann N Y Acad Sci 2007; 1099:326-38. [PMID: 17303827 DOI: 10.1196/annals.1387.060] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
We are studying both Na:Ca exchange stoichiometry and cytosolic [Ca] ([Ca]i)-dependent regulation of Na-Ca exchange (NCX) in intact rabbit ventricular myocytes. Analysis of NCX fluxes in subcellular systems strongly supports a dominant 3Na:1Ca exchange, and our measurements in intact cells confirm this. However, in intact native cells, local ion gradients and other factors complicate the process of inferring stoichiometry. From a functional viewpoint, NCX stoichiometry is near 3:1 but is affected by ion accumulation/depletion as well as non-NCX fluxes. We and others have viewed [Ca]i-dependent NCX regulation as a static process (dependent on instantaneous local [Ca]i). However, evidence from subcellular and expression systems shows the process to be dynamic, and our observations confirm this to be the case in intact cardiac cells as well.
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Affiliation(s)
- Donald M Bers
- Department of Physiology, Loyola University Chicago, Stritch School of Medicine, 2160 South First Avenue, Maywood, IL 60153, USA.
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