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Varró A, Tomek J, Nagy N, Virág L, Passini E, Rodriguez B, Baczkó I. Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior. Physiol Rev 2020; 101:1083-1176. [PMID: 33118864 DOI: 10.1152/physrev.00024.2019] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.
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Affiliation(s)
- András Varró
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary.,MTA-SZTE Cardiovascular Pharmacology Research Group, Hungarian Academy of Sciences, Szeged, Hungary
| | - Jakub Tomek
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Norbert Nagy
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary.,MTA-SZTE Cardiovascular Pharmacology Research Group, Hungarian Academy of Sciences, Szeged, Hungary
| | - László Virág
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Elisa Passini
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Blanca Rodriguez
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - István Baczkó
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
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2
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Lemnalol Modulates the Electrophysiological Characteristics and Calcium Homeostasis of Atrial Myocytes. Mar Drugs 2019; 17:md17110619. [PMID: 31671563 PMCID: PMC6891404 DOI: 10.3390/md17110619] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2019] [Revised: 10/26/2019] [Accepted: 10/29/2019] [Indexed: 11/17/2022] Open
Abstract
Sepsis, an inflammatory response to infection provoked by lipopolysaccharide (LPS), is associated with high mortality, as well as ischemic stroke and new-onset atrial arrhythmia. Severe bacterial infections causing sepsis always result in profound physiological changes, including fever, hypotension, arrhythmia, necrosis of tissue, systemic multi-organ dysfunction and finally death. LPS challenge-induced inflammatory responses during sepsis may increase the likelihood of the arrhythmogenesis. Lemnalol is known to possess potent anti-inflammatory effects. This study examined whether Lemnalol (0.1 μM) could modulate the electrophysiological characteristics and calcium homeostasis of atrial myocytes under the influence of LPS (1μg/mL). Under challenge with LPS, Lemnalol-treated LA myocytes, had a longer AP duration at 20%, 50% and 90% repolarization of the amplitude, compared to the LPS-treated cells. LPS-challenged LA myocytes showed increased late sodium current, Na+-Ca2+ exchanger current, transient outward current, rapid component of delayed rectifier potassium current, tumor necrosis factor-α, NF-κB and increased phosphorylation of ryanodine receptor (RyR), but a lower L-type Ca2+ current than the control LA myocytes. Exposure to Lemnalol reversed the LPS-induced effects. The LPS-treated and control groups of LA myocytes, with or without the existence of Lemnalol. showed no apparent alterations in the sodium current amplitude or Cav1.2 expression. The expression of sarcoendoplasmic reticulum calcium transport ATPase (SERCA2) was reduced by LPS treatment, while Lemnalol ameliorated the LPS-induced alterations. The phosphorylation of RyR was enhanced by LPS treatment, while Lemnalol attenuated the LPS-induced alterations. In conclusion, Lemnalol modulates LPS-induced alterations of LA calcium homeostasis and blocks the NF-κB pathways, which may contribute to the attenuation of LPS-induced arrhythmogenesis.
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Zhao Y, Rafatian N, Feric NT, Cox BJ, Aschar-Sobbi R, Wang EY, Aggarwal P, Zhang B, Conant G, Ronaldson-Bouchard K, Pahnke A, Protze S, Lee JH, Davenport Huyer L, Jekic D, Wickeler A, Naguib HE, Keller GM, Vunjak-Novakovic G, Broeckel U, Backx PH, Radisic M. A Platform for Generation of Chamber-Specific Cardiac Tissues and Disease Modeling. Cell 2019; 176:913-927.e18. [PMID: 30686581 PMCID: PMC6456036 DOI: 10.1016/j.cell.2018.11.042] [Citation(s) in RCA: 330] [Impact Index Per Article: 66.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2018] [Revised: 09/19/2018] [Accepted: 11/28/2018] [Indexed: 12/12/2022]
Abstract
Tissue engineering using cardiomyocytes derived from human pluripotent stem cells holds a promise to revolutionize drug discovery, but only if limitations related to cardiac chamber specification and platform versatility can be overcome. We describe here a scalable tissue-cultivation platform that is cell source agnostic and enables drug testing under electrical pacing. The plastic platform enabled on-line noninvasive recording of passive tension, active force, contractile dynamics, and Ca2+ transients, as well as endpoint assessments of action potentials and conduction velocity. By combining directed cell differentiation with electrical field conditioning, we engineered electrophysiologically distinct atrial and ventricular tissues with chamber-specific drug responses and gene expression. We report, for the first time, engineering of heteropolar cardiac tissues containing distinct atrial and ventricular ends, and we demonstrate their spatially confined responses to serotonin and ranolazine. Uniquely, electrical conditioning for up to 8 months enabled modeling of polygenic left ventricular hypertrophy starting from patient cells.
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Affiliation(s)
- Yimu Zhao
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON M5S 3E5, Canada
| | - Naimeh Rafatian
- Division of Cardiology and Peter Munk Cardiac Center, University of Health Network; Toronto, ON M5G 2N2, Canada
| | - Nicole T Feric
- TARA Biosystems, Inc., New York, NY 10016, USA; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
| | - Brian J Cox
- Department of Physiology, Faculty of Medicine; University of Toronto; Toronto; Ontario, M5S 1A8, Canada; Department of Obstetrics and Gynaecology, Faculty of Medicine, University of Toronto, Toronto, ON M5S 1A8, Canada
| | - Roozbeh Aschar-Sobbi
- Division of Cardiology and Peter Munk Cardiac Center, University of Health Network; Toronto, ON M5G 2N2, Canada; TARA Biosystems, Inc., New York, NY 10016, USA
| | - Erika Yan Wang
- Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
| | - Praful Aggarwal
- Section of Genomic Pediatrics, Department of Pediatrics and Genomic Sciences and Precision Medicine Center, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Boyang Zhang
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON M5S 3E5, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
| | - Genevieve Conant
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON M5S 3E5, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
| | - Kacey Ronaldson-Bouchard
- TARA Biosystems, Inc., New York, NY 10016, USA; Department of Biomedical Engineering and Department of Medicine, Columbia University, New York, NY 10032, USA
| | - Aric Pahnke
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON M5S 3E5, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
| | - Stephanie Protze
- Department of Molecular Genetics, University of Toronto, Toronto, ON M5G 1A8, Canada; McEwen Stem Cell Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Jee Hoon Lee
- McEwen Stem Cell Institute, University Health Network, Toronto, ON M5G 1L7, Canada; BlueRock Therapeutics, MaRS Discovery District, Toronto, ON M5G 1L7, Canada
| | - Locke Davenport Huyer
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON M5S 3E5, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada
| | - Danica Jekic
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON M5S 3E5, Canada; Department of Anatomy and Cell Biology, Faculty of Science, McGill University, Montreal, QC H3A 2K6, Canada
| | - Anastasia Wickeler
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S 3G8, Canada
| | - Hani E Naguib
- Department of Mechanical and Industrial Engineering, University of Toronto, Toronto, ON M5S 3G8, Canada
| | - Gordon M Keller
- McEwen Stem Cell Institute, University Health Network, Toronto, ON M5G 1L7, Canada
| | - Gordana Vunjak-Novakovic
- Department of Biomedical Engineering and Department of Medicine, Columbia University, New York, NY 10032, USA
| | - Ulrich Broeckel
- Section of Genomic Pediatrics, Department of Pediatrics and Genomic Sciences and Precision Medicine Center, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Peter H Backx
- Division of Cardiology and Peter Munk Cardiac Center, University of Health Network; Toronto, ON M5G 2N2, Canada; Department of Physiology, Faculty of Medicine; University of Toronto; Toronto; Ontario, M5S 1A8, Canada; Department of Biology; York University, Toronto, ON M3J 1P3, Canada; Toronto General Hospital Research Institute, Toronto, ON M5G 2C4, Canada.
| | - Milica Radisic
- Department of Chemical Engineering and Applied Chemistry, University of Toronto, Toronto, ON M5S 3E5, Canada; Institute of Biomaterials and Biomedical Engineering, University of Toronto, Toronto, ON M5S 3G9, Canada; Toronto General Hospital Research Institute, Toronto, ON M5G 2C4, Canada.
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Tong M, Wang J, Ji Y, Chen X, Wang J, Wang S, Ruan L, Cui H, Zhou Y, Zhang Q, Watanabe E. Effect of eicosapentaenoic acid and pitavastatin on electrophysiology and anticoagulant gene expression in mice with rapid atrial pacing. Exp Ther Med 2017; 14:2310-2316. [PMID: 28962160 DOI: 10.3892/etm.2017.4741] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2016] [Accepted: 04/21/2017] [Indexed: 12/19/2022] Open
Abstract
Atrial remodeling is considered to be any persistent change in atrial structure or function, and is responsible for the development and perpetuation of atrial fibrillation (AF). Oxidative stress and intracellular pH regulation may also be linked to AF; however it remains unclear whether eicosapentaenoic acid (EPA) or statins have beneficial therapeutic effects. The aim of the present study was to investigate the effects of EPA and pitavastatin on the electrophysiology of and gene expressions in mice with rapidly-paced atria. Mice were treated with EPA (10 mg/g/day) or pitavastatin (30 ng/g/day) for 6 weeks, following which AF was simulated by 8-h atrial pacing at 1,800 bpm. The atrial electrophysiological properties and the expression of cardiac genes, potassium voltage-gated channel subfamily A member 5 (Kcna5), Kcn subfamily D member 2 (Kcnd2), Kv channel-interacting protein 2 (KChIP2), solute carrier family 9 member A1, thrombomodulin (TM) and tissue factor pathway inhibitor (TFPI) were examined using reverse transcription-quantitative polymerase chain reaction. In control mice, significant atrial electrical remodeling was observed (P<0.05); however, treatment with either EPA or pitavastatin ameliorated these electrophysiological changes (P>0.05). mRNA levels of Kcnd2, KChIP2 and Kcna5 were significantly upregulated in control mice (P<0.05), whereas treatment with EPA or pitavastatin attenuated this upregulation (P>0.05). Administration of pitavastatin significantly reduced the downregulation of both TFPI and TM (P<0.05). EPA treatment attenuated the TFPI downregulation compared with control mice (P>0.05), however no significant effect on TM expression was observed. In addition, both EPA (P>0.05) and pitavastatin (P<0.05) suppressed the overexpression of endothelial nitric oxide synthase. This was also exhibited in Ras-related C3 botulinum toxin substrate 1 genes (P<0.01 for both treatments). In conclusion, the results of the present study suggested that EPA and pitavastatin are able to prevent atrial electrical remodeling, thrombotic states and oxidative stress in rapidly-paced murine atria.
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Affiliation(s)
- Maoqing Tong
- Department of Cardiology, Key Laboratory of Molecular Medicine, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Jiewen Wang
- Department of Gynecology and Obstetrics, The Second Affiliated Hospital of Bengbu Medical College, Bengbu, Anhui 233040, P.R. China
| | - Yunxin Ji
- Department of Psychosomatic Medicine, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Xiaomin Chen
- Department of Cardiology, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Jieru Wang
- Department of International Health, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Shuangshuang Wang
- Department of Cardiology, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Liemin Ruan
- Department of Psychosomatic Medicine, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Hanbin Cui
- Department of Cardiology, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Ying Zhou
- Department of Cardiology, Key Laboratory of Molecular Medicine, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Qingyu Zhang
- Department of Psychosomatic Medicine, The Affiliated Ningbo First Hospital, School of Medicine, Ningbo University, Ningbo, Zhejiang 315010, P.R. China
| | - Eiichi Watanabe
- Department of Cardiology, Fujita Health University School of Medicine, Toyoake 470-1192, Japan
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Hwang HR, Tai BY, Cheng PY, Chen PN, Sung PJ, Wen ZH, Hsu CH. Excavatolide B Modulates the Electrophysiological Characteristics and Calcium Homeostasis of Atrial Myocytes. Mar Drugs 2017; 15:md15020025. [PMID: 28125029 PMCID: PMC5334606 DOI: 10.3390/md15020025] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Revised: 01/10/2017] [Accepted: 01/18/2017] [Indexed: 12/19/2022] Open
Abstract
Severe bacterial infections caused by sepsis always result in profound physiological changes, including fever, hypotension, arrhythmia, necrosis of tissue, systemic multi-organ dysfunction, and finally death. The lipopolysaccharide (LPS) provokes an inflammatory response under sepsis, which may increase propensity to arrhythmogenesis. Excavatolide B (EXCB) possesses potent anti-inflammatory effects. However, it is not clear whether EXCB could modulate the electrophysiological characteristics and calcium homeostasis of atrial myocytes. This study investigated the effects of EXCB on the atrial myocytes exposed to lipopolysaccharide. A whole-cell patch clamp and indo-1 fluorimetric ratio technique was employed to record the action potential (AP), ionic currents, and intracellular calcium ([Ca2+]i) in single, isolated rabbit left atrial (LA) cardiomyocytes, with and without LPS (1 μg/mL) and LPS + EXCB administration (10 μM) for 6 ± 1 h, in order to investigate the role of EXCB on atrial electrophysiology. In the presence of LPS, EXCB-treated LA myocytes (n = 13) had a longer AP duration at 20% (29 ± 2 vs. 20 ± 2 ms, p < 0.05), 50% (52 ± 4 vs. 40 ± 3 ms, p < 0.05), and 90% (85 ± 5 vs. 68 ± 3 ms, p < 0.05), compared to the LPS-treated cells (n = 12). LPS-treated LA myocytes showed a higher late sodium current, Na+/Ca2+ exchanger current, transient outward current, and delayed rectifier potassium current, but a lower l-type Ca2+ current, than the control LA myocytes. Treatment with EXCB reversed the LPS-induced alterations of the ionic currents. LPS-treated, EXCB-treated, and control LA myocytes exhibited similar Na+ currents. In addition, the LPS-treated LA myocytes exhibited a lower [Ca2+]i content and higher sarcoplasmic reticulum calcium content, than the controls. EXCB reversed the LPS-induced calcium alterations. In conclusion, EXCB modulates LPS-induced LA electrophysiological characteristics and calcium homeostasis, which may contribute to attenuating LPS-induced arrhythmogenesis.
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Affiliation(s)
- Hwong-Ru Hwang
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 804, Taiwan.
- Division of Cardiology, Department of Medicine, E-Da Hospital, Kaohsiung 824, Taiwan.
- Division of Cardiology, Department of Internal Medicine, Kaohsiung Veterans General Hospital, Kaohsiung 813, Taiwan.
| | - Buh-Yuan Tai
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 804, Taiwan.
- Department of Traditional Medicine, Jianan Mental Hospital, Tainan 717, Taiwan.
| | - Pao-Yun Cheng
- Department of Physiology and Biophysics and Graduate Institute of Physiology, National Defense Medical Center, Taipei 114, Taiwan.
| | - Ping-Nan Chen
- Department of Biomedical Engineering, National Defense Medical Center, Taipei 114, Taiwan.
| | - Ping-Jyun Sung
- National Museum of Marine Biology and Aquarium, Pingtung 944, Taiwan.
- Chinese Medicine Research and Development Center, China Medical University Hospital, Taichung 404, Taiwan.
- Graduate Institute of Natural Products, Kaohsiung Medical University, Kaohsiung 807, Taiwan.
| | - Zhi-Hong Wen
- Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung 804, Taiwan.
- Doctoral Degree Program in Marine Biotechnology, National Sun Yat-Sen University and Academia Sinica, Kaohsiung 804, Taiwan.
| | - Chih-Hsueng Hsu
- Division of Cardiology, Tri-Service General Hospital, National Defense Medical Center, Taipei 114, Taiwan.
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Kanaporis G, Blatter LA. Ca(2+)-activated chloride channel activity during Ca(2+) alternans in ventricular myocytes. Channels (Austin) 2016; 10:507-17. [PMID: 27356267 DOI: 10.1080/19336950.2016.1207020] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Cardiac alternans, defined beat-to-beat alternations in contraction, action potential (AP) morphology or cytosolic Ca transient (CaT) amplitude, is a high risk indicator for cardiac arrhythmias. We investigated mechanisms of cardiac alternans in single rabbit ventricular myocytes. CaTs were monitored simultaneously with membrane currents or APs recorded with the patch clamp technique. A strong correlation between beat-to-beat alternations of AP morphology and CaT alternans was observed. During CaT alternans application of voltage clamp protocols in form of pre-recorded APs revealed a prominent Ca(2+)-dependent membrane current consisting of a large outward component coinciding with AP phases 1 and 2, followed by an inward current during AP repolarization. Approximately 85% of the initial outward current was blocked by Cl(-) channel blocker DIDS or lowering external Cl(-) concentration identifying it as a Ca(2+)-activated Cl(-) current (ICaCC). The data suggest that ICaCC plays a critical role in shaping beat-to-beat alternations in AP morphology during alternans.
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Affiliation(s)
- Giedrius Kanaporis
- a Department of Molecular Biophysics and Physiology , Rush University Medical Center , Chicago , IL , USA
| | - Lothar A Blatter
- a Department of Molecular Biophysics and Physiology , Rush University Medical Center , Chicago , IL , USA
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7
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Abstract
The QT interval reflects the time between the depolarization of ventricles until their repolarization and is usually used as a predictive marker for the occurrence of arrhythmias. This parameter varies with the heart rate, expressed as the RR interval (time between two successive ventricular depolarizations). To calculate the QT independently of the RR, correction formulae are currently used. In mice, the QT-RR relationship as such has never been studied in conscious animals, and correction formulas are mainly empirical. In the present paper we studied how QT varies when the RR changes physiologically (comparison of nocturnal and diurnal periods) or after dosing mice with tachycardic agents (norepinephrine or nitroprusside). Our results show that there is significant variability of QT and RR in a given condition, resulting in the need to average at least 200 consecutive complexes to accurately compare the QT. Even following this method, no obvious shortening of the QT was observed with increased heart rate, regardless of whether or not this change occurs abruptly. In conclusion, the relationship between QT and RR in mice is weak, which renders the use of correction formulae inappropriate and misleading in this species.
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8
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Kanaporis G, Blatter LA. Calcium-activated chloride current determines action potential morphology during calcium alternans in atrial myocytes. J Physiol 2016; 594:699-714. [PMID: 26662365 DOI: 10.1113/jp271887] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Accepted: 12/05/2015] [Indexed: 01/16/2023] Open
Abstract
KEY POINTS Cardiac alternans--periodic beat-to-beat alternations in contraction, action potential (AP) morphology or cytosolic calcium transient (CaT) amplitude--is a high risk indicator for cardiac arrhythmias and sudden cardiac death. However, it remains an unresolved issue whether beat-to-beat alternations in intracellular Ca(2+) ([Ca(2+)]i ) or AP morphology are the primary cause of pro-arrhythmic alternans. Here we show that in atria AP alternans occurs secondary to CaT alternans. CaT alternans leads to complex beat-to-beat changes in Ca(2+)-regulated ion currents that determine alternans of AP morphology. We report the novel finding that alternans of AP morphology is largely sustained by the activity of Ca(2+)-activated Cl(-) channels (CaCCs). Suppression of the CaCCs significantly reduces AP alternans, while CaT alternans remains unaffected. The demonstration of a major role of CaCCs in the development of AP alternans opens new possibilities for atrial alternans and arrhythmia prevention. Cardiac alternans, described as periodic beat-to-beat alternations in contraction, action potential (AP) morphology or cytosolic Ca transient (CaT) amplitude, is a high risk indicator for cardiac arrhythmias and sudden cardiac death. We investigated mechanisms of cardiac alternans in single rabbit atrial myocytes. CaTs were monitored simultaneously with membrane currents or APs recorded with the patch clamp technique. Beat-to-beat alternations of AP morphology and CaT amplitude revealed a strong quantitative correlation. Application of voltage clamp protocols in the form of pre-recorded APs (AP-clamp) during pacing-induced CaT alternans revealed a Ca(2+)-dependent current consisting of a large outward component (4.78 ± 0.58 pA pF(-1) in amplitude) coinciding with AP phases 1 and 2 that was followed by an inward current (-0.42 ± 0.03 pA pF(-1); n = 21) during AP repolarization. Approximately 90% of the initial outward current was blocked by substitution of Cl(-) ions or application of the Cl(-) channel blocker DIDS identifying it as a Ca(2+)-activated Cl(-) current (ICaCC). The prominent AP prolongation at action potential duration at 30% repolarization level during the small alternans CaT was due to reduced ICaCC. Inhibition of Cl(-) currents abolished AP alternans, but failed to affect CaT alternans, indicating that disturbances in Ca(2+) signalling were the primary event leading to alternans, and ICaCC played a decisive role in shaping the beat-to-beat alternations in AP morphology observed during alternans.
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Affiliation(s)
- Giedrius Kanaporis
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL, 60612, USA
| | - Lothar A Blatter
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, IL, 60612, USA
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9
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Nguyen TP, Singh N, Xie Y, Qu Z, Weiss JN. Repolarization reserve evolves dynamically during the cardiac action potential: effects of transient outward currents on early afterdepolarizations. Circ Arrhythm Electrophysiol 2015; 8:694-702. [PMID: 25772542 DOI: 10.1161/circep.114.002451] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 02/20/2015] [Indexed: 11/16/2022]
Abstract
BACKGROUND Transient outward K currents (Ito) have been reported both to suppress and to facilitate early afterdepolarizations (EADs) when repolarization reserve is reduced. Here, we used the dynamic clamp technique to analyze how Ito accounts for these paradoxical effects on EADs by influencing the dynamic evolution of repolarization reserve during the action potential. METHODS AND RESULTS Isolated patch-clamped rabbit ventricular myocytes were exposed to either oxidative stress (H2O2) or hypokalemia to induce bradycardia-dependent EADs at a long pacing cycle length of 6 s, when native rabbit Ito is substantial. EADs disappeared when the pacing cycle length was shortened to 1 s, when Ito becomes negligible because of incomplete recovery from inactivation. During 6-s pacing cycle length, EADs were blocked by the Ito blocker 4-aminopyridine, but reappeared when a virtual current with appropriate Ito-like properties was reintroduced using the dynamic clamp (n=141 trials). During 1-s pacing cycle length in the absence of 4-aminopyridine, adding a virtual Ito-like current (n=1113 trials) caused EADs to reappear over a wide range of Ito conductance (0.005-0.15 nS/pF), particularly when inactivation kinetics were slow (τinact≥20 ms) and the pedestal (noninactivating component) was small (<25% of peak Ito). Faster inactivation or larger pedestals tended to suppress EADs. CONCLUSIONS Repolarization reserve evolves dynamically during the cardiac action potential. Whereas sufficiently large Ito can suppress EADs, a wide range of intermediate Ito properties can promote EADs by influencing the temporal evolution of other currents affecting late repolarization reserve. These findings raise caution in targeting Ito as an antiarrhythmic strategy.
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Affiliation(s)
- Thao P Nguyen
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles.
| | - Neha Singh
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
| | - Yuanfang Xie
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
| | - Zhilin Qu
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
| | - James N Weiss
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
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Zhang J, Ho JCY, Chan YC, Lian Q, Siu CW, Tse HF. Overexpression of myocardin induces partial transdifferentiation of human-induced pluripotent stem cell-derived mesenchymal stem cells into cardiomyocytes. Physiol Rep 2014; 2:e00237. [PMID: 24744906 PMCID: PMC3966242 DOI: 10.1002/phy2.237] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Revised: 01/21/2014] [Accepted: 01/26/2014] [Indexed: 12/13/2022] Open
Abstract
Mesenchymal stem cells (MSCs) derived from human‐induced pluripotent stem cells (iPSCs) show superior proliferative capacity and therapeutic potential than those derived from bone marrow (BM). Ectopic expression of myocardin further improved the therapeutic potential of BM‐MSCs in a mouse model of myocardial infarction. The aim was of this study was to assess whether forced myocardin expression in iPSC‐MSCs could further enhance their transdifferentiation to cardiomyocytes and improve their electrophysiological properties for cardiac regeneration. Myocardin was overexpressed in iPSC‐MSCs using viral vectors (adenovirus or lentivirus). The expression of smooth muscle cell and cardiomyocyte markers, and ion channel genes was examined by reverse transcription‐polymerase chain reaction (RT‐PCR), immunofluorescence staining and patch clamp. The conduction velocity of the neonatal rat ventricular cardiomyocytes cocultured with iPSC‐MSC monolayer was measured by multielectrode arrays recording plate. Myocardin induced the expression of α‐MHC, GATA4, α‐actinin, cardiac MHC, MYH11, calponin, and SM α‐actin, but not cTnT, β‐MHC, and MLC2v in iPSC‐MSCs. Overexpression of myocardin in iPSC‐MSC enhanced the expression of SCN9A and CACNA1C, but reduced that of KCa3.1 and Kir2.2 in iPSC‐MSCs. Moreover, BKCa, IKir, ICl, Ito and INa.TTX were detected in iPSC‐MSC with myocardin overexpression; while only BKCa, IKir, ICl, IKDR, and IKCa were noted in iPSC‐MSC transfected with green florescence protein. Furthermore, the conduction velocity of iPSC‐MSC was significantly increased after myocardin overexpression. Overexpression of myocardin in iPSC‐MSCs resulted in partial transdifferentiation into cardiomyocytes phenotype and improved the electrical conduction during integration with mature cardiomyocytes. Forced myocardin expression in human‐induced pluripotent stem cell (hiPSC)‐derived mesenchymal stem cells lead to partial transdifferentiation into cardiomyocytes and smooth muscle cells phenotypes through modification in ion channel expression profile and electrical conduction velocity.
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Affiliation(s)
- Jiao Zhang
- Division of Cardiology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China
| | - Jenny Chung-Yee Ho
- Division of Cardiology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China ; Research Centre of Heart, Brain, Hormone & Healthy Aging, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Yau-Chi Chan
- Division of Cardiology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China
| | - Qizhou Lian
- Division of Cardiology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China ; Research Centre of Heart, Brain, Hormone & Healthy Aging, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China ; Department of Ophthalmology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Chung-Wah Siu
- Division of Cardiology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China ; Research Centre of Heart, Brain, Hormone & Healthy Aging, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
| | - Hung-Fat Tse
- Division of Cardiology, Department of Medicine, Queen Mary Hospital, The University of Hong Kong, Hong Kong SAR, China ; Research Centre of Heart, Brain, Hormone & Healthy Aging, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong SAR, China
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11
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Wu HJ, Sun HY, Wu W, Zhang YH, Qin GW, Li GR. Properties and molecular determinants of the natural flavone acacetin for blocking hKv4.3 channels. PLoS One 2013; 8:e57864. [PMID: 23526953 PMCID: PMC3603988 DOI: 10.1371/journal.pone.0057864] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 01/27/2013] [Indexed: 11/20/2022] Open
Abstract
The natural flavone acacetin has been demonstrated to inhibit transient outward potassium current (Ito) in human atrial myocytes. However, the molecular determinants of acacetin for blocking Ito are unknown. The present study was designed to investigate the properties and molecular determinants of this compound for blocking hKv4.3 channels (coding Ito) stably expressed in HEK 293 cells using the approaches of whole-cell patch voltage-clamp technique and mutagenesis. It was found that acacetin inhibited hKv4.3 current by binding to both the closed and open channels, and decreased the recovery from inactivation. The blockade of hKv4.3 channels by acacetin was use- and frequency-dependent, and IC50s of acacetin for inhibiting hKv4.3 were 7.9, 6.1, 3.9, and 3.2 µM, respectively, at 0.2, 0.5, 1, and 3.3 Hz. The mutagenesis study revealed that the hKv4.3 mutants T366A and T367A in the P-loop helix, and V392A, I395A and V399A in the S6-segment had a reduced channel blocking efficacy of acacetin (IC50, 44.5 µM for T366A, 25.8 µM for T367A, 17.6 µM for V392A, 16.2 µM for I395A, and 19.1 µM for V399A). These results demonstrate the novel information that acacetin may inhibit the closed channels and block the open state of the channels by binding to their P-loop filter helix and S6 domain. The use- and rate-dependent blocking of hKv4.3 by acacetin is likely beneficial for managing atrial fibrillation.
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Affiliation(s)
- Hui-Jun Wu
- Department and Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Hai-Ying Sun
- Department and Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Wei Wu
- Department and Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Yan-Hui Zhang
- Department and Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
| | - Guo-Wei Qin
- Shanghai Institute of Materia Medica, Chinese Academy of Science, Shanghai, China
| | - Gui-Rong Li
- Department and Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
- Department of Physiology, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
- * E-mail:
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12
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Xu XH, Sun HY, Zhang YH, Wu W, Chen KH, Liu Y, Deng CY, Yu XY, Jin MW, Li GR. Allitridi inhibits multiple cardiac potassium channels expressed in HEK 293 cells. PLoS One 2012; 7:e51550. [PMID: 23272117 PMCID: PMC3522701 DOI: 10.1371/journal.pone.0051550] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2012] [Accepted: 11/02/2012] [Indexed: 02/02/2023] Open
Abstract
Allitridi (diallyl trisulfide) is an active compound (volatile oil) from garlic. The previous studies reported that allitridi had anti-arrhythmic effect. The potential ionic mechanisms are, however, not understood. The present study was designed to determine the effects of allitridi on cardiac potassium channels expressed in HEK 293 cells using a whole-cell patch voltage-clamp technique and mutagenesis. It was found that allitridi inhibited hKv4.3 channels (IC50 = 11.4 µM) by binding to the open channel, shifting availability potential to hyperpolarization, and accelerating closed-state inactivation of the channel. The hKv4.3 mutants T366A, T367A, V392A, and I395A showed a reduced response to allitridi with IC50s of 35.5 µM, 44.7 µM, 23.7 µM, and 42.4 µM. In addition, allitridi decreased hKv1.5, hERG, hKCNQ1/hKCNE1 channels stably expressed in HEK 293 cells with IC50s of 40.2 µM, 19.6 µM and 17.7 µM. However, it slightly inhibited hKir2.1 current (100 µM, inhibited by 9.8% at −120 mV). Our results demonstrate for the first time that allitridi preferably blocks hKv4.3 current by binding to the open channel at T366 and T367 of P-loop helix, and at V392 and I395 of S6 domain. It has a weak inhibition of hKv1.5, hERG, and hKCNQ1/hKCNE1 currents. These effects may account for its anti-arrhythmic effect observed in experimental animal models.
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Affiliation(s)
- Xiao-Hui Xu
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Hai-Ying Sun
- Department of Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
| | - Yan-Hui Zhang
- Department of Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
| | - Wei Wu
- Department of Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
| | - Kui-Hao Chen
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Yi Liu
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Chun-Yu Deng
- Research Centre, Guangdong General Hospital, Guangzhou, China
| | - Xi-Yong Yu
- Research Centre, Guangdong General Hospital, Guangzhou, China
| | - Man-Wen Jin
- Department of Pharmacology, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- * E-mail: (GRL); (MWJ)
| | - Gui-Rong Li
- Department of Medicine, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
- Department of Physiology, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
- * E-mail: (GRL); (MWJ)
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Zhang YH, Sun HY, Chen KH, Du XL, Liu B, Cheng LC, Li X, Jin MW, Li GR. Evidence for functional expression of TRPM7 channels in human atrial myocytes. Basic Res Cardiol 2012; 107:282. [PMID: 22802050 PMCID: PMC3442166 DOI: 10.1007/s00395-012-0282-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/14/2011] [Revised: 06/15/2012] [Accepted: 07/05/2012] [Indexed: 12/16/2022]
Abstract
Transient receptor potential melastatin-7 (TRPM7) channels have been recently reported in human atrial fibroblasts and are believed to mediate fibrogenesis in human atrial fibrillation. The present study investigates whether TRPM7 channels are expressed in human atrial myocytes using whole-cell patch voltage-clamp, RT-PCR and Western blotting analysis. It was found that a gradually activated TRPM7-like current was recorded with a K+- and Mg2+-free pipette solution in human atrial myocytes. The current was enhanced by removing extracellular Ca2+ and Mg2+, and the current increase could be inhibited by Ni2+ or Ba2+. The TRPM7-like current was potentiated by acidic pH and inhibited by La3+ and 2-aminoethoxydiphenyl borate. In addition, Ca2+-activated TRPM4-like current was recorded in human atrial myocytes with the addition of the Ca2+ ionophore A23187 in bath solution. RT-PCR and Western immunoblot analysis revealed that in addition to TRPM4, TRPM7 channel current, mRNA and protein expression were evident in human atrial myocytes. Interestingly, TRPM7 channel protein, but not TRPM4 channel protein, was significantly increased in human atrial specimens from the patients with atrial fibrillation. Our results demonstrate for the first time that functional TRPM7 channels are present in human atrial myocytes, and the channel expression is upregulated in the atria with atrial fibrillation.
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Affiliation(s)
- Yan-Hui Zhang
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong, China
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14
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Zhang YH, Wu W, Sun HY, Deng XL, Cheng LC, Li X, Tse HF, Lau CP, Li GR. Modulation of human cardiac transient outward potassium current by EGFR tyrosine kinase and Src-family kinases. Cardiovasc Res 2011; 93:424-33. [PMID: 22198508 DOI: 10.1093/cvr/cvr347] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
AIMS The human cardiac transient outward K(+) current I(to) (encoded by Kv4.3 or KCND3) plays an important role in phase 1 rapid repolarization of cardiac action potentials in the heart. However, modulation of I(to) by intracellular signal transduction is not fully understood. The present study was therefore designed to determine whether/how human atrial I(to) and hKv4.3 channels stably expressed in HEK 293 cells are regulated by protein tyrosine kinases (PTKs). METHODS AND RESULTS Whole-cell patch voltage-clamp, immunoprecipitation, western blotting, and site-directed mutagenesis approaches were employed in the present study. We found that human atrial I(to) was inhibited by the broad-spectrum PTK inhibitor genistein, the selective epidermal growth factor receptor (EGFR) kinase inhibitor AG556, and the Src-family kinases inhibitor PP2. The inhibitory effect was countered by the protein tyrosine phosphatase inhibitor orthovanadate. In HEK 293 cells stably expressing human KCND3, genistein, AG556, and PP2 significantly reduced the hKv4.3 current, and the reduction was antagonized by orthovanadate. Interestingly, orthovanadate also reversed the reduced tyrosine phosphorylation level of hKv4.3 channels by genistein, AG556, or PP2. Mutagenesis revealed that the hKv4.3 mutant Y136F lost the inhibitory response to AG556, while Y108F lost response to PP2. The double-mutant Y108F-Y136F hKv4.3 channels showed no response to either AG556 or PP2. CONCLUSION Our results demonstrate that human atrial I(to) and cloned hKv4.3 channels are modulated by EGFR kinase via phosphorylation of the Y136 residue and by Src-family kinases via phosphorylation of the Y108 residue; tyrosine phosphorylation of the channel may be involved in regulating cardiac electrophysiology.
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Affiliation(s)
- Yan-Hui Zhang
- Department of Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, L4-59, Laboratory Block, FMB, 21 Sassoon Road, Pokfulam, Hong Kong, China
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15
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Li GR, Dong MQ. Pharmacology of Cardiac Potassium Channels. CARDIOVASCULAR PHARMACOLOGY - HEART AND CIRCULATION 2010; 59:93-134. [DOI: 10.1016/s1054-3589(10)59004-5] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
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16
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Li GR, Sun HY, Chen JB, Zhou Y, Tse HF, Lau CP. Characterization of multiple ion channels in cultured human cardiac fibroblasts. PLoS One 2009; 4:e7307. [PMID: 19806193 PMCID: PMC2751830 DOI: 10.1371/journal.pone.0007307] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2009] [Accepted: 09/14/2009] [Indexed: 01/11/2023] Open
Abstract
Background Although fibroblast-to-myocyte electrical coupling is experimentally suggested, electrophysiology of cardiac fibroblasts is not as well established as contractile cardiac myocytes. The present study was therefore designed to characterize ion channels in cultured human cardiac fibroblasts. Methods and Findings A whole-cell patch voltage clamp technique and RT-PCR were employed to determine ion channels expression and their molecular identities. We found that multiple ion channels were heterogeneously expressed in human cardiac fibroblasts. These include a big conductance Ca2+-activated K+ current (BKCa) in most (88%) human cardiac fibroblasts, a delayed rectifier K+ current (IKDR) and a transient outward K+ current (Ito) in a small population (15 and 14%, respectively) of cells, an inwardly-rectifying K+ current (IKir) in 24% of cells, and a chloride current (ICl) in 7% of cells under isotonic conditions. In addition, two types of voltage-gated Na+ currents (INa) with distinct properties were present in most (61%) human cardiac fibroblasts. One was a slowly inactivated current with a persistent component, sensitive to tetrodotoxin (TTX) inhibition (INa.TTX, IC50 = 7.8 nM), the other was a rapidly inactivated current, relatively resistant to TTX (INa.TTXR, IC50 = 1.8 µM). RT-PCR revealed the molecular identities (mRNAs) of these ion channels in human cardiac fibroblasts, including KCa.1.1 (responsible for BKCa), Kv1.5, Kv1.6 (responsible for IKDR), Kv4.2, Kv4.3 (responsible for Ito), Kir2.1, Kir2.3 (for IKir), Clnc3 (for ICl), NaV1.2, NaV1.3, NaV1.6, NaV1.7 (for INa.TTX), and NaV1.5 (for INa.TTXR). Conclusions These results provide the first information that multiple ion channels are present in cultured human cardiac fibroblasts, and suggest the potential contribution of these ion channels to fibroblast-myocytes electrical coupling.
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Affiliation(s)
- Gui-Rong Li
- Department of Medicine and Research Centre of Heart, Brain, Hormone and Healthy Aging, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China.
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Zhang DY, Lau CP, Li GR. Human Kir2.1 channel carries a transient outward potassium current with inward rectification. Pflugers Arch 2008; 457:1275-85. [PMID: 19002489 DOI: 10.1007/s00424-008-0608-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2008] [Accepted: 10/22/2008] [Indexed: 11/27/2022]
Abstract
We have previously reported a depolarization-activated 4-aminopyridine-resistant transient outward K(+) current with inward rectification (I (to.ir)) in canine and guinea pig cardiac myocytes. However, molecular identity of this current is not clear. The present study was designed to investigate whether Kir2.1 channel carries this current in stably transfected human embryonic kidney (HEK) 293 cells using whole-cell patch-clamp technique. It was found that HEK 293 cells stably expressing human Kir2.1 gene had a transient outward current elicited by voltage steps positive to the membrane potential (around -70 mV). The current exhibited a current-voltage relationship with intermediate inward rectification and showed time-dependent inactivation and rapid recovery from inactivation. The half potential (V (0.5)) of availability of the current was -49.4 +/- 2.1 mV at 5 mM K(+) in bath solution. Action potential waveform clamp revealed two components of outward currents; one was immediately elicited and then rapidly inactivated during depolarization, and another was slowly activated during repolarization of action potential. These properties were similar to those of I (to.ir) observed previously in native cardiac myocytes. Interestingly, inactivation of the I (to.ir) was strongly slowed by increasing intracellular free Mg(2+) (Mg(2+) ( i ), from 0.03 to 1.0, 4.0, and 8.0 mM). The component elicited by action potential depolarization increased with the elevation of Mg(2+) ( i ). Inclusion of spermine (100 muM) in the pipette solution remarkably inhibited both the I (to.ir) and steady-state current. These results demonstrate that the Mg(2+) ( i )-dependent current carried by Kir2.1 likely is the molecular identity of I (to.ir) observed previously in cardiac myocytes.
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Affiliation(s)
- De-Yong Zhang
- Department of Medicine and Research Centre of Heart, Brain, Hormone and Healthy Aging, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
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Abstract
Triggered activity in cardiac muscle and intracellular Ca2+ have been linked in the past. However, today not only are there a number of cellular proteins that show clear Ca2+ dependence but also there are a number of arrhythmias whose mechanism appears to be linked to Ca2+-dependent processes. Thus we present a systematic review of the mechanisms of Ca2+ transport (forward excitation-contraction coupling) in the ventricular cell as well as what is known for other cardiac cell types. Second, we review the molecular nature of the proteins that are involved in this process as well as the functional consequences of both normal and abnormal Ca2+ cycling (e.g., Ca2+ waves). Finally, we review what we understand to be the role of Ca2+ cycling in various forms of arrhythmias, that is, those associated with inherited mutations and those that are acquired and resulting from reentrant excitation and/or abnormal impulse generation (e.g., triggered activity). Further solving the nature of these intricate and dynamic interactions promises to be an important area of research for a better recognition and understanding of the nature of Ca2+ and arrhythmias. Our solutions will provide a more complete understanding of the molecular basis for the targeted control of cellular calcium in the treatment and prevention of such.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Medicine, Physiology and Biophysics, University of Calgary, Alberta, Canada
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Choi BH, Park JA, Kim KR, Lee GI, Lee YT, Choe H, Ko SH, Kim MH, Seo YH, Kwak YG. Direct block of cloned hKv1.5 channel by cytochalasins, actin-disrupting agents. Am J Physiol Cell Physiol 2005; 289:C425-36. [PMID: 15800051 DOI: 10.1152/ajpcell.00450.2004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The action of cytochalasins, actin-disrupting agents on human Kv1.5 channel (hKv1.5) stably expressed in Ltk−cells was investigated using the whole cell patch-clamp technique. Cytochalasin B inhibited hKv1.5 currents rapidly and reversibly at +60 mV in a concentration-dependent manner with an IC50of 4.2 μM. Cytochalasin A, which has a structure very similar to cytochalasin B, inhibited hKv1.5 (IC50of 1.4 μM at +60 mV). Pretreatment with other actin filament disruptors cytochalasin D and cytochalasin J, and an actin filament stabilizing agent phalloidin had no effect on the cytochalasin B-induced inhibition of hKv1.5 currents. Cytochalasin B accelerated the decay rate of inactivation for the hKv1.5 currents. Cytochalasin B-induced inhibition of the hKv1.5 channels was voltage dependent with a steep increase over the voltage range of the channel's opening. However, the inhibition exhibited voltage independence over the voltage range in which channels are fully activated. Cytochalasin B produced no significant effect on the steady-state activation or inactivation curves. The rate constants for association and dissociation of cytochalasin B were 3.7 μM/s and 7.5 s−1, respectively. Cytochalasin B produced a use-dependent inhibition of hKv1.5 current that was consistent with the slow recovery from inactivation in the presence of the drug. Cytochalasin B (10 μM) also inhibited an ultrarapid delayed rectifier K+current ( IK,ur) in human atrial myocytes. These results indicate that cytochalasin B primarily blocks activated hKv1.5 channels and endogenous IK,urin a cytoskeleton-independent manner as an open-channel blocker.
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Affiliation(s)
- Bok Hee Choi
- Department of Pharmacology, Chonbuk National University Medical School, Chonju, Chonbuk 561-180, Republic of Korea
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Gao Z, Sun H, Chiu SW, Lau CP, Li GR. Effects of diltiazem and nifedipine on transient outward and ultra-rapid delayed rectifier potassium currents in human atrial myocytes. Br J Pharmacol 2005; 144:595-604. [PMID: 15678082 PMCID: PMC1576039 DOI: 10.1038/sj.bjp.0706113] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. It is unknown whether the widely used L-type Ca(2+) channel antagonists diltiazem and nifedipine would block the repolarization K(+) currents, transient outward current (I(to1)) and ultra-rapid delayed rectifier K(+) current (I(Kur)), in human atrium. The present study was to determine the effects of diltiazem and nifedipine on I(to1) and I(Kur) in human atrial myocytes with whole-cell patch-clamp technique. 2. It was found that diltiazem substantially inhibited I(to1) in a concentration-dependent manner, with an IC(50) of 29.2+/-2.4 microM, and nifedipine showed a similar effect (IC(50)=26.8+/-2.1 muM). The two drugs had no effect on voltage-dependent kinetics of the current; however, they accelerated I(to1) inactivation significantly, suggesting an open channel block. 3. In addition, diltiazem and nifedipine suppressed I(Kur) in a concentration-dependent manner (at +50 mV, IC(50)=11.2+/-0.9 and 8.2+/-0.8 microM, respectively). These results indicate that the Ca(2+) channel blockers diltiazem and nifedipine substantially inhibit I(to1) and I(Kur) in human atrial myocytes.
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Affiliation(s)
- Zhan Gao
- Department of Medicine and Research Centre of Heart, Brain, Hormone and Health Aging, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
| | - Haiying Sun
- Department of Medicine and Research Centre of Heart, Brain, Hormone and Health Aging, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
| | - Shui-Wah Chiu
- Cardiothoracic Unit, Faculty of Medicine, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
| | - Chu-Pak Lau
- Department of Medicine and Research Centre of Heart, Brain, Hormone and Health Aging, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
| | - Gui-Rong Li
- Department of Medicine and Research Centre of Heart, Brain, Hormone and Health Aging, The University of Hong Kong, Pokfulam, Hong Kong SAR, China
- Author for correspondence:
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Xu Y, Dong PH, Zhang Z, Ahmmed GU, Chiamvimonvat N. Presence of a calcium-activated chloride current in mouse ventricular myocytes. Am J Physiol Heart Circ Physiol 2002; 283:H302-14. [PMID: 12063303 DOI: 10.1152/ajpheart.00044.2002] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The properties of several components of outward K(+) currents, including the pharmacological and kinetics profiles as well as the respective molecular correlates, have been identified in mouse cardiac myocytes. Surprisingly little is known with regard to the Ca(2+)-activated ionic currents. We studied the Ca(2+)-activated transient outward currents in mouse ventricular myocytes. We have identified a 4-aminopyridine (4-AP)- and tetraethyl ammonium-resistant transient outward current that is Ca(2+) dependent. The current is carried by Cl(-) and is critically dependent on Ca(2+) influx via voltage-gated Ca(2+) channels and the sarcoplasmic reticulum Ca(2+) store. The current can be blocked by the anion transport blockers niflumic acid and 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid. Single channel recordings reveal small conductance channels (approximately 1 pS in 140 mM Cl(-)) that can be blocked by anion transport blockers. Ensemble-averaged current faithfully mirrors the transient kinetics observed at the whole level. Niflumic acid (in the presence of 4-AP) leads to prolongation of the early repolarization. Thus this current may contribute to early repolarization of action potentials in mouse ventricular myocytes.
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Affiliation(s)
- Yanfang Xu
- Division of Cardiovascular Medicine, Department of Medicine, University of California, Davis, California 95616, USA
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Li GR, Zhang M, Satin LS, Baumgarten CM. Biphasic effects of cell volume on excitation-contraction coupling in rabbit ventricular myocytes. Am J Physiol Heart Circ Physiol 2002; 282:H1270-7. [PMID: 11893561 DOI: 10.1152/ajpheart.00946.2001] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We studied the effects of osmotic swelling on the components of excitation-contraction coupling in ventricular myocytes. Myocyte volume rapidly increased 30% in hyposmotic (0.6T) solution and was constant thereafter. Cell shortening transiently increased 31% after 4 min in 0.6T but then decreased to 68% of control after 20 min. In parallel, the L-type Ca(2+) current (I(Ca-L)) transiently increased 10% and then declined to 70% of control. Similar biphasic effects on shortening were observed under current clamp. In contrast, action potential duration was unchanged at 4 min but decreased to 72% of control after 20 min. Ca(2+) transients were measured with fura 2-AM. The emission ratio with excitation at 340 and 380 nm (f(340)/f(380)) decreased by 12% after 3 min in 0.6T, whereas shortening and I(Ca-L) increased at the same time. After 8 min, shortening, I(Ca-L), and the f(340)/f(380) ratio decreased 28, 25, and 59%, respectively. The results suggest that osmotic swelling causes biphasic changes in I(Ca-L) that contribute to its biphasic effects on contraction. In addition, swelling initially appears to reduce the Ca(2+) transient initiated by a given I(Ca-L), and later, both I(Ca-L) and the Ca(2+) transient are inhibited.
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Affiliation(s)
- Gui-Rong Li
- Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298, USA
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Li GR, Baumgarten CM. Modulation of cardiac Na(+) current by gadolinium, a blocker of stretch-induced arrhythmias. Am J Physiol Heart Circ Physiol 2001; 280:H272-9. [PMID: 11123242 DOI: 10.1152/ajpheart.2001.280.1.h272] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gd(3+) blocks stretch-activated channels and suppresses stretch-induced arrhythmias. We used whole cell voltage clamp to examine whether effects on Na(+) channels might contribute to the antiarrhythmic efficacy of Gd(3+). Gd(3+) inhibited Na(+) current (I(Na)) in rabbit ventricle (IC(50) = 48 microM at -35 mV, holding potential -120 mV), and block increased at more negative test potentials. Gd(3+) made the threshold for I(Na) more positive and reduced the maximum conductance. Gd(3+) (50 microM) shifted the midpoints for activation and inactivation of I(Na) 7.9 and 5.7 mV positive but did not alter the slope factor for either relationship. Activation and inactivation kinetics were slowed in a manner that could not be explained solely by altered surface potential. Paradoxically, Gd(3+) increased I(Na) under certain conditions. With membrane potential held at -75 mV, Gd(3+) still shifted threshold for activation positive, but I(Na) increased positive to -40 mV, causing the current-voltage curves to cross over. When availability initially was low, increased availability induced by Gd(3+) dominated the response at test potentials positive to -40 mV. The results indicate that Gd(3+) has complex effects on cardiac Na(+) channels. Independent of holding potential, Gd(3+) is a potent I(Na) blocker near threshold potential, and inhibition of I(Na) by Gd(3+) is likely to contribute to suppression of stretch-induced arrhythmias.
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Affiliation(s)
- G R Li
- Department of Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, Virginia 23298-0551, USA
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