1
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Wolfson DW, Kim NK, Lee KH, Beyersdorf JP, Langberg JJ, Fernandez N, Choi D, Zureick N, Kim TY, Bae S, Gu JM, Kirschman JL, Fan J, Sheng CY, Gottlieb Sen D, Mettler B, Sung JH, Yoon YS, Park SJ, Santangelo PJ, Cho HC. Transient pacing in pigs with complete heart block via myocardial injection of mRNA coding for the T-box transcription factor 18. Nat Biomed Eng 2024:10.1038/s41551-024-01211-9. [PMID: 38698155 DOI: 10.1038/s41551-024-01211-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Accepted: 04/02/2024] [Indexed: 05/05/2024]
Abstract
The adenovirus-mediated somatic transfer of the embryonic T-box transcription factor 18 (TBX18) gene can convert chamber cardiomyocytes into induced pacemaker cells. However, the translation of therapeutic TBX18-induced cardiac pacing faces safety challenges. Here we show that the myocardial expression of synthetic TBX18 mRNA in animals generates de novo pacing and limits innate and inflammatory immune responses. In rats, intramyocardially injected mRNA remained localized, whereas direct myocardial injection of an adenovirus carrying a reporter gene resulted in diffuse expression and in substantial spillover to the liver, spleen and lungs. Transient expression of TBX18 mRNA in rats led to de novo automaticity and pacemaker properties and, compared with the injection of adenovirus, to substantial reductions in the expression of inflammatory genes and in activated macrophage populations. In rodent and clinically relevant porcine models of complete heart block, intramyocardially injected TBX18 mRNA provided rate-adaptive cardiac pacing for one month that strongly correlated with the animal's sinus rhythm and physical activity. TBX18 mRNA may aid the development of biological pacemakers.
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Affiliation(s)
- David W Wolfson
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Nam Kyun Kim
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
| | - Ki Hong Lee
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
- Chonnam National University Medical School, Gwangju, South Korea
| | - Jared P Beyersdorf
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Jonathan J Langberg
- Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA
| | - Natasha Fernandez
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
| | - Dahim Choi
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Nadine Zureick
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Tae Yun Kim
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
| | - Seongho Bae
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
- Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA
| | - Jin-Mo Gu
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
| | - Jonathan L Kirschman
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Jinqi Fan
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA
- Division of Pediatric Cardiac Surgery, Department of Surgery, Johns Hopkins School of Medicine, Baltimore, MD, USA
| | - Christina Y Sheng
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Danielle Gottlieb Sen
- Division of Pediatric Cardiac Surgery, Department of Surgery, Johns Hopkins School of Medicine, Baltimore, MD, USA
| | - Bret Mettler
- Division of Pediatric Cardiac Surgery, Department of Surgery, Johns Hopkins School of Medicine, Baltimore, MD, USA
| | - Jung Hoon Sung
- Department of Cardiology, CHA Bundang Medical Center, CHA University, Seongnam, South Korea
| | - Young-Sup Yoon
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
- Division of Cardiology, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA
| | - Sung-Jin Park
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA
| | - Philip J Santangelo
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA.
| | - Hee Cheol Cho
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta, GA, USA.
- Department of Pediatrics, Emory University School of Medicine, Atlanta, GA, USA.
- Division of Pediatric Cardiac Surgery, Department of Surgery, Johns Hopkins School of Medicine, Baltimore, MD, USA.
- Blalock-Taussig-Thomas Pediatric and Congenital Heart Center, The Johns Hopkins Children's Center, Baltimore, MD, USA.
- Department of Biomedical Engineering, Johns Hopkins Whiting School of Engineering, Baltimore, MD, USA.
- Department of Anesthesia and Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, MD, USA.
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2
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Liu CM, Chen YC, Hu YF. Harnessing cell reprogramming for cardiac biological pacing. J Biomed Sci 2023; 30:74. [PMID: 37633890 PMCID: PMC10463311 DOI: 10.1186/s12929-023-00970-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2023] [Accepted: 08/22/2023] [Indexed: 08/28/2023] Open
Abstract
Electrical impulses from cardiac pacemaker cardiomyocytes initiate cardiac contraction and blood pumping and maintain life. Abnormal electrical impulses bring patients with low heart rates to cardiac arrest. The current therapy is to implant electronic devices to generate backup electricity. However, complications inherent to electronic devices remain unbearable suffering. Therefore, cardiac biological pacing has been developed as a hardware-free alternative. The approaches to generating biological pacing have evolved recently using cell reprogramming technology to generate pacemaker cardiomyocytes in-vivo or in-vitro. Different from conventional methods by electrical re-engineering, reprogramming-based biological pacing recapitulates various phenotypes of de novo pacemaker cardiomyocytes and is more physiological, efficient, and easy for clinical implementation. This article reviews the present state of the art in reprogramming-based biological pacing. We begin with the rationale for this new approach and review its advances in creating a biological pacemaker to treat bradyarrhythmia.
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Affiliation(s)
- Chih-Min Liu
- Division of Cardiology, Department of Medicine, Heart Rhythm Center, Taipei Veterans General Hospital, Taipei, Taiwan
- Faculty of Medicine and Institute of Clinical Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Yi-Chun Chen
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan
- Institute of Biopharmaceutical Sciences, College of Pharmaceutical Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan
| | - Yu-Feng Hu
- Division of Cardiology, Department of Medicine, Heart Rhythm Center, Taipei Veterans General Hospital, Taipei, Taiwan.
- Faculty of Medicine and Institute of Clinical Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan.
- Institute of Biomedical Sciences, Academia Sinica, Taipei, Taiwan.
- Institute of Biopharmaceutical Sciences, College of Pharmaceutical Sciences, National Yang Ming Chiao Tung University, Taipei, Taiwan.
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3
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Yang D, Deschênes I, Fu JD. Multilayer control of cardiac electrophysiology by microRNAs. J Mol Cell Cardiol 2022; 166:107-115. [PMID: 35247375 PMCID: PMC9035102 DOI: 10.1016/j.yjmcc.2022.02.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/22/2021] [Revised: 02/22/2022] [Accepted: 02/26/2022] [Indexed: 10/18/2022]
Abstract
The electrophysiological properties of the heart include cardiac automaticity, excitation (i.e., depolarization and repolarization of action potential) of individual cardiomyocytes, and highly coordinated electrical propagation through the whole heart. An abnormality in any of these properties can cause arrhythmias. MicroRNAs (miRs) have been recognized as essential regulators of gene expression through the conventional RNA interference (RNAi) mechanism and are involved in a variety of biological events. Recent evidence has demonstrated that miRs regulate the electrophysiology of the heart through fine regulation by the conventional RNAi mechanism of the expression of ion channels, transporters, intracellular Ca2+-handling proteins, and other relevant factors. Recently, a direct interaction between miRs and ion channels has also been reported in the heart, revealing a biophysical modulation by miRs of cardiac electrophysiology. These advanced discoveries suggest that miR controls cardiac electrophysiology through two distinct mechanisms: immediate action through biophysical modulation and long-term conventional RNAi regulation. Here, we review the recent research progress and summarize the current understanding of how miR manipulates the function of ion channels to maintain the homeostasis of cardiac electrophysiology.
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Affiliation(s)
- Dandan Yang
- The Dorothy M. Davis Heart and Lung Research Institute, Frick Center for Heart Failure and Arrhythmia, Department of Physiology and Cell Biology, The Ohio State University, 333 W. 10(th) Avenue, Columbus, OH 43210, USA
| | - Isabelle Deschênes
- The Dorothy M. Davis Heart and Lung Research Institute, Frick Center for Heart Failure and Arrhythmia, Department of Physiology and Cell Biology, The Ohio State University, 333 W. 10(th) Avenue, Columbus, OH 43210, USA
| | - Ji-Dong Fu
- The Dorothy M. Davis Heart and Lung Research Institute, Frick Center for Heart Failure and Arrhythmia, Department of Physiology and Cell Biology, The Ohio State University, 333 W. 10(th) Avenue, Columbus, OH 43210, USA.
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4
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Komosa ER, Wolfson DW, Bressan M, Cho HC, Ogle BM. Implementing Biological Pacemakers: Design Criteria for Successful. Circ Arrhythm Electrophysiol 2021; 14:e009957. [PMID: 34592837 PMCID: PMC8530973 DOI: 10.1161/circep.121.009957] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Each heartbeat that pumps blood throughout the body is initiated by an electrical impulse generated in the sinoatrial node (SAN). However, a number of disease conditions can hamper the ability of the SAN's pacemaker cells to generate consistent action potentials and maintain an orderly conduction path, leading to arrhythmias. For symptomatic patients, current treatments rely on implantation of an electronic pacing device. However, complications inherent to the indwelling hardware give pause to categorical use of device therapy for a subset of populations, including pediatric patients or those with temporary pacing needs. Cellular-based biological pacemakers, derived in vitro or in situ, could function as a therapeutic alternative to current electronic pacemakers. Understanding how biological pacemakers measure up to the SAN would facilitate defining and demonstrating its advantages over current treatments. In this review, we discuss recent approaches to creating biological pacemakers and delineate design criteria to guide future progress based on insights from basic biology of the SAN. We emphasize the need for long-term efficacy in vivo via maintenance of relevant proteins, source-sink balance, a niche reflective of the native SAN microenvironment, and chronotropic competence. With a focus on such criteria, combined with delivery methods tailored for disease indications, clinical implementation will be attainable.
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Affiliation(s)
- Elizabeth R Komosa
- Department of Biomedical Engineering (E.R.K., B.M.O.), University of Minnesota-Twin Cities, Minneapolis
- Stem Cell Institute (E.R.K., B.M.O.), University of Minnesota-Twin Cities, Minneapolis
| | - David W Wolfson
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta (D.W.W., H.C.C.)
| | - Michael Bressan
- Department of Cell Biology and Physiology (M.B.), University of North Carolina-Chapel Hill
- McAllister Heart Institute (M.B.), University of North Carolina-Chapel Hill
| | - Hee Cheol Cho
- Wallace H. Coulter Department of Biomedical Engineering, Georgia Institute of Technology and Emory University, Atlanta (D.W.W., H.C.C.)
- Department of Pediatrics, Emory University, Atlanta, GA (H.C.C.)
| | - Brenda M Ogle
- Department of Biomedical Engineering (E.R.K., B.M.O.), University of Minnesota-Twin Cities, Minneapolis
- Stem Cell Institute (E.R.K., B.M.O.), University of Minnesota-Twin Cities, Minneapolis
- Department of Pediatrics (B.M.O), University of Minnesota-Twin Cities, Minneapolis
- Lillehei Heart Institute (B.M.O), University of Minnesota-Twin Cities, Minneapolis
- Institute for Engineering in Medicine (B.M.O), University of Minnesota-Twin Cities, Minneapolis
- Masonic Cancer Center (B.M.O), University of Minnesota-Twin Cities, Minneapolis
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5
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Li Y, Wang K, Li Q, Hancox JC, Zhang H. Reciprocal interaction between IK1 and If in biological pacemakers: A simulation study. PLoS Comput Biol 2021; 17:e1008177. [PMID: 33690622 PMCID: PMC7984617 DOI: 10.1371/journal.pcbi.1008177] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Revised: 03/22/2021] [Accepted: 02/17/2021] [Indexed: 11/19/2022] Open
Abstract
Pacemaking dysfunction (PD) may result in heart rhythm disorders, syncope or even death. Current treatment of PD using implanted electronic pacemakers has some limitations, such as finite battery life and the risk of repeated surgery. As such, the biological pacemaker has been proposed as a potential alternative to the electronic pacemaker for PD treatment. Experimentally and computationally, it has been shown that bio-engineered pacemaker cells can be generated from non-rhythmic ventricular myocytes (VMs) by knocking out genes related to the inward rectifier potassium channel current (IK1) or by overexpressing hyperpolarization-activated cyclic nucleotide gated channel genes responsible for the "funny" current (If). However, it is unclear if a bio-engineered pacemaker based on the modification of IK1- and If-related channels simultaneously would enhance the ability and stability of bio-engineered pacemaking action potentials. In this study, the possible mechanism(s) responsible for VMs to generate spontaneous pacemaking activity by regulating IK1 and If density were investigated by a computational approach. Our results showed that there was a reciprocal interaction between IK1 and If in ventricular pacemaker model. The effect of IK1 depression on generating ventricular pacemaker was mono-phasic while that of If augmentation was bi-phasic. A moderate increase of If promoted pacemaking activity but excessive increase of If resulted in a slowdown in the pacemaking rate and even an unstable pacemaking state. The dedicated interplay between IK1 and If in generating stable pacemaking and dysrhythmias was evaluated. Finally, a theoretical analysis in the IK1/If parameter space for generating pacemaking action potentials in different states was provided. In conclusion, to the best of our knowledge, this study provides a wide theoretical insight into understandings for generating stable and robust pacemaker cells from non-pacemaking VMs by the interplay of IK1 and If, which may be helpful in designing engineered biological pacemakers for application purposes.
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Affiliation(s)
- Yacong Li
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
| | - Kuanquan Wang
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
- * E-mail: (KW); (HZ)
| | - Qince Li
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin, China
- Peng Cheng Laboratory, Shenzhen, China
| | - Jules C. Hancox
- School of Physiology, Pharmacology and Neuroscience, Medical Sciences Building, University Walk, Bristol, United Kingdom
- Biological Physics Group, School of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom
| | - Henggui Zhang
- Peng Cheng Laboratory, Shenzhen, China
- Biological Physics Group, School of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom
- Key Laboratory of Medical Electrophysiology of Ministry of Education and Medical Electrophysiological Key Laboratory of Sichuan Province, Institute of Cardiovascular Research, Southwest Medical University, Luzhou, China
- * E-mail: (KW); (HZ)
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6
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Li Y, Wang K, Li Q, Zhang H. Biological pacemaker: from biological experiments to computational simulation. J Zhejiang Univ Sci B 2020; 21:524-536. [PMID: 32633107 DOI: 10.1631/jzus.b1900632] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Pacemaking dysfunction has become a significant disease that may contribute to heart rhythm disorders, syncope, and even death. Up to now, the best way to treat it is to implant electronic pacemakers. However, these have many disadvantages such as limited battery life, infection, and fixed pacing rate. There is an urgent need for a biological pacemaker (bio-pacemaker). This is expected to replace electronic devices because of its low risk of complications and the ability to respond to emotion. Here we survey the contemporary development of the bio-pacemaker by both experimental and computational approaches. The former mainly includes gene therapy and cell therapy, whilst the latter involves the use of multi-scale computer models of the heart, ranging from the single cell to the tissue slice. Up to now, a bio-pacemaker has been successfully applied in big mammals, but it still has a long way from clinical uses for the treatment of human heart diseases. It is hoped that the use of the computational model of a bio-pacemaker may accelerate this process. Finally, we propose potential research directions for generating a bio-pacemaker based on cardiac computational modeling.
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Affiliation(s)
- Yacong Li
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin 150001, China
| | - Kuanquan Wang
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin 150001, China
| | - Qince Li
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin 150001, China.,Peng Cheng Laboratory, Shenzhen 518052, China
| | - Henggui Zhang
- School of Computer Science and Technology, Harbin Institute of Technology, Harbin 150001, China.,School of Physics and Astronomy, The University of Manchester, Manchester, M13 9PL, UK.,Peng Cheng Laboratory, Shenzhen 518052, China
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7
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Abstract
Cardiac pacemaking is a most fundamental cardiac function, thoroughly investigated for decades with a multiscale approach at organ, tissue, cell and molecular levels, to clarify the basic mechanisms underlying generation and control of cardiac rhythm. Understanding the processes involved in pacemaker activity is of paramount importance for a basic physiological knowledge, but also as a way to reveal details of pathological dysfunctions useful in the perspective of a therapeutic approach. Among the mechanisms involved in pacemaking, the "funny" (If) current has properties most specifically fitting the requirements for generation and control of repetitive activity, and has consequently received the most attention in studies of the pacemaker function. Present knowledge of the basic mechanisms of pacemaking and the properties of funny channels has led to important developments of clinical relevance. These include: (1) the successful development of heart rate-reducing agents, such as ivabradine, able to control cardiac rhythm and useful in the treatment of diseases such as coronary artery disease, heart failure and tachyarrhythmias; (2) the understanding of the genetic basis of disorders of cardiac rhythm caused by HCN channelopathies; (3) the design of strategies to implement biological pacemakers based on transfer of HCN channels or of stem cell-derived pacemaker cells expressing If, with the ultimate goal to replace electronic devices. In this review, I will give a brief historical account of the discovery of the funny current and the development of the concept of If-based pacemaking, in the context of a wider, more complex model of cardiac rhythmic function.
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Affiliation(s)
- Dario DiFrancesco
- Department of Biosciences, University of Milano, IBF-CNR University of Milano Unit, Milan, Italy
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8
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Zhao H, Yang M, Wang F, Yang A, Zhao Q, Wang X, Tang Y, Wang T, Huang C. Overexpression of the medium‑conductance calcium‑activated potassium channel (SK4) and the HCN2 channel to generate a biological pacemaker. Mol Med Rep 2019; 20:3406-3414. [PMID: 31432175 DOI: 10.3892/mmr.2019.10591] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2019] [Accepted: 07/25/2019] [Indexed: 11/06/2022] Open
Abstract
Ion channels serve important roles in the excitation‑contraction coupling of cardiac myocytes. Previous studies have shown that the overexpression or activation of intermediate‑conductance calcium‑activated potassium channel (SK4, encoded by KCNN4) in embryonic stem cell‑derived cardiomyocytes can significantly increase their automaticity. The mechanism underlying this effect is hypothesized to be associated with the activation of hyperpolarization‑activated cyclic nucleotide‑gated channel 2 (HCN2). The aim of the present study was to explore whether a biological pacemaker could be constructed by overexpressing SK4 alone or in combination with HCN2 in a rat model. Ad‑green fluorescent protein (GFP), Ad‑KCNN4 and Ad‑HCN2 recombinant adenoviruses were injected into the left ventricle of Sprague‑Dawley rat hearts. The rats were divided into a GFP group (n=10), an SK4 group (n=10), a HCN2 group (n=10) and an SK4 + HCN2 (SK4/HCN2) group (n=10). The isolated hearts were perfused at 5‑7 days following injection, and a complete heart block model was established. Compared with the GFP group, overexpressing SK4 alone did not significantly increase the heart rate after establishment of a complete heart block model [98.1±8.9 vs. 96.7±7.6 beats per min (BPM)], The heart rates in the SK4/HCN2 (139.9±21.9 BPM) and HCN2 groups (111.7±5.5 BPM) were significantly increased compared with the GFP and SK4 groups, and the heart rates in the SK4/HCN2 group were significantly increased compared with the SK4 or HCN2 groups. In the HCN2 (n=8) and the SK4/HCN2 (n=7) groups, the shape of the spontaneous ventricular rhythm was the same as the pacing‑induced ectopic rhythm in the transgenically altered site. By contrast, these rhythms were different in the SK4 (n=10) and GFP (n=10) groups. There were no significant differences in action potential duration alternans or ventricular arrhythmia inducibility between the four groups (all P>0.05). Western blotting, reverse transcription‑quantitative PCR and immunohistochemistry analyses showed that the expression levels of SK4 and HCN2 were significantly increased at the transgene site. Biological pacemaker activity could be successfully generated by co‑overexpression of SK4 and HCN2 without increasing the risk of ventricular arrhythmias. The overexpression of SK4 alone is insufficient to generate biological pacemaker activity. The present study provided evidence that SK4 and HCN2 combined could construct an ectopic pacemaker, laying the groundwork for the development of improved biological pacing mechanisms in the future.
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Affiliation(s)
- Hongyi Zhao
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Mei Yang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Fengyuan Wang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Ankang Yang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Qingyan Zhao
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Xi Wang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Yanhong Tang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Teng Wang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
| | - Congxin Huang
- Department of Cardiology, Renmin Hospital of Wuhan University, Wuhan, Hubei 430060, P.R. China
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Baruscotti M, Bucchi A, Milanesi R, Paina M, Barbuti A, Gnecchi-Ruscone T, Bianco E, Vitali-Serdoz L, Cappato R, DiFrancesco D. A gain-of-function mutation in the cardiac pacemaker HCN4 channel increasing cAMP sensitivity is associated with familial Inappropriate Sinus Tachycardia. Eur Heart J 2019; 38:280-288. [PMID: 28182231 DOI: 10.1093/eurheartj/ehv582] [Citation(s) in RCA: 58] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/09/2015] [Revised: 10/01/2015] [Accepted: 10/07/2015] [Indexed: 01/09/2023] Open
Affiliation(s)
- Mirko Baruscotti
- Department of Biosciences, The PaceLab and 'Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata', Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy
| | - Annalisa Bucchi
- Department of Biosciences, The PaceLab and 'Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata', Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy
| | - Raffaella Milanesi
- Department of Biosciences, The PaceLab and 'Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata', Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy
| | - Manuel Paina
- Department of Biosciences, The PaceLab and 'Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata', Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy
| | - Andrea Barbuti
- Department of Biosciences, The PaceLab and 'Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata', Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy
| | | | - Elisabetta Bianco
- Cardiovascular Department, 'Ospedali Riuniti di Trieste', University Hospital, Trieste, Italy
| | | | | | - Dario DiFrancesco
- Department of Biosciences, The PaceLab and 'Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata', Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy
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Cardiomyocyte Progenitor Cells as a Functional Gene Delivery Vehicle for Long-Term Biological Pacing. Molecules 2019; 24:molecules24010181. [PMID: 30621310 PMCID: PMC6337610 DOI: 10.3390/molecules24010181] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2018] [Revised: 12/28/2018] [Accepted: 12/31/2018] [Indexed: 01/16/2023] Open
Abstract
Sustained pacemaker function is a challenge in biological pacemaker engineering. Human cardiomyocyte progenitor cells (CMPCs) have exhibited extended survival in the heart after transplantation. We studied whether lentivirally transduced CMPCs that express the pacemaker current If (encoded by HCN4) can be used as functional gene delivery vehicle in biological pacing. Human CMPCs were isolated from fetal hearts using magnetic beads coated with Sca-1 antibody, cultured in nondifferentiating conditions, and transduced with a green fluorescent protein (GFP)- or HCN4-GFP-expressing lentivirus. A patch-clamp analysis showed a large hyperpolarization-activated, time-dependent inward current (−20 pA/pF at −140 mV, n = 14) with properties typical of If in HCN4-GFP-expressing CMPCs. Gap-junctional coupling between CMPCs and neonatal rat ventricular myocytes (NRVMs) was demonstrated by efficient dye transfer and changes in spontaneous beating activity. In organ explant cultures, the number of preparations showing spontaneous beating activity increased from 6.3% in CMPC/GFP-injected preparations to 68.2% in CMPC/HCN4-GFP-injected preparations (P < 0.05). Furthermore, in CMPC/HCN4-GFP-injected preparations, isoproterenol induced a significant reduction in cycle lengths from 648 ± 169 to 392 ± 71 ms (P < 0.05). In sum, CMPCs expressing HCN4-GFP functionally couple to NRVMs and induce physiologically controlled pacemaker activity and may therefore provide an attractive delivery platform for sustained pacemaker function.
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11
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Sun Y, Timofeyev V, Dennis A, Bektik E, Wan X, Laurita KR, Deschênes I, Li RA, Fu JD. A Singular Role of I K1 Promoting the Development of Cardiac Automaticity during Cardiomyocyte Differentiation by I K1 -Induced Activation of Pacemaker Current. Stem Cell Rev Rep 2018. [PMID: 28623610 DOI: 10.1007/s12015-017-9745-1] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
The inward rectifier potassium current (IK1) is generally thought to suppress cardiac automaticity by hyperpolarizing membrane potential (MP). We recently observed that IK1 could promote the spontaneously-firing automaticity induced by upregulation of pacemaker funny current (If) in adult ventricular cardiomyocytes (CMs). However, the intriguing ability of IK1 to activate If and thereby promote automaticity has not been explored. In this study, we combined mathematical and experimental assays and found that only IK1 and If, at a proper-ratio of densities, were sufficient to generate rhythmic MP-oscillations even in unexcitable cells (i.e. HEK293T cells and undifferentiated mouse embryonic stem cells [ESCs]). We termed this effect IK1-induced If activation. Consistent with previous findings, our electrophysiological recordings observed that around 50% of mouse (m) and human (h) ESC-differentiated CMs could spontaneously fire action potentials (APs). We found that spontaneously-firing ESC-CMs displayed more hyperpolarized maximum diastolic potential and more outward IK1 current than quiescent-yet-excitable m/hESC-CMs. Rather than classical depolarization pacing, quiescent mESC-CMs were able to fire APs spontaneously with an electrode-injected small outward-current that hyperpolarizes MP. The automaticity to spontaneously fire APs was also promoted in quiescent hESC-CMs by an IK1-specific agonist zacopride. In addition, we found that the number of spontaneously-firing m/hESC-CMs was significantly decreased when If was acutely upregulated by Ad-CGI-HCN infection. Our study reveals a novel role of IK1 promoting the development of cardiac automaticity in m/hESC-CMs through a mechanism of IK1-induced If activation and demonstrates a synergistic interaction between IK1 and If that regulates cardiac automaticity.
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Affiliation(s)
- Yu Sun
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Valeriy Timofeyev
- Department of Internal Medicine, University of California, Davis, CA, USA
| | - Adrienne Dennis
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Emre Bektik
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA.,Ph.D. Program in Human Biology, School of Integrative and Global Majors, University of Tsukuba, Tsukuba, Japan
| | - Xiaoping Wan
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Kenneth R Laurita
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Isabelle Deschênes
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA
| | - Ronald A Li
- Dr. Li Dak-Sum Center for Regenerative Medicine, University of Hong Kong, The Hong Kong Jockey Club Building for Interdisciplinary Research, LB 5-06, 5 Sassoon Road, Pokfulam, Hong Kong. .,Ming-Wai Lau Center for Regenerative Medicine, Karolinska Institutet, Solna, Sweden.
| | - Ji-Dong Fu
- Department of Medicine, Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, 2500 Metrohealth Drive, Rammelkamp 650, Cleveland, OH, 44109, USA.
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12
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Sartiani L, Mannaioni G, Masi A, Novella Romanelli M, Cerbai E. The Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels: from Biophysics to Pharmacology of a Unique Family of Ion Channels. Pharmacol Rev 2017; 69:354-395. [PMID: 28878030 DOI: 10.1124/pr.117.014035] [Citation(s) in RCA: 82] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2017] [Accepted: 07/07/2017] [Indexed: 12/22/2022] Open
Abstract
Hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels are important members of the voltage-gated pore loop channels family. They show unique features: they open at hyperpolarizing potential, carry a mixed Na/K current, and are regulated by cyclic nucleotides. Four different isoforms have been cloned (HCN1-4) that can assemble to form homo- or heterotetramers, characterized by different biophysical properties. These proteins are widely distributed throughout the body and involved in different physiologic processes, the most important being the generation of spontaneous electrical activity in the heart and the regulation of synaptic transmission in the brain. Their role in heart rate, neuronal pacemaking, dendritic integration, learning and memory, and visual and pain perceptions has been extensively studied; these channels have been found also in some peripheral tissues, where their functions still need to be fully elucidated. Genetic defects and altered expression of HCN channels are linked to several pathologies, which makes these proteins attractive targets for translational research; at the moment only one drug (ivabradine), which specifically blocks the hyperpolarization-activated current, is clinically available. This review discusses current knowledge about HCN channels, starting from their biophysical properties, origin, and developmental features, to (patho)physiologic role in different tissues and pharmacological modulation, ending with their present and future relevance as drug targets.
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Affiliation(s)
- Laura Sartiani
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Guido Mannaioni
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Alessio Masi
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Maria Novella Romanelli
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
| | - Elisabetta Cerbai
- Department of Neurosciences, Psychology, Drug Research, and Child Health, University of Florence, Firenze, Italy
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13
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Tse G, Liu T, Li KHC, Laxton V, Wong AOT, Chan YWF, Keung W, Chan CW, Li RA. Tachycardia-bradycardia syndrome: Electrophysiological mechanisms and future therapeutic approaches (Review). Int J Mol Med 2017; 39:519-526. [PMID: 28204831 PMCID: PMC5360359 DOI: 10.3892/ijmm.2017.2877] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Accepted: 01/09/2017] [Indexed: 02/07/2023] Open
Abstract
Sick sinus syndrome (SSS) encompasses a group of disorders whereby the heart is unable to perform its pacemaker function, due to genetic and acquired causes. Tachycardia‑bradycardia syndrome (TBS) is a complication of SSS characterized by alternating tachycardia and bradycardia. Techniques such as genetic screening and molecular diagnostics together with the use of pre-clinical models have elucidated the electrophysiological mechanisms of this condition. Dysfunction of ion channels responsible for initiation or conduction of cardiac action potentials may underlie both bradycardia and tachycardia; bradycardia can also increase the risk of tachycardia, and vice versa. The mainstay treatment option for SSS is pacemaker implantation, an effective approach, but has disadvantages such as infection, limited battery life, dislodgement of leads and catheters to be permanently implanted in situ. Alternatives to electronic pacemakers are gene‑based bio‑artificial sinoatrial node and cell‑based bio‑artificial pacemakers, which are promising techniques whose long-term safety and efficacy need to be established. The aim of this article is to review the different ion channels involved in TBS, examine the three‑way relationship between ion channel dysfunction, tachycardia and bradycardia in TBS and to consider its current and future therapies.
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Affiliation(s)
- Gary Tse
- Department of Medicine and Therapeutics, Chinese University of Hong Kong
- Li Ka Shing Institute of Health Sciences, Faculty of Medicine, Chinese University of Hong Kong, Hong Kong, SAR
| | - Tong Liu
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin 300211, P.R. China
| | | | - Victoria Laxton
- Intensive Care Department, Royal Brompton and Harefield NHS Foundation Trust, London SW3 6NP, UK
| | - Andy On-Tik Wong
- Stem Cell and Regenerative Medicine Consortium, Li Ka Shing Faculty of Medicine, The University of Hong Kong
- Li Dak-Sum Research Centre-HKU-Karolinska Institutet Collaboration on Regenerative Medicine, University of Hong Kong, Hong Kong, SAR, P.R. China
| | - Yin Wah Fiona Chan
- School of Biological Sciences, University of Cambridge, Cambridge CB2 1AG, UK
| | - Wendy Keung
- Stem Cell and Regenerative Medicine Consortium, Li Ka Shing Faculty of Medicine, The University of Hong Kong
- Li Dak-Sum Research Centre-HKU-Karolinska Institutet Collaboration on Regenerative Medicine, University of Hong Kong, Hong Kong, SAR, P.R. China
| | - Camie W.Y. Chan
- Stem Cell and Regenerative Medicine Consortium, Li Ka Shing Faculty of Medicine, The University of Hong Kong
| | - Ronald A. Li
- Li Dak-Sum Research Centre-HKU-Karolinska Institutet Collaboration on Regenerative Medicine, University of Hong Kong, Hong Kong, SAR, P.R. China
- Ming Wai Lau Centre for Reparative Medicine, Karolinska Institutet, Hong Kong, SAR, P.R. China
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14
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Huang X, Zhong N, Zhang H, Ma A, Yuan Z, Guo N. Reduced expression of HCN channels in the sinoatrial node of streptozotocin-induced diabetic rats. Can J Physiol Pharmacol 2016; 95:586-594. [PMID: 28177679 DOI: 10.1139/cjpp-2016-0418] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Diabetes mellitus (DM) is associated with an electrical remodeling of the heart, increasing the risk of arrhythmias. However, knowledge of electrical remodeling in the sinoatrial node (SAN) by DM is limited. We investigated the expression of HCN channel isoforms, HCN1-HCN4, in SAN from streptozotocin (STZ)-induced diabetic rats and the age-matched controls. We found that the STZ-induced diabetic rats have a lower intrinsic heart rate, a lengthened sinoatrial conduction time, and rate-corrected maximal sinoatrial node recovery time in vivo as well as a longer cycle length (CL) in vitro, as compared with the control. Optical mapping of the SAN demonstrated an inferior leading pacemaker site, reduced SAN conduction velocity and diastolic depolarization slope, and a longer action potential duration in the STZ-induced diabetic rats than in the control. The transcripts and proteins of HCN2 and HCN4 in diabetic SAN were reduced. Specific blockade of HCN channels by 3 μmol/L ivabradine significantly prolonged the CL of a Langendorff heart by 18% in the diabetic rats and 26% in the control. The reduced expression of HCN channel isoforms in the SAN of the STZ-induced diabetic rat may be an important contributor to the reduced SAN function in DM.
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Affiliation(s)
- Xin Huang
- a Department of Cardiology, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi, P.R. China, 710061
| | - Nier Zhong
- b Department of Cardiology, Shaanxi Provincial People's Hospital, Xi'an, Shaanxi, P.R. China, 710068
| | - Hong Zhang
- c School of Electrical Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi, P.R. China, 710049
| | - Aiqun Ma
- a Department of Cardiology, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi, P.R. China, 710061
| | - Zuyi Yuan
- a Department of Cardiology, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi, P.R. China, 710061
| | - Ning Guo
- a Department of Cardiology, First Affiliated Hospital of Xi'an Jiaotong University, Xi'an, Shaanxi, P.R. China, 710061
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15
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Boink GJ, Christoffels VM, Robinson RB, Tan HL. The past, present, and future of pacemaker therapies. Trends Cardiovasc Med 2015; 25:661-73. [DOI: 10.1016/j.tcm.2015.02.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 01/24/2015] [Accepted: 02/11/2015] [Indexed: 01/01/2023]
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16
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Huang X, Yang P, Yang Z, Zhang H, Ma A. Age-associated expression of HCN channel isoforms in rat sinoatrial node. Exp Biol Med (Maywood) 2015; 241:331-9. [PMID: 26341471 DOI: 10.1177/1535370215603515] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2015] [Accepted: 08/04/2015] [Indexed: 11/16/2022] Open
Abstract
The expression of hyperpolarization-activated cyclic nucleotide-gated cation (HCN) channel isoforms varies among species, cardiac tissues, developmental stages, and disease generation. However, alterations in the HCN channels during aging remain unclear. We investigated the protein expressions of HCN channel isoforms, HCN1-HCN4, in the sinoatrial nodes (SANs) from young (1-month-old), adult (4-month-old), and aged (30-month-old) rats. We found that HCN2 and HCN4 proteins were present in rat SAN using immunohistochemistry; therefore, we quantitatively analyzed their expression by Western blot. Aim to correlate protein expression and pacemaking function, specific blockade of HCN channels with 3 µmol/L ivabradine prolonged the cycle length in the intact rat heart. During the senescent process, the HCN2 and HCN4 protein levels declined, which was accompanied with a decreased effect of ivabradine on rat SAN automaticity. These results indicated the age-associated expression and relative function of HCN channel isoforms.
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Affiliation(s)
- Xin Huang
- Department of Cardiology, First Affiliated Hospital of Xi'an Jiaotong University Health Science Center, Ion Channel Disease Laboratory, Key Laboratory of Environment and Genes related to Diseases of Education Ministry, Xi'an, Shaanxi 710061, P.R. China
| | - Pei Yang
- Department of Orthopedics, Second Affiliated Hospital of Xi'an Jiaotong University Health Science Center, Xi'an, Shaanxi 710004, P.R. China
| | - Zhao Yang
- Institute of Medical Electronics in Medical School, Key Laboratory of Biomedical Information Engineering, Ministry of Education, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, P.R. China
| | - Hong Zhang
- School of Electrical Engineering, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, P.R. China
| | - Aiqun Ma
- Department of Cardiology, First Affiliated Hospital of Xi'an Jiaotong University Health Science Center, Ion Channel Disease Laboratory, Key Laboratory of Environment and Genes related to Diseases of Education Ministry, Xi'an, Shaanxi 710061, P.R. China
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17
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Magee KEA, Madden Z, Young EC. HCN Channel C-Terminal Region Speeds Activation Rates Independently of Autoinhibition. J Membr Biol 2015; 248:1043-60. [PMID: 26123597 DOI: 10.1007/s00232-015-9816-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2014] [Accepted: 06/08/2015] [Indexed: 01/13/2023]
Abstract
Hyperpolarization- and cyclic nucleotide-activated (HCN) channels contribute to rhythmic oscillations in excitable cells. They possess an intrinsic autoinhibition with a hyperpolarized V 1/2, which can be relieved by cAMP binding to the cyclic nucleotide binding (CNB) fold in the C-terminal region or by deletion of the CNB fold. We questioned whether V 1/2 shifts caused by altering the autoinhibitory CNB fold would be accompanied by parallel changes in activation rates. We used two-electrode voltage clamp on Xenopus oocytes to compare wildtype (WT) HCN2, a constitutively autoinhibited point mutant incapable of cAMP binding (HCN2 R591E), and derivatives with various C-terminal truncations. Activation V 1/2 and deactivation t 1/2 measurements confirmed that a truncated channel lacking the helix αC of the CNB fold (ΔαC) had autoinhibition comparable to HCN2 R591E; however, ΔαC activated approximately two-fold slower than HCN2 R591E over a 60-mV range of hyperpolarizations. A channel with a more drastic truncation deleting the entire CNB fold (ΔCNB) had similar V 1/2 values to HCN2 WT with endogenous cAMP bound, confirming autoinhibition relief, yet it surprisingly activated slower than the autoinhibited HCN2 R591E. Whereas CNB fold truncation slowed down voltage-dependent reaction steps, the voltage-independent closed-open equilibrium subject to autoinhibition in HCN2 was not rate-limiting. Chemically inhibiting formation of the endogenous lipid PIP2 hyperpolarized the V 1/2 of HCN2 WT but did not slow down activation to match ΔCNB rates. Our findings suggest a "quickening conformation" mechanism, requiring a full-length CNB that ensures fast rates for voltage-dependent steps during activation regardless of potentiation by cAMP or PIP2.
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Affiliation(s)
- Kaylee E A Magee
- Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada
| | - Zarina Madden
- Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada
| | - Edgar C Young
- Department of Molecular Biology and Biochemistry, Simon Fraser University, 8888 University Drive, Burnaby, BC, V5A 1S6, Canada.
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18
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Spatiotemporal stability of neonatal rat cardiomyocyte monolayers spontaneous activity is dependent on the culture substrate. PLoS One 2015; 10:e0127977. [PMID: 26035822 PMCID: PMC4452796 DOI: 10.1371/journal.pone.0127977] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2014] [Accepted: 04/21/2015] [Indexed: 11/27/2022] Open
Abstract
In native conditions, cardiac cells must continuously comply with diverse stimuli necessitating a perpetual adaptation. Polydimethylsiloxane (PDMS) is commonly used in cell culture to study cellular response to changes in the mechanical environment. The aim of this study was to evaluate the impact of using PDMS substrates on the properties of spontaneous activity of cardiomyocyte monolayer cultures. We compared PDMS to the gold standard normally used in culture: a glass substrate. Although mean frequency of spontaneous activity remained unaltered, incidence of reentrant activity was significantly higher in samples cultured on glass compared to PDMS substrates. Higher spatial and temporal instability of the spontaneous rate activation was found when cardiomyocytes were cultured on PDMS, and correlated with decreased connexin-43 and increased CaV3.1 and HCN2 mRNA levels. Compared to cultures on glass, cultures on PDMS were associated with the strongest response to isoproterenol and acetylcholine. These results reveal the importance of carefully selecting the culture substrate for studies involving mechanical stimulation, especially for tissue engineering or pharmacological high-throughput screening of cardiac tissue analog.
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19
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Chauveau S, Brink PR, Cohen IS. Stem cell-based biological pacemakers from proof of principle to therapy: a review. Cytotherapy 2014; 16:873-80. [PMID: 24831844 PMCID: PMC4051829 DOI: 10.1016/j.jcyt.2014.02.014] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 02/11/2014] [Accepted: 02/23/2014] [Indexed: 12/12/2022]
Abstract
Electronic pacemakers are the standard therapy for bradycardia-related symptoms but have shortcomings. Over the past 15 years, experimental evidence has demonstrated that gene and cell-based therapies can create a biological pacemaker. Recently, physiologically acceptable rates have been reported with an adenovirus-based approach. However, adenovirus-based protein expression does not last more than 4 weeks, which limits its clinical applicability. Cell-based platforms are potential candidates for longer expression. Currently there are two cell-based approaches being tested: (i) mesenchymal stem cells used as a suitcase for delivering pacemaker genes and (ii) pluripotent stem cells differentiated down a cardiac lineage with endogenous pacemaker activity. This review examines the current achievements in engineering a biological pacemaker, defines the patient population for whom this device would be useful and identifies the challenges still ahead before cell therapy can replace current electronic devices.
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Affiliation(s)
- Samuel Chauveau
- Department of Physiology and Biophysics, Institute for Molecular Cardiology, Stony Brook University, Stony Brook, NY, USA
| | - Peter R Brink
- Department of Physiology and Biophysics, Institute for Molecular Cardiology, Stony Brook University, Stony Brook, NY, USA
| | - Ira S Cohen
- Department of Physiology and Biophysics, Institute for Molecular Cardiology, Stony Brook University, Stony Brook, NY, USA.
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20
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Abstract
Efforts to use gene therapy to create a biological pacemaker as an adjunct or replacement of electronic pacemakers have been ongoing for about 15 years. For the past decade, most of these efforts have focused on the hyperpolarization-activated cyclic nucleotide gated-(HCN) gene family of channels alone or in combination with other genes. The HCN gene family is the molecular correlate of the cardiac pacemaker current, If. It is a suitable basis for a biological pacemaker because it generates a depolarizing inward current primarily during diastole and is directly regulated by cyclic adenosine monophosphate (cAMP), thereby incorporating autonomic responsiveness. However, biological pacemakers based either on native HCN channels or on mutated HCN channels designed to optimize biophysical characteristics have failed to attain the desired basal and maximal physiological heart rates in large animals. More recent work has explored dual gene therapy approaches, combining an HCN variant with another gene to reduce outward current, increase an additional inward current, or enhance cAMP synthesis. Several of these dual gene therapy approaches have demonstrated appropriate basal and maximal heart rates with little or no reliance on a backup electronic pacemaker during the period of study. Future research, besides examining the efficacy of other gene combinations, will need to consider the additional issues of safety and persistence of the viral vectors often used to deliver these genes to a specific cardiac region.
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Affiliation(s)
- Gerard J. J. Boink
- Heart Center, Department of Clinical & Experimental Cardiology, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
- Netherlands Heart Institute, ICIN, Utrecht, the Netherlands
| | - Richard B. Robinson
- Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, New York, NY, USA
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21
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Costet A, Provost J, Gambhir A, Bobkov Y, Danilo P, Boink GJ, Rosen MR, Konofagou E. Electromechanical wave imaging of biologically and electrically paced canine hearts in vivo. ULTRASOUND IN MEDICINE & BIOLOGY 2014; 40:177-187. [PMID: 24239363 PMCID: PMC3897195 DOI: 10.1016/j.ultrasmedbio.2013.08.019] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Revised: 08/20/2013] [Accepted: 08/26/2013] [Indexed: 06/02/2023]
Abstract
Electromechanical wave imaging (EWI) has been show capable of directly and entirely non-invasively mapping the trans mural electromechanical activation in all four cardiac chambers in vivo. In this study, we assessed EWI repeatability and reproducibility, as well as its capability of localizing electronic and, for the first time, biological pacing locations in closed-chest, conscious canines. Electromechanical activation was obtained in six conscious animals during normal sinus rhythm (NSR) and idioventricular rhythms occurring in dogs with complete heart block instrumented with electronic and biologic pacemakers (EPM and BPM respectively). After atrioventricular node ablation, dogs were implanted with an EPM in the right ventricular (RV) endocardial apex (n = 4) and two additionally received a BPM at the left ventricular (LV) epicardial base (n = 2). EWI was performed trans thoracically during NSR, BPM and EPM pacing, in conscious dogs, using an unfocused transmit sequence at 2000 frames/s. During NSR, the EW originated at the right atrium (RA), propagated to the left atrium (LA) and emerged from multiple sources in both ventricles. During EPM, the EW originated at the RV apex and propagated throughout both ventricles. During BPM, the EW originated from the LV basal lateral wall and subsequently propagated throughout the ventricles. EWI differentiated BPM from EPM and NSR and identified the distinct pacing origins. Isochrone comparison indicated that EWI was repeatable and reliable. These findings thus indicate the potential for EWI to serve as a simple, non-invasive and direct imaging technology for mapping and characterizing arrhythmias as well as the treatments thereof.
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Affiliation(s)
- Alexandre Costet
- Department of Biomedical Engineering, Columbia University, New York, NY, 10027, USA
| | - Jean Provost
- Department of Biomedical Engineering, Columbia University, New York, NY, 10027, USA
| | - Alok Gambhir
- Department of Medicine-Cardiology, Columbia University, New York, NY, 10032, USA
| | - Yevgeniy Bobkov
- Department of Pharmacology, Columbia University, New York, NY, 10032, USA
| | - Peter Danilo
- Department of Pharmacology, Columbia University, New York, NY, 10032, USA
| | - Gerard J.J. Boink
- Department of Pharmacology, Columbia University, New York, NY, 10032, USA
- Interuniversity Cardiology Institute of the Netherlands (ICIN), Utrecht, the Netherlands
- Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
| | - Michael R. Rosen
- Department of Pharmacology, Columbia University, New York, NY, 10032, USA
| | - Elisa Konofagou
- Department of Biomedical Engineering, Columbia University, New York, NY, 10027, USA
- Department of Radiology, Columbia University, New York, NY, 10032, USA
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22
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Abstract
Ion channels and transporters are expressed in every living cell, where they participate in controlling a plethora of biological processes and physiological functions, such as excitation of cells in response to stimulation, electrical activities of cells, excitation-contraction coupling, cellular osmolarity, and even cell growth and death. Alterations of ion channels/transporters can have profound impacts on the cellular physiology associated with these proteins. Expression of ion channels/transporters is tightly regulated and expression deregulation can trigger abnormal processes, leading to pathogenesis, the channelopathies. While transcription factors play a critical role in controlling the transcriptome of ion channels/transporters at the transcriptional level by acting on the 5'-flanking region of the genes, microribonucleic acids (miRNAs), a newly discovered class of regulators in the gene network, are also crucial for expression regulation at the posttranscriptional level through binding to the 3'untranslated region of the genes. These small noncoding RNAs fine tune expression of genes involved in a wide variety of cellular processes. Recent studies revealed the role of miRNAs in regulating expression of ion channels/transporters and the associated physiological functions. miRNAs can target ion channel genes to alter cardiac excitability (conduction, repolarization, and automaticity) and affect arrhythmogenic potential of heart. They can modulate circadian rhythm, pain threshold, neuroadaptation to alcohol, brain edema, etc., through targeting ion channel genes in the neuronal systems. miRNAs can also control cell growth and tumorigenesis by acting on the relevant ion channel genes. Future studies are expected to rapidly increase to unravel a new repertoire of ion channels/transporters for miRNA regulation.
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Affiliation(s)
- Zhiguo Wang
- Harbin Medical University, Harbin, Heilongjiang, People's Republic of China.
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23
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Wang Y, Zankov DP, Jiang M, Zhang M, Henderson SC, Tseng GN. [Ca2+]i elevation and oxidative stress induce KCNQ1 protein translocation from the cytosol to the cell surface and increase slow delayed rectifier (IKs) in cardiac myocytes. J Biol Chem 2013; 288:35358-71. [PMID: 24142691 DOI: 10.1074/jbc.m113.504746] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Our goals are to simultaneously determine the three-dimensional distribution patterns of KCNQ1 and KCNE1 in cardiac myocytes and to study the mechanism and functional implications for variations in KCNQ1/KCNE1 colocalization in myocytes. We monitored the distribution patterns of KCNQ1, KCNE1, and markers for subcellular compartments/organelles using immunofluorescence/confocal microscopy and confirmed the findings in ventricular myocytes by directly observing fluorescently tagged KCNQ1-GFP and KCNE1-dsRed expressed in these cells. We also monitored the effects of stress on KCNQ1-GFP and endoplasmic reticulum (ER) remodeling during live cell imaging. The data showed that 1) KCNE1 maintained a stable cell surface localization, whereas KCNQ1 exhibited variations in the cytosolic compartment (striations versus vesicles) and the degree of presence on the cell surface; 2) the degree of cell surface KCNQ1/KCNE1 colocalization was positively correlated with slow delayed rectifier (IKs) current density; 3) KCNQ1 and calnexin (an ER marker) shared a cytosolic compartment; and 4) in response to stress ([Ca(2+)]i elevation, oxidative overload, or AT1R stimulation), KCNQ1 exited the cytosolic compartment and trafficked to the cell periphery in vesicles. This was accompanied by partial ER fragmentation. We conclude that the cellular milieu regulates KCNQ1 distribution in cardiac myocytes and that stressful conditions can increase IKs by inducing KCNQ1 movement to the cell surface. This represents a hitherto unrecognized mechanism by which IKs fulfills its function as a repolarization reserve in ventricular myocytes.
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Affiliation(s)
- Yuhong Wang
- From the Department of Physiology and Biophysics and
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Morris GM, D'Souza A, Dobrzynski H, Lei M, Choudhury M, Billeter R, Kryukova Y, Robinson RB, Kingston PA, Boyett MR. Characterization of a right atrial subsidiary pacemaker and acceleration of the pacing rate by HCN over-expression. Cardiovasc Res 2013; 100:160-9. [DOI: 10.1093/cvr/cvt164] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
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Nawathe PA, Kryukova Y, Oren RV, Milanesi R, Clancy CE, Lu JT, Moss AJ, Difrancesco D, Robinson RB. An LQTS6 MiRP1 mutation suppresses pacemaker current and is associated with sinus bradycardia. J Cardiovasc Electrophysiol 2013; 24:1021-7. [PMID: 23631727 DOI: 10.1111/jce.12163] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/24/2012] [Revised: 12/20/2012] [Accepted: 03/13/2013] [Indexed: 01/20/2023]
Abstract
BACKGROUND Sinus node (SN) dysfunction is observed in some long-QT syndrome (LQTS) patients, but has not been studied as a function of LQTS genotype. LQTS6 involves mutations in the hERG β-subunit MiRP1, which also interacts with hyperpolarization-activated, cyclic nucleotide gated (HCN) channels-the molecular correlate of SN pacemaker current (If ). An LQTS registry search identified a 55-year male with M54T MiRP1 mutation, history of sinus bradycardia (39-56 bpm), and prolonged QTc. OBJECTIVE We tested if LQTS6 incorporates sinus bradycardia due to abnormal If . METHODS We transiently co-transfected neonatal rat ventricular myocytes (to study currents in a myocyte background) with human HCN4 (hHCN4, primary SN isoform) or human HCN2 (hHCN2) and one of the following: empty vector, wild-type hMiRP1 (WT), M54T hMiRP1 (M54T). Current amplitude, voltage dependence, and kinetics were measured by whole cell patch clamp. RESULTS M54T co-expression decreased HCN4 current density by 80% compared to hHCN4 alone or with WT, and also slowed HCN4 activation at physiologically relevant voltages. Neither WT nor M54T altered HCN4 voltage dependence. A computer simulation predicts that these changes in HCN4 current would decrease rate and be additive with published effects of M54T mutation on hERG kinetics on rate. CONCLUSIONS We conclude that M54T LQTS6 mutation can cause sinus bradycardia through effects on both hERG and HCN currents. Patients with other LQTS6 mutations should be examined for SN dysfunction, and the effect on HCN current determined.
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Kurata Y, Hisatome I, Tanida M, Shibamoto T. Effect of hyperpolarization-activated current I(f) on robustness of sinoatrial node pacemaking: theoretical study on influence of intracellular Na(+) concentration. Am J Physiol Heart Circ Physiol 2013; 304:H1337-51. [PMID: 23504184 DOI: 10.1152/ajpheart.00777.2012] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
To elucidate the effects of hyperpolarization-activated current I(f) on robustness of sinoatrial node (SAN) pacemaking in connection with intracellular Na(+) concentration (Na(i)) changes, we theoretically investigated 1) the impacts of I(f) on dynamical properties of SAN model cells during inhibition of L-type Ca(2+) channel currents (I(CaL)) or hyperpolarizing loads and 2) I(f)-dependent changes in Na(i) and their effects on dynamical properties of model cells. Bifurcation analyses were performed for Na(i)-variable and Na(i)-fixed versions of mathematical models for rabbit SAN cells; equilibrium points (EPs), limit cycles (LCs), and their stability were determined as functions of model parameters. Increasing I(f) conductance (g(f)) shrank I(CaL) conductance (g(CaL)) regions of unstable EPs and stable LCs (rhythmic firings) in the Na(i)-variable system but slightly broadened that of rhythmic firings at lower g(f) in the Na(i)-fixed system. In the Na(i)-variable system, increased g(f) yielded elevations in Na(i) at EPs and during spontaneous oscillations, which caused EP stabilization and shrinkage in the parameter regions of unstable EPs and rhythmic firings. As g(f) increased, parameter regions of unstable EPs and stable LCs determined for hyperpolarizing loads shrank in the Na(i)-variable system but were enlarged in the Na(i)-fixed system. These findings suggest that 1) I(f) does not enhance but rather attenuates robustness of rabbit SAN cells via facilitating EP stabilization and LC destabilization even in physiological g(f) ranges; and 2) the enhancing effect of I(f) on robustness of pacemaker activity, which could be observed at lower g(f) when Na(i) was fixed, is actually reversed by I(f)-dependent changes in Na(i).
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Affiliation(s)
- Yasutaka Kurata
- Department of Physiology, Kanazawa Medical University, Ishikawa, Japan.
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Li RA. Gene- and cell-based bio-artificial pacemaker: what basic and translational lessons have we learned? Gene Ther 2012; 19:588-95. [PMID: 22673497 DOI: 10.1038/gt.2012.33] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Normal rhythms originate in the sino-atrial node, a specialized cardiac tissue consisting of only a few thousands of nodal pacemaker cells. Malfunction of pacemaker cells due to diseases or aging leads to rhythm generation disorders (for example, bradycardias and sick-sinus syndrome (SSS)), which often necessitate the implantation of electronic pacemakers. Although effective, electronic devices are associated with such shortcomings as limited battery life, permanent implantation of leads, lead dislodging, the lack of autonomic responses and so on. Here, various gene- and cell-based approaches, with a particular emphasis placed on the use of pluripotent stem cells and the hyperpolarization-activated cyclic nucleotide-gated-encoded pacemaker gene family, that have been pursued in the past decade to reconstruct bio-artificial pacemakers as alternatives will be discussed in relation to the basic biological insights and translational regenerative potential.
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Affiliation(s)
- R A Li
- Center of Cardiovascular Research, Mount Sinai School of Medicine, New York, NY 10029, USA.
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Abd Allah ES, Aslanidi OV, Tellez JO, Yanni J, Billeter R, Zhang H, Dobrzynski H, Boyett MR. Postnatal development of transmural gradients in expression of ion channels and Ca2+-handling proteins in the ventricle. J Mol Cell Cardiol 2012; 53:145-55. [DOI: 10.1016/j.yjmcc.2012.04.004] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/16/2011] [Revised: 03/06/2012] [Accepted: 04/06/2012] [Indexed: 01/30/2023]
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Boink GJJ, Nearing BD, Shlapakova IN, Duan L, Kryukova Y, Bobkov Y, Tan HL, Cohen IS, Danilo P, Robinson RB, Verrier RL, Rosen MR. Ca(2+)-stimulated adenylyl cyclase AC1 generates efficient biological pacing as single gene therapy and in combination with HCN2. Circulation 2012; 126:528-36. [PMID: 22753192 DOI: 10.1161/circulationaha.111.083584] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
BACKGROUND Biological pacing performed solely via HCN2 gene transfer in vivo results in relatively slow idioventricular rates and only moderate autonomic responsiveness. We induced biological pacing using the Ca(2+)-stimulated adenylyl cyclase AC1 gene expressed alone or in combination with HCN2 and compared outcomes with those with single-gene HCN2 transfer. METHODS AND RESULTS We implanted adenoviral HCN2, AC1, or HCN2/AC1 constructs into the left bundle branches of atrioventricular-blocked dogs. During steady-state gene expression (days 5-7), differences between AC1, HCN2/AC1, and HCN2 alone were evident in basal beating rate, escape time, and dependence on electronic backup pacing. In HCN2, AC1, and HCN2/AC1, these parameters were as follows: basal beating rate: 50±1.5, 60±5.0, and 129±28.9 bpm (P<0.05 for HCN2/AC1 versus HCN2 or AC1 alone), respectively; escape time: 2.4±0.2, 1.3±0.2, and 1.1±.0.4 seconds (P<0.05 for AC1 and HCN2/AC1 versus HCN2); and percent electronic beats: 34±8%, 2±1%, and 6±2% (P<0.05 for AC1 and HCN2/AC1 versus HCN2). Instantaneous (SD1) and long-term (SD2) heart rate variability and circadian rhythm analyzed via 24-hour Holter recordings showed a shift toward greater sensitivity to parasympathetic modulation in animals injected with AC1 and a high degree of sympathetic modulation in animals injected with HCN2/AC1. CONCLUSION AC1 or HCN2/AC1 overexpression in left bundle branches provides highly efficient biological pacing and greater sensitivity to autonomic modulation than HCN2 alone.
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Affiliation(s)
- Gerard J J Boink
- Department of Pharmacology, Center for Molecular Therapeutics, Columbia University, New York, NY 10032, USA
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Barbuti A, Scavone A, Mazzocchi N, Terragni B, Baruscotti M, Difrancesco D. A caveolin-binding domain in the HCN4 channels mediates functional interaction with caveolin proteins. J Mol Cell Cardiol 2012; 53:187-95. [PMID: 22659290 DOI: 10.1016/j.yjmcc.2012.05.013] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2012] [Revised: 04/18/2012] [Accepted: 05/10/2012] [Indexed: 12/17/2022]
Abstract
Pacemaker (HCN) channels have a key role in the generation and modulation of spontaneous activity of sinoatrial node myocytes. Previous work has shown that compartmentation of HCN4 pacemaker channels within caveolae regulates important functions, but the molecular mechanism responsible is still unknown. HCN channels have a conserved caveolin-binding domain (CBD) composed of three aromatic amino acids at the N-terminus; we sought to evaluate the role of this CBD in channel-protein interaction by mutational analysis. We generated two HCN4 mutants with a disrupted CBD (Y259S, F262V) and two with conservative mutations (Y259F, F262Y). In CHO cells expressing endogenous caveolin-1 (cav-1), alteration of the CBD shifted channels activation to more positive potentials, slowed deactivation and made Y259S and F262V mutants insensitive to cholesterol depletion-induced caveolar disorganization. CBD alteration also caused a significant decrease of current density, due to a weaker HCN4-cav-1 interaction and accumulation of cytoplasmic channels. These effects were absent in mutants with a preserved CBD. In caveolin-1-free fibroblasts, HCN4 trafficking was impaired and current density reduced with all constructs; the activation curve of F262V was not altered relative to wt, and that of Y259S displayed only half the shift than in CHO cells. The conserved CBD present in all HCN isoforms mediates their functional interaction with caveolins. The elucidation of the molecular details of HCN4-cav-1 interaction can provide novel information to understand the basis of cardiac phenotypes associated with some forms of caveolinopathies.
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Affiliation(s)
- Andrea Barbuti
- Department of Biomolecular Sciences and Biotechnology, The PaceLab, Università degli Studi di Milano, via Celoria 26, 20133 Milano, Italy.
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Kryukova YN, Protas L, Robinson RB. Ca2+-activated adenylyl cyclase 1 introduces Ca2+-dependence to beta-adrenergic stimulation of HCN2 current. J Mol Cell Cardiol 2012; 52:1233-9. [PMID: 22484253 DOI: 10.1016/j.yjmcc.2012.03.010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/03/2011] [Revised: 02/15/2012] [Accepted: 03/19/2012] [Indexed: 01/01/2023]
Abstract
Previous observations show that β-adrenergic modulation of pacemaker current (I(f)) in sinoatrial node (SAN) cells is impaired by disruption of normal Ca(2+)-homeostasis with ryanodine or BAPTA. Recently, the presence of Ca(2+)-activated adenylyl cyclase (AC) 1 was reported in SAN, and was proposed as a possible mechanism of Ca(2+)-dependence of β-adrenergic modulation. However, direct evidence that pacemaker (HCN) channels can be regulated by Ca(2+)-activated AC and that such regulation introduces Ca(2+) dependence, is lacking. Here we co-expressed AC1 or AC6 with HCN2 in neonatal rat ventricular myocytes, which lack AC1. Although both isoforms have equivalent expression level and ability to interact with HCN2, only AC1 increases intracellular cAMP content, accelerates spontaneous beating rate and modifies HCN2 biophysics. Measured HCN2 current in the AC1 group activated ~10mV more positive than in GFP or AC6. The β-adrenergic agonist isoproterenol induced a further positive shift under control conditions, but failed to do so after pretreatment with the Ca(2+) chelator BAPTA. In the AC6 group, isoproterenol shifted the HCN2 activation relation to a similar extent in the absence and presence of BAPTA. Thus, AC1 but not AC6 over-expression introduces Ca(2+)-sensitivity to the β-adrenergic response of HCN2. These results demonstrate physical and functional interaction between AC isoforms and the HCN2 pacemaker channel and support a key role of Ca(2+) activated AC1 as a molecular mechanism in Ca(2+)-dependent modulation of β-adrenergic response of heart rate.
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Affiliation(s)
- Yelena N Kryukova
- Department of Pharmacology, Columbia University, 630 West 168th Street, New York, NY 10032, USA
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Abstract
The field of biological pacing is entering its second decade of active investigation. The inception of this area of study was serendipitous, deriving largely from observations made by several teams of investigators, whose common interest was to understand the mechanisms governing cardiac impulse initiation. Research directions taken have fallen under the broad headings of gene therapy and cell therapy, and biomaterials research has also begun to enter the field. In this Review, we revisit certain milestones achieved through the construction of a 'roadmap' in biological pacing. Whether the end result will be a clinically applicable biological pacemaker is still uncertain. However, promising constructs that achieve physiologically relevant heart rates and good autonomic responsiveness are now available, and proof of principle studies are giving way to translation to large-animal models in long-term studies. Provided that interest in the field continues, the next decade should see either biological pacemakers become a clinical reality or the improvement of electronic pacemakers to a point where the biological approach is no longer a viable alternative.
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Avitabile D, Crespi A, Brioschi C, Parente V, Toietta G, Devanna P, Baruscotti M, Truffa S, Scavone A, Rusconi F, Biondi A, D'Alessandra Y, Vigna E, Difrancesco D, Pesce M, Capogrossi MC, Barbuti A. Human cord blood CD34+ progenitor cells acquire functional cardiac properties through a cell fusion process. Am J Physiol Heart Circ Physiol 2011; 300:H1875-84. [PMID: 21357510 DOI: 10.1152/ajpheart.00523.2010] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The efficacy of cardiac repair by stem cell administration relies on a successful functional integration of injected cells into the host myocardium. Safety concerns have been raised about the possibility that stem cells may induce foci of arrhythmia in the ischemic myocardium. In a previous work (36), we showed that human cord blood CD34(+) cells, when cocultured on neonatal mouse cardiomyocytes, exhibit excitation-contraction coupling features similar to those of cardiomyocytes, even though no human genes were upregulated. The aims of the present work are to investigate whether human CD34(+) cells, isolated after 1 wk of coculture with neonatal ventricular myocytes, possess molecular and functional properties of cardiomyocytes and to discriminate, using a reporter gene system, whether cardiac differentiation derives from a (trans)differentiation or a cell fusion process. Umbilical cord blood CD34(+) cells were isolated by a magnetic cell sorting method, transduced with a lentiviral vector carrying the enhanced green fluorescent protein (EGFP) gene, and seeded onto primary cultures of spontaneously beating rat neonatal cardiomyocytes. Cocultured EGFP(+)/CD34(+)-derived cells were analyzed for their electrophysiological features at different time points. After 1 wk in coculture, EGFP(+) cells, in contact with cardiomyocytes, were spontaneously contracting and had a maximum diastolic potential (MDP) of -53.1 mV, while those that remained isolated from the surrounding myocytes did not contract and had a depolarized resting potential of -11.4 mV. Cells were then resuspended and cultured at low density to identify EGFP(+) progenitor cell derivatives. Under these conditions, we observed single EGFP(+) beating cells that had acquired an hyperpolarization-activated current typical of neonatal cardiomyocytes (EGFP(+) cells, -2.24 ± 0.89 pA/pF; myocytes, -1.99 ± 0.63 pA/pF, at -125 mV). To discriminate between cell autonomous differentiation and fusion, EGFP(+)/CD34(+) cells were cocultured with cardiac myocytes infected with a red fluorescence protein-lentiviral vector; under these conditions we found that 100% of EGFP(+) cells were also red fluorescent protein positive, suggesting cell fusion as the mechanism by which cardiac functional features are acquired.
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Affiliation(s)
- Daniele Avitabile
- Department of Biomolecular Sciences and Biotechnology, University of Milan, Milan, Italy
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Shlapakova IN, Nearing BD, Lau DH, Boink GJJ, Danilo P, Kryukova Y, Robinson RB, Cohen IS, Rosen MR, Verrier RL. Biological pacemakers in canines exhibit positive chronotropic response to emotional arousal. Heart Rhythm 2010; 7:1835-40. [PMID: 20708103 DOI: 10.1016/j.hrthm.2010.08.004] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2009] [Accepted: 08/06/2010] [Indexed: 11/30/2022]
Abstract
BACKGROUND Biological pacemakers based on the HCN2 channel isoform respond to beta-adrenergic and muscarinic stimulation, suggesting a capacity to respond to autonomic input. OBJECTIVE The purpose of this study was to investigate autonomic response to emotional arousal in canines implanted with murine HCN2-based biological pacemakers using gene therapy. METHODS An electronic pacemaker was implanted with its lead in the right ventricular apical endocardium (VVI 35 bpm). An adenoviral HCN2/GFP construct (Ad-HCN2, n = 7) or saline (control, n = 5) was injected into the left bundle branch on day 2 after radiofrequency ablation of the atrioventricular node to induce complete atrioventricular block. Emotional arousal was achieved by presenting food following an overnight fast. Autonomic control was evaluated with Poincaré plots of R-R(N) against R-R(N+1) intervals to characterize heart rate variability (HRV) and with continuous RR interval assessment via 24-hour ambulatory ECG. The 24-hour ECG and Poincaré plot shape were analyzed. RESULTS During day 1 after biological pacemaker implantation, Poincaré HRV parameters and RR intervals were unchanged with food presentation. However, on day 7, food presentation was accompanied by an increase in HRV (SD1, p < 0.07, and SD2, p < 0.05) and shortening of RR interval (P < .05) in dogs with Ad-HCN2 but not in controls. CONCLUSION This is the first demonstration that biological pacemakers are capable of responding to natural arousal stimuli to elicit appropriate chronotropic responses, a potential advantage over electronic pacemakers.
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Affiliation(s)
- Iryna N Shlapakova
- Columbia University College of Physicians and Surgeons, New York, New York, USA
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Tong WC, Holden AV. Bifurcation analysis of genetically engineered pacemaking in mammalian heart. J Biol Phys 2010; 32:169-72. [PMID: 19669459 DOI: 10.1007/s10867-006-9004-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
Genetically engineered pacemaking in ventricular cells has been achieved by down-regulation of the time independent inward rectifying current (I(K1)), or insertion of the hyperpolarisation-activated funny current (I(f)). We analyse the membrane system (i.e. ionic concentrations clamped) of an epicardial Luo-Rudy dynamic cell model using continuation algorithms with the maximum conductance (g) of I(K1) and I(f) as bifurcation parameters. Pacemaker activity can be induced either via Hopf or homoclinic bifurcations. As g(K1) is decreased by approximately 74%, autorhythmicity emerged via a homoclinic bifurcation, i.e., the periodicity first appear with infinitely large periods. In contrast, the insertion of g(f) induced periodicity via a subcritical Hopf bifurcation at g(f) approximately 0.25 mSmicroF(-1). Stable autorhythmic action potentials occurred at g(f) > 0.329 mSmicroF(-1).
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Affiliation(s)
- Wing Chiu Tong
- Computational Biology Laboratory, Institute of Membrane and Systems Biology, University of Leeds, Leeds LS2 9JT, UK
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Chan YC, Tse HF, Siu CW, Wang K, Li RA. Automaticity and conduction properties of bio-artificial pacemakers assessed in an in vitro monolayer model of neonatal rat ventricular myocytes. Europace 2010; 12:1178-87. [PMID: 20472688 DOI: 10.1093/europace/euq120] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
AIMS A better understanding of the ionic mechanisms for cardiac automaticity can lead to better strategies for engineering bio-artificial pacemakers. Here, we attempted to better define the relative contribution of I(f) and I(K1) in the generation of spontaneous action potentials (SAPs) in cardiomyocytes (CMs). METHODS AND RESULTS Monolayers of neonatal rat ventricular myocytes (NRVMs) were transduced with a recombinant adenovirus (Ad) to express a gating-engineered HCN1 construct (HCN1-DeltaDeltaDelta) for patch-clamp and multielectrode array (MEA) recordings. Single NRVMs exhibited a bi-phasic response in the generation of SAPs (62.6 +/- 17.4 b.p.m., Days 1-2; 194.3 +/- 12.3 b.p.m., Days 3-4; 73% quiescent, Days 9-10). Although automaticity time-dependently decreased and subsequently ceased, I(f) remained fairly stable (-5.2 +/- 1.1 pA/pF, Days 1-2; -5.1 +/- 1.4 pA/pF, Days 7-8; -4.3 +/- 1.3 pA/pF, Days 13-14). In contrast, I(K1) declined rapidly (from -16.9 +/- 2.7 pA/pF on Days 1-2 to -4.4 +/- 1.6 pA/pF on Days 5-6). Maximum diastolic potential/resting membrane potential (r = 0.89) and action potential duration at 50% (APD(50), r = 0.73) and 90% (APD(90), r = 0.75) but not the firing rate (r = -0.3) were positively correlated to the I(K1). Similarly, monolayer NRVMs ceased to spontaneously fire after long-term culture. Ad-HCN1-DeltaDeltaDelta transduction restored pacing in silenced individual and monolayer NRVMs but with reduced conduction velocity and field potential amplitude. CONCLUSION We conclude that the combination of I(K1) and I(f) primes CMs for bio-artificial pacing by determining the threshold. However, I(f) functions as a membrane potential oscillator to determine the basal firing frequency. Future engineering of automaticity in the multicellular setting needs to have conduction taken into consideration.
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Affiliation(s)
- Yau-Chi Chan
- Cardiology Division, Department of Medicine, University of Hong Kong, Queen Mary Hospital, Hong Kong, SAR
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Chan YC, Siu CW, Lau YM, Lau CP, Li RA, Tse HF. Synergistic effects of inward rectifier (I) and pacemaker (I) currents on the induction of bioengineered cardiac automaticity. J Cardiovasc Electrophysiol 2009; 20:1048-54. [PMID: 19460073 DOI: 10.1111/j.1540-8167.2009.01475.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
INTRODUCTION Normal heart rhythms originate in the sinoatrial node. HCN-encoded funny current (I(f)) and the Kir2-encoded inward rectifier (I(K1)) counteract each other by respectively oscillating and stabilizing the negative resting membrane potential, and controlling action potential firing. Therefore, I(K1) suppression and I(f) overexpression have been independently exploited to convert cardiomyocytes (CMs) into AP-firing bioartificial pacemakers. Although the 2 strategies have been largely assumed synergistic, their complementarity has not been investigated. METHODS AND RESULTS We explored the interrelationships of automaticity, I(f) and I(K1) by transducing single left ventricular (LV) CMs isolated from guinea pig hearts with the recombinant adenoviruses Ad-CMV-GFP-IRES-HCN1-AAA and/or Ad-CGI-Kir2.1 to mediate their current densities via a whole-cell patch clamp technique at 37 degrees C. Results showed that Ad-CGI-HCN1-AAA but not Ad-CGI-Kir2.1 transduction induced automaticity (181.1 +/- 13.1 bpm). Interestingly, Ad-CGI-HCN1-AAA/Ad-CGI-Kir2.1 cotransduction significantly promoted the induced firing frequency (320.0 +/- 15.8 bpm; P < 0.05). Correlation analysis revealed that the firing frequency, phase-4 slope and APD(90) of AP-firing LV CMs were correlated with I(f) (R(2) > 0.7) only when -2 >I(K1) >-4 pA/pF but not with I(K1) over the entire I(f) ranges examined (0.02 < R(2) < 0.4). Unlike I(f), I(K1) displayed correlation with neither the phase-4 slope (R(2)= 0.02) nor phase-4 length (R(2)= 0.04) when -2 > I(f) > -4 pA/pF. As anticipated, however, APD(90) was correlated with I(K1) (R(2)= 0.4). CONCLUSION We conclude that an optimal level of I(K1) maintains a voltage range for I(f) to operate most effectively during a dynamic cardiac cycle.
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Affiliation(s)
- Yau-Chi Chan
- Cardiology Division, Department of Medicine, University of Hong Kong, Hong Kong
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Zhang Y, Liu Y, Qu J, Hardy A, Zhang N, Diao J, Strijbos PJ, Tsushima R, Robinson RB, Gaisano HY, Wang Q, Wheeler MB. Functional characterization of hyperpolarization-activated cyclic nucleotide-gated channels in rat pancreatic beta cells. J Endocrinol 2009; 203:45-53. [PMID: 19654142 PMCID: PMC2876733 DOI: 10.1677/joe-09-0068] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels regulate pacemaker activity in some cardiac cells and neurons. In the present study, we have identified the presence of HCN channels in pancreatic beta-cells. We then examined the functional characterization of these channels in beta-cells via modulating HCN channel activity genetically and pharmacologically. Voltage-clamp experiments showed that over-expression of HCN2 in rat beta-cells significantly increased HCN current (I(h)), whereas expression of dominant-negative HCN2 (HCN2-AYA) completely suppressed endogenous I(h). Compared to control beta-cells, over-expression of I(h) increased insulin secretion at 2.8 mmol/l glucose. However, suppression of I(h) did not affect insulin secretion at both 2.8 and 11.1 mmol/l glucose. Current-clamp measurements revealed that HCN2 over-expression significantly reduced beta-cell membrane input resistance (R(in)), and resulted in a less-hyperpolarizing membrane response to the currents injected into the cell. Conversely, dominant negative HCN2-AYA expression led to a substantial increase of R(in), which was associated with a more hyperpolarizing membrane response to the currents injected. Remarkably, under low extracellular potassium conditions (2.5 mmol/l K(+)), suppression of I(h) resulted in increased membrane hyperpolarization and decreased insulin secretion. We conclude that I(h) in beta-cells possess the potential to modulate beta-cell membrane potential and insulin secretion under hypokalemic conditions.
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Affiliation(s)
- Yi Zhang
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
- Address correspondence to: Dr. Y Zhang, Departments of Physiology and Medicine, Room 7310, Medical Sciences Building, University of Toronto, 1 King’s College Circle, Toronto, ON, Canada M5S 1A8 Tel: (416)-978-7160; Fax: (416)-978-8765; . Dr. Q Wang, St. Michael’s Hospital, Room 7005, Queen Wing, 30 Bond Street, Toronto, ON,, Canada M5B 1W8. Tel: (416) 864-6060 x6767; Fax: (416) 864-6043;
| | - Yunfeng Liu
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
| | - Jihong Qu
- Department of Pharmacology, Columbia University, New York, U.S.A
| | - Alexandre Hardy
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
| | - Nina Zhang
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
- Division of Endocrinology and Metabolism, Li Ka-Shing Knowledge Institute, St Michael’s Hospital, Toronto, Canada
| | - Jingyu Diao
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
| | - Paul J. Strijbos
- Neurology and GI Centre of Excellence for Drug Discovery, GlaxoSmithKline, New Frontiers Science Park, Harlow CM19 5AW, UK
| | - Robert Tsushima
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
| | | | - Herbert Y. Gaisano
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
| | - Qinghua Wang
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
- Division of Endocrinology and Metabolism, Li Ka-Shing Knowledge Institute, St Michael’s Hospital, Toronto, Canada
- Address correspondence to: Dr. Y Zhang, Departments of Physiology and Medicine, Room 7310, Medical Sciences Building, University of Toronto, 1 King’s College Circle, Toronto, ON, Canada M5S 1A8 Tel: (416)-978-7160; Fax: (416)-978-8765; . Dr. Q Wang, St. Michael’s Hospital, Room 7005, Queen Wing, 30 Bond Street, Toronto, ON,, Canada M5B 1W8. Tel: (416) 864-6060 x6767; Fax: (416) 864-6043;
| | - Michael B. Wheeler
- Departments of Physiology and Medicine, University of Toronto, Ontario, Canada
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Abstract
Several hundred thousand electronic pacemakers are implanted in the US each year to treat abnormally slow heart rates. Biological pacemaker research strives to replace this hardware, and the associated monitoring and maintenance, by using gene or cell therapy to create a permanent and autonomically responsive pacemaker. While there are numerous technological hurdles to overcome before this is a therapeutic reality, one critical issue is determining the optimal channel gene to employ in creating a biological pacemaker. This review discusses the pros and cons of various model systems for characterizing and evaluating the function of candidate channel genes. It is argued that a sequential approach that combines in silico, in vitro and in vivo models is required.
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Biel M, Wahl-Schott C, Michalakis S, Zong X. Hyperpolarization-activated cation channels: from genes to function. Physiol Rev 2009; 89:847-85. [PMID: 19584315 DOI: 10.1152/physrev.00029.2008] [Citation(s) in RCA: 719] [Impact Index Per Article: 47.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels comprise a small subfamily of proteins within the superfamily of pore-loop cation channels. In mammals, the HCN channel family comprises four members (HCN1-4) that are expressed in heart and nervous system. The current produced by HCN channels has been known as I(h) (or I(f) or I(q)). I(h) has also been designated as pacemaker current, because it plays a key role in controlling rhythmic activity of cardiac pacemaker cells and spontaneously firing neurons. Extensive studies over the last decade have provided convincing evidence that I(h) is also involved in a number of basic physiological processes that are not directly associated with rhythmicity. Examples for these non-pacemaking functions of I(h) are the determination of the resting membrane potential, dendritic integration, synaptic transmission, and learning. In this review we summarize recent insights into the structure, function, and cellular regulation of HCN channels. We also discuss in detail the different aspects of HCN channel physiology in the heart and nervous system. To this end, evidence on the role of individual HCN channel types arising from the analysis of HCN knockout mouse models is discussed. Finally, we provide an overview of the impact of HCN channels on the pathogenesis of several diseases and discuss recent attempts to establish HCN channels as drug targets.
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Affiliation(s)
- Martin Biel
- Center for Integrated Protein Science CIPS-M and Zentrum für Pharmaforschung, Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, Munich D-81377, Germany.
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41
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Baruscotti M, Barbuti A, Bucchi A. The cardiac pacemaker current. J Mol Cell Cardiol 2009; 48:55-64. [PMID: 19591835 DOI: 10.1016/j.yjmcc.2009.06.019] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/29/2009] [Revised: 06/15/2009] [Accepted: 06/26/2009] [Indexed: 12/17/2022]
Abstract
In mammals cardiac rate is determined by the duration of the diastolic depolarization of sinoatrial node (SAN) cells which is mainly determined by the pacemaker I(f) current. f-channels are encoded by four members of the hyperpolarization-activated cyclic nucleotide-gated gene (HCN1-4) family. HCN4 is the most abundant isoform in the SAN, and its relevance to pacemaking has been further supported by the discovery of four loss-of-function mutations in patients with mild or severe forms of cardiac rate disturbances. Due to its selective contribution to pacemaking, the I(f) current is also the pharmacological target of a selective heart rate-reducing agent (ivabradine) currently used in the clinical practice. Albeit to a minor extent, the I(f) current is also present in other spontaneously active myocytes of the cardiac conduction system (atrioventricular node and Purkinje fibres). In working atrial and ventricular myocytes f-channels are expressed at a very low level and do not play any physiological role; however in certain pathological conditions over-expression of HCN proteins may represent an arrhythmogenic mechanism. In this review some of the most recent findings on f/HCN channels contribution to pacemaking are described.
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Affiliation(s)
- Mirko Baruscotti
- Department of Biomolecular Sciences and Biotechnology, Laboratory of Molecular Physiology and Neurobiology, Università degli Studi di Milano, Centro Interuniversitario di Medicina Molecolare e Biofisica Applicata (CIMMBA), via Celoria 26, 20133 Milano, Italy.
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42
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Brandt MC, Endres-Becker J, Zagidullin N, Motloch LJ, Er F, Rottlaender D, Michels G, Herzig S, Hoppe UC. Effects of KCNE2 on HCN isoforms: distinct modulation of membrane expression and single channel properties. Am J Physiol Heart Circ Physiol 2009; 297:H355-63. [DOI: 10.1152/ajpheart.00154.2009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Hyperpolarization-activated cation (HCN) channels give rise to an inward current with similar but not identical characteristics compared with the pacemaker current ( If), suggesting that HCN channel function is modulated by regulatory β-subunits in native tissue. KCNE2 has been proposed to serve as a β-subunit of HCN channels; however, available data remain contradictory. To further clarify this situation, we therefore analyzed the effect of KCNE2 on whole cell currents, single channel properties, and membrane protein expression of all cardiac HCN isoforms in the CHO cell system. On the whole cell level, current densities of all HCN isoforms were significantly increased by KCNE2 without altering voltage dependence or current reversal. While these results correlated well with the KCNE2-mediated 2.2-fold and 1.6-fold increases of membrane protein levels of HCN2 and HCN4, respectively, no effect of KCNE2 on HCN1 expression was obtained. All HCN subtypes displayed faster activation kinetics upon coexpression with KCNE2. Most importantly, for the first time, we demonstrated modulation of single channel function by KCNE2, thus supporting direct functional interaction with HCN subunits. In the presence of KCNE2, the single channel amplitudes and conductance of HCN1, HCN2, and HCN4 were significantly increased versus control recordings. Mean open time was significantly increased in cells coexpressing HCN2 + KCNE2, whereas it was unaffected in HCN1 + KCNE2 cotransfected cells and reduced in HCN4 + KCNE2 cotransfected cells compared with the respective HCN subunits alone. Thus, we demonstrate KCNE2-mediated distinct effects on HCN membrane expression and direct functional modulation of HCN isoforms, further supporting that KCNE2 surves as a regulatory β-subunit of HCN channels.
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Lakatta EG, DiFrancesco D. What keeps us ticking: a funny current, a calcium clock, or both? J Mol Cell Cardiol 2009; 47:157-70. [PMID: 19361514 DOI: 10.1016/j.yjmcc.2009.03.022] [Citation(s) in RCA: 205] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/05/2009] [Revised: 03/10/2009] [Accepted: 03/19/2009] [Indexed: 12/14/2022]
Affiliation(s)
- Edward G Lakatta
- Laboratory of Cardiovascular Science, National Institute on Aging, Intramural Research Program, NIH, 5600 Nathan Shock Drive, Baltimore, MD 21224-6825, USA.
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Pacemaker activity of the human sinoatrial node: role of the hyperpolarization-activated current, I(f). Int J Cardiol 2009; 132:318-36. [PMID: 19181406 DOI: 10.1016/j.ijcard.2008.12.196] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2008] [Revised: 12/16/2008] [Accepted: 12/22/2008] [Indexed: 11/20/2022]
Abstract
The mechanism of primary, spontaneous cardiac pacemaker activity of the sinoatrial node (SAN) has extensively been studied in several animal species, but is virtually unexplored in man. Understanding the mechanisms of human SAN pacemaker activity is important for developing new therapeutic approaches for controlling the heart rate in the sick sinus syndrome and in diseased myocardium. Here we review the functional role of the hyperpolarization-activated 'funny' current, I(f), in human SAN pacemaker activity. Despite the many animal studies performed over the years, the contribution of I(f) to pacemaker activity is still controversial and not fully established. However, recent clinical data on mutations in the I(f) encoding HCN4 gene, which is thought to be the most abundant isoform of the HCN gene family in SAN, suggest a functional role of I(f) in human pacemaker activity. These clinical findings are supported by recent experimental data from single isolated human SAN cells that provide direct evidence that I(f) contributes to human SAN pacemaker activity. Therefore, controlling heart rate in clinical practice via I(f) blockers offers a valuable approach to lowering heart rate and provides an attractive alternative to conventional treatment for a wide range of patients with confirmed stable angina, while upregulation or artificial expression of I(f) may relieve disease-causing bradycardias.
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45
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Zhao X, Bucchi A, Oren RV, Kryukova Y, Dun W, Clancy CE, Robinson RB. In vitro characterization of HCN channel kinetics and frequency dependence in myocytes predicts biological pacemaker functionality. J Physiol 2009; 587:1513-25. [PMID: 19171659 DOI: 10.1113/jphysiol.2008.163444] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The pacemaker current, mediated by hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, contributes to the initiation and regulation of cardiac rhythm. Previous experiments creating HCN-based biological pacemakers in vivo found that an engineered HCN2/HCN1 chimeric channel (HCN212) resulted in significantly faster rates than HCN2, interrupted by 1-5 s pauses. To elucidate the mechanisms underlying the differences in HCN212 and HCN2 in vivo functionality as biological pacemakers, we studied newborn rat ventricular myocytes over-expressing either HCN2 or HCN212 channels. The HCN2- and HCN212-over-expressing myocytes manifest similar voltage dependence, current density and sensitivity to saturating cAMP concentrations, but HCN212 has faster activation/deactivation kinetics. Compared with HCN2, myocytes expressing HCN212 exhibit a faster spontaneous rate and greater incidence of irregular rhythms (i.e. periods of rapid spontaneous rate followed by pauses). To explore these rhythm differences further, we imposed consecutive pacing and found that activation kinetics of the two channels are slower at faster pacing frequencies. As a result, time-dependent HCN current flowing during diastole decreases for both constructs during a train of stimuli at a rapid frequency, with the effect more pronounced for HCN2. In addition, the slower deactivation kinetics of HCN2 contributes to more pronounced instantaneous current at a slower frequency. As a result of the frequency dependence of both instantaneous and time-dependent current, HCN2 exhibits more robust negative feedback than HCN212, contributing to the maintenance of a stable pacing rhythm. These results illustrate the benefit of screening HCN constructs in spontaneously active myocyte cultures and may provide the basis for future optimization of HCN-based biological pacemakers.
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Affiliation(s)
- Xin Zhao
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, New York, NY, USA
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47
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Protas L, Dun W, Jia Z, Lu J, Bucchi A, Kumari S, Chen M, Cohen IS, Rosen MR, Entcheva E, Robinson RB. Expression of skeletal but not cardiac Na+ channel isoform preserves normal conduction in a depolarized cardiac syncytium. Cardiovasc Res 2008; 81:528-35. [PMID: 18977767 DOI: 10.1093/cvr/cvn290] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
AIMS Reentrant arrhythmias often develop in the setting of myocardial infarction and ensuing slow propagation. Increased Na(+) channel expression could prevent or disrupt reentrant circuits by speeding conduction if channel availability is not limited by membrane depolarization within the diseased myocardium. We therefore asked if, in the setting of membrane depolarization, action potential (AP) upstroke and normal conduction can be better preserved by the expression of a Na(+) channel isoform with altered biophysical properties compared to the native cardiac Na(+) channel isoform, namely having a positively shifted, voltage-dependent inactivation. METHODS AND RESULTS The skeletal Na(+) channel isoform (SkM1) and the cardiac Na(+) channel isoform (Nav1.5) were expressed in newborn rat ventricular myocyte cultures with a point mutation introduced in Nav1.5 to increase tetrodotoxin (TTX) sensitivity so native and expressed currents could be distinguished. External K(+) was increased from 5.4 to 10 mmol/L to induce membrane depolarization. APs, Na(+) currents, and conduction velocity (CV) were measured. In control cultures, elevated K(+) significantly reduced AP upstroke ( approximately 75%) and CV ( approximately 25%). Expression of Nav1.5 did not protect AP upstroke from K(+) depolarization. In contrast, in SkM1 expressing cultures, high K(+) reduced AP upstroke <50% and conduction was not significantly reduced. In a simulated anatomical reentry setting (using a void), the angular velocity (AV) of induced reentry was faster and the excitable gap shorter in SkM1 cultures compared to control for both normal and high K(+). CONCLUSION Expression of SkM1 but not Nav1.5 preserves AP upstroke and CV in a K(+)-depolarized syncytium. The higher AV and shorter excitable gap observed during reentry excitation around a void in SkM1 cultures would be expected to facilitate reentry self-termination. SkM1 Na(+) channel expression represents a novel gene therapy for the treatment of reentrant arrhythmias.
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Affiliation(s)
- Lev Protas
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, 630 West 168 Street, Room PH7West-318, New York, NY 10032, USA
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48
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Boink GJJ, Verkerk AO, van Amersfoorth SCM, Tasseron SJ, van der Rijt R, Bakker D, Linnenbank AC, van der Meulen J, de Bakker JMT, Seppen J, Tan HL. Engineering physiologically controlled pacemaker cells with lentiviral HCN4 gene transfer. J Gene Med 2008; 10:487-97. [PMID: 18383475 DOI: 10.1002/jgm.1172] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND Research on biological pacemakers for the heart has so far mainly focused on short-term gene and cell therapies. To develop a clinically relevant biological pacemaker, long-term function and incorporation of autonomic modulation are crucial. Lentiviral vectors can mediate long-term gene expression, while isoform 4 of the Hyperpolarization-activated Cyclic Nucleotide-gated channel (encoded by HCN4) contributes to pacemaker function and responds maximally to cAMP, the second messenger in autonomic modulation. MATERIAL AND METHODS Action potential (AP) properties and pacemaker current (I(f)) were studied in single neonatal rat ventricular myocytes that overexpressed HCN4 after lentiviral gene transduction. Autonomic responsiveness and cycle length stability were studied using extracellular electrograms of confluent cultured monolayers. RESULTS Perforated patch-clamp experiments demonstrated that HCN4-transduced single cardiac myocytes exhibited a 10-fold higher I(f) than non-transduced single myocytes, along with slow diastolic depolarization, comparable to pacemaker cells of the sinoatrial node, the dominant native pacemaker. HCN4-transduced monolayers exhibited a 47% increase in beating rate, compared to controls. Upon addition of DBcAMP, HCN4-transduced monolayers had beating rates which were 54% faster than baseline and significantly more regular than controls. CONCLUSIONS Lentiviral vectors efficiently transduce cardiac myocytes and mediate functional gene expression. Because HCN4-transduced myocytes demonstrate an increase in spontaneous beating rate and responsiveness to autonomic modulation, this approach may be useful to create a biological pacemaker.
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Affiliation(s)
- Gerard J J Boink
- Heart Failure Research Center, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
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49
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Abstract
The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations. The exact cascade of steps initiating the pacemaker cycle in automatic cells has not yet been entirely elucidated. Nevertheless, ion channels and intracellular Ca(2+) signaling are necessary for the proper setting of the pacemaker mechanism. Here, we review the current knowledge on the cellular mechanisms underlying the generation and regulation of cardiac automaticity. We discuss evidence on the functional role of different families of ion channels in cardiac pacemaking and review recent results obtained on genetically engineered mouse strains displaying dysfunction in heart automaticity. Beside ion channels, intracellular Ca(2+) release has been indicated as an important mechanism for promoting automaticity at rest as well as for acceleration of the heart rate under sympathetic nerve input. The potential links between the activity of ion channels and Ca(2+) release will be discussed with the aim to propose an integrated framework of the mechanism of automaticity.
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Affiliation(s)
- Matteo E Mangoni
- Institute of Functional Genomics, Department of Physiology, Centre National de la Recherche Scientifique UMR5203, INSERM U661, University of Montpellier I and II, Montpellier, France.
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50
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Kryukova Y, Rybin VO, Qu J, Steinberg SF, Robinson RB. Age-dependent differences in the inhibition of HCN2 current in rat ventricular myocytes by the tyrosine kinase inhibitor erbstatin. Pflugers Arch 2008; 457:821-30. [PMID: 18696104 DOI: 10.1007/s00424-008-0565-7] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2008] [Revised: 06/27/2008] [Accepted: 07/26/2008] [Indexed: 10/21/2022]
Abstract
Previously, we have shown that murine HCN2 channels over-expressed in newborn and adult cardiac myocytes produce currents with different biophysical characteristics. To investigate the role of tyrosine kinase modulation in these age-dependent differences, we employed the broad spectrum tyrosine kinase inhibitor erbstatin. Our results demonstrated distinct and separable effects of erbstatin on channel gating and current amplitude and a marked age dependence to these effects. In newborn myocytes, erbstatin decreased current amplitude, shifted the activation relation negative, and slowed activation kinetics. The effect on activation voltage but not that on amplitude was absent when expressing a cAMP-insensitive mutant (HCN2R/E), while a C-terminal truncated form of HCN2 (HCN2DeltaCx) exhibited only the voltage dependent but not the amplitude effect of erbstatin. Thus, the action of erbstatin on the activation relation and current amplitude are distinct and separable in newborn myocytes, and the effect on activation voltage depends on the cAMP status of HCN2 channels. In contrast to newborn myocytes, erbstatin had no effect on HCN2 under control conditions in adult myocytes but induced a negative shift with no change in amplitude when saturated cAMP was added to the pipette solution. We conclude that erbstatin's effects on HCN2 current magnitude and voltage dependence are distinct and separable, and there are fundamental developmental differences in the heart that affect channel function and its modulation by the tyrosine kinase inhibitor erbstatin.
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Affiliation(s)
- Yelena Kryukova
- Department of Pharmacology, College of Physicians and Surgeons, Columbia University, 630 West 168th Street, New York, NY 10032, USA
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