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Abstract
Cardiac arrhythmias can follow disruption of the normal cellular electrophysiological processes underlying excitable activity and their tissue propagation as coherent wavefronts from the primary sinoatrial node pacemaker, through the atria, conducting structures and ventricular myocardium. These physiological events are driven by interacting, voltage-dependent, processes of activation, inactivation, and recovery in the ion channels present in cardiomyocyte membranes. Generation and conduction of these events are further modulated by intracellular Ca2+ homeostasis, and metabolic and structural change. This review describes experimental studies on murine models for known clinical arrhythmic conditions in which these mechanisms were modified by genetic, physiological, or pharmacological manipulation. These exemplars yielded molecular, physiological, and structural phenotypes often directly translatable to their corresponding clinical conditions, which could be investigated at the molecular, cellular, tissue, organ, and whole animal levels. Arrhythmogenesis could be explored during normal pacing activity, regular stimulation, following imposed extra-stimuli, or during progressively incremented steady pacing frequencies. Arrhythmic substrate was identified with temporal and spatial functional heterogeneities predisposing to reentrant excitation phenomena. These could arise from abnormalities in cardiac pacing function, tissue electrical connectivity, and cellular excitation and recovery. Triggering events during or following recovery from action potential excitation could thereby lead to sustained arrhythmia. These surface membrane processes were modified by alterations in cellular Ca2+ homeostasis and energetics, as well as cellular and tissue structural change. Study of murine systems thus offers major insights into both our understanding of normal cardiac activity and its propagation, and their relationship to mechanisms generating clinical arrhythmias.
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Affiliation(s)
- Christopher L-H Huang
- Physiological Laboratory and the Department of Biochemistry, University of Cambridge, Cambridge, United Kingdom
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52
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Barbuti A, Benzoni P, Campostrini G, Dell'Era P. Human derived cardiomyocytes: A decade of knowledge after the discovery of induced pluripotent stem cells. Dev Dyn 2016; 245:1145-1158. [DOI: 10.1002/dvdy.24455] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2016] [Revised: 05/05/2016] [Accepted: 05/05/2016] [Indexed: 12/27/2022] Open
Affiliation(s)
- Andrea Barbuti
- Department of Biosciences; Università degli Studi di Milano; Milan Italy
| | - Patrizia Benzoni
- Department of Biosciences; Università degli Studi di Milano; Milan Italy
| | - Giulia Campostrini
- Department of Biosciences; Università degli Studi di Milano; Milan Italy
| | - Patrizia Dell'Era
- Cellular Fate Reprogramming Unit, Department of Molecular and Translational Medicine; Università degli Studi di Brescia; Brescia Italy
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53
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Enhancement of hERG channel activity by scFv antibody fragments targeted to the PAS domain. Proc Natl Acad Sci U S A 2016; 113:9916-21. [PMID: 27516548 DOI: 10.1073/pnas.1601116113] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
The human human ether-à-go-go-related gene (hERG) potassium channel plays a critical role in the repolarization of the cardiac action potential. Changes in hERG channel function underlie long QT syndrome (LQTS) and are associated with cardiac arrhythmias and sudden death. A striking feature of this channel and KCNH channels in general is the presence of an N-terminal Per-Arnt-Sim (PAS) domain. In other proteins, PAS domains bind ligands and modulate effector domains. However, the PAS domains of KCNH channels are orphan receptors. We have uncovered a family of positive modulators of hERG that specifically bind to the PAS domain. We generated two single-chain variable fragments (scFvs) that recognize different epitopes on the PAS domain. Both antibodies increase the rate of deactivation but have different effects on channel activation and inactivation. Importantly, we show that both antibodies, on binding to the PAS domain, increase the total amount of current that permeates the channel during a ventricular action potential and significantly reduce the action potential duration recorded in human cardiomyocytes. Overall, these molecules constitute a previously unidentified class of positive modulators and establish that allosteric modulation of hERG channel function through ligand binding to the PAS domain can be attained.
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54
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Abstract
Multiple types of voltage-gated K(+) and non-voltage-gated K(+) currents have been distinguished in mammalian cardiac myocytes based on differences in time-dependent and voltage-dependent properties and pharmacologic sensitivities. Many of the genes encoding voltage-gated K(+) (Kv) and non-voltage-gated K(+) (Kir and K2P) channel pore-forming and accessory subunits are expressed in the heart, and a variety of approaches have been, and continue to be, used to define the molecular determinants of native cardiac K(+) channels and to explore the molecular mechanisms controlling the diversity, regulation, and remodeling of these channels in the normal and diseased myocardium.
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Affiliation(s)
- Jeanne M Nerbonne
- Department of Internal Medicine, Washington University Medical School, 660 South Euclid Avenue, Box 8086, St Louis, MO 63110, USA; Department of Developmental Biology, Washington University Medical School, St Louis, MO 63110, USA.
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55
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Cotranslational association of mRNA encoding subunits of heteromeric ion channels. Proc Natl Acad Sci U S A 2016; 113:4859-64. [PMID: 27078096 DOI: 10.1073/pnas.1521577113] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Oligomers of homomeric voltage-gated potassium channels associate early in biogenesis as the nascent proteins emerge from the polysome. Less is known about how proteins emerging from different polysomes associate to form hetero-oligomeric channels. Here, we report that alternate mRNA transcripts encoding human ether-à-go-go-related gene (hERG) 1a and 1b subunits, which assemble to produce ion channels mediating cardiac repolarization, are physically associated during translation. We show that shRNA specifically targeting either hERG 1a or 1b transcripts reduced levels of both transcripts, but only when they were coexpressed heterologously. Both transcripts could be copurified with an Ab against the nascent hERG 1a N terminus. This interaction occurred even when translation of 1b was prevented, indicating the transcripts associate independent of their encoded proteins. The association was also demonstrated in cardiomyocytes, where levels of both hERG transcripts were reduced by either 1a or 1b shRNA, but native KCNE1 and ryanodine receptor 2 (RYR2) transcripts were unaffected. Changes in protein levels and membrane currents mirrored changes in transcript levels, indicating the targeted transcripts were undergoing translation. The physical association of transcripts encoding different subunits provides the spatial proximity required for nascent proteins to interact during biogenesis, and may represent a general mechanism facilitating assembly of heteromeric protein complexes involved in a range of biological processes.
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56
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Wu W, Sanguinetti MC. Molecular Basis of Cardiac Delayed Rectifier Potassium Channel Function and Pharmacology. Card Electrophysiol Clin 2016; 8:275-84. [PMID: 27261821 DOI: 10.1016/j.ccep.2016.01.002] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Human cardiomyocytes express 3 distinct types of delayed rectifier potassium channels. Human ether-a-go-go-related gene (hERG) channels conduct the rapidly activating current IKr; KCNQ1/KCNE1 channels conduct the slowly activating current IKs; and Kv1.5 channels conduct an ultrarapid activating current IKur. Here the authors provide a general overview of the mechanistic and structural basis of ion selectivity, gating, and pharmacology of the 3 types of cardiac delayed rectifier potassium ion channels. Most blockers bind to S6 residues that line the central cavity of the channel, whereas activators interact with the channel at 4 symmetric binding sites outside the cavity.
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Affiliation(s)
- Wei Wu
- Department of Medicine, Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112, USA
| | - Michael C Sanguinetti
- Department of Medicine, Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, 95 South 2000 East, Salt Lake City, UT 84112, USA.
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57
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Foo B, Williamson B, Young JC, Lukacs G, Shrier A. hERG quality control and the long QT syndrome. J Physiol 2016; 594:2469-81. [PMID: 26718903 DOI: 10.1113/jp270531] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2015] [Accepted: 12/07/2015] [Indexed: 11/08/2022] Open
Abstract
Long-QT syndrome type-2 (LQT2) is characterized by reduced functional expression of the human ether-à-go-go related (hERG) gene product, resulting in impaired cardiac repolarization and predisposition to fatal arrhythmia. Previous studies have implicated abnormal trafficking of misfolded hERG as the primary mechanism of LQT2, with misfolding being caused by mutations in the hERG gene (inherited) or drug treatment (acquired). More generally, environmental and metabolic stresses present a constant challenge to the folding of proteins, including hERG, and must be countered by robust protein quality control (QC) systems. Disposal of partially unfolded yet functional plasma membrane (PM) proteins by protein QC contributes to the loss-of-function phenotype in various conformational diseases including cystic fibrosis (CF) and long-QT syndrome type-2 (LQT2). The prevalent view has been that the loss of PM expression of hERG is attributed to biosynthetic block by endoplasmic reticulum (ER) QC pathways. However, there is a growing appreciation for protein QC pathways acting at post-ER cellular compartments, which may contribute to conformational disease pathogenesis. This article will provide a background on the structure and cellular trafficking of hERG as well as inherited and acquired LQT2. We will review previous work on hERG ER QC and introduce the more novel view that there is a significant peripheral QC at the PM and peripheral cellular compartments. Particular attention is drawn to the unique role of the peripheral QC system in acquired LQT2. Understanding the QC process and players may provide targets for therapeutic intervention in dealing with LQT2.
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Affiliation(s)
- Brian Foo
- Department of Physiology, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Brittany Williamson
- Department of Biochemistry, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Jason C Young
- Department of Biochemistry, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Gergely Lukacs
- Department of Physiology, McGill University, Montréal, Québec, Canada, H3G 1Y6
| | - Alvin Shrier
- Department of Physiology, McGill University, Montréal, Québec, Canada, H3G 1Y6
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58
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Autonomous beating rate adaptation in human stem cell-derived cardiomyocytes. Nat Commun 2016; 7:10312. [PMID: 26785135 PMCID: PMC4735644 DOI: 10.1038/ncomms10312] [Citation(s) in RCA: 127] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2015] [Accepted: 11/27/2015] [Indexed: 02/06/2023] Open
Abstract
The therapeutic success of human stem cell-derived cardiomyocytes critically depends on their ability to respond to and integrate with the surrounding electromechanical environment. Currently, the immaturity of human cardiomyocytes derived from stem cells limits their utility for regenerative medicine and biological research. We hypothesize that biomimetic electrical signals regulate the intrinsic beating properties of cardiomyocytes. Here we show that electrical conditioning of human stem cell-derived cardiomyocytes in three-dimensional culture promotes cardiomyocyte maturation, alters their automaticity and enhances connexin expression. Cardiomyocytes adapt their autonomous beating rate to the frequency at which they were stimulated, an effect mediated by the emergence of a rapidly depolarizing cell population, and the expression of hERG. This rate-adaptive behaviour is long lasting and transferable to the surrounding cardiomyocytes. Thus, electrical conditioning may be used to promote cardiomyocyte maturation and establish their automaticity, with implications for cell-based reduction of arrhythmia during heart regeneration.
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59
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Maturing human pluripotent stem cell-derived cardiomyocytes in human engineered cardiac tissues. Adv Drug Deliv Rev 2016; 96:110-34. [PMID: 25956564 DOI: 10.1016/j.addr.2015.04.019] [Citation(s) in RCA: 167] [Impact Index Per Article: 20.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2015] [Revised: 04/24/2015] [Accepted: 04/25/2015] [Indexed: 12/19/2022]
Abstract
Engineering functional human cardiac tissue that mimics the native adult morphological and functional phenotype has been a long held objective. In the last 5 years, the field of cardiac tissue engineering has transitioned from cardiac tissues derived from various animal species to the production of the first generation of human engineered cardiac tissues (hECTs), due to recent advances in human stem cell biology. Despite this progress, the hECTs generated to date remain immature relative to the native adult myocardium. In this review, we focus on the maturation challenge in the context of hECTs, the present state of the art, and future perspectives in terms of regenerative medicine, drug discovery, preclinical safety testing and pathophysiological studies.
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60
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Puckerin A, Aromolaran KA, Chang DD, Zukin RS, Colecraft HM, Boutjdir M, Aromolaran AS. hERG 1a LQT2 C-terminus truncation mutants display hERG 1b-dependent dominant negative mechanisms. Heart Rhythm 2016; 13:1121-1130. [PMID: 26775140 DOI: 10.1016/j.hrthm.2016.01.012] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/19/2015] [Indexed: 12/01/2022]
Abstract
BACKGROUND The human ether-à-go-go-related gene (hERG 1a) potassium channel is critical for cardiac repolarization. hERG 1b, another variant subunit, co-assembles with hERG 1a, modulates channel biophysical properties and plays an important role in repolarization. Mutations of hERG 1a lead to type 2 long QT syndrome (LQT2), and increased risk for fatal arrhythmias. The functional consequences of these mutations in the presence of hERG 1b are not known. OBJECTIVE To investigate whether hERG 1a mutants exert dominant negative gating and trafficking defects when co-expressed with hERG 1b. METHODS Electrophysiology, co-immunoprecipitation, and fluorescence resonance energy transfer (FRET) experiments in HEK293 cells and guinea pig cardiomyocytes were used to assess the mutants on gating and trafficking. Mutations of 1a-G965X and 1a-R1014X, relevant to gating and trafficking were introduced in the C-terminus region. RESULTS The hERG 1a mutants when expressed alone did not result in decreased current amplitude. Compared to wild-type hERG 1a currents, 1a-G965X currents were significantly larger, whereas those produced by the 1a-R1014X mutant were similar in magnitude. Only when co-expressed with wild-type hERG 1a and 1b did a mutant phenotype emerge, with a marked reduction in surface expression, current amplitude, and a corresponding positive shift in the V1/2 of the activation curve. Co-immunoprecipitation and FRET assays confirmed association of mutant and wild-type subunits. CONCLUSION Heterologously expressed hERG 1a C-terminus truncation mutants, exert a dominant negative gating and trafficking effect only when co-expressed with hERG 1b. These findings may have potentially profound implications for LQT2 therapy.
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Affiliation(s)
- Akil Puckerin
- Department of Physiology & Cellular Biophysics, Columbia University, New York, New York
| | - Kelly A Aromolaran
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, New York
| | - Donald D Chang
- Department of Physiology & Cellular Biophysics, Columbia University, New York, New York
| | - R Suzanne Zukin
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, New York, New York
| | - Henry M Colecraft
- Department of Physiology & Cellular Biophysics, Columbia University, New York, New York
| | - Mohamed Boutjdir
- Cardiovascular Research Program, VA New York Harbor Healthcare System, Brooklyn, New York; Departments of Medicine, Cell Biology and Pharmacology, State University of New York Downstate Medical Center, Brooklyn, New York,; Department of Medicine, New York University School of Medicine, New York, New York
| | - Ademuyiwa S Aromolaran
- Department of Physiology & Cellular Biophysics, Columbia University, New York, New York.
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61
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Jones DK, Liu F, Dombrowski N, Joshi S, Robertson GA. Dominant negative consequences of a hERG 1b-specific mutation associated with intrauterine fetal death. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 120:67-76. [PMID: 26772437 DOI: 10.1016/j.pbiomolbio.2016.01.002] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/19/2015] [Revised: 12/07/2015] [Accepted: 01/04/2016] [Indexed: 12/16/2022]
Abstract
The human ether-a-go-go related gene (hERG) encodes two subunits, hERG 1a and hERG 1b, that combine in vivo to conduct the rapid delayed rectifier potassium current (IKr). Reduced IKr slows cardiac action potential (AP) repolarization and is an underlying cause of cardiac arrhythmias associated with long QT syndrome (LQTS). Although the physiological importance of hERG 1b has been elucidated, the effects of hERG 1b disease mutations on cardiac IKr and AP behavior have not been described. To explore the disease mechanism of a 1b-specific mutation associated with a case of intrauterine fetal death, we examined the effects of the 1b-R25W mutation on total protein, trafficking and membrane current levels in HEK293 cells at physiological temperatures. By all measures the 1b-R25W mutation conferred diminished expression, and exerted a temperature-sensitive, dominant-negative effect over the WT hERG 1a protein with which it was co-expressed. Membrane currents were reduced by 60% with no apparent effect on voltage dependence or deactivation kinetics. The dominant-negative effects of R25W were demonstrated in iPSC-CMs, where 1b-R25W transfection diminished native IKr compared to controls. R25W also slowed AP repolarization, and increased AP triangulation and variability in iPSC-CMs, reflecting cellular manifestations of pro-arrhythmia. These data demonstrate that R25W is a dominant-negative mutation with significant pathophysiological consequences, and provide the first direct link between hERG 1b mutation and cardiomyocyte dysfunction.
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Affiliation(s)
- David K Jones
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Fang Liu
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Natasha Dombrowski
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Sunita Joshi
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA
| | - Gail A Robertson
- Dept. of Neuroscience, University of Wisconsin School of Medicine and Public Health, 1111 Highland Avenue, Madison WI 53705, USA.
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62
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Abstract
The zebrafish (Danio rerio) has become a popular model for human cardiac diseases and pharmacology including cardiac arrhythmias and its electrophysiological basis. Notably, the phenotype of zebrafish cardiac action potential is similar to the human cardiac action potential in that both have a long plateau phase. Also the major inward and outward current systems are qualitatively similar in zebrafish and human hearts. However, there are also significant differences in ionic current composition between human and zebrafish hearts, and the molecular basis and pharmacological properties of human and zebrafish cardiac ionic currents differ in several ways. Cardiac ionic currents may be produced by non-orthologous genes in zebrafish and humans, and paralogous gene products of some ion channels are expressed in the zebrafish heart. More research on molecular basis of cardiac ion channels, and regulation and drug sensitivity of the cardiac ionic currents are needed to enable rational use of the zebrafish heart as an electrophysiological model for the human heart.
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Affiliation(s)
- Matti Vornanen
- a Department of Biology , University of Eastern Finland , Joensuu , Finland
| | - Minna Hassinen
- a Department of Biology , University of Eastern Finland , Joensuu , Finland
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63
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Hassinen M, Haverinen J, Vornanen M. Molecular basis and drug sensitivity of the delayed rectifier (IKr) in the fish heart. Comp Biochem Physiol C Toxicol Pharmacol 2015. [PMID: 26215639 DOI: 10.1016/j.cbpc.2015.07.005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Fishes are increasingly used as models for human cardiac diseases, creating a need for a better understanding of the molecular basis of fish cardiac ion currents. To this end we cloned KCNH6 channel of the crucian carp (Carassius carassius) that produces the rapid component of the delayed rectifier K(+) current (IKr), the main repolarising current of the fish heart. KCNH6 (ccErg2) was the main isoform of the Kv11 potassium channel family with relative transcript levels of 98.9% and 99.6% in crucian carp atrium and ventricle, respectively. KCNH2 (ccErg1), an orthologue to human cardiac Erg (Herg) channel, was only slightly expressed in the crucian carp heart. The native atrial IKr and the cloned ccErg2 were inhibited by similar concentrations of verapamil, terfenadine and KB-R7943 (P>0.05), while the atrial IKr was about an order of magnitude more sensitive to E-4031 than ccErg2 (P<0.05) suggesting that some accessory β-subunits may be involved. Sensitivity of the crucian carp atrial IKr to E-4031, terfenadine and KB-R7943 was similar to what has been reported for the Herg channel. In contrast, the sensitivity of the crucian carp IKr to verapamil was approximately 30 times higher than the previously reported values for the Herg current. In conclusion, the cardiac IKr is produced by non-orthologous gene products in fish (Erg2) and mammalian hearts (Erg1) and some marked differences exist in drug sensitivity between fish and mammalian Erg1/2 which need to be taken into account when using fish heart as a model for human heart.
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Affiliation(s)
- Minna Hassinen
- University of Eastern Finland, Department of Biology, P.O. Box 111, 80101 Joensuu, Finland.
| | - Jaakko Haverinen
- University of Eastern Finland, Department of Biology, P.O. Box 111, 80101 Joensuu, Finland
| | - Matti Vornanen
- University of Eastern Finland, Department of Biology, P.O. Box 111, 80101 Joensuu, Finland
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64
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Lees-Miller JP, Guo J, Wang Y, Perissinotti LL, Noskov SY, Duff HJ. Ivabradine prolongs phase 3 of cardiac repolarization and blocks the hERG1 (KCNH2) current over a concentration-range overlapping with that required to block HCN4. J Mol Cell Cardiol 2015; 85:71-8. [DOI: 10.1016/j.yjmcc.2015.05.009] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Revised: 05/08/2015] [Accepted: 05/11/2015] [Indexed: 10/23/2022]
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65
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Fermini B, Hancox JC, Abi-Gerges N, Bridgland-Taylor M, Chaudhary KW, Colatsky T, Correll K, Crumb W, Damiano B, Erdemli G, Gintant G, Imredy J, Koerner J, Kramer J, Levesque P, Li Z, Lindqvist A, Obejero-Paz CA, Rampe D, Sawada K, Strauss DG, Vandenberg JI. A New Perspective in the Field of Cardiac Safety Testing through the Comprehensive In Vitro Proarrhythmia Assay Paradigm. ACTA ACUST UNITED AC 2015; 21:1-11. [PMID: 26170255 DOI: 10.1177/1087057115594589] [Citation(s) in RCA: 198] [Impact Index Per Article: 22.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2015] [Accepted: 06/11/2015] [Indexed: 12/31/2022]
Abstract
For the past decade, cardiac safety screening to evaluate the propensity of drugs to produce QT interval prolongation and Torsades de Pointes (TdP) arrhythmia has been conducted according to ICH S7B and ICH E14 guidelines. Central to the existing approach are hERG channel assays and in vivo QT measurements. Although effective, the present paradigm carries a risk of unnecessary compound attrition and high cost, especially when considering costly thorough QT (TQT) studies conducted later in drug development. The C: omprehensive I: n Vitro P: roarrhythmia A: ssay (CiPA) initiative is a public-private collaboration with the aim of updating the existing cardiac safety testing paradigm to better evaluate arrhythmia risk and remove the need for TQT studies. It is hoped that CiPA will produce a standardized ion channel assay approach, incorporating defined tests against major cardiac ion channels, the results of which then inform evaluation of proarrhythmic actions in silico, using human ventricular action potential reconstructions. Results are then to be confirmed using human (stem cell-derived) cardiomyocytes. This perspective article reviews the rationale, progress of, and challenges for the CiPA initiative, if this new paradigm is to replace existing practice and, in time, lead to improved and widely accepted cardiac safety testing guidelines.
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Affiliation(s)
| | - Jules C Hancox
- School of Physiology and Pharmacology, University of Bristol, Bristol, UK
| | - Najah Abi-Gerges
- Translational Safety, Drug Safety and Metabolism, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield, UK AnaBios Corporation, San Diego, CA, USA
| | - Matthew Bridgland-Taylor
- Discovery Sciences, Innovative Medicines and Early Development, AstraZeneca R&D, Macclesfield, UK
| | | | - Thomas Colatsky
- Division of Applied Regulatory Science, CDER, US Food and Drug Administration, Silver Spring, MD, USA
| | | | | | - Bruce Damiano
- Global Safety Pharmacology, Discovery Sciences, Janssen Research & Development LLC, Spring House, PA, USA
| | - Gul Erdemli
- Center for Proteomic Chemistry, Novartis Institutes for BioMedical Research, Inc, Cambridge, MA, USA
| | - Gary Gintant
- Department of Integrative Pharmacology, Integrated Sciences & Technology, AbbVie, North Chicago, IL, USA
| | - John Imredy
- Department of Safety Assessment, Merck & Co, Kenilworth, NJ, USA
| | - John Koerner
- Division of Cardiovascular and Renal Products, CDER, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - James Kramer
- ChanTest, A Charles River Company, Cleveland, OH, USA
| | - Paul Levesque
- Bristol Myers Squibb Research & Development, Princeton, NJ, USA
| | - Zhihua Li
- Division of Applied Regulatory Science, CDER, US Food and Drug Administration, Silver Spring, MD, USA
| | | | | | - David Rampe
- Preclinical Safety, Sanofi, Bridgewater, NJ, USA
| | - Kohei Sawada
- Global Cardiovascular Assessment, Eisai Co., Ltd., Ibaraki, Japan
| | - David G Strauss
- Center for Devices and Radiological Health, U.S. Food and Drug Administration, Silver Spring, MD, USA
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute, St Vincent's Clinical School, University of NSW, Darlinghurst, NSW, Australia
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Perry MD, Ng CA, Mann SA, Sadrieh A, Imtiaz M, Hill AP, Vandenberg JI. Getting to the heart of hERG K(+) channel gating. J Physiol 2015; 593:2575-85. [PMID: 25820318 PMCID: PMC4500344 DOI: 10.1113/jp270095] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 03/13/2015] [Indexed: 12/24/2022] Open
Abstract
Potassium ion channels encoded by the human ether-a-go-go related gene (hERG) form the ion-conducting subunit of the rapid delayed rectifier potassium current (IKr ). Although hERG channels exhibit a widespread tissue distribution they play a particularly important role in the heart. There has been considerable interest in hERG K(+) channels for three main reasons. First, they have very unusual gating kinetics, most notably rapid and voltage-dependent inactivation coupled to slow deactivation, which has led to the suggestion that they may play a specific role in the suppression of arrhythmias. Second, mutations in hERG are the cause of 30-40% of cases of congenital long QT syndrome (LQTS), the commonest inherited primary arrhythmia syndrome. Third, hERG is the molecular target for the vast majority of drugs that cause drug-induced LQTS, the commonest cause of drug-induced arrhythmias and cardiac death. Drug-induced LQTS has now been reported for a large range of both cardiac and non-cardiac drugs, in which this side effect is entirely undesired. In recent years there have been comprehensive reviews published on hERG K(+) channels (Vandenberg et al. 2012) and we will not re-cover this ground. Rather, we focus on more recent work on the structural basis and dynamics of hERG gating with an emphasis on how the latest developments may facilitate translational research in the area of stratifying risk of arrhythmias.
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Affiliation(s)
- Matthew D Perry
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Chai-Ann Ng
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Stefan A Mann
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Arash Sadrieh
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Mohammad Imtiaz
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Adam P Hill
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
| | - Jamie I Vandenberg
- Victor Chang Cardiac Research Institute405 Liverpool Street, Darlinghurst, NSW 2010, Australia
- St Vincent’s Clinical School, University of NSWDarlinghurst, NSW 2010, Australia
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67
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Osterbur ML, Zheng R, Marion R, Walsh C, McDonald TV. An Interdomain KCNH2 Mutation Produces an Intermediate Long QT Syndrome. Hum Mutat 2015; 36:764-73. [PMID: 25914329 DOI: 10.1002/humu.22805] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Accepted: 04/08/2015] [Indexed: 12/19/2022]
Abstract
Hereditary long QT syndrome is caused by deleterious mutation in one of several genetic loci, including locus LQT2 that contains the KCNH2 gene (or hERG, human ether-a-go-go related gene), causing faulty cardiac repolarization. Here, we describe and characterize a novel mutation, p.Asp219Val in the hERG channel, identified in an 11-year-old male with syncope and prolonged QT interval. Genetic sequencing showed a nonsynonymous variation in KCNH2 (c.656A>T: amino acid p.Asp219Val). p.Asp219Val resides in a region of the channel predicted to be unstructured and flexible, located between the PAS (Per-Arnt-Sim) domain and its interaction sites in the transmembrane domain. The p.Asp219Val hERG channel produced K(+) current that activated with modest changes in voltage dependence. Mutant channels were also slower to inactivate, recovered from inactivation more readily and demonstrated a significantly accelerated deactivation rate compared with the slow deactivation of wild-type channels. The intermediate nature of the biophysical perturbation is consistent with the degree of severity in the clinical phenotype. The findings of this study demonstrate a previously unknown role of the proximal N-terminus in deactivation and support the hypothesis that the proximal N-terminal domain is essential in maintaining slow hERG deactivation.
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Affiliation(s)
- Marika L Osterbur
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY
| | - Renjian Zheng
- Wilf Cardiovascular Research Institute, Albert Einstein College of Medicine, Bronx, NY
| | - Robert Marion
- Department of Pediatrics, Division of Genetics, Children's Hospital at Montefiore, Bronx, NY
| | - Christine Walsh
- Department of Pediatrics, Division of Cardiology, Children's Hospital at Montefiore, Bronx, NY
| | - Thomas V McDonald
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY.,Wilf Cardiovascular Research Institute, Albert Einstein College of Medicine, Bronx, NY.,Department of Medicine, Division of Cardiology, Albert Einstein College of Medicine, Bronx, NY
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68
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Melgari D, Brack KE, Zhang C, Zhang Y, El Harchi A, Mitcheson JS, Dempsey CE, Ng GA, Hancox JC. hERG potassium channel blockade by the HCN channel inhibitor bradycardic agent ivabradine. J Am Heart Assoc 2015; 4:jah3927. [PMID: 25911606 PMCID: PMC4579960 DOI: 10.1161/jaha.115.001813] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Background Ivabradine is a specific bradycardic agent used in coronary artery disease and heart failure, lowering heart rate through inhibition of sinoatrial nodal HCN‐channels. This study investigated the propensity of ivabradine to interact with KCNH2‐encoded human Ether‐à‐go‐go–Related Gene (hERG) potassium channels, which strongly influence ventricular repolarization and susceptibility to torsades de pointes arrhythmia. Methods and Results Patch clamp recordings of hERG current (IhERG) were made from hERG expressing cells at 37°C. IhERG was inhibited with an IC50 of 2.07 μmol/L for the hERG 1a isoform and 3.31 μmol/L for coexpressed hERG 1a/1b. The voltage and time‐dependent characteristics of IhERG block were consistent with preferential gated‐state‐dependent channel block. Inhibition was partially attenuated by the N588K inactivation‐mutant and the S624A pore‐helix mutant and was strongly reduced by the Y652A and F656A S6 helix mutants. In docking simulations to a MthK‐based homology model of hERG, the 2 aromatic rings of the drug could form multiple π‐π interactions with the aromatic side chains of both Y652 and F656. In monophasic action potential (MAP) recordings from guinea‐pig Langendorff‐perfused hearts, ivabradine delayed ventricular repolarization and produced a steepening of the MAPD90 restitution curve. Conclusions Ivabradine prolongs ventricular repolarization and alters electrical restitution properties at concentrations relevant to the upper therapeutic range. In absolute terms ivabradine does not discriminate between hERG and HCN channels: it inhibits IhERG with similar potency to that reported for native If and HCN channels, with S6 binding determinants resembling those observed for HCN4. These findings may have important implications both clinically and for future bradycardic drug design.
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Affiliation(s)
- Dario Melgari
- School of Physiology & Pharmacology, Medical Sciences Building, Bristol, United Kingdom (D.M., Y.Z., A.E.H., J.C.H.)
| | - Kieran E Brack
- Department of Cardiovascular Sciences, Cardiology Group, Glenfield Hospital, University of Leicester, United Kingdom (K.E.B., C.Z., A.N.)
| | - Chuan Zhang
- Department of Cardiovascular Sciences, Cardiology Group, Glenfield Hospital, University of Leicester, United Kingdom (K.E.B., C.Z., A.N.)
| | - Yihong Zhang
- School of Physiology & Pharmacology, Medical Sciences Building, Bristol, United Kingdom (D.M., Y.Z., A.E.H., J.C.H.)
| | - Aziza El Harchi
- School of Physiology & Pharmacology, Medical Sciences Building, Bristol, United Kingdom (D.M., Y.Z., A.E.H., J.C.H.)
| | - John S Mitcheson
- Department of Cell Physiology and Pharmacology, Maurice Shock Medical Sciences Building, Leicester, United Kingdom (J.S.M.)
| | | | - G André Ng
- Department of Cardiovascular Sciences, Cardiology Group, Glenfield Hospital, University of Leicester, United Kingdom (K.E.B., C.Z., A.N.) NIHR Leicester Cardiovascular Biomedical Research Unit, Leicester, United Kingdom (A.N.)
| | - Jules C Hancox
- School of Physiology & Pharmacology, Medical Sciences Building, Bristol, United Kingdom (D.M., Y.Z., A.E.H., J.C.H.)
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