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Bazoukis G, Saplaouras A, Efthymiou P, Yiannikourides A, Liu T, Letsas KP, Efremidis M, Lampropoulos K, Xydonas S, Tse G, Armoundas AA. Cardiac contractility modulation in patients with heart failure - A review of the literature. Heart Fail Rev 2024; 29:689-705. [PMID: 38393423 DOI: 10.1007/s10741-024-10390-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 01/30/2024] [Indexed: 02/25/2024]
Abstract
Experimental in vivo and in vitro studies showed that electric currents applied during the absolute refractory period can modulate cardiac contractility. In preclinical studies, cardiac contractility modulation (CCM) was found to improve calcium handling, reverse the foetal myocyte gene programming associated with heart failure (HF), and facilitate reverse remodeling. Randomized control trials and observational studies have provided evidence about the safety and efficacy of CCM in patients with HF. Clinically, CCM therapy is indicated to improve the 6-min hall walk, quality of life, and functional status of HF patients who remain symptomatic despite guideline-directed medical treatment without an indication for cardiac resynchronization therapy (CRT) and have a left ventricular ejection fraction (LVEF) ranging from 25 to 45%. Although there are promising results about the role of CCM in HF patients with preserved LVEF (HFpEF), further studies are needed to elucidate the role of CCM therapy in this population. Late gadolinium enhancement (LGE) assessment before CCM implantation has been proposed for guiding the lead placement. Furthermore, the optimal duration of CCM application needs further investigation. This review aims to present the existing evidence regarding the role of CCM therapy in HF patients and identify gaps and challenges that require further studies.
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Affiliation(s)
- George Bazoukis
- Department of Cardiology, Larnaca General Hospital, Inomenon Polition Amerikis, Larnaca, Cyprus.
- Medical School, European University Cyprus, Nicosia, Cyprus.
| | | | - Polyxeni Efthymiou
- Department of Cardiology, Larnaca General Hospital, Inomenon Polition Amerikis, Larnaca, Cyprus
| | | | - 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, China
| | | | - Michael Efremidis
- Department of Cardiology, Onassis Cardiac Surgery Center, Athens, Greece
| | | | - Sotirios Xydonas
- Second Department of Cardiology, Evangelismos General Hospital, Athens, Greece
| | - Gary Tse
- Tianjin Key Laboratory of Ionic-Molecular Function of Cardiovascular Disease, Department of Cardiology, Tianjin Institute of Cardiology, Second Hospital of Tianjin Medical University, Tianjin, China
- Kent and Medway Medical School, University of Kent, Canterbury, Kent, UK
- Canterbury Christ Church University, Canterbury, Kent, UK
- School of Nursing and Health Studies, Hong Kong Metropolitan University, Hong Kong, China
| | - Antonis A Armoundas
- Cardiovascular Research Center, Massachusetts General Hospital, 149 13th Street, Charlestown, Boston, MA, 02129, USA.
- Broad Institute, Massachusetts Institute of Technology, Cambridge, MA, USA.
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Reisqs JB, Qu YS, Boutjdir M. Ion channel trafficking implications in heart failure. Front Cardiovasc Med 2024; 11:1351496. [PMID: 38420267 PMCID: PMC10899472 DOI: 10.3389/fcvm.2024.1351496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Accepted: 01/25/2024] [Indexed: 03/02/2024] Open
Abstract
Heart failure (HF) is recognized as an epidemic in the contemporary world, impacting around 1%-2% of the adult population and affecting around 6 million Americans. HF remains a major cause of mortality, morbidity, and poor quality of life. Several therapies are used to treat HF and improve the survival of patients; however, despite these substantial improvements in treating HF, the incidence of HF is increasing rapidly, posing a significant burden to human health. The total cost of care for HF is USD 69.8 billion in 2023, warranting a better understanding of the mechanisms involved in HF. Among the most serious manifestations associated with HF is arrhythmia due to the electrophysiological changes within the cardiomyocyte. Among these electrophysiological changes, disruptions in sodium and potassium currents' function and trafficking, as well as calcium handling, all of which impact arrhythmia in HF. The mechanisms responsible for the trafficking, anchoring, organization, and recycling of ion channels at the plasma membrane seem to be significant contributors to ion channels dysfunction in HF. Variants, microtubule alterations, or disturbances of anchoring proteins lead to ion channel trafficking defects and the alteration of the cardiomyocyte's electrophysiology. Understanding the mechanisms of ion channels trafficking could provide new therapeutic approaches for the treatment of HF. This review provides an overview of the recent advances in ion channel trafficking in HF.
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Affiliation(s)
- Jean-Baptiste Reisqs
- Cardiovascular Research Program, VA New York Harbor Healthcare System, New York, NY, United States
| | - Yongxia Sarah Qu
- Cardiovascular Research Program, VA New York Harbor Healthcare System, New York, NY, United States
- Department of Cardiology, New York Presbyterian Brooklyn Methodist Hospital, New York, NY, United States
| | - Mohamed Boutjdir
- Cardiovascular Research Program, VA New York Harbor Healthcare System, New York, NY, United States
- Department of Medicine, Cell Biology and Pharmacology, State University of New York Downstate Health Sciences University, New York, NY, United States
- Department of Medicine, New York University Grossman School of Medicine, New York, NY, United States
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Dago M, Crespo-García T, Cámara-Checa A, Rapún J, Rubio-Alarcón M, Marín M, Tamargo J, Caballero R, Delpón E. Empagliflozin and Dapagliflozin Increase Na + and Inward Rectifier K + Current Densities in Human Cardiomyocytes Derived from Induced Pluripotent Stem Cells (hiPSC-CMs). Cells 2022; 11:3707. [PMID: 36496967 PMCID: PMC9738206 DOI: 10.3390/cells11233707] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2022] [Revised: 11/14/2022] [Accepted: 11/15/2022] [Indexed: 11/23/2022] Open
Abstract
Dapagliflozin (dapa) and empagliflozin (empa) are sodium-glucose cotransporter-2 inhibitors (SGLT2is) that reduce morbidity and mortality in heart failure (HF) patients. Sodium and inward rectifier K+ currents (INa and IK1), carried by Nav1.5 and Kir2.1 channels, respectively, are responsible for cardiac excitability, conduction velocity, and refractoriness. In HF patients, Nav1.5 and Kir2.1 expression are reduced, enhancing risk of arrhythmia. Incubation with dapa or empa (24-h,1 µM) significantly increased INa and IK1 densities recorded in human-induced pluripotent stem cell-cardiomyocytes (hiPSC-CMs) using patch-clamp techniques. Dapa and empa, respectively, shifted to more hyperpolarized potentials the INa activation and inactivation curves. Identical effects were observed in Chinese hamster ovary (CHO) cells that were incubated with dapa or empa and transiently expressed human Nav1.5 channels. Conversely, empa but not dapa significantly increased human Kir2.1 currents in CHO cells. Dapa and empa effects on INa and IK1 were also apparent in Ca-calmodulin kinase II-silenced CHO cells. Cariporide, a Na+/H+ exchanger type 1 (NHE1) inhibitor, did not increase INa or IK1 in hiPSC-CMs. Dapa and empa at therapeutic concentrations increased INa and IK1 in healthy human cardiomyocytes. These SGLT2is could represent a new class of drugs with a novel and long-pursued antiarrhythmic mechanism of action.
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Affiliation(s)
- María Dago
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Teresa Crespo-García
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Anabel Cámara-Checa
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Josu Rapún
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Marcos Rubio-Alarcón
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - María Marín
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Juan Tamargo
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
| | - Ricardo Caballero
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
| | - Eva Delpón
- Department of Pharmacology and Toxicology, School of Medicine, Instituto de Investigación Sanitaria Gregorio Marañón, Universidad Complutense de Madrid, 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red Enfermedades Cardiovasculares (CIBERCV), Instituto de Salud Carlos III, 28029 Madrid, Spain
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Jian K, Li C, Hancox JC, Zhang H. Pro-Arrhythmic Effects of Discontinuous Conduction at the Purkinje Fiber-Ventricle Junction Arising From Heart Failure-Induced Ionic Remodeling - Insights From Computational Modelling. Front Physiol 2022; 13:877428. [PMID: 35547576 PMCID: PMC9081695 DOI: 10.3389/fphys.2022.877428] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Accepted: 03/18/2022] [Indexed: 11/18/2022] Open
Abstract
Heart failure is associated with electrical remodeling of the electrical properties and kinetics of the ion channels and transporters that are responsible for cardiac action potentials. However, it is still unclear whether heart failure-induced ionic remodeling can affect the conduction of excitation waves at the Purkinje fiber-ventricle junction contributing to pro-arrhythmic effects of heart failure, as the complexity of the heart impedes a detailed experimental analysis. The aim of this study was to employ computational models to investigate the pro-arrhythmic effects of heart failure-induced ionic remodeling on the cardiac action potentials and excitation wave conduction at the Purkinje fiber-ventricle junction. Single cell models of canine Purkinje fiber and ventricular myocytes were developed for control and heart failure. These single cell models were then incorporated into one-dimensional strand and three-dimensional wedge models to investigate the effects of heart failure-induced remodeling on propagation of action potentials in Purkinje fiber and ventricular tissue and at the Purkinje fiber-ventricle junction. This revealed that heart failure-induced ionic remodeling of Purkinje fiber and ventricular tissue reduced conduction safety and increased tissue vulnerability to the genesis of the unidirectional conduction block. This was marked at the Purkinje fiber-ventricle junction, forming a potential substrate for the genesis of conduction failure that led to re-entry. This study provides new insights into proarrhythmic consequences of heart failure-induced ionic remodeling.
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Affiliation(s)
- Kun Jian
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom
| | - Chen Li
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom
| | - Jules C. Hancox
- Biological Physics Group, Department of Physics and Astronomy, The University of Manchester, Manchester, United Kingdom
- School of Physiology, Pharmacology and Neuroscience, Medical Sciences Building, University Walk, Bristol, United Kingdom
| | - Henggui Zhang
- Biological Physics Group, Department 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
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Isaev D, Shabbir W, Dinc EY, Lorke DE, Petroianu G, Oz M. Cannabidiol Inhibits Multiple Ion Channels in Rabbit Ventricular Cardiomyocytes. Front Pharmacol 2022; 13:821758. [PMID: 35185573 PMCID: PMC8850628 DOI: 10.3389/fphar.2022.821758] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2021] [Accepted: 01/04/2022] [Indexed: 11/13/2022] Open
Abstract
Cannabidiol (CBD), a major non-psychotropic cannabinoid found in the Cannabis plant, has been shown to exert anti-nociceptive, anti-psychotic, and anti-convulsant effects and to also influence the cardiovascular system. In this study, the effects of CBD on major ion currents were investigated using the patch-clamp technique in rabbit ventricular myocytes. CBD inhibited voltage-gated Na+ and Ca2+ channels with IC50 values of 5.4 and 4.8 µM, respectively. In addition, CBD, at lower concentrations, suppressed ion currents mediated by rapidly and slowly activated delayed rectifier K+ channels with IC50 of 2.4 and 2.1 µM, respectively. CBD, up to 10 μM, did not have any significant effect on inward rectifier IK1 and transient outward Ito currents. The effects of CBD on these currents developed gradually, reaching steady-state levels within 5–8 min, and recoveries were usually slow and partial. Hill coefficients higher than unity in concentration-inhibition curves suggested multiple CBD binding sites on these channels. These findings indicate that CBD affects cardiac electrophysiology by acting on a diverse range of ion channels and suggest that caution should be exercised when CBD is administered to carriers of cardiac channelopathies or to individuals using drugs known to affect the rhythm or the contractility of the heart.
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Affiliation(s)
- Dmytro Isaev
- Department of Cellular Membranology, Bogomoletz Institute of Physiology, Kiev, Ukraine
| | - Waheed Shabbir
- Department of Medicine, Division of Nephrology and Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, CA, United States
| | - Ege Y. Dinc
- Department of Neurology, Diskapi Training and Research Hospital, Ankara, Turkey
| | - Dietrich E Lorke
- Department of Anatomy and Cellular Biology, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates
- Center for Biotechnology, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates
| | - Georg Petroianu
- Department of Pharmacology and Therapeutics, College of Medicine and Health Sciences, Khalifa University, Abu Dhabi, United Arab Emirates
| | - Murat Oz
- Department of Pharmacology and Therapeutics, Faculty of Pharmacy, Kuwait University, Safat, Kuwait
- *Correspondence: Murat Oz,
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Protective Effect of Trimetazidine on Potassium Ion Homeostasis in Myocardial Tissue in Mice with Heart Failure. BIOMED RESEARCH INTERNATIONAL 2022; 2022:2387860. [PMID: 35097112 PMCID: PMC8791749 DOI: 10.1155/2022/2387860] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/22/2021] [Revised: 12/28/2021] [Accepted: 12/29/2021] [Indexed: 12/20/2022]
Abstract
The occurrence of heart failure (HF) is closely correlated with the disturbance of mitochondrial energy metabolism, and trimetazidine (TMZ) has been regarded as an effective agent in treating HF. Intracellular potassium ion (K+) homeostasis, which is modulated by K+ channels and transporters, is crucial for maintaining normal myocardial function and can be disrupted by HF. This study is aimed at exploring the protective effect of TMZ on K+ homeostasis within myocardial tissue in mice with HF. We observed the pathological changes of myocardial tissue under microscopes and further measured the content of adenosine triphosphate (ATP), the activity of Na+-K+ ATPase, and the expression of ATP1α1 at the mRNA and protein levels. Moreover, we also analyzed the changes in K+ flux across the myocardial tissue in mice. As a result, we found that there was a large amount of myocardial fiber lysis and fracture in HF myocardial tissue. Meanwhile, the potassium flux of mice with HF was reduced, and the expression of ATP1α1, the activity of Na+-K+ ATPase, and the supply and delivery of ATP were also decreased. In contrast, TMZ can effectively treat HF by restoring K+ homeostasis in the local microenvironment of myocardial tissues.
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Torres-Jacome J, Ortiz-Fuentes BS, Bernabe-Sanchez D, Lopez-Silva B, Velasco M, Ita-Amador ML, Albarado-Ibañez A. Ventricular Dysfunction in Obese and Nonobese Rats with Metabolic Syndrome. J Diabetes Res 2022; 2022:9321445. [PMID: 35242881 PMCID: PMC8888058 DOI: 10.1155/2022/9321445] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/15/2021] [Revised: 01/26/2022] [Accepted: 01/28/2022] [Indexed: 11/18/2022] Open
Abstract
Obesity and dyslipidemias are both signs of metabolic syndrome, usually associated with ventricular arrhythmias. Here, we tried to identify cardiac electrical alteration and biomarkers in nonobese rats with metabolic syndrome (MetS), and these findings might lead to more lethal arrhythmias than obese animals. The MetS model was developed in Wistar rats with high-sucrose diet (20%), and after twenty-eight weeks were obtained two subgroups: obese (OMetS) and nonobese (NOMetS). The electrocardiogram was used to measure the ventricular arrhythmias and changes in the heart rate variability. Also, we measured ventricular hypertrophy and its relationship with electrical activity alterations of both ventricles, using micro-electrode and voltage clamp techniques. Also, we observed alterations in the contraction force of ventricles where a transducer was used to record mechanical and electrical papillary muscle, simultaneously. Despite both subgroups presenting long QT syndrome (0.66 ± 0.05 and 0.66 ± 0.07 ms with respect to the control 0.55 ± 0.1 ms), the changes in the heart rate variability were present only in OMetS, while the NOMetS subgroup presented changes in QT interval variability (NOMetS SD = 1.8, SD2 = 2.8; SD1/SD2 = 0.75). Also, the NOMetS revealed tachycardia (10%; p < 0.05) with changes in action potential duration (63% in the right papillary and 50% in the left papillary) in the ventricular papillary which are correlated with certain alterations in the potassium currents and the force of contraction. The OMetS showed an increase in action potential duration and the force of contraction in both ventricles, which are explained as bradycardia. Our results revealed lethal arrhythmias in both MetS subgroups, irrespectively of the presence of obesity. Consequently, the NOMetS showed mechanical-electrical alterations regarding ventricle hypertrophy that should be at the NOMetS, leading to an increase of CV mortality.
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Affiliation(s)
- Julian Torres-Jacome
- Laboratorio de Fisiopatología Cardiovascular, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Brian Sabino Ortiz-Fuentes
- Laboratorio de Fisiopatología Cardiovascular, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Daniela Bernabe-Sanchez
- Laboratorio de Fisiopatología Cardiovascular, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Benjamin Lopez-Silva
- Laboratorio de Fisiopatología Cardiovascular, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Myrian Velasco
- Neuroscience Division, Instituto de Fisiología Celular, Department of Cognitive Neuroscience, Universidad Nacional Autónoma de México, México City, Mexico
| | - Martha Lucia Ita-Amador
- Laboratorio de Fisiopatología Cardiovascular, Complejo Nororiental, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
| | - Alondra Albarado-Ibañez
- Laboratorio de Fisiopatología Cardiovascular, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
- Laboratorio de Aplicaciones Biotecnológicas, Instituto de Ciencias, Benemérita Universidad Autónoma de Puebla, Puebla, Mexico
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The Identification of Key Genes and Biological Pathways in Heart Failure by Integrated Bioinformatics Analysis. COMPUTATIONAL AND MATHEMATICAL METHODS IN MEDICINE 2021; 2021:3859338. [PMID: 34868339 PMCID: PMC8642006 DOI: 10.1155/2021/3859338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 09/07/2021] [Accepted: 10/30/2021] [Indexed: 11/23/2022]
Abstract
Purpose Heart failure (HF) is a clinical syndrome caused by ventricular insufficiency. In order to further explore the biomarkers related to HF, we apply the high-throughput database. Materials and Methods The GSE21610 was applied for the differentially expressed gene (DEG) analysis. The Database for Annotation, Visualization, and Integrated Discovery (DAVID) was performed to assess Gene ontology (GO) and the Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. The Gene Set Enrichment Analysis (GSEA) was used for gene expression profile GSE21610. The Protein-Protein Interaction (PPI) network and modules were also constructed for research. These hub gene function pathways were estimated in HF progression. Result We have identified 434 DEGs in total, including 304 downregulated DEGs and 130 upregulated DEGs. GO and KEGG illustrated that DEGs in HF were significantly enriched in G protein-coupled receptor binding, peroxisome, and cAMP signaling pathway. GSEA results showed gene set GSE21610 was gathered in lipid digestion, defense response to fungus, and intestinal lipid absorption. Finally, through analyzing the PPI network, we screened hub genes CDH1, TFRC, CCL2, BUB1B, and CD19 by the Cytoscape software. Conclusion This study uses a series of bioinformatics technologies to obtain hug genes and key pathways related to HF. These analysis results provide us with new ideas for finding biomarkers and treatment methods for HF.
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Husti Z, Varró A, Baczkó I. Arrhythmogenic Remodeling in the Failing Heart. Cells 2021; 10:cells10113203. [PMID: 34831426 PMCID: PMC8623396 DOI: 10.3390/cells10113203] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2021] [Revised: 11/05/2021] [Accepted: 11/11/2021] [Indexed: 12/12/2022] Open
Abstract
Chronic heart failure is a clinical syndrome with multiple etiologies, associated with significant morbidity and mortality. Cardiac arrhythmias, including ventricular tachyarrhythmias and atrial fibrillation, are common in heart failure. A number of cardiac diseases including heart failure alter the expression and regulation of ion channels and transporters leading to arrhythmogenic electrical remodeling. Myocardial hypertrophy, fibrosis and scar formation are key elements of arrhythmogenic structural remodeling in heart failure. In this article, the mechanisms responsible for increased arrhythmia susceptibility as well as the underlying changes in ion channel, transporter expression and function as well as alterations in calcium handling in heart failure are discussed. Understanding the mechanisms of arrhythmogenic remodeling is key to improving arrhythmia management and the prevention of sudden cardiac death in patients with heart failure.
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Affiliation(s)
- Zoltán Husti
- Department of Pharmacology and Pharmacotherapy, University of Szeged, 6720 Szeged, Hungary; (Z.H.); (A.V.)
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, 6720 Szeged, Hungary
| | - András Varró
- Department of Pharmacology and Pharmacotherapy, University of Szeged, 6720 Szeged, Hungary; (Z.H.); (A.V.)
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, 6720 Szeged, Hungary
- ELKH-SZTE Research Group for Cardiovascular Pharmacology, Eötvös Loránd Research Network, 6720 Szeged, Hungary
| | - István Baczkó
- Department of Pharmacology and Pharmacotherapy, University of Szeged, 6720 Szeged, Hungary; (Z.H.); (A.V.)
- Department of Pharmacology and Pharmacotherapy, Interdisciplinary Excellence Centre, University of Szeged, 6720 Szeged, Hungary
- Correspondence:
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10
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Qauli AI, Marcellinus A, Lim KM. Sensitivity Analysis of Ion Channel Conductance on Myocardial Electromechanical Delay: Computational Study. Front Physiol 2021; 12:697693. [PMID: 34512377 PMCID: PMC8430256 DOI: 10.3389/fphys.2021.697693] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2021] [Accepted: 07/29/2021] [Indexed: 02/03/2023] Open
Abstract
It is well known that cardiac electromechanical delay (EMD) can cause dyssynchronous heart failure (DHF), a prominent cardiovascular disease (CVD). This work computationally assesses the conductance variation of every ion channel on the cardiac cell to give rise to EMD prolongation. The electrical and mechanical models of human ventricular tissue were simulated, using a population approach with four conductance reductions for each ion channel. Then, EMD was calculated by determining the difference between the onset of action potential and the start of cell shortening. Finally, EMD data were put into the optimized conductance dimensional stacking to show which ion channel has the most influence in elongating the EMD. We found that major ion channels, such as L-type calcium (CaL), slow-delayed rectifier potassium (Ks), rapid-delayed rectifier potassium (Kr), and inward rectifier potassium (K1), can significantly extend the action potential duration (APD) up to 580 ms. Additionally, the maximum intracellular calcium (Cai) concentration is greatly affected by the reduction in channel CaL, Ks, background calcium, and Kr. However, among the aforementioned major ion channels, only the CaL channel can play a superior role in prolonging the EMD up to 83 ms. Furthermore, ventricular cells with long EMD have been shown to inherit insignificant mechanical response (in terms of how strong the tension can grow and how far length shortening can go) compared with that in normal cells. In conclusion, despite all variations in every ion channel conductance, only the CaL channel can play a significant role in extending EMD. In addition, cardiac cells with long EMD tend to have inferior mechanical responses due to a lack of Cai compared with normal conditions, which are highly likely to result in a compromised pump function of the heart.
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Affiliation(s)
- Ali Ikhsanul Qauli
- Department of IT Convergence Engineering, Kumoh National Institute of Technology, Gumi, South Korea
| | - Aroli Marcellinus
- Department of IT Convergence Engineering, Kumoh National Institute of Technology, Gumi, South Korea
| | - Ki Moo Lim
- Department of IT Convergence Engineering, Kumoh National Institute of Technology, Gumi, South Korea
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11
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Kabakov AY, Sengun E, Lu Y, Roder K, Bronk P, Baggett B, Turan NN, Moshal KS, Koren G. Three-Week-Old Rabbit Ventricular Cardiomyocytes as a Novel System to Study Cardiac Excitation and EC Coupling. Front Physiol 2021; 12:672360. [PMID: 34867432 PMCID: PMC8637404 DOI: 10.3389/fphys.2021.672360] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2021] [Accepted: 10/06/2021] [Indexed: 01/14/2023] Open
Abstract
Cardiac arrhythmias significantly contribute to cardiovascular morbidity and mortality. The rabbit heart serves as an accepted model system for studying cardiac cell excitation and arrhythmogenicity. Accordingly, primary cultures of adult rabbit ventricular cardiomyocytes serve as a preferable model to study molecular mechanisms of human cardiac excitation. However, the use of adult rabbit cardiomyocytes is often regarded as excessively costly. Therefore, we developed and characterized a novel low-cost rabbit cardiomyocyte model, namely, 3-week-old ventricular cardiomyocytes (3wRbCMs). Ventricular myocytes were isolated from whole ventricles of 3-week-old New Zealand White rabbits of both sexes by standard enzymatic techniques. Using wheat germ agglutinin, we found a clear T-tubule structure in acutely isolated 3wRbCMs. Cells were adenovirally infected (multiplicity of infection of 10) to express Green Fluorescent Protein (GFP) and cultured for 48 h. The cells showed action potential duration (APD90 = 253 ± 24 ms) and calcium transients similar to adult rabbit cardiomyocytes. Freshly isolated and 48-h-old-cultured cells expressed critical ion channel proteins: calcium voltage-gated channel subunit alpha1 C (Cavα1c), sodium voltage-gated channel alpha subunit 5 (Nav1.5), potassium voltage-gated channel subfamily D member 3 (Kv4.3), and subfamily A member 4 (Kv1.4), and also subfamily H member 2 (RERG. Kv11.1), KvLQT1 (K7.1) protein and inward-rectifier potassium channel (Kir2.1). The cells displayed an appropriate electrophysiological phenotype, including fast sodium current (I Na), transient outward potassium current (I to), L-type calcium channel peak current (I Ca,L), rapid and slow components of the delayed rectifier potassium current (I Kr and I Ks), and inward rectifier (I K1). Although expression of the channel proteins and some currents decreased during the 48 h of culturing, we conclude that 3wRbCMs are a new, low-cost alternative to the adult-rabbit-cardiomyocytes system, which allows the investigation of molecular mechanisms of cardiac excitation on morphological, biochemical, genetic, physiological, and biophysical levels.
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Affiliation(s)
- Anatoli Y Kabakov
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Elif Sengun
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States.,Department of Pharmacology, Institute of Graduate Studies in Health Sciences, Istanbul University, Istanbul, Türkiye
| | - Yichun Lu
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karim Roder
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Peter Bronk
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Brett Baggett
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Nilüfer N Turan
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Karni S Moshal
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
| | - Gideon Koren
- Department of Medicine, Division of Cardiology, Cardiovascular Research Center, Rhode Island Hospital, The Warren Alpert Medical School of Brown University, Providence, RI, United States
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12
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Shugg T, Hudmon A, Overholser BR. Neurohormonal Regulation of I Ks in Heart Failure: Implications for Ventricular Arrhythmogenesis and Sudden Cardiac Death. J Am Heart Assoc 2020; 9:e016900. [PMID: 32865116 PMCID: PMC7726975 DOI: 10.1161/jaha.120.016900] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Heart failure (HF) results in sustained alterations in neurohormonal signaling, including enhanced signaling through the sympathetic nervous system and renin-angiotensin-aldosterone system pathways. While enhanced sympathetic nervous system and renin-angiotensin-aldosterone system activity initially help compensate for the failing myocardium, sustained signaling through these pathways ultimately contributes to HF pathophysiology. HF remains a leading cause of mortality, with arrhythmogenic sudden cardiac death comprising a common mechanism of HF-related death. The propensity for arrhythmia development in HF occurs secondary to cardiac electrical remodeling that involves pathological regulation of ventricular ion channels, including the slow component of the delayed rectifier potassium current, that contribute to action potential duration prolongation. To elucidate a mechanistic explanation for how HF-mediated electrical remodeling predisposes to arrhythmia development, a multitude of investigations have investigated the specific regulatory effects of HF-associated stimuli, including enhanced sympathetic nervous system and renin-angiotensin-aldosterone system signaling, on the slow component of the delayed rectifier potassium current. The objective of this review is to summarize the current knowledge related to the regulation of the slow component of the delayed rectifier potassium current in response to HF-associated stimuli, including the intracellular pathways involved and the specific regulatory mechanisms.
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Affiliation(s)
- Tyler Shugg
- Division of Clinical PharmacologyIndiana University School of MedicineIndianapolisIN
| | - Andy Hudmon
- Department of Medicinal Chemistry and Molecular PharmacologyPurdue University College of PharmacyWest LafayetteIN
| | - Brian R. Overholser
- Division of Clinical PharmacologyIndiana University School of MedicineIndianapolisIN
- Department of Pharmacy PracticePurdue University College of PharmacyIndianapolisIN
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13
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Towards the Development of AgoKirs: New Pharmacological Activators to Study K ir2.x Channel and Target Cardiac Disease. Int J Mol Sci 2020; 21:ijms21165746. [PMID: 32796537 PMCID: PMC7461056 DOI: 10.3390/ijms21165746] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2020] [Revised: 08/05/2020] [Accepted: 08/06/2020] [Indexed: 12/15/2022] Open
Abstract
Inward rectifier potassium ion channels (IK1-channels) of the Kir2.x family are responsible for maintaining a stable negative resting membrane potential in excitable cells, but also play a role in processes of non-excitable tissues, such as bone development. IK1-channel loss-of-function, either congenital or acquired, has been associated with cardiac disease. Currently, basic research and specific treatment are hindered by the absence of specific and efficient Kir2.x channel activators. However, twelve different compounds, including approved drugs, show off-target IK1 activation. Therefore, these compounds contain valuable information towards the development of agonists of Kir channels, AgoKirs. We reviewed the mechanism of IK1 channel activation of these compounds, which can be classified as direct or indirect activators. Subsequently, we examined the most viable starting points for rationalized drug development and possible safety concerns with emphasis on cardiac and skeletal muscle adverse effects of AgoKirs. Finally, the potential value of AgoKirs is discussed in view of the current clinical applications of potentiators and activators in cystic fibrosis therapy.
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14
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Rahm AK, Müller ME, Gramlich D, Lugenbiel P, Uludag E, Rivinius R, Ullrich ND, Schmack B, Ruhparwar A, Heimberger T, Weis T, Karck M, Katus HA, Thomas D. Inhibition of cardiac K v4.3 (I to) channel isoforms by class I antiarrhythmic drugs lidocaine and mexiletine. Eur J Pharmacol 2020; 880:173159. [PMID: 32360350 DOI: 10.1016/j.ejphar.2020.173159] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 04/01/2020] [Accepted: 04/23/2020] [Indexed: 12/29/2022]
Abstract
Transient outward K+ current, Ito, contributes to cardiac action potential generation and is primarily carried by Kv4.3 (KCND3) channels. Two Kv4.3 isoforms are expressed in human ventricle and show differential remodeling in heart failure (HF). Lidocaine and mexiletine may be applied in selected patients to suppress ventricular arrhythmias, without effects on sudden cardiac death or mortality. Isoform-dependent effects of antiarrhythmic drugs on Kv4.3 channels and potential implications for remodeling-based antiarrhythmic management have not been assessed to date. We sought to test the hypotheses that Kv4.3 channels are targeted by lidocaine and mexiletine, and that drug sensitivity is determined in isoform-specific manner. Expression of KCND3 isoforms was quantified using qRT-PCR in left ventricular samples of patients with HF due to either ischemic or dilated cardiomyopathies (ICM or DCM). Long (Kv4.3-L) and short (Kv4.3-S) isoforms were heterologously expressed in Xenopus laevis oocytes to study drug sensitivity and effects on biophysical characteristics activation, deactivation, inactivation, and recovery from inactivation. In the present HF patient cohort KCND3 isoform expression did not differ between ICM and DCM. In vitro, lidocaine (IC50-Kv4.3-L: 0.8 mM; IC50-Kv4.3-S: 1.2 mM) and mexiletine (IC50-Kv4.3-L: 146 μM; IC50-Kv4.3-S: 160 μM) inhibited Kv4.3 with different sensitivity. Biophysical analyses identified accelerated and enhanced inactivation combined with delayed recovery from inactivation as primary biophysical mechanisms underlying Kv4.3 current reduction. In conclusion, differential effects on Kv4.3 isoforms extend the electropharmacological profile of lidocaine and mexiletine. Patient-specific remodeling of Kv4.3 isoforms may determine individual drug responses and requires consideration during clinical application of compounds targeting Kv4.3.
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Affiliation(s)
- Ann-Kathrin Rahm
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Mara Elena Müller
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Dominik Gramlich
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Patrick Lugenbiel
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Ecem Uludag
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Rasmus Rivinius
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Nina D Ullrich
- DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; Institute of Physiology and Pathophysiology, Division of Cardiovascular Physiology, University of Heidelberg, Im Neuenheimer Feld 307, 69120, Heidelberg, Germany
| | - Bastian Schmack
- Department of Cardiac Surgery, University Hospital Heidelberg, Im Neuenheimer Feld 110, 69120, Heidelberg, Germany
| | - Arjang Ruhparwar
- Department of Cardiac Surgery, University Hospital Heidelberg, Im Neuenheimer Feld 110, 69120, Heidelberg, Germany
| | - Tanja Heimberger
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Tanja Weis
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Matthias Karck
- Department of Cardiac Surgery, University Hospital Heidelberg, Im Neuenheimer Feld 110, 69120, Heidelberg, Germany
| | - Hugo A Katus
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany
| | - Dierk Thomas
- Department of Cardiology, Medical University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; HCR (Heidelberg Center for Heart Rhythm Disorders), University Hospital Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany; DZHK (German Centre for Cardiovascular Research), Partner Site Heidelberg/Mannheim, University of Heidelberg, Im Neuenheimer Feld 410, 69120, Heidelberg, Germany.
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15
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Abstract
Human heart failure is characterized by arrhythmogenic electrical remodeling consisting mostly of ion channel downregulations. Reversing these downregulations is a logical approach to antiarrhythmic therapy, but understanding the pathophysiological mechanisms of the reduced currents is crucial for finding the proper treatments. The unfolded protein response (UPR) is activated by endoplasmic reticulum (ER) stress and has been found to play pivotal roles in different diseases including neurodegenerative diseases, diabetes mellitus, and heart disease. Recently, the UPR is reported to regulate multiple cardiac ion channels, contributing to arrhythmias in heart disease. In this review, we will discuss which UPR modulators and effectors could be involved in regulation of cardiac ion channels in heart disease, and how the understanding of these regulating mechanisms may lead to new antiarrhythmic therapeutics that lack the proarrhythmic risk of current ion channel blocking therapies.
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Affiliation(s)
- Man Liu
- a Division of Cardiology, Department of Medicine, The Lillehei Heart Institute , University of Minnesota at Twin Cities , Minneapolis , USA
| | - Samuel C Dudley
- a Division of Cardiology, Department of Medicine, The Lillehei Heart Institute , University of Minnesota at Twin Cities , Minneapolis , USA
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16
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Rahm AK, Lugenbiel P, Schweizer PA, Katus HA, Thomas D. Role of ion channels in heart failure and channelopathies. Biophys Rev 2018; 10:1097-1106. [PMID: 30019205 PMCID: PMC6082303 DOI: 10.1007/s12551-018-0442-3] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Accepted: 07/05/2018] [Indexed: 12/13/2022] Open
Abstract
Heart failure (HF) is a complication of multiple cardiac diseases and is characterized by impaired contractile and electric function. Patients with HF are not only limited by reduced contractile function but are also prone to life-threatening ventricular arrhythmias. HF itself leads to remodeling of ion channels, gap junctions, and intracellular calcium handling abnormalities that in combination with structural remodeling, e.g., fibrosis, produce a substrate for an arrhythmogenic disorders. Not only ventricular life-threatening arrhythmias contribute to increased morbidity and mortality but also atrial arrhythmias, especially atrial fibrillation (AF), are common in HF patients and contribute to morbidity and mortality. The distinct ion channel remodeling processes in HF and in channelopathies associated with HF will be discussed. Further basic research and clinical studies are needed to identify underlying molecular pathways of HF pathophysiology to provide the basis for improved patient care and individualized therapy based on individualized ion channel composition and remodeling.
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Affiliation(s)
- Ann-Kathrin Rahm
- Department of Cardiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Patrick Lugenbiel
- Department of Cardiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Patrick A. Schweizer
- Department of Cardiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Hugo A. Katus
- Department of Cardiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
| | - Dierk Thomas
- Department of Cardiology, University of Heidelberg, Im Neuenheimer Feld 410, 69120 Heidelberg, Germany
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17
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Fu JD, Laurita KR. Repolarization Reserve and Action Potential Dynamics in Failing Myocytes. Circ Arrhythm Electrophysiol 2018; 11:e006137. [PMID: 29437765 DOI: 10.1161/circep.118.006137] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Ji-Dong Fu
- From the Heart and Vascular Research Center, MetroHealth Campus of Case Western Reserve University, Cleveland, OH
| | - Kenneth R Laurita
- From the Heart and Vascular Research Center, MetroHealth Campus of Case Western Reserve University, Cleveland, OH.
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18
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Hegyi B, Bossuyt J, Ginsburg KS, Mendoza LM, Talken L, Ferrier WT, Pogwizd SM, Izu LT, Chen-Izu Y, Bers DM. Altered Repolarization Reserve in Failing Rabbit Ventricular Myocytes: Calcium and β-Adrenergic Effects on Delayed- and Inward-Rectifier Potassium Currents. Circ Arrhythm Electrophysiol 2018; 11:e005852. [PMID: 29437761 PMCID: PMC5813707 DOI: 10.1161/circep.117.005852] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2017] [Accepted: 12/11/2017] [Indexed: 12/25/2022]
Abstract
BACKGROUND Electrophysiological remodeling and increased susceptibility for cardiac arrhythmias are hallmarks of heart failure (HF). Ventricular action potential duration (APD) is typically prolonged in HF, with reduced repolarization reserve. However, underlying K+ current changes are often measured in nonphysiological conditions (voltage clamp, low pacing rates, cytosolic Ca2+ buffers). METHODS AND RESULTS We measured the major K+ currents (IKr, IKs, and IK1) and their Ca2+- and β-adrenergic dependence in rabbit ventricular myocytes in chronic pressure/volume overload-induced HF (versus age-matched controls). APD was significantly prolonged only at lower pacing rates (0.2-1 Hz) in HF under physiological ionic conditions and temperature. However, when cytosolic Ca2+ was buffered, APD prolongation in HF was also significant at higher pacing rates. Beat-to-beat variability of APD was also significantly increased in HF. Both IKr and IKs were significantly upregulated in HF under action potential clamp, but only when cytosolic Ca2+ was not buffered. CaMKII (Ca2+/calmodulin-dependent protein kinase II) inhibition abolished IKs upregulation in HF, but it did not affect IKr. IKs response to β-adrenergic stimulation was also significantly diminished in HF. IK1 was also decreased in HF regardless of Ca2+ buffering, CaMKII inhibition, or β-adrenergic stimulation. CONCLUSIONS At baseline Ca2+-dependent upregulation of IKr and IKs in HF counterbalances the reduced IK1, maintaining repolarization reserve (especially at higher heart rates) in physiological conditions, unlike conditions of strong cytosolic Ca2+ buffering. However, under β-adrenergic stimulation, reduced IKs responsiveness severely limits integrated repolarizing K+ current and repolarization reserve in HF. This would increase arrhythmia propensity in HF, especially during adrenergic stress.
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Affiliation(s)
- Bence Hegyi
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Julie Bossuyt
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Kenneth S Ginsburg
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Lynette M Mendoza
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Linda Talken
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - William T Ferrier
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Steven M Pogwizd
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Leighton T Izu
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Ye Chen-Izu
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.)
| | - Donald M Bers
- From the Department of Pharmacology (B.H., J.B., K.S.G., L.T.I., Y.C.-I., D.M.B.), School of Medicine, Dean's Office (L.T.), Surgical Research Facility, School of Medicine (W.T.F.), Department of Biomedical Engineering (Y.C.-I.), Department of Internal Medicine/Cardiology (Y.C.-I.), University of California, Davis; Echocardiography Laboratory, University of California, Davis Medical Center, Sacramento (L.M.M.); and Department of Medicine, University of Alabama at Birmingham (S.M.P.).
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19
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Cheng H, Cannell MB, Hancox JC. Differential responses of rabbit ventricular and atrial transient outward current (I to) to the I to modulator NS5806. Physiol Rep 2017; 5:5/5/e13172. [PMID: 28270595 PMCID: PMC5350179 DOI: 10.14814/phy2.13172] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Revised: 01/26/2017] [Accepted: 01/27/2017] [Indexed: 02/06/2023] Open
Abstract
Transient outward potassium current (Ito) in the heart underlies phase 1 repolarization of cardiac action potentials and thereby affects excitation–contraction coupling. Small molecule activators of Ito may therefore offer novel treatments for cardiac dysfunction, including heart failure and atrial fibrillation. NS5806 has been identified as a prototypic activator of canine Ito. This study investigated, for the first time, actions of NS5806 on rabbit atrial and ventricular Ito. Whole cell patch‐clamp recordings of Ito and action potentials were made at physiological temperature from rabbit ventricular and atrial myocytes. 10 μmol/L NS5806 increased ventricular Ito with a leftward shift in Ito activation and accelerated restitution. At higher concentrations, stimulation of Ito was followed by inhibition. The EC50 for stimulation was 1.6 μmol/L and inhibition had an IC50 of 40.7 μmol/L. NS5806 only inhibited atrial Ito (IC50 of 18 μmol/L) and produced a modest leftward shifts in Ito activation and inactivation, without an effect on restitution. 10 μmol/L NS5806 shortened ventricular action potential duration (APD) at APD20‐APD90 but prolonged atrial APD. NS5806 also reduced atrial AP upstroke and amplitude, consistent with an additional atrio‐selective effect on Na+ channels. In contrast to NS5806, flecainide, which discriminates between Kv1.4 and 4.x channels, produced similar levels of inhibition of ventricular and atrial Ito. NS5806 discriminates between rabbit ventricular and atrial Ito, with mixed activator and inhibitor actions on the former and inhibitor actions against the later. NS5806 may be of significant value for pharmacological interrogation of regional differences in native cardiac Ito.
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Affiliation(s)
- Hongwei Cheng
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, U.K
| | - Mark B Cannell
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, U.K
| | - Jules C Hancox
- School of Physiology, Pharmacology and Neuroscience, Biomedical Sciences Building, University Walk, Bristol, U.K
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20
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Klein MG, Shou M, Stohlman J, Solhjoo S, Haigney M, Tidwell RR, Goldstein RE, Flagg TP, Haigney MC. Role of suppression of the inward rectifier current in terminal action potential repolarization in the failing heart. Heart Rhythm 2017; 14:1217-1223. [PMID: 28396172 DOI: 10.1016/j.hrthm.2017.04.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2016] [Indexed: 11/19/2022]
Abstract
BACKGROUND The failing heart exhibits an increased arrhythmia susceptibility that is often attributed to action potential (AP) prolongation due to significant ion channel remodeling. The inwardly rectifying K+ current (IK1) has been reported to be reduced, but its contribution to shaping the AP waveform and cell excitability in the failing heart remains unclear. OBJECTIVE The purpose of this study was to define the effect of IK1 suppression on the cardiac AP and excitability in the normal and failing hearts. METHODS We used electrophysiological and pharmacological approaches to investigate IK1 function in a swine tachy-pacing model of heart failure (HF). RESULTS Terminal repolarization of the AP (TRAP; the time constant of the exponential fit to terminal repolarization) was markedly prolonged in both myocytes and arterially perfused wedges from animals with HF. TRAP was increased by 54.1% in HF myocytes (P < .001) and 26.2% in HF wedges (P = .014). The increase in TRAP was recapitulated by the potent and specific IK1 inhibitor, PA-6 (pentamidine analog 6), indicating that IK1 is the primary determinant of the final phase of repolarization. Moreover, we find that IK1 suppression reduced the ratio of effective refractory period to AP duration at 90% of repolarization, permitting re-excitation before full repolarization, reduction of AP upstroke velocity, and likely promotion of slow conduction. CONCLUSION Using an objective measure of terminal repolarization, we conclude that IK1 is the major determinant of the terminal repolarization time course. Moreover, suppression of IK1 prolongs repolarization and reduces postrepolarization refractoriness without marked effects on the overall AP duration. Collectively, these findings demonstrate how IK1 suppression may contribute to arrhythmogenesis in the failing heart.
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Affiliation(s)
- Michael G Klein
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland.
| | - Matie Shou
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Jayna Stohlman
- Center for Devices and Radiological Health, Food and Drug Administration, Silver Spring, Maryland
| | - Soroosh Solhjoo
- Department of Biomedical Engineering, Johns Hopkins University, Baltimore, Maryland
| | - Myles Haigney
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Richard R Tidwell
- Department of Pathology and Laboratory Medicine, School of Medicine, The University of North Carolina, Chapel Hill, North Carolina
| | - Robert E Goldstein
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Thomas P Flagg
- Department of Anatomy, Physiology and Genetics, Uniformed Services University of the Health Sciences, Bethesda, Maryland
| | - Mark C Haigney
- Division of Cardiology, Department of Medicine, Uniformed Services University of the Health Sciences, Bethesda, Maryland
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21
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Cdon deficiency causes cardiac remodeling through hyperactivation of WNT/β-catenin signaling. Proc Natl Acad Sci U S A 2017; 114:E1345-E1354. [PMID: 28154134 DOI: 10.1073/pnas.1615105114] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
On pathological stress, Wnt signaling is reactivated and induces genes associated with cardiac remodeling and fibrosis. We have previously shown that a cell surface receptor Cdon (cell-adhesion associated, oncogene regulated) suppresses Wnt signaling to promote neuronal differentiation however its role in heart is unknown. Here, we demonstrate a critical role of Cdon in cardiac function and remodeling. Cdon is expressed and predominantly localized at intercalated disk in both mouse and human hearts. Cdon-deficient mice develop cardiac dysfunction including reduced ejection fraction and ECG abnormalities. Cdon-/- hearts exhibit increased fibrosis and up-regulation of genes associated with cardiac remodeling and fibrosis. Electrical remodeling was demonstrated by up-regulation and mislocalization of the gap junction protein, Connexin 43 (Cx43) in Cdon-/- hearts. In agreement with altered Cx43 expression, functional analysis both using Cdon-/- cardiomyocytes and shRNA-mediated knockdown in rat cardiomyocytes shows aberrant gap junction activities. Analysis of the underlying mechanism reveals that Cdon-/- hearts exhibit hyperactive Wnt signaling as evident by β-catenin accumulation and Axin2 up-regulation. On the other hand, the treatment of rat cardiomyocytes with a Wnt activator TWS119 reduces Cdon levels and aberrant Cx43 activities, similarly to Cdon-deficient cardiomyocytes, suggesting a negative feedback between Cdon and Wnt signaling. Finally, inhibition of Wnt/β-catenin signaling by XAV939, IWP2 or dickkopf (DKK)1 prevented Cdon depletion-induced up-regulation of collagen 1a and Cx43. Taken together, these results demonstrate that Cdon deficiency causes hyperactive Wnt signaling leading to aberrant intercellular coupling and cardiac fibrosis. Cdon exhibits great potential as a target for the treatment of cardiac fibrosis and cardiomyopathy.
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22
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McKinnon D, Rosati B. Transmural gradients in ion channel and auxiliary subunit expression. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 122:165-186. [PMID: 27702655 DOI: 10.1016/j.pbiomolbio.2016.09.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 09/30/2016] [Indexed: 12/11/2022]
Abstract
Evolution has acted to shape the action potential in different regions of the heart in order to produce a maximally stable and efficient pump. This has been achieved by creating regional differences in ion channel expression levels within the heart as well as differences between equivalent cardiac tissues in different species. These region- and species-dependent differences in channel expression are established by regulatory evolution, evolution of the regulatory mechanisms that control channel expression levels. Ion channel auxiliary subunits are obvious targets for regulatory evolution, in order to change channel expression levels and/or modify channel function. This review focuses on the transmural gradients of ion channel expression in the heart and the role that regulation of auxiliary subunit expression plays in generating and shaping these gradients.
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Affiliation(s)
- David McKinnon
- Department of Veterans Affairs Medical Center, Northport, NY, USA; Institute of Molecular Cardiology, Stony Brook University, Stony Brook, NY, USA; Department of Neurobiology and Behavior, Stony Brook University, Stony Brook, NY, 11794, USA
| | - Barbara Rosati
- Department of Veterans Affairs Medical Center, Northport, NY, USA; Institute of Molecular Cardiology, Stony Brook University, Stony Brook, NY, USA; Department of Physiology and Biophysics, Stony Brook University, Stony Brook, NY, 11794, USA.
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23
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Electrophysiology of Heart Failure Using a Rabbit Model: From the Failing Myocyte to Ventricular Fibrillation. PLoS Comput Biol 2016; 12:e1004968. [PMID: 27336310 PMCID: PMC4919062 DOI: 10.1371/journal.pcbi.1004968] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2015] [Accepted: 05/05/2016] [Indexed: 02/07/2023] Open
Abstract
Heart failure is a leading cause of death, yet its underlying electrophysiological (EP) mechanisms are not well understood. In this study, we use a multiscale approach to analyze a model of heart failure and connect its results to features of the electrocardiogram (ECG). The heart failure model is derived by modifying a previously validated electrophysiology model for a healthy rabbit heart. Specifically, in accordance with the heart failure literature, we modified the cell EP by changing both membrane currents and calcium handling. At the tissue level, we modeled the increased gap junction lateralization and lower conduction velocity due to downregulation of Connexin 43. At the biventricular level, we reduced the apex-to-base and transmural gradients of action potential duration (APD). The failing cell model was first validated by reproducing the longer action potential, slower and lower calcium transient, and earlier alternans characteristic of heart failure EP. Subsequently, we compared the electrical wave propagation in one dimensional cables of healthy and failing cells. The validated cell model was then used to simulate the EP of heart failure in an anatomically accurate biventricular rabbit model. As pacing cycle length decreases, both the normal and failing heart develop T-wave alternans, but only the failing heart shows QRS alternans (although moderate) at rapid pacing. Moreover, T-wave alternans is significantly more pronounced in the failing heart. At rapid pacing, APD maps show areas of conduction block in the failing heart. Finally, accelerated pacing initiated wave reentry and breakup in the failing heart. Further, the onset of VF was not observed with an upregulation of SERCA, a potential drug therapy, using the same protocol. The changes introduced at the cell and tissue level have increased the failing heart’s susceptibility to dynamic instabilities and arrhythmias under rapid pacing. However, the observed increase in arrhythmogenic potential is not due to a steepening of the restitution curve (not present in our model), but rather to a novel blocking mechanism. Ventricular fibrillation (VF) is one of the leading causes of sudden death. During VF, the electrical wave of activation in the heart breaks up chaotically. Consequently, the heart is unable to contract synchronously and pump blood to the rest of the body. In our work we formulate and validate a model of heart failure (HF) that allows us to evaluate the arrhythmogenic potential of individual and combined electrophysiological changes. In diagnostic cardiology, the electrocardiogram (ECG) is one of the most commonly used tools for detecting abnormalities in the heart electrophysiology. One of our goals is to use our numerical model to link changes at the cellular and tissue level in a failing heart to a numerically computed ECG. This allows us to characterize the precursor to and the risk of VF. In order to understand the mechanisms underlying VF in HF, we design a test that simulates a HF patient performing physical exercise. We show that under fast heart rates with changes in pacing, HF patients are more prone to VF due to a new conduction blocking mechanism. In the long term, our mathematical model is suitable for investigating the effect of drug therapies in HF.
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24
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Gloschat CR, Koppel AC, Aras KK, Brennan JA, Holzem KM, Efimov IR. Arrhythmogenic and metabolic remodelling of failing human heart. J Physiol 2016; 594:3963-80. [PMID: 27019074 DOI: 10.1113/jp271992] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2015] [Accepted: 03/21/2016] [Indexed: 12/24/2022] Open
Abstract
Heart failure (HF) is a major cause of morbidity and mortality worldwide. The global burden of HF continues to rise, with prevalence rates estimated at 1-2% and incidence approaching 5-10 per 1000 persons annually. The complex pathophysiology of HF impacts virtually all aspects of normal cardiac function - from structure and mechanics to metabolism and electrophysiology - leading to impaired mechanical contraction and sudden cardiac death. Pharmacotherapy and device therapy are the primary methods of treating HF, but neither is able to stop or reverse disease progression. Thus, there is an acute need to translate basic research into improved HF therapy. Animal model investigations are a critical component of HF research. However, the translation from cellular and animal models to the bedside is hampered by significant differences between species and among physiological scales. Our studies over the last 8 years show that hypotheses generated in animal models need to be validated in human in vitro models. Importantly, however, human heart investigations can establish translational platforms for safety and efficacy studies before embarking on costly and risky clinical trials. This review summarizes recent developments in human HF investigations of electrophysiology remodelling, metabolic remodelling, and β-adrenergic remodelling and discusses promising new technologies for HF research.
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Affiliation(s)
- C R Gloschat
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - A C Koppel
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - K K Aras
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - J A Brennan
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - K M Holzem
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
| | - I R Efimov
- Department of Biomedical Engineering, The George Washington University, Washington, DC, USA
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25
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Abstract
Heart disease produces substantial remodeling of K(+) channels that in general promotes arrhythmia occurrence. In the case of ventricular arrhythmias, K(+) channel remodeling contributes to the arrhythmic risk and increases vulnerability to torsades de pointes with K(+) channel inhibiting drugs. Atrial K(+) channel remodeling caused by atrial fibrillation promotes arrhythmia stability and presents opportunities for the development of new drugs targeting atrial inward rectifier K(+) currents. A better understanding of K(+) channel remodeling will help clinicians to appreciate arrhythmia mechanisms and determinants in a variety of clinical situations and to better manage arrhythmia therapy in patients with heart disease.
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Affiliation(s)
- Vincent Algalarrondo
- Department of Medicine, Research Center, Montreal Heart Institute, University of Montreal, 5000 Belanger Street East, Montreal, Quebec H1T 1C8, Canada; Department of Pharmacology and Therapeutics, McGill University, 3655 Promenade Sir-William-Osler, Montréal, Québec H3G 1Y6, Canada; Faculty of Medicine, University Duisburg-Essen, Hufelandstr. 55, Essen 45122, Germany
| | - Stanley Nattel
- Department of Medicine, Research Center, Montreal Heart Institute, University of Montreal, 5000 Belanger Street East, Montreal, Quebec H1T 1C8, Canada; Department of Pharmacology and Therapeutics, McGill University, 3655 Promenade Sir-William-Osler, Montréal, Québec H3G 1Y6, Canada; Faculty of Medicine, University Duisburg-Essen, Hufelandstr. 55, Essen 45122, Germany.
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26
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Baczkó I, Jost N, Virág L, Bősze Z, Varró A. Rabbit models as tools for preclinical cardiac electrophysiological safety testing: Importance of repolarization reserve. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2016; 121:157-68. [PMID: 27208697 DOI: 10.1016/j.pbiomolbio.2016.05.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2016] [Accepted: 05/01/2016] [Indexed: 01/26/2023]
Abstract
It is essential to more reliably assess the pro-arrhythmic liability of compounds in development. Current guidelines for pre-clinical and clinical testing of drug candidates advocate the use of healthy animals/tissues and healthy individuals and focus on the test compound's ability to block the hERG current and prolong cardiac ventricular repolarization. Also, pre-clinical safety tests utilize several species commonly used in cardiac electrophysiological studies. In this review, important species differences in cardiac ventricular repolarizing ion currents are considered, followed by the discussion on electrical remodeling associated with chronic cardiovascular diseases that leads to altered ion channel and transporter expression and densities in pathological settings. We argue that the choice of species strongly influences experimental outcome and extrapolation of results to human clinical settings. We suggest that based on cardiac cellular electrophysiology, the rabbit is a useful species for pharmacological pro-arrhythmic investigations. In addition to healthy animals and tissues, the use of animal models (e.g. those with impaired repolarization reserve) is suggested that more closely resemble subsets of patients exhibiting increased vulnerability towards the development of ventricular arrhythmias and sudden cardiac death.
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Affiliation(s)
- István Baczkó
- Department of Pharmacology & Pharmacotherapy, University of Szeged, Dóm tér 12., 6720 Szeged, Hungary.
| | - Norbert Jost
- Department of Pharmacology & Pharmacotherapy, University of Szeged, Dóm tér 12., 6720 Szeged, Hungary; MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Dóm tér 12., 6720 Szeged, Hungary
| | - László Virág
- Department of Pharmacology & Pharmacotherapy, University of Szeged, Dóm tér 12., 6720 Szeged, Hungary
| | - Zsuzsanna Bősze
- Rabbit Genome and Biomodel Group, NARIC-Agricultural Biotechnology Institute, 2100 Gödöllő, Hungary
| | - András Varró
- Department of Pharmacology & Pharmacotherapy, University of Szeged, Dóm tér 12., 6720 Szeged, Hungary; MTA-SZTE Research Group of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Dóm tér 12., 6720 Szeged, Hungary
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27
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Suppression of Ventricular Arrhythmias After Myocardial Infarction by AT1 Receptor Blockade: Role of the AT2 Receptor and Casein Kinase 2/Kir2.1 Pathway. Editorial to: "Valsartan Upregulates Kir2.1 in Rats Suffering from Myocardial Infarction Via Casein Kinase 2" by Xinran Li et al. Cardiovasc Drugs Ther 2015; 29:201-6. [PMID: 26175121 DOI: 10.1007/s10557-015-6608-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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28
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Abstract
Optimal cardiac function depends on proper timing of excitation and contraction in various regions of the heart, as well as on appropriate heart rate. This is accomplished via specialized electrical properties of various components of the system, including the sinoatrial node, atria, atrioventricular node, His-Purkinje system, and ventricles. Here we review the major regionally determined electrical properties of these cardiac regions and present the available data regarding the molecular and ionic bases of regional cardiac function and dysfunction. Understanding these differences is of fundamental importance for the investigation of arrhythmia mechanisms and pharmacotherapy.
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Affiliation(s)
- Daniel C Bartos
- Department of Pharmacology, University of California Davis, Davis, California, USA
| | - Eleonora Grandi
- Department of Pharmacology, University of California Davis, Davis, California, USA
| | - Crystal M Ripplinger
- Department of Pharmacology, University of California Davis, Davis, California, USA
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29
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Elshrif MM, Shi P, Cherry EM. Representing variability and transmural differences in a model of human heart failure. IEEE J Biomed Health Inform 2015; 19:1308-20. [PMID: 26068919 DOI: 10.1109/jbhi.2015.2442833] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
During heart failure (HF) at the cellular level, the electrophysiological properties of single myocytes get remodeled, which can trigger the occurrence of ventricular arrhythmias that could be manifested in many forms such as early afterdepolarizations (EADs) and alternans (ALTs). In this paper, based on experimentally observed human HF data, specific ionic and exchanger current strengths are modified from a recently developed human ventricular cell model: the O'Hara-Virág-Varró-Rudy (OVVR) model. A new transmural HF-OVVR model is developed that incorporates HF changes and variability of the observed remodeling. This new heterogeneous HF-OVVR model is able to replicate many of the failing action potential (AP) properties and the dynamics of both [Ca(2+)]i and [Na(+)]i in accordance with experimental data. Moreover, it is able to generate EADs for different cell types and exhibits ALTs at modest pacing rate for transmural cell types. We have assessed the HF-OVVR model through the examination of the AP duration and the major ionic currents' rate dependence in single myocytes. The evaluation of the model comes from utilizing the steady-state (S-S) and S1-S2 restitution curves and from probing the accommodation of the HF-OVVR model to an abrupt change in cycle length. In addition, we have investigated the effect of chosen currents on the AP properties, such as blocking the slow sodium current to shorten the AP duration and suppress the EADs, and have found good agreement with experimental observations. This study should help elucidate arrhythmogenic mechanisms at the cellular level and predict unseen properties under HF conditions. In addition, this AP cell model might be useful for modeling and simulating HF at the tissue and organ levels.
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30
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Nguyen TP, Singh N, Xie Y, Qu Z, Weiss JN. Repolarization reserve evolves dynamically during the cardiac action potential: effects of transient outward currents on early afterdepolarizations. Circ Arrhythm Electrophysiol 2015; 8:694-702. [PMID: 25772542 DOI: 10.1161/circep.114.002451] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 02/20/2015] [Indexed: 11/16/2022]
Abstract
BACKGROUND Transient outward K currents (Ito) have been reported both to suppress and to facilitate early afterdepolarizations (EADs) when repolarization reserve is reduced. Here, we used the dynamic clamp technique to analyze how Ito accounts for these paradoxical effects on EADs by influencing the dynamic evolution of repolarization reserve during the action potential. METHODS AND RESULTS Isolated patch-clamped rabbit ventricular myocytes were exposed to either oxidative stress (H2O2) or hypokalemia to induce bradycardia-dependent EADs at a long pacing cycle length of 6 s, when native rabbit Ito is substantial. EADs disappeared when the pacing cycle length was shortened to 1 s, when Ito becomes negligible because of incomplete recovery from inactivation. During 6-s pacing cycle length, EADs were blocked by the Ito blocker 4-aminopyridine, but reappeared when a virtual current with appropriate Ito-like properties was reintroduced using the dynamic clamp (n=141 trials). During 1-s pacing cycle length in the absence of 4-aminopyridine, adding a virtual Ito-like current (n=1113 trials) caused EADs to reappear over a wide range of Ito conductance (0.005-0.15 nS/pF), particularly when inactivation kinetics were slow (τinact≥20 ms) and the pedestal (noninactivating component) was small (<25% of peak Ito). Faster inactivation or larger pedestals tended to suppress EADs. CONCLUSIONS Repolarization reserve evolves dynamically during the cardiac action potential. Whereas sufficiently large Ito can suppress EADs, a wide range of intermediate Ito properties can promote EADs by influencing the temporal evolution of other currents affecting late repolarization reserve. These findings raise caution in targeting Ito as an antiarrhythmic strategy.
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Affiliation(s)
- Thao P Nguyen
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles.
| | - Neha Singh
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
| | - Yuanfang Xie
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
| | - Zhilin Qu
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
| | - James N Weiss
- From the UCLA Cardiovascular Research Laboratory, Division of Cardiology, Department of Medicine, David Geffen School of Medicine, University of California, Los Angeles
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31
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Long VP, Bonilla IM, Vargas-Pinto P, Nishijima Y, Sridhar A, Li C, Mowrey K, Wright P, Velayutham M, Kumar S, Lee NY, Zweier JL, Mohler PJ, Györke S, Carnes CA. Heart failure duration progressively modulates the arrhythmia substrate through structural and electrical remodeling. Life Sci 2015; 123:61-71. [PMID: 25596015 PMCID: PMC4763601 DOI: 10.1016/j.lfs.2014.12.024] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2014] [Revised: 12/15/2014] [Accepted: 12/19/2014] [Indexed: 01/10/2023]
Abstract
AIMS Ventricular arrhythmias are a common cause of death in patients with heart failure (HF). Structural and electrical abnormalities in the heart provide a substrate for such arrhythmias. Canine tachypacing-induced HF models of 4-6 weeks duration are often used to study pathophysiology and therapies for HF. We hypothesized that a chronic canine model of HF would result in greater electrical and structural remodeling than a short term model, leading to a more arrhythmogenic substrate. MAIN METHODS HF was induced by ventricular tachypacing for one (short-term) or four (chronic) months to study remodeling. KEY FINDINGS Left ventricular contractility was progressively reduced, while ventricular hypertrophy and interstitial fibrosis were evident at 4 month but not 1 month of HF. Left ventricular myocyte action potentials were prolonged after 4 (p<0.05) but not 1 month of HF. Repolarization instability and early afterdepolarizations were evident only after 4 months of HF (p<0.05), coinciding with a prolonged QTc interval (p<0.05). The transient outward potassium current was reduced in both HF groups (p<0.05). The outward component of the inward rectifier potassium current was reduced only in the 4 month HF group (p<0.05). The delayed rectifier potassium currents were reduced in 4 (p<0.05) but not 1 month of HF. Reactive oxygen species were increased at both 1 and 4 months of HF (p<0.05). SIGNIFICANCE Reduced Ito, outward IK1, IKs, and IKr in HF contribute to EAD formation. Chronic, but not short term canine HF, results in the altered electrophysiology and repolarization instability characteristic of end-stage human HF.
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Affiliation(s)
- Victor P Long
- College of Pharmacy, The Ohio State University, Columbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA
| | - Ingrid M Bonilla
- College of Pharmacy, The Ohio State University, Columbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA
| | - Pedro Vargas-Pinto
- College of Veterinary Medicine, The Ohio State University, Columbus, OH, USA
| | | | - Arun Sridhar
- College of Pharmacy, The Ohio State University, Columbus, OH, USA
| | - Chun Li
- College of Pharmacy, The Ohio State University, Columbus, OH, USA
| | | | - Patrick Wright
- Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA
| | - Murugesan Velayutham
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA
| | - Sanjay Kumar
- College of Pharmacy, The Ohio State University, Columbus, OH, USA
| | - Nam Y Lee
- College of Pharmacy, The Ohio State University, Columbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA
| | - Jay L Zweier
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA; Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA
| | - Peter J Mohler
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA; Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA
| | - Sandor Györke
- Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA; Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA
| | - Cynthia A Carnes
- College of Pharmacy, The Ohio State University, Columbus, OH, USA; Dorothy M. Davis Heart and Lung Research Institute, The Ohio State University, Columbus, OH, USA; Department of Physiology and Cell Biology, The Ohio State University, Columbus, OH, USA.
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32
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Activation of IK1 Channel by Zacopride Attenuates Left Ventricular Remodeling in Rats With Myocardial Infarction. J Cardiovasc Pharmacol 2014; 64:345-56. [DOI: 10.1097/fjc.0000000000000127] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
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33
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On the risk concerns of zacopride, a moderate IK1 channel agonist with cardiac protective action. J Cardiovasc Pharmacol 2014; 64:357-9. [PMID: 25072868 DOI: 10.1097/fjc.0000000000000148] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Zacopride, an IK1 agonist with moderate potency, could exert significant antiarrhythmic and cardiac protective effects. To date, there is no report to show that zacopride is proarrhythmic in both experimental studies and clinical trials. However, in certain cardiac pathological conditions, especially short QT syndrome and certain reentry tachycardia, zacopride is not suggested. Further studies are needed to precisely evaluate the potential arrhythmogenic risk of zacopride.
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34
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Schmitt N, Grunnet M, Olesen SP. Cardiac potassium channel subtypes: new roles in repolarization and arrhythmia. Physiol Rev 2014; 94:609-53. [PMID: 24692356 DOI: 10.1152/physrev.00022.2013] [Citation(s) in RCA: 160] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
About 10 distinct potassium channels in the heart are involved in shaping the action potential. Some of the K+ channels are primarily responsible for early repolarization, whereas others drive late repolarization and still others are open throughout the cardiac cycle. Three main K+ channels drive the late repolarization of the ventricle with some redundancy, and in atria this repolarization reserve is supplemented by the fairly atrial-specific KV1.5, Kir3, KCa, and K2P channels. The role of the latter two subtypes in atria is currently being clarified, and several findings indicate that they could constitute targets for new pharmacological treatment of atrial fibrillation. The interplay between the different K+ channel subtypes in both atria and ventricle is dynamic, and a significant up- and downregulation occurs in disease states such as atrial fibrillation or heart failure. The underlying posttranscriptional and posttranslational remodeling of the individual K+ channels changes their activity and significance relative to each other, and they must be viewed together to understand their role in keeping a stable heart rhythm, also under menacing conditions like attacks of reentry arrhythmia.
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35
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Mustroph J, Maier LS, Wagner S. CaMKII regulation of cardiac K channels. Front Pharmacol 2014; 5:20. [PMID: 24600393 PMCID: PMC3930912 DOI: 10.3389/fphar.2014.00020] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2013] [Accepted: 01/31/2014] [Indexed: 11/23/2022] Open
Abstract
Cardiac K channels are critical determinants of cardiac excitability. In hypertrophied and failing myocardium, alterations in the expression and activity of voltage-gated K channels are frequently observed and contribute to the increased propensity for life-threatening arrhythmias. Thus, understanding the mechanisms of disturbed K channel regulation in heart failure (HF) is of critical importance. Amongst others, Ca/calmodulin-dependent protein kinase II (CaMKII) has been identified as an important regulator of K channel activity. In human HF but also various animal models, increased CaMKII expression and activity has been linked to deteriorated contractile function and arrhythmias. This review will discuss the current knowledge about CaMKII regulation of several K channels, its influence on action potential properties, dispersion of repolarization, and arrhythmias with special focus on HF.
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Affiliation(s)
- Julian Mustroph
- Department of Cardiology, University Medical Center Göttingen Göttingen, Germany
| | - Lars S Maier
- Department of Cardiology, University Medical Center Göttingen Göttingen, Germany
| | - Stefan Wagner
- Department of Cardiology, University Medical Center Göttingen Göttingen, Germany
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Aflaki M, Qi XY, Xiao L, Ordog B, Tadevosyan A, Luo X, Maguy A, Shi Y, Tardif JC, Nattel S. Exchange protein directly activated by cAMP mediates slow delayed-rectifier current remodeling by sustained β-adrenergic activation in guinea pig hearts. Circ Res 2014; 114:993-1003. [PMID: 24508724 DOI: 10.1161/circresaha.113.302982] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
RATIONALE β-Adrenoceptor activation contributes to sudden death risk in heart failure. Chronic β-adrenergic stimulation, as occurs in patients with heart failure, causes potentially arrhythmogenic reductions in slow delayed-rectifier K(+) current (IKs). OBJECTIVE To assess the molecular mechanisms of IKs downregulation caused by chronic β-adrenergic activation, particularly the role of exchange protein directly activated by cAMP (Epac). METHODS AND RESULTS Isolated guinea pig left ventricular cardiomyocytes were incubated in primary culture and exposed to isoproterenol (1 μmol/L) or vehicle for 30 hours. Sustained isoproterenol exposure decreased IKs density (whole cell patch clamp) by 58% (P<0.0001), with corresponding decreases in potassium voltage-gated channel subfamily E member 1 (KCNE1) mRNA and membrane protein expression (by 45% and 51%, respectively). Potassium voltage-gated channel, KQT-like subfamily, member 1 (KCNQ1) mRNA expression was unchanged. The β1-adrenoceptor antagonist 1-[2-((3-Carbamoyl-4-hydroxy)phenoxy)ethylamino]-3-[4-(1-methyl-4-trifluoromethyl-2-imidazolyl)phenoxy]-2-propanol dihydrochloride (CGP-20712A) prevented isoproterenol-induced IKs downregulation, whereas the β2-antagonist ICI-118551 had no effect. The selective Epac activator 8-pCPT-2'-O-Me-cAMP decreased IKs density to an extent similar to isoproterenol exposure, and adenoviral-mediated knockdown of Epac1 prevented isoproterenol-induced IKs/KCNE1 downregulation. In contrast, protein kinase A inhibition with a cell-permeable highly selective peptide blocker did not affect IKs downregulation. 1,2-Bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetate-AM acetoxymethyl ester (BAPTA-AM), cyclosporine, and inhibitor of nuclear factor of activated T cell (NFAT)-calcineurin association-6 (INCA6) prevented IKs reduction by isoproterenol and INCA6 suppressed isoproterenol-induced KCNE1 downregulation, consistent with signal-transduction via the Ca(2+)/calcineurin/NFAT pathway. Isoproterenol induced nuclear NFATc3/c4 translocation (immunofluorescence), which was suppressed by Epac1 knockdown. Chronic in vivo administration of isoproterenol to guinea pigs reduced IKs density and KCNE1 mRNA and protein expression while inducing cardiac dysfunction and action potential prolongation. Selective in vivo activation of Epac via sp-8-pCPT-2'-O-Me-cAMP infusion decreased IKs density and KCNE1 mRNA/protein expression. CONCLUSIONS Prolonged β1-adrenoceptor stimulation suppresses IKs by downregulating KCNE1 mRNA and protein via Epac-mediated Ca(2+)/calcineurin/NFAT signaling. These results provide new insights into the molecular basis of K(+) channel remodeling under sustained adrenergic stimulation.
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Affiliation(s)
- Mona Aflaki
- From the Department of Medicine, Research Center, Montreal Heart Institute, Université de Montréal, Montreal, Quebec, Canada (M.A., X.-Y.Q., L.X., B.O., A.T., X.L., A.M., Y.S., J.-C.T., S.N.); and Department of Pharmacology and Therapeutics, McGill University, Montreal, Quebec, Canada (M.A., S.N.)
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Not left ventricular lead position, but the extent of immediate asynchrony reduction predicts long-term response to cardiac resynchronization therapy. Clin Res Cardiol 2014; 103:457-66. [DOI: 10.1007/s00392-014-0672-8] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/04/2013] [Accepted: 01/14/2014] [Indexed: 10/25/2022]
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38
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CURRAN JERRY, MOHLER PETERJ. Revisiting K +
Channel-Dependent Electrical Remodeling in the Border Zone. J Cardiovasc Electrophysiol 2013; 24:1154-6. [DOI: 10.1111/jce.12189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- JERRY CURRAN
- The Dorothy M. Davis Heart & Lung Research Institute
| | - PETER J. MOHLER
- The Dorothy M. Davis Heart & Lung Research Institute
- Department of Internal Medicine
- Department of Physiology and Cell Biology; The Ohio State University Wexner Medical Center; Columbus Ohio USA
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39
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Gao G, Xie A, Zhang J, Herman AM, Jeong EM, Gu L, Liu M, Yang KC, Kamp TJ, Dudley SC. Unfolded protein response regulates cardiac sodium current in systolic human heart failure. Circ Arrhythm Electrophysiol 2013; 6:1018-24. [PMID: 24036084 DOI: 10.1161/circep.113.000274] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
BACKGROUND Human heart failure (HF) increases alternative mRNA splicing of the type V, voltage-gated cardiac Na+ channel α-subunit (SCN5A), generating variants encoding truncated, nonfunctional channels that are trapped in the endoplasmic reticulum. In this work, we tested whether truncated Na+ channels activate the unfolded protein response (UPR), contributing to SCN5A electric remodeling in HF. METHODS AND RESULTS UPR and SCN5A were analyzed in human ventricular systolic HF tissue samples and human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). Cells were exposed to angiotensin II (AngII) and hypoxia, known activators of abnormal SCN5A mRNA splicing, or were induced to overexpress SCN5A variants. UPR effectors, protein kinase R-like ER kinase (PERK), calreticulin, and CHOP, were increased in human HF tissues. Induction of SCN5A variants with AngII or hypoxia or the expression of exogenous variants induced the UPR with concomitant downregulation of Na+ current. PERK activation destabilized SCN5A and, surprisingly, Kv4.3 channel mRNAs but not transient receptor potential cation channel M7 (TRPM7) channel mRNA. PERK inhibition prevented the loss of full-length SCN5A and Kv4.3 mRNA levels resulting from expressing Na+ channel mRNA splice variants. CONCLUSIONS UPR can be initiated by Na+ channel mRNA splice variants and is involved in the reduction of cardiac Na+ current during human HF. Because the effect is not entirely specific to the SCN5A transcript, the UPR may play an important role in downregulation of multiple cardiac genes in HF.
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Affiliation(s)
- Ge Gao
- Lifespan Cardiovascular Research Center, the Warren Alpert School of Medicine, Brown University and Providence Veterans Administration Medical Center, Providence, RI
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40
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Li X, Wang T, Han K, Zhuo X, Lu Q, Ma A. Bisoprolol reverses down-regulation of potassium channel proteins in ventricular tissues of rabbits with heart failure. J Biomed Res 2013; 25:274-9. [PMID: 23554701 PMCID: PMC3597065 DOI: 10.1016/s1674-8301(11)60037-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2011] [Revised: 04/28/2011] [Accepted: 05/14/2011] [Indexed: 11/24/2022] Open
Abstract
Remodeling of ion channels is an important mechanism of arrhythmia induced by heart failure (HF). We investigated the expression of potassium channel encoding genes in the ventricles of rabbit established by volume-overload operation followed with pressure-overload. The reversible effect of these changes with bisoprolol was also evaluated. The HF group exhibited left ventricular enlargement, systolic dysfunction, prolongation of corrected QT interval (QTc), and increased plasma brain natriuretic peptide levels in the HF rabbits. Several potassium channel subunit encoding genes were consistently down-regulated in the HF rabbits. After bisoprolol treatment, heart function was improved significantly and QTc was shortened. Additionally, the mRNA expression of potassium channel subunit genes could be partially reversed. The down-regulated expression of potassium channel subunits Kv4.3, Kv1.4, KvLQT1, minK and Kir 2.1 may contribute to the prolongation of action potential duration in the heart of rabbits induced by volume combined with pressure overload HF. Bisoprolol could partially reverse these down-regulations and improve heart function.
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Affiliation(s)
- Xi Li
- Department of Cardiovascular Medicine, the First Affiliated Hospital of Medical School, Xi'an Jiaotong University, Xi'an, Shaanxi 710061, China
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41
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Holzem KM, Efimov IR. Arrhythmogenic remodelling of activation and repolarization in the failing human heart. Europace 2013; 14 Suppl 5:v50-v57. [PMID: 23104915 DOI: 10.1093/europace/eus275] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Heart failure is a major cause of disability and death worldwide, and approximately half of heart failure-related deaths are sudden and presumably due to ventricular arrhythmias. Patients with heart failure have been shown to be at 6- to 9-fold increased risk of sudden cardiac death compared to the general population. (AHA. Heart Disease and Stroke Statistics-2003 Update. Heart and Stroke Facts. Dallas, TX: American Heart Association; 2002) Thus, electrophysiological remodelling associated with heart failure is a leading cause of disease mortality and has been a major investigational focus examined using many animal models of heart failure. While these studies have provided an important foundation for understanding the arrhythmogenic pathophysiology of heart failure, the need for corroborating studies conducted on human heart tissue has been increasingly recognized. Many human heart studies of conduction and repolarization remodelling have now been published and shed some light on important, potentially arrhythmogenic, changes in human heart failure. These studies are being conducted at multiple experimental scales from isolated cells to whole-tissue preparations and have provided insight into regulatory mechanisms such as decreased protein expression, alternative mRNA splicing of ion channel genes, and defective cellular trafficking. Further investigations of heart failure in the human myocardium will be essential for determining possible therapeutic targets to prevent arrhythmia in heart failure and for facilitating the translation of basic research findings to the clinical realm.
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Affiliation(s)
- Katherine M Holzem
- Department of Biomedical Engineering, Washington University in St Louis, One Brookings Drive, St Louis, MO 63130, USA
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42
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Antiarrhythmic effects and ionic mechanisms of allicin on myocardial injury of diabetic rats induced by streptozotocin. Naunyn Schmiedebergs Arch Pharmacol 2013; 386:697-704. [DOI: 10.1007/s00210-013-0872-1] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2012] [Accepted: 04/08/2013] [Indexed: 01/11/2023]
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Saegusa N, Garg V, Spitzer KW. Modulation of ventricular transient outward K⁺ current by acidosis and its effects on excitation-contraction coupling. Am J Physiol Heart Circ Physiol 2013; 304:H1680-96. [PMID: 23585132 DOI: 10.1152/ajpheart.00070.2013] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The contribution of transient outward current (Ito) to changes in ventricular action potential (AP) repolarization induced by acidosis is unresolved, as is the indirect effect of these changes on calcium handling. To address this issue we measured intracellular pH (pHi), Ito, L-type calcium current (ICa,L), and calcium transients (CaTs) in rabbit ventricular myocytes. Intracellular acidosis [pHi 6.75 with extracellular pH (pHo) 7.4] reduced Ito by ~50% in myocytes with both high (epicardial) and low (papillary muscle) Ito densities, with little effect on steady-state inactivation and activation. Of the two candidate α-subunits underlying Ito, human (h)Kv4.3 and hKv1.4, only hKv4.3 current was reduced by intracellular acidosis. Extracellular acidosis (pHo 6.5) shifted Ito inactivation toward less negative potentials but had negligible effect on peak current at +60 mV when initiated from -80 mV. The effects of low pHi-induced inhibition of Ito on AP repolarization were much greater in epicardial than papillary muscle myocytes and included slowing of phase 1, attenuation of the notch, and elevation of the plateau. Low pHi increased AP duration in both cell types, with the greatest lengthening occurring in epicardial myocytes. The changes in epicardial AP repolarization induced by intracellular acidosis reduced peak ICa,L, increased net calcium influx via ICa,L, and increased CaT amplitude. In summary, in contrast to low pHo, intracellular acidosis has a marked inhibitory effect on ventricular Ito, perhaps mediated by Kv4.3. By altering the trajectory of the AP repolarization, low pHi has a significant indirect effect on calcium handling, especially evident in epicardial cells.
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Affiliation(s)
- Noriko Saegusa
- Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA
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44
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Szuts V, Ménesi D, Varga-Orvos Z, Zvara Á, Houshmand N, Bitay M, Bogáts G, Virág L, Baczkó I, Szalontai B, Geramipoor A, Cotella D, Wettwer E, Ravens U, Deák F, Puskás LG, Papp JG, Kiss I, Varró A, Jost N. Altered expression of genes for Kir ion channels in dilated cardiomyopathy. Can J Physiol Pharmacol 2013; 91:648-56. [PMID: 23889090 DOI: 10.1139/cjpp-2012-0413] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Dilated cardiomyopathy (DCM) is a multifactorial disease characterized by left ventricular dilation that is associated with systolic dysfunction and increased action potential duration. The Kir2.x K⁺ channels (encoded by KCNJ genes) regulate the inward rectifier current (IK1) contributing to the final repolarization in cardiac muscle. Here, we describe the transitions in the gene expression profiles of 4 KCNJ genes from healthy or dilated cardiomyopathic human hearts. In the healthy adult ventricles, KCNJ2, KCNJ12, and KCNJ4 (Kir2.1-2.3, respectively) genes were expressed at high levels, while expression of the KCNJ14 (Kir2.4) gene was low. In DCM ventricles, the levels of Kir2.1 and Kir2.3 were upregulated, but those of Kir2.2 channels were downregulated. Additionally, the expression of the DLG1 gene coding for the synapse-associated protein 97 (SAP97) anchoring molecule exhibited a 2-fold decline with increasing age in normal hearts, and it was robustly downregulated in young DCM patients. These adaptations could offer a new aspect for the explanation of the generally observed physiological and molecular alterations found in DCM.
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Affiliation(s)
- Viktoria Szuts
- Institute of Biochemistry, Biological Research Centre, Hungarian Academy of Sciences, Szeged, Hungary
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45
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Goldoni D, Yarham J, McGahon M, O’Connor A, Guduric-Fuchs J, Edgar K, McDonald D, Simpson D, Collins A. A novel dual-fluorescence strategy for functionally validating microRNA targets in 3' untranslated regions: regulation of the inward rectifier potassium channel K(ir)2.1 by miR-212. Biochem J 2012; 448:103-13. [PMID: 22880819 PMCID: PMC3475433 DOI: 10.1042/bj20120578] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2012] [Revised: 08/03/2012] [Accepted: 08/13/2012] [Indexed: 01/16/2023]
Abstract
Gene targeting by microRNAs is important in health and disease. We developed a functional assay for identifying microRNA targets and applied it to the K(+) channel K(ir)2.1 [KCNJ2 (potassium inwardly-rectifying channel, subfamily J, member 2)] which is dysregulated in cardiac and vascular disorders. The 3'UTR (untranslated region) was inserted downstream of the mCherry red fluorescent protein coding sequence in a mammalian expression plasmid. MicroRNA sequences were inserted into the pSM30 expression vector which provides enhanced green fluorescent protein as an indicator of microRNA expression. HEK (human embryonic kidney)-293 cells were co-transfected with the mCherry-3'UTR plasmid and a pSM30-based plasmid with a microRNA insert. The principle of the assay is that functional targeting of the 3'UTR by the microRNA results in a decrease in the red/green fluorescence intensity ratio as determined by automated image analysis. The method was validated with miR-1, a known down-regulator of K(ir)2.1 expression, and was used to investigate the targeting of the K(ir)2.1 3'UTR by miR-212. The red/green ratio was lower in miR-212-expressing cells compared with the non-targeting controls, an effect that was attenuated by mutating the predicted target site. miR-212 also reduced inward rectifier current and K(ir)2.1 protein in HeLa cells. This novel assay has several advantages over traditional luciferase-based assays including larger sample size, amenability to time course studies and adaptability to high-throughput screening.
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Key Words
- hela cell
- hek-293 cell
- image analysis
- microrna
- patch clamp
- cmv, cytomegalovirus
- dmem, dulbecco’s modified eagle’s medium
- egfp, enhanced green fluorescent protein
- gapdh, glyceraldehyde-3-phosphate dehydrogenase
- hek, human embryonic kidney
- hprt1, hypoxanthine–phosphoribosyltransferase 1
- ik1, inward-rectifier k+ current
- kcnj2, potassium inwardly-rectifying channel, subfamily j, member 2
- mirna, microrna
- qrt–pcr, quantitative reverse transcription pcr
- race, rapid amplification of cdna ends
- sirna, short interfering rna
- utr, untranslated region
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Affiliation(s)
- Dana Goldoni
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - Janet M. Yarham
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - Mary K. McGahon
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - Anna O’Connor
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - Jasenka Guduric-Fuchs
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - Kevin Edgar
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - Denise M. McDonald
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - David A. Simpson
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
| | - Anthony Collins
- Centre for Vision and Vascular Science, Queen's University of Belfast, Institute of Clinical Science, Block A, Royal Victoria Hospital, Grosvenor Road, Belfast, BT12 6BA, U.K
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Cho H, Barth AS, Tomaselli GF. Basic science of cardiac resynchronization therapy: molecular and electrophysiological mechanisms. Circ Arrhythm Electrophysiol 2012; 5:594-603. [PMID: 22715238 DOI: 10.1161/circep.111.962746] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Affiliation(s)
- Hana Cho
- Department of Physiology, Sungkyunkwan University School of Medicine, Suwon, Korea.
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47
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Yang D, Lyashkov AE, Li Y, Ziman BD, Lakatta EG. RGS2 overexpression or G(i) inhibition rescues the impaired PKA signaling and slow AP firing of cultured adult rabbit pacemaker cells. J Mol Cell Cardiol 2012; 53:687-94. [PMID: 22921807 DOI: 10.1016/j.yjmcc.2012.08.007] [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: 12/06/2011] [Revised: 07/23/2012] [Accepted: 08/10/2012] [Indexed: 12/16/2022]
Abstract
Freshly isolated adult rabbit sinoatrial node cells (f-SANC) are an excellent model for studies of autonomic signaling, but are not amenable to genetic manipulation. We have developed and characterized a stable cultured rabbit SANC (c-SANC) model that is suitable for genetic manipulation to probe mechanisms of spontaneous action potential (AP) firing. After 48 h in culture, c-SANC generate stable, rhythmic APs at 34±0.5°C, at a rate that is 50% less than f-SANC. In c- vs. f-SANC: AP duration is prolonged; phosphorylation of phospholamban at Ser(16) and type2 ryanodine receptor (RyR2) at Ser(2809) are reduced; and the level of type2 regulator of G-protein signaling (RGS2), that facilitates adenylyl cyclases/cAMP/protein kinase A (PKA) via G(i) inhibition, is substantially reduced. Consistent with the interpretation that cAMP/PKA signaling becomes impaired in c-SANC, acute β-adrenergic receptor stimulation increases phospholamban and RyR2 phosphorylation, enhances RGS2-labeling density, and accelerates the AP firing rate to the similar maximum in c- and f-SANC. Specific PKA inhibition completely inhibits all β-adrenergic receptor effects. Adv-RGS2 infection, or pertussis toxin treatment to disable G(i)-signaling, each partially rescues the c-SANC spontaneous AP firing rate. Thus, a G(i)-dependent reduction in PKA-dependent protein phosphorylation, including that of Ca(2+) cycling proteins, reduces the spontaneous AP firing rate of c-SANC, and can be reversed by genetic or pharmacologic manipulation of PKA signaling.
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Affiliation(s)
- Dongmei Yang
- Laboratory of Cardiovascular Science, IRP, National Institute on Aging, National Institutes of Health, Baltimore, MD 21224-6825, USA
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48
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Cherry EM, Fenton FH, Gilmour RF. Mechanisms of ventricular arrhythmias: a dynamical systems-based perspective. Am J Physiol Heart Circ Physiol 2012; 302:H2451-63. [PMID: 22467299 PMCID: PMC3378269 DOI: 10.1152/ajpheart.00770.2011] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/02/2011] [Accepted: 03/26/2012] [Indexed: 01/23/2023]
Abstract
Defining the cellular electrophysiological mechanisms for ventricular tachyarrhythmias is difficult, given the wide array of potential mechanisms, ranging from abnormal automaticity to various types of reentry and kk activity. The degree of difficulty is increased further by the fact that any particular mechanism may be influenced by the evolving ionic and anatomic environments associated with many forms of heart disease. Consequently, static measures of a single electrophysiological characteristic are unlikely to be useful in establishing mechanisms. Rather, the dynamics of the electrophysiological triggers and substrates that predispose to arrhythmia development need to be considered. Moreover, the dynamics need to be considered in the context of a system, one that displays certain predictable behaviors, but also one that may contain seemingly stochastic elements. It also is essential to recognize that even the predictable behaviors of this complex nonlinear system are subject to small changes in the state of the system at any given time. Here we briefly review some of the short-, medium-, and long-term alterations of the electrophysiological substrate that accompany myocardial disease and their potential impact on the initiation and maintenance of ventricular arrhythmias. We also provide examples of cases in which small changes in the electrophysiological substrate can result in rather large differences in arrhythmia outcome. These results suggest that an interrogation of cardiac electrical dynamics is required to provide a meaningful assessment of the immediate risk for arrhythmia development and for evaluating the effects of putative antiarrhythmic interventions.
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Affiliation(s)
- Elizabeth M Cherry
- Department of Biomedical Sciences, College of Veterinary Medicine, Cornell University, Ithaca, New York 14853-6401, USA
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Kijtawornrat A, Sawangkoon S, Hamlin RL. Assessment of QT-prolonging drugs in the isolated normal and failing rabbit hearts. J Toxicol Sci 2012; 37:455-62. [PMID: 22687985 DOI: 10.2131/jts.37.455] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Lengthening of QTc is the usual signal to indicate torsadogenic potential of a therapeutic agent. The ICH S7B guideline recommends that new chemical entities should be assessed for potential of delayed ventricular repolarization in animal models. The aim of this study was to determine a feasibility of using isolated failing heart rabbit to assess the QT-lengthening drugs in comparison with their effects on isolated normal heart rabbits. Heart failure was induced by ligation of the left anterior descending and descending branch of left circumflex coronary arteries. One month after ligation, all rabbits were anesthetized and the hearts were removed quickly, and they were perfused with the oxygenated Krebs-Henseleit solution to which escalating concentrations of QT-lengthening compounds were added. RR, QT, and QTc(F) were not significantly different, at rest, between failing and normal hearts. During baseline, dP/dt<inf>max</inf> was lower and dP/dt<inf>min</inf> was higher for failing hearts than for normals. In responses to all three QT-lengthening compounds, RR, QT and QTc(F) lengthened similarly in a dose-response manner in both the failing and normal hearts. Neither the failing nor the normal hearts developed fatal arrhythmias, torsades de pointes. Langendorff preparations of failing hearts are as good as normal isolated hearts and can be use to assess the potential of delayed ventricular repolarization of test articles.
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Affiliation(s)
- Anusak Kijtawornrat
- Department of Veterinary Physiology, Faculty of Veterinary Science, Chulalongkorn University, Thailand.
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50
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Attenuated ventricular β-adrenergic response and reduced repolarization reserve in a rabbit model of chronic heart failure. J Cardiovasc Pharmacol 2012; 59:142-50. [PMID: 21992969 DOI: 10.1097/fjc.0b013e318238727a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Animal models of pacing-induced heart failure (HF) are often associated with high acute mortality secondary to high pacing frequencies. The present study therefore exploits lower-frequency left ventricular pacing (300 beats per minute) in rabbits for 11 weeks to produce chronic HF with low acute mortality but profound structural, functional, and electrical remodeling and compare with nonpaced controls. Pacing increased heart weight/body weight ratio and decreased left ventricular fractional shortening in tachypaced only. Electrocardiogram recordings during sinus rhythm revealed QTc prolongation in paced animals. Ventricular arrhythmias or sudden death was not observed. Isoproterenol increased heart rate similarly in both groups but showed a blunted QT-shortening effect in tachypaced rabbits compared with controls. Langendorff experiments revealed significant monophasic action potential duration prolongation in tachypaced hearts and reduced contractility at cycle lengths from 400 to 250 ms. Hyperkalemia caused monophasic action potential duration shortening in controls, whereas crossover was seen in tachypaced with monophasic action potential duration prolongation at short cycle length. Hypokalemia prolonged monophasic action potential duration and increased short-term variability of repolarization in tachypaced hearts. A blunted monophasic action potential duration response was observed ex vivo in tachypaced hearts after isoproterenol. The HF rabbits showed structural, functional, and electrical remodeling but very low mortality. Isokalemic and hyperkalemic responses indicate downregulation of functional IKs. Increased short-term variability during hypokalemia unmasks a reduced repolarization reserve.
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