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Shemarova I. The Dysfunction of Ca 2+ Channels in Hereditary and Chronic Human Heart Diseases and Experimental Animal Models. Int J Mol Sci 2023; 24:15682. [PMID: 37958665 PMCID: PMC10650855 DOI: 10.3390/ijms242115682] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2023] [Revised: 10/20/2023] [Accepted: 10/23/2023] [Indexed: 11/15/2023] Open
Abstract
Chronic heart diseases, such as coronary heart disease, heart failure, secondary arterial hypertension, and dilated and hypertrophic cardiomyopathies, are widespread and have a fairly high incidence of mortality and disability. Most of these diseases are characterized by cardiac arrhythmias, conduction, and contractility disorders. Additionally, interruption of the electrical activity of the heart, the appearance of extensive ectopic foci, and heart failure are all symptoms of a number of severe hereditary diseases. The molecular mechanisms leading to the development of heart diseases are associated with impaired permeability and excitability of cell membranes and are mainly caused by the dysfunction of cardiac Ca2+ channels. Over the past 50 years, more than 100 varieties of ion channels have been found in the cardiovascular cells. The relationship between the activity of these channels and cardiac pathology, as well as the general cellular biological function, has been intensively studied on several cell types and experimental animal models in vivo and in situ. In this review, I discuss the origin of genetic Ca2+ channelopathies of L- and T-type voltage-gated calcium channels in humans and the role of the non-genetic dysfunctions of Ca2+ channels of various types: L-, R-, and T-type voltage-gated calcium channels, RyR2, including Ca2+ permeable nonselective cation hyperpolarization-activated cyclic nucleotide-gated (HCN), and transient receptor potential (TRP) channels, in the development of cardiac pathology in humans, as well as various aspects of promising experimental studies of the dysfunctions of these channels performed on animal models or in vitro.
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Affiliation(s)
- Irina Shemarova
- I.M. Sechenov Institute of Evolutionary Physiology and Biochemistry of the Russian Academy of Sciences, 194223 Saint-Petersburg, Russia
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Kola JB, Turarova B, Csige D, Sipos Á, Varga L, Gergely B, Refai FA, Uray IP, Docsa T, Uray K. Stretch-Induced Down-Regulation of HCN2 Suppresses Contractile Activity. Molecules 2023; 28:molecules28114359. [PMID: 37298834 DOI: 10.3390/molecules28114359] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2023] [Revised: 05/12/2023] [Accepted: 05/24/2023] [Indexed: 06/12/2023] Open
Abstract
Although hyperpolarization-activated and cyclic nucleotide-gated 2 channels (HCN2) are expressed in multiple cell types in the gut, the role of HCN2 in intestinal motility is poorly understood. HCN2 is down-regulated in intestinal smooth muscle in a rodent model of ileus. Thus, the purpose of this study was to determine the effects of HCN inhibition on intestinal motility. HCN inhibition with ZD7288 or zatebradine significantly suppressed both spontaneous and agonist-induced contractile activity in the small intestine in a dose-dependent and tetrodotoxin-independent manner. HCN inhibition significantly suppressed intestinal tone but not contractile amplitude. The calcium sensitivity of contractile activity was significantly suppressed by HCN inhibition. Inflammatory mediators did not affect the suppression of intestinal contractile activity by HCN inhibition but increased stretch of the intestinal tissue partially attenuated the effects of HCN inhibition on agonist-induced intestinal contractile activity. HCN2 protein and mRNA levels in intestinal smooth muscle tissue were significantly down-regulated by increased mechanical stretch compared to unstretched tissue. Increased cyclical stretch down-regulated HCN2 protein and mRNA levels in primary human intestinal smooth muscle cells and macrophages. Overall, our results suggest that decreased HCN2 expression induced by mechanical signals, such as intestinal wall distension or edema development, may contribute to the development of ileus.
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Affiliation(s)
- Job Baffin Kola
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Botagoz Turarova
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Dora Csige
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Ádám Sipos
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Luca Varga
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Bence Gergely
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Farah Al Refai
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Iván P Uray
- Department of Clinical Oncology, Faculty of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Tibor Docsa
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
| | - Karen Uray
- Department of Medical Chemistry, School of Medicine, University of Debrecen, 4032 Debrecen, Hungary
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Zhang S, Li R, Ma Y, Yan Y, Ma M, Zhang K, Zhou Y, Li L, Pan L, Ying H, Xue Y. Thyroid-stimulating hormone regulates cardiac function through modulating HCN2 via targeting microRNA-1a. FASEB J 2022; 36:e22561. [PMID: 36125044 DOI: 10.1096/fj.202200574r] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2022] [Revised: 08/11/2022] [Accepted: 09/09/2022] [Indexed: 11/11/2022]
Abstract
Previous studies have found microRNA-1 (miR-1) and hyperpolarization-activated cyclic nucleotide-gated channel 2 (HCN2) may be involved in the pathogenesis of thyroid hormone (TH) induced cardiac hypertrophy. However, little is known about the role of miR-1 and HCN2 in thyroid stimulation hormone (TSH)-induced cardiac dysfunction. In order to investigate the molecular mechanisms of TSH induced cardiac dysfunction and the role of miR-1/HCN2 in that process, we evaluated the expression of miR-1a/HCN2 in the ventricular myocardium of hypothyroid mice and in TSH-stimulated H9c2 cardiomyocytes. Our data revealed that hypothyroidism mice had smaller hearts, ventricular muscle atrophy, and cardiac contractile dysfunction compared with euthyroid controls. The upregulation of miR-1a and downregulation of HCN2 were found in ventricular myocardium of hypothyroid mice and TSH-stimulated H9c2 cardiomyocytes, indicating that miR-1a and HCN2 may be involved in TSH-induced cardiac dysfunction. We also found that the regulation of miR-1a and HCN2 expression and HCN2 channel activity by TSH requires TSHR, while the regulation of HCN2 expression and HCN2 channel function by TSH requires miR-1a. Thus, our data revealed the potential mechanism of TSH-induced cardiac dysfunction and might shed new light on the pathological role of miR-1a/HCN2 in hypothyroid heart disease.
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Affiliation(s)
- Shengjie Zhang
- Department of Endocrinology and Metabolism, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China.,CAS Key Laboratory of Nutrition, Metabolism and Food Safety, Shanghai Institute of Nutrition and Health, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Ran Li
- Department of Endocrinology and Metabolism, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Yiruo Ma
- CAS Key Laboratory of Nutrition, Metabolism and Food Safety, Shanghai Institute of Nutrition and Health, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Ying Yan
- CAS Key Laboratory of Nutrition, Metabolism and Food Safety, Shanghai Institute of Nutrition and Health, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Mei Ma
- CAS Key Laboratory of Nutrition, Metabolism and Food Safety, Shanghai Institute of Nutrition and Health, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Keqin Zhang
- Department of Endocrinology and Metabolism, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Yun Zhou
- Department of Endocrinology and Metabolism, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Ling Li
- Department of Endocrinology and Metabolism, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Lingling Pan
- Department of Endocrinology and Metabolism, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China
| | - Hao Ying
- CAS Key Laboratory of Nutrition, Metabolism and Food Safety, Shanghai Institute of Nutrition and Health, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai, China
| | - Ying Xue
- Department of Endocrinology and Metabolism, Tongji Hospital, School of Medicine, Tongji University, Shanghai, China
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Miao B, Mao G, Wu J, Zhao B, Shi H, Fei S. Protective effect of HCN2-induced SON sensitization on chronic visceral hypersensitivity in neonatal-CRD rat model. Brain Res 2021; 1767:147538. [PMID: 34052259 DOI: 10.1016/j.brainres.2021.147538] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2021] [Revised: 03/23/2021] [Accepted: 04/25/2021] [Indexed: 02/07/2023]
Abstract
Abnormal brain-gut interactions contribute to the development of chronic visceral hypersensitivity (CVH), which is the pivotal feature of irritable bowel syndrome (IBS). Despite the consensus with respect to the vital role of hyperpolarization-activated cyclic nucleotide-gated 2 (HCN2) channels in promoting painful symptoms in the peripheral nervous system, we identified that the upregulation of HCN2 in supraoptic nucleus (SON) was involved in the modulation of CVH in rat model of neonatal colorectal distention (n-CRD). Specifically, colorectal distention (CRD) upregulated the expression of c-Fos in SON in adult CVH rats, indicating the involvement of SON sensitazation in visceral sensation. Moreover, the administration of ZD7288 (the pan-HCN channel inhibitor) rather than 8-Br-cAMP (the non-specific HCN channel agonist) aggravated the CVH symptoms and reduced the phosphorylation level of CaMKII-CREB cascade. Together, the findings indicated that the upregulation of supraoptic HCN2 contributed to the sensitization of SON, which had protective effects on the modulation of CVH with the involvement of CaMKII-CREB cascade in n-CRD rat model.
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Affiliation(s)
- Bei Miao
- Department of Gastroenterology, Affiliated Hospital of Xuzhou Medical University, 99 West Huaihai Road, Xuzhou 221002, Jiangsu Province, China; Institute of Digestive Diseases, Xuzhou Medical University, 84 West Huaihai Road, Xuzhou 221002, Jiangsu Province, China
| | - Guangtong Mao
- Department of Pathology, Xinyi People's Hospital, 16 Renmin Road, Xinyi 221400, Jiangsu Province, China
| | - Jiaojiao Wu
- Department of Gastroenterology, Affiliated Hospital of Xuzhou Medical University, 99 West Huaihai Road, Xuzhou 221002, Jiangsu Province, China
| | - Benhuo Zhao
- Department of Gastroenterology, Affiliated Hospital of Xuzhou Medical University, 99 West Huaihai Road, Xuzhou 221002, Jiangsu Province, China
| | - Hengliang Shi
- Central Laboratory, Affiliated Hospital of Xuzhou Medical University, 99 West Huaihai Road, Xuzhou 221002, Jiangsu Province, China.
| | - Sujuan Fei
- Department of Gastroenterology, Affiliated Hospital of Xuzhou Medical University, 99 West Huaihai Road, Xuzhou 221002, Jiangsu Province, China; Institute of Digestive Diseases, Xuzhou Medical University, 84 West Huaihai Road, Xuzhou 221002, Jiangsu Province, China.
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Yadav V, Chong N, Ellis B, Ren X, Senapati S, Chang HC, Zorlutuna P. Constant-potential environment for activating and synchronizing cardiomyocyte colonies with on-chip ion-depleting perm-selective membranes. LAB ON A CHIP 2020; 20:4273-4284. [PMID: 33090162 DOI: 10.1039/d0lc00809e] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
In this study, an ion depleted zone created by an ion-selective membrane was used to impose a high and uniform constant extracellular potential over an entire ∼1000 cell rat cardiomyocyte (rCM) colony on-a-chip to trigger synchronized voltage-gated ion channel activities while preserving cell viability, thus extending single-cell voltage-clamp ion channel studies to an entire normalized colony. Image analysis indicated that rCM beating was strengthened and accelerated (by a factor of ∼2) within minutes of ion depletion and the duration of contraction and relaxation phases was significantly reduced. After the initial synchronization, the entire colony responds collectively to external potential changes such that beating over the entire colony can be activated or deactivated within 0.1 s. These newly observed collective dynamic responses, due to simultaneous ion channel activation/deactivation by a uniform constant-potential extracellular environment, suggest that perm-selective membrane modules on cell culture chips can facilitate studies of extracellular cardiac cell electrical communication and how ion-channel related pathologies affect cardiac cell synchronization. The future applications of this new technology can lead to better drug screening platforms for cardiotoxicity as well as platforms that can facilitate synchronized maturation of pluripotent stem cells into colonies with high electrical connectivity.
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Affiliation(s)
- Vivek Yadav
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA. and Center for Microfluidics and Medical Diagnostics, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Nicholas Chong
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Bradley Ellis
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Xiang Ren
- Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Satyajyoti Senapati
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA. and Center for Microfluidics and Medical Diagnostics, University of Notre Dame, Notre Dame, IN 46556, USA and Harper Cancer Research Institute, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Hsueh-Chia Chang
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA. and Center for Microfluidics and Medical Diagnostics, University of Notre Dame, Notre Dame, IN 46556, USA and Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA and Harper Cancer Research Institute, University of Notre Dame, Notre Dame, IN 46556, USA
| | - Pinar Zorlutuna
- Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556, USA. and Department of Aerospace and Mechanical Engineering, University of Notre Dame, Notre Dame, IN 46556, USA and Harper Cancer Research Institute, University of Notre Dame, Notre Dame, IN 46556, USA
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HCN Channels: New Therapeutic Targets for Pain Treatment. Molecules 2018; 23:molecules23092094. [PMID: 30134541 PMCID: PMC6225464 DOI: 10.3390/molecules23092094] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2018] [Revised: 08/17/2018] [Accepted: 08/18/2018] [Indexed: 12/28/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are highly regulated proteins which respond to different cellular stimuli. The HCN currents (Ih) mediated by HCN1 and HCN2 drive the repetitive firing in nociceptive neurons. The role of HCN channels in pain has been widely investigated as targets for the development of new therapeutic drugs, but the comprehensive design of HCN channel modulators has been restricted due to the lack of crystallographic data. The three-dimensional structure of the human HCN1 channel was recently reported, opening new possibilities for the rational design of highly-selective HCN modulators. In this review, we discuss the structural and functional properties of HCN channels, their pharmacological inhibitors, and the potential strategies for designing new drugs to block the HCN channel function associated with pain perception.
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Ivabradine improves left ventricular twist and untwist during chronic hypertension. Int J Cardiol 2018; 252:175-180. [PMID: 29196088 DOI: 10.1016/j.ijcard.2017.11.049] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Accepted: 11/14/2017] [Indexed: 11/23/2022]
Abstract
BACKGROUND Left ventricular (LV) dysfunction develops during LV hypertrophy and particularly during tachycardia. Thus we investigated the effects of heart rate (HR) reduction with ivabradine, an If-channel blocker, on LV twist and untwist which represents myocardial deformation occurring during the overall systole and diastole and therefore provide valuable evaluation of global LV systolic and diastolic function. METHODS Eight chronically instrumented pigs receiving continuous angiotensin II infusion during 28days to induce chronic hypertension and LV hypertrophy. Measurements were performed at Days 0 and 28 after stopping angiotensin II infusion in the presence and absence of ivabradine. RESULTS At Day 0, reducing HR from 75±3 to 55±2beats/min with ivabradine did not affect LV twist but slowed LV untwist along with an increase in LV end-diastolic pressure. At Day 28, LV posterior and septal wall thickness as well as the estimated LV mass increased, indicating LV hypertrophy. LV twist and untwist were significantly reduced by 33±4% from 16±1° and 32±6% from -154±9°/s, respectively, showing global LV systolic and diastolic dysfunction. In this context, ivabradine decreased HR by 25% from 86±5beats/min and significantly improved LV twist from 11±1 to 14±1° and LV untwist from -104±8 to -146±5°/s. CONCLUSIONS Administration of ivabradine during chronic hypertension and LV hypertrophy improved LV twist and untwist. This further supports the beneficial effect of this drug on both LV systolic and diastolic function during the development of LV hypertrophy.
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Jaffer S, Valasek P, Luke G, Batarfi M, Whalley BJ, Patel K. Characterisation of Development and Electrophysiological Mechanisms Underlying Rhythmicity of the Avian Lymph Heart. PLoS One 2016; 11:e0166428. [PMID: 27930653 PMCID: PMC5145147 DOI: 10.1371/journal.pone.0166428] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2015] [Accepted: 10/29/2016] [Indexed: 11/18/2022] Open
Abstract
Despite significant advances in tissue engineering such as the use of scaffolds, bioreactors and pluripotent stem cells, effective cardiac tissue engineering for therapeutic purposes has remained a largely intractable challenge. For this area to capitalise on such advances, a novel approach may be to unravel the physiological mechanisms underlying the development of tissues that exhibit rhythmic contraction yet do not originate from the cardiac lineage. Considerable attention has been focused on the physiology of the avian lymph heart, a discrete organ with skeletal muscle origins yet which displays pacemaker properties normally only found in the heart. A functional lymph heart is essential for avian survival and growth in ovo. The histological nature of the lymph heart is similar to skeletal muscle although molecular and bioelectrical characterisation during development to assess mechanisms that contribute towards lymph heart contractile rhythmicity have not been undertaken. A better understanding of these processes may provide exploitable insights for therapeutic rhythmically contractile tissue engineering approaches in this area of significant unmet clinical need. Here, using molecular and electrophysiological approaches, we describe the molecular development of the lymph heart to understand how this skeletal muscle becomes fully functional during discrete in ovo stages of development. Our results show that the lymph heart does not follow the normal transitional programme of myogenesis as documented in most skeletal muscle, but instead develops through a concurrent programme of precursor expansion, commitment to myogenesis and functional differentiation which offers a mechanistic explanation for its rapid development. Extracellular electrophysiological field potential recordings revealed that the peak-to-peak amplitude of electrically evoked local field potentials elicited from isolated lymph heart were significantly reduced by treatment with carbachol; an effect that could be fully reversed by atropine. Moreover, nifedipine and cyclopiazonic acid both significantly reduced peak-to-peak local field potential amplitude. Optical recordings of lymph heart showed that the organ’s rhythmicity can be blocked by the HCN channel blocker, ZD7288; an effect also associated with a significant reduction in peak-to-peak local field potential amplitude. Additionally, we also show that isoforms of HCN channels are expressed in avian lymph heart. These results demonstrate that cholinergic signalling and L-type Ca2+ channels are important in excitation and contraction coupling, while HCN channels contribute to maintenance of lymph heart rhythmicity.
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Affiliation(s)
- Sajjida Jaffer
- School of Biological Sciences, University of Reading, Whiteknights, Reading, United Kingdom
| | - Petr Valasek
- School of Biological Sciences, University of Reading, Whiteknights, Reading, United Kingdom
| | - Graham Luke
- School of Biological Sciences, University of Reading, Whiteknights, Reading, United Kingdom
| | - Munirah Batarfi
- School of Biological Sciences, University of Reading, Whiteknights, Reading, United Kingdom
| | - Benjamin Jason Whalley
- School of Chemistry, Food and Nutritional Sciences and Pharmacy, University of Reading, Whiteknights, Reading, United Kingdom
| | - Ketan Patel
- School of Biological Sciences, University of Reading, Whiteknights, Reading, United Kingdom
- * E-mail:
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Melka J, Rienzo M, Bizé A, Jozwiak M, Sambin L, Hittinger L, Su JB, Berdeaux A, Ghaleh B. Improvement of left ventricular filling by ivabradine during chronic hypertension: involvement of contraction-relaxation coupling. Basic Res Cardiol 2016; 111:30. [PMID: 27040115 DOI: 10.1007/s00395-016-0550-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2016] [Accepted: 03/24/2016] [Indexed: 11/30/2022]
Abstract
Chronic hypertension is associated with left ventricular (LV) hypertrophy and LV diastolic dysfunction with impaired isovolumic relaxation and abnormal LV filling. Increased heart rate (HR) worsens these alterations. We investigated whether the I f channel blocker ivabradine exerts beneficial effects on LV filling dynamic. In this setting, we also evaluated the relationship between LV filling and isovolumic contraction as a consequence of contraction-relaxation coupling. Therefore, hypertension was induced by a continuous infusion of angiotensin II during 28 days in 10 chronically instrumented pigs. LV function was investigated after stopping angiotensin II infusion to offset the changes in loading conditions. In the normal heart, LV relaxation filling, LV early filling, LV peak early filling rate were positively correlated to HR. In contrast, these parameters were significantly reduced at day 28 vs. day 0 (18, 42, and 26 %, respectively) despite the increase in HR (108 ± 6 beats/min vs. 73 ± 2 beats/min, respectively). These abnormalities were corrected by acute administration of ivabradine (1 mg/kg, iv). Ivabradine still exerted these effects when HR was controlled at 150 beats/min by atrial pacing. Interestingly, LV relaxation filling, LV early filling and LV peak early filling were strongly correlated with both isovolumic contraction and relaxation. In conclusion, ivabradine improves LV filling during chronic hypertension. The mechanism involves LV contraction-relaxation coupling through normalization of isovolumic contraction and relaxation as well as HR-independent mechanisms.
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Affiliation(s)
- Jonathan Melka
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
| | - Mario Rienzo
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
- AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, 75015, Paris, France
| | - Alain Bizé
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
| | - Mathieu Jozwiak
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
| | - Lucien Sambin
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
| | - Luc Hittinger
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
- AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, 94000, Créteil, France
| | - Jin Bo Su
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
| | - Alain Berdeaux
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France
- AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, 94000, Créteil, France
| | - Bijan Ghaleh
- Faculté de Médecine, Inserm, U955, Equipe 03, 8 rue du Général Sarrail, 94000, Créteil, France.
- Université Paris-Est, UMR_S955, DHU A-TVB, UPEC, 94000, Créteil, France.
- Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, 94000, Maisons-Alfort, France.
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Ectopic automaticity induced in ventricular myocytes by transgenic overexpression of HCN2. J Mol Cell Cardiol 2015; 80:81-9. [DOI: 10.1016/j.yjmcc.2014.12.019] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/16/2014] [Revised: 12/05/2014] [Accepted: 12/22/2014] [Indexed: 11/22/2022]
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Rienzo M, Melka J, Bizé A, Sambin L, Jozwiak M, Su JB, Hittinger L, Berdeaux A, Ghaleh B. Ivabradine improves left ventricular function during chronic hypertension in conscious pigs. Hypertension 2014; 65:122-9. [PMID: 25350985 DOI: 10.1161/hypertensionaha.114.04323] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
During chronic hypertension, increases in heart rate (HR) or adrenergic stimulation are associated with maladaptive left ventricular responses as isovolumic contraction and relaxation durations failed to reduce, impeding filling. We, therefore, investigated the effects of acute selective HR reduction with ivabradine on left ventricular dysfunction during chronic hypertension. Accordingly, chronically instrumented pigs received angiotensin II infusion during 4 weeks to induce chronic hypertension. Left ventricular function was investigated while angiotensin II infusion was stopped. A single intravenous dose of ivabradine was administered at days 0 and 28. Dobutamine infusion was also performed. HR was increased at day 28 versus day 0. Paradoxically, both isovolumic contraction and relaxation times failed to reduce and remained unchanged (57±3 versus 58±3 ms and 74±3 versus 70±3 at day 28 versus day 0, respectively). At day 28, ivabradine significantly reduced HR by 27%. Concomitantly, abnormal ventricular responses were corrected because both isovolumic contraction and relaxation times were significantly reduced while filling time was improved. Similarly at day 28, maladaptive responses of isovolumic contraction and relaxation to dobutamine were no longer observed during HR reduction with ivabradine. Correction of HR reduction with pacing showed that non-HR-related mechanisms also participated to these beneficial effects. In this model of chronic hypertension and left ventricular hypertrophy, acute HR reduction with ivabradine corrects the maladaptive responses of cardiac cycle phases by restoring a normal profile for isovolumic contraction and relaxation both at rest and under adrenergic stimuli, ultimately favoring filling.
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Affiliation(s)
- Mario Rienzo
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Jonathan Melka
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Alain Bizé
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Lucien Sambin
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Mathieu Jozwiak
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Jin Bo Su
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Luc Hittinger
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Alain Berdeaux
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.)
| | - Bijan Ghaleh
- From the Inserm, U955, Equipe 03, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, UMR_S955, UPEC, F-94000, Créteil, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); Université Paris-Est, Ecole Nationale Vétérinaire d'Alfort, F-94700, Maisons-Alfort, France (M.R., J.M., A.B., L.S., M.J., J.B.S., L.H., A.B., B.G.); AP-HP, Groupe Hospitalier Henri Mondor, Fédération de Cardiologie, F-94000, Créteil, France (L.H., A.B.); and AP-HP, Hôpital Européen Georges Pompidou, Service d'Anesthésie-Réanimation Chirurgicale, F-75015, Paris, France (M.R.).
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Lyashchenko AK, Redd KJ, Goldstein PA, Tibbs GR. cAMP control of HCN2 channel Mg2+ block reveals loose coupling between the cyclic nucleotide-gating ring and the pore. PLoS One 2014; 9:e101236. [PMID: 24983358 PMCID: PMC4077740 DOI: 10.1371/journal.pone.0101236] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Accepted: 06/04/2014] [Indexed: 12/24/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-regulated HCN channels underlie the Na+-K+ permeable IH pacemaker current. As with other voltage-gated members of the 6-transmembrane KV channel superfamily, opening of HCN channels involves dilation of a helical bundle formed by the intracellular ends of S6 albeit this is promoted by inward, not outward, displacement of S4. Direct agonist binding to a ring of cyclic nucleotide-binding sites, one of which lies immediately distal to each S6 helix, imparts cAMP sensitivity to HCN channel opening. At depolarized potentials, HCN channels are further modulated by intracellular Mg2+ which blocks the open channel pore and blunts the inhibitory effect of outward K+ flux. Here, we show that cAMP binding to the gating ring enhances not only channel opening but also the kinetics of Mg2+ block. A combination of experimental and simulation studies demonstrates that agonist acceleration of block is mediated via acceleration of the blocking reaction itself rather than as a secondary consequence of the cAMP enhancement of channel opening. These results suggest that the activation status of the gating ring and the open state of the pore are not coupled in an obligate manner (as required by the often invoked Monod-Wyman-Changeux allosteric model) but couple more loosely (as envisioned in a modular model of protein activation). Importantly, the emergence of second messenger sensitivity of open channel rectification suggests that loose coupling may have an unexpected consequence: it may endow these erstwhile “slow” channels with an ability to exert voltage and ligand-modulated control over cellular excitability on the fastest of physiologically relevant time scales.
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Affiliation(s)
- Alex K. Lyashchenko
- Department of Anesthesiology, Columbia University, New York, New York, United States of America
| | - Kacy J. Redd
- Department of Neuroscience, Columbia University, New York, New York, United States of America
| | - Peter A. Goldstein
- Department of Anesthesiology, Weill Cornell Medical College, New York, New York, United States of America
| | - Gareth R. Tibbs
- Department of Anesthesiology, Columbia University, New York, New York, United States of America
- Department of Anesthesiology, Weill Cornell Medical College, New York, New York, United States of America
- * E-mail:
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13
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Hyperpolarization-activated current, If, in mathematical models of rabbit sinoatrial node pacemaker cells. BIOMED RESEARCH INTERNATIONAL 2013; 2013:872454. [PMID: 23936852 PMCID: PMC3722861 DOI: 10.1155/2013/872454] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/04/2013] [Accepted: 05/31/2013] [Indexed: 01/01/2023]
Abstract
A typical feature of sinoatrial (SA) node pacemaker cells is the presence of an ionic current that activates upon hyperpolarization. The role of this hyperpolarization-activated current, If, which is also known as the “funny current” or “pacemaker current,” in the spontaneous pacemaker activity of SA nodal cells remains a matter of intense debate. Whereas some conclude that If plays a fundamental role in the generation of pacemaker activity and its rate control, others conclude that the role of If is limited to a modest contribution to rate control. The ongoing debate is often accompanied with arguments from computer simulations, either to support one's personal view or to invalidate that of the antagonist. In the present paper, we review the various mathematical descriptions of If that have been used in computer simulations and compare their strikingly different characteristics with our experimental data. We identify caveats and propose a novel model for If based on our experimental data.
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14
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Greally E, Davison BJ, Blain A, Laval S, Blamire A, Straub V, MacGowan GA. Heterogeneous abnormalities of in-vivo left ventricular calcium influx and function in mouse models of muscular dystrophy cardiomyopathy. J Cardiovasc Magn Reson 2013; 15:4. [PMID: 23324314 PMCID: PMC3564732 DOI: 10.1186/1532-429x-15-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2012] [Accepted: 12/14/2012] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Manganese-enhanced cardiovascular magnetic resonance (MECMR) can non-invasively assess myocardial calcium influx, and calcium levels are known to be elevated in muscular dystrophy cardiomyopathy based on cellular studies. METHODS Left ventricular functional studies and MECMR were performed in mdx mice (model of Duchenne muscular dystrophy, 24 and 40 weeks) and Sgcd -/- mice (limb girdle muscular dystrophy 2 F, 16 and 32 weeks), compared to wild type controls (C57Bl/10, WT). RESULTS Both models had left ventricular hypertrophy at the later age compared to WT, though the mdx mice had reduced stroke volumes and the Sgcd -/- mice increased heart rate and cardiac index. Especially at the younger ages, MECMR was significantly elevated in both models (both P < 0.05 versus WT). The L-type calcium channel inhibitor diltiazem (5 mg/kg i.p.) significantly reduced MECMR in the mdx mice (P < 0.01), though only with a higher dose (10 mg/kg i.p.) in the Sgcd -/- mice (P < 0.05). As the Sgcd -/- mice had increased heart rates, to determine the role of heart rate in MECMR we studied the hyperpolarization-activated cyclic nucleotide-gated channel inhibitor ZD 7288 which selectively reduces heart rate. This reduced heart rate and MECMR in all mouse groups. However, when looking at the time course of reduction of MECMR in the Sgcd -/- mice at up to 5 minutes of the manganese infusion when heart rates were matched to the WT mice, MECMR was still significantly elevated in the Sgcd -/- mice (P < 0.01) indicating that heart rate alone could not account for all the increased MECMR. CONCLUSIONS Despite both mouse models exhibiting increased in-vivo calcium influx at an early stage in the development of the cardiomyopathy before left ventricular hypertrophy, there are distinct phenotypical differences between the 2 models in terms of heart rates, hemodynamics and responses to calcium channel inhibitors.
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MESH Headings
- Age Factors
- Animals
- Calcium Channel Blockers/pharmacology
- Calcium Channels, L-Type/drug effects
- Calcium Channels, L-Type/metabolism
- Calcium Signaling/drug effects
- Cardiomyopathies/genetics
- Cardiomyopathies/metabolism
- Cardiomyopathies/pathology
- Cardiomyopathies/physiopathology
- Chlorides
- Contrast Media
- Disease Models, Animal
- Disease Progression
- Genotype
- Heart Rate
- Hypertrophy, Left Ventricular/metabolism
- Hypertrophy, Left Ventricular/pathology
- Hypertrophy, Left Ventricular/physiopathology
- Magnetic Resonance Imaging
- Male
- Manganese Compounds
- Mice
- Mice, Inbred mdx
- Mice, Knockout
- Muscular Dystrophy, Duchenne/genetics
- Muscular Dystrophy, Duchenne/metabolism
- Muscular Dystrophy, Duchenne/pathology
- Muscular Dystrophy, Duchenne/physiopathology
- Myocardium/metabolism
- Myocardium/pathology
- Phenotype
- Sarcoglycans/deficiency
- Sarcoglycans/genetics
- Stroke Volume
- Time Factors
- Ventricular Function, Left/drug effects
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Affiliation(s)
- Elizabeth Greally
- Institute of Genetic Medicine, Newcastle University, International Center for Life, Newcastle, UK
| | - Benjamin J Davison
- Institute of Genetic Medicine, Newcastle University, International Center for Life, Newcastle, UK
| | - Alison Blain
- Institute of Genetic Medicine, Newcastle University, International Center for Life, Newcastle, UK
| | - Steve Laval
- Institute of Genetic Medicine, Newcastle University, International Center for Life, Newcastle, UK
| | | | - Volker Straub
- Institute of Genetic Medicine, Newcastle University, International Center for Life, Newcastle, UK
| | - Guy A MacGowan
- Institute of Genetic Medicine, Newcastle University, International Center for Life, Newcastle, UK
- Dept of Cardiology, Freeman Hospital and Newcastle University, Newcastle upon Tyne, NE7 7DN, UK
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15
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Rusznák Z, Pál B, Kőszeghy A, Fu Y, Szücs G, Paxinos G. The hyperpolarization-activated non-specific cation current (In ) adjusts the membrane properties, excitability, and activity pattern of the giant cells in the rat dorsal cochlear nucleus. Eur J Neurosci 2013; 37:876-90. [PMID: 23301797 DOI: 10.1111/ejn.12116] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2012] [Revised: 11/19/2012] [Accepted: 11/30/2012] [Indexed: 12/16/2022]
Abstract
Giant cells of the cochlear nucleus are thought to integrate multimodal sensory inputs and participate in monaural sound source localization. Our aim was to explore the significance of a hyperpolarization-activated current in determining the activity of giant neurones in slices prepared from 10 to 14-day-old rats. When subjected to hyperpolarizing stimuli, giant cells produced a 4-(N-ethyl-N-phenylamino)-1,2-dimethyl-6-(methylamino) pyridinium chloride (ZD7288)-sensitive inward current with a reversal potential and half-activation voltage of -36 and -88 mV, respectively. Consequently, the current was identified as the hyperpolarization-activated non-specific cationic current (Ih ). At the resting membrane potential, 3.5% of the maximum Ih conductance was available. Immunohistochemistry experiments suggested that hyperpolarization-activated, cyclic nucleotide-gated, cation non-selective (HCN)1, HCN2, and HCN4 subunits contribute to the assembly of the functional channels. Inhibition of Ih hyperpolarized the membrane by 6 mV and impeded spontaneous firing. The frequencies of spontaneous inhibitory and excitatory postsynaptic currents reaching the giant cell bodies were reduced but no significant change was observed when evoked postsynaptic currents were recorded. Giant cells are affected by biphasic postsynaptic currents consisting of an excitatory and a subsequent inhibitory component. Inhibition of Ih reduced the frequency of these biphasic events by 65% and increased the decay time constants of the inhibitory component. We conclude that Ih adjusts the resting membrane potential, contributes to spontaneous action potential firing, and may participate in the dendritic integration of the synaptic inputs of the giant neurones. Because its amplitude was higher in young than in adult rats, Ih of the giant cells may be especially important during the postnatal maturation of the auditory system.
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Affiliation(s)
- Zoltán Rusznák
- Neuroscience Research Australia, Sydney, NSW 2031, Australia.
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Quinn TA, Kohl P. Mechano-sensitivity of cardiac pacemaker function: pathophysiological relevance, experimental implications, and conceptual integration with other mechanisms of rhythmicity. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2012; 110:257-68. [PMID: 23046620 PMCID: PMC3526794 DOI: 10.1016/j.pbiomolbio.2012.08.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 08/06/2012] [Accepted: 08/09/2012] [Indexed: 12/11/2022]
Abstract
Cardiac pacemaker cells exhibit spontaneous, rhythmic electrical excitation, termed automaticity. This automatic initiation of action potentials requires spontaneous diastolic depolarisation, whose rate determines normal rhythm generation in the heart. Pacemaker mechanisms have been split recently into: (i) cyclic changes in trans-sarcolemmal ion flows (termed the ‘membrane-clock’), and (ii) rhythmic intracellular calcium cycling (the ‘calcium-clock’). These two ‘clocks’ undoubtedly interact, as trans-sarcolemmal currents involved in pacemaking include calcium-carrying mechanisms, while intracellular calcium cycling requires trans-sarcolemmal ion flux as the mechanism by which it affects membrane potential. The split into separate ‘clocks’ is, therefore, somewhat arbitrary. Nonetheless, the ‘clock’ metaphor has been conceptually stimulating, in particular since there is evidence to support the view that either ‘clock’ could be sufficient in principle to set the rate of pacemaker activation. Of course, the same has also been shown for sub-sets of ‘membrane-clock’ ion currents, illustrating the redundancy of mechanisms involved in maintaining such basic functionality as the heartbeat, a theme that is common for vital physiological systems. Following the conceptual path of identifying individual groups of sub-mechanisms, it is important to remember that the heart is able to adapt pacemaker rate to changes in haemodynamic load, even after isolation or transplantation, and on a beat-by-beat basis. Neither the ‘membrane-’ nor the ‘calcium-clock’ do, as such, inherently account for this rapid adaptation to circulatory demand (cellular Ca2+ balance changes over multiple beats, while variation of sarcolemmal ion channel presence takes even longer). This suggests that a third set of mechanisms must be involved in setting the pace. These mechanisms are characterised by their sensitivity to the cyclically changing mechanical environment, and – in analogy to the above terminology – this might be considered a ‘mechanics-clock’. In this review, we discuss possible roles of mechano-sensitive mechanisms for the entrainment of membrane current dynamics and calcium-handling. This can occur directly via stretch-activation of mechano-sensitive ion channels in the sarcolemma and/or in intracellular membrane compartments, as well as by modulation of ‘standard’ components of the ‘membrane-’ or ‘calcium-clock’. Together, these mechanisms allow rapid adaptation to changes in haemodynamic load, on a beat-by-beat basis. Additional relevance arises from the fact that mechano-sensitivity of pacemaking may help to explain pacemaker dysfunction in mechanically over- or under-loaded tissue. As the combined contributions of the various underlying oscillatory mechanisms are integrated at the pacemaker cell level into a single output – a train of pacemaker action potentials – we will not adhere to a metaphor that implies separate time-keeping units (‘clocks’), and rather focus on cardiac pacemaking as the result of interactions of a set of coupled oscillators, whose individual contributions vary depending on the pathophysiological context. We conclude by considering the utility and limitations of viewing the pacemaker as a coupled system of voltage-, calcium-, and mechanics-modulated oscillators that, by integrating a multitude of inputs, offers the high level of functional redundancy that is vitally important for cardiac automaticity.
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Affiliation(s)
- T Alexander Quinn
- National Heart and Lung Institute, Imperial College London, London, UK.
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18
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Lin YC, Huang J, Kan H, Castranova V, Frisbee JC, Yu HG. Defective calcium inactivation causes long QT in obese insulin-resistant rat. Am J Physiol Heart Circ Physiol 2011; 302:H1013-22. [PMID: 22198168 DOI: 10.1152/ajpheart.00837.2011] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The majority of diabetic patients who are overweight or obese die of heart disease. We suspect that the obesity-induced insulin resistance may lead to abnormal cardiac electrophysiology. We tested this hypothesis by studying an obese insulin-resistant rat model, the obese Zucker rat (OZR). Compared with the age-matched control, lean Zucker rat (LZR), OZR of 16-17 wk old exhibited an increase in QTc interval, action potential duration, and cell capacitance. Furthermore, the L-type calcium current (I(CaL)) in OZR exhibited defective inactivation and lost the complete inactivation back to the closed state, leading to increased Ca(2+) influx. The current density of I(CaL) was reduced in OZR, whereas the threshold activation and the current-voltage relationship of I(CaL) were not significantly altered. L-type Ba(2+) current (I(BaL)) in OZR also exhibited defective inactivation, and steady-state inactivation was not significantly altered. However, the current-voltage relationship and activation threshold of I(BaL) in OZR exhibited a depolarized shift compared with LZR. The total and membrane protein expression levels of Cav1.2 [pore-forming subunit of L-type calcium channels (LTCC)], but not the insulin receptors, were decreased in OZR. The insulin receptor was found to be associated with the Cav1.2, which was weakened in OZR. The total protein expression of calmodulin was reduced, but that of Cavβ2 subunit was not altered in OZR. Together, these results suggested that the 16- to 17-wk-old OZR has 1) developed cardiac hypertrophy, 2) exhibited altered electrophysiology manifested by the prolonged QTc interval, 3) increased duration of action potential in isolated ventricular myocytes, 4) defective inactivation of I(CaL) and I(BaL), 5) weakened the association of LTCC with the insulin receptor, and 6) decreased protein expression of Cav1.2 and calmodulin. These results also provided mechanistic insights into a remodeled cardiac electrophysiology under the condition of insulin resistance, enhancing our understanding of long QT associated with obese type 2 diabetic patients.
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Affiliation(s)
- Yen-Chang Lin
- Center for Cardiovascular and Respiratory Sciences, Department of Physiology and Pharmacology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26056, USA.
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Structural correlates of selectivity and inactivation in potassium channels. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2011; 1818:272-85. [PMID: 21958666 DOI: 10.1016/j.bbamem.2011.09.007] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/17/2011] [Revised: 09/07/2011] [Accepted: 09/09/2011] [Indexed: 12/23/2022]
Abstract
Potassium channels are involved in a tremendously diverse range of physiological applications requiring distinctly different functional properties. Not surprisingly, the amino acid sequences for these proteins are diverse as well, except for the region that has been ordained the "selectivity filter". The goal of this review is to examine our current understanding of the role of the selectivity filter and regions adjacent to it in specifying selectivity as well as its role in gating/inactivation and possible mechanisms by which these processes are coupled. Our working hypothesis is that an amino acid network behind the filter modulates selectivity in channels with the same signature sequence while at the same time affecting channel inactivation properties. This article is part of a Special Issue entitled: Membrane protein structure and function.
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20
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Hyperpolarization-activated current (I(h)) in ganglion-cell photoreceptors. PLoS One 2010; 5:e15344. [PMID: 21187958 PMCID: PMC3004865 DOI: 10.1371/journal.pone.0015344] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2010] [Accepted: 11/10/2010] [Indexed: 12/31/2022] Open
Abstract
Intrinsically photosensitive retinal ganglion cells (ipRGCs) express the photopigment melanopsin and serve as the primary retinal drivers of non-image-forming visual functions such as circadian photoentrainment, the pupillary light reflex, and suppression of melatonin production in the pineal. Past electrophysiological studies of these cells have focused on their intrinsic photosensitivity and synaptic inputs. Much less is known about their voltage-gated channels and how these might shape their output to non-image-forming visual centers. Here, we show that rat ipRGCs retrolabeled from the suprachiasmatic nucleus (SCN) express a hyperpolarization-activated inwardly-rectifying current (Ih). This current is blocked by the known Ih blockers ZD7288 and extracellular cesium. As in other systems, including other retinal ganglion cells, Ih in ipRGCs is characterized by slow kinetics and a slightly greater permeability for K+ than for Na+. Unlike in other systems, however, Ih in ipRGCs apparently does not actively contribute to resting membrane potential. We also explore non-specific effects of the common Ih blocker ZD7288 on rebound depolarization and evoked spiking and discuss possible functional roles of Ih in non-image-forming vision. This study is the first to characterize Ih in a well-defined population of retinal ganglion cells, namely SCN-projecting ipRGCs.
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Chen QH, Andrade MA, Calderon AS, Toney GM. Hypertension induced by angiotensin II and a high salt diet involves reduced SK current and increased excitability of RVLM projecting PVN neurons. J Neurophysiol 2010; 104:2329-37. [PMID: 20719931 DOI: 10.1152/jn.01013.2009] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although evidence indicates that activation of presympathetic paraventricular nucleus (PVN) neurons contributes to the pathogenesis of salt-sensitive hypertension, the underlying cellular mechanisms are not fully understood. Recent evidence indicates that small conductance Ca(2+)-activated K(+) (SK) channels play a significant role in regulating the excitability of a key group of sympathetic regulatory PVN neurons, those with axonal projections to the rostral ventrolateral medulla (RVLM; i.e., PVN-RVLM neurons). In the present study, rats consuming a high salt (2% NaCl) diet were made hypertensive by systemic infusion of angiotensin II (AngII), and whole cell patch-clamp recordings were made in brain slice from retrogradely labeled PVN-RVLM neurons. To determine if the amplitude of SK current was altered in neurons from hypertensive rats, voltage-clamp recordings were performed to isolate SK current. Results indicate that SK current amplitude (P < 0.05) and density (P < 0.01) were significantly smaller in the hypertensive group. To investigate the impact of this on intrinsic excitability, current-clamp recordings were performed in separate groups of PVN-RVLM neurons. Results indicate that the frequency of spikes evoked by current injection was significantly higher in the hypertensive group (P < 0.05-0.01). Whereas bath application of the SK channel blocker apamin significantly increased discharge of neurons from normotensive rats (P < 0.05-0.01), no effect was observed in the hypertensive group. In response to ramp current injections, subthreshold depolarizing input resistance was greater in the hypertensive group compared with the normotensive group (P < 0.05). Blockade of SK channels increased depolarizing input resistance in normotensive controls (P < 0.05) but had no effect in the hypertensive group. On termination of current pulses, a medium afterhyperpolarization potential (mAHP) was observed in most neurons of the normotensive group. In the hypertensive group, the mAHP was either small or absent. In the latter case, an afterdepolarization potential (ADP) was observed that was unaffected by apamin. Apamin treatment in the normotensive group blocked the mAHP and revealed an ADP resembling that seen in the hypertensive group. We conclude that diminished SK current likely underlies the absence of mAHPs in PVN-RVLM neurons from hypertensive rats. Both the ADP and greater depolarizing input resistance likely contribute to increased excitability of PVN-RVLM neurons from rats with AngII-Salt hypertension.
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Affiliation(s)
- Qing-Hui Chen
- Exercise Science, Health and Physical Education Department, Michigan Technological University, Houghton, Michigan; USA.
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22
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Lin YC, Huang J, Zhang Q, Hollander JM, Frisbee JC, Martin KH, Nestor C, Goodman R, Yu HG. Inactivation of L-type calcium channel modulated by HCN2 channel. Am J Physiol Cell Physiol 2010; 298:C1029-37. [PMID: 20164379 DOI: 10.1152/ajpcell.00355.2009] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ca(2+) entry is delicately controlled by inactivation of L-type calcium channel (LTCC) composed of the pore-forming subunit alpha1C and the auxiliary subunits beta1 and alpha2delta. Calmodulin is the key protein that interacts with the COOH-terminal motifs of alpha1C, leading to the fine control of LTCC inactivation. In this study we show evidence that a hyperpolarization-activated cyclic nucleotide-gated channel, HCN2, can act as a nonchannel regulatory protein to narrow the L-type Ca(2+) channel current-voltage curve. In the absence of LTCC auxiliary subunits, HCN2 can induce alpha1C inactivation. Without alpha2delta, HCN2-induced fast inactivation of alpha1C requires calmodulin. With alpha2delta, the alpha1C/HCN2/alpha2delta channel inactivation does not require calmodulin. In contrast, beta1-subunit plays a relatively minor role in the interaction of alpha1C with HCN2. The NH(2) terminus of HCN2 and the IQ motif of alpha1C subunit are required for alpha1C/HCN2 channel interaction. Ca(2+) channel inactivation is significantly slowed in hippocampus neurons (HNs) overexpressing HCN2 mutant lacking NH(2) terminus and accelerated in HNs overexpressing the wild-type HCN2 compared with HN controls. Collectively, these results revealed a potentially novel protection mechanism for achieving the LTCC inactivation via interaction with HCN2.
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Affiliation(s)
- Yen-Chang Lin
- Center for Cardiovascular and Respiratory Sciences, West Virginia Univ. School of Medicine, Morgantown, 26506, USA
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23
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Biel M, Wahl-Schott C, Michalakis S, Zong X. Hyperpolarization-activated cation channels: from genes to function. Physiol Rev 2009; 89:847-85. [PMID: 19584315 DOI: 10.1152/physrev.00029.2008] [Citation(s) in RCA: 719] [Impact Index Per Article: 47.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels comprise a small subfamily of proteins within the superfamily of pore-loop cation channels. In mammals, the HCN channel family comprises four members (HCN1-4) that are expressed in heart and nervous system. The current produced by HCN channels has been known as I(h) (or I(f) or I(q)). I(h) has also been designated as pacemaker current, because it plays a key role in controlling rhythmic activity of cardiac pacemaker cells and spontaneously firing neurons. Extensive studies over the last decade have provided convincing evidence that I(h) is also involved in a number of basic physiological processes that are not directly associated with rhythmicity. Examples for these non-pacemaking functions of I(h) are the determination of the resting membrane potential, dendritic integration, synaptic transmission, and learning. In this review we summarize recent insights into the structure, function, and cellular regulation of HCN channels. We also discuss in detail the different aspects of HCN channel physiology in the heart and nervous system. To this end, evidence on the role of individual HCN channel types arising from the analysis of HCN knockout mouse models is discussed. Finally, we provide an overview of the impact of HCN channels on the pathogenesis of several diseases and discuss recent attempts to establish HCN channels as drug targets.
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Affiliation(s)
- Martin Biel
- Center for Integrated Protein Science CIPS-M and Zentrum für Pharmaforschung, Department Pharmazie, Pharmakologie für Naturwissenschaften, Ludwig-Maximilians-Universität München, Butenandtstr. 5-13, Munich D-81377, Germany.
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24
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Zhang Q, Huang A, Lin YC, Yu HG. Associated changes in HCN2 and HCN4 transcripts and I(f) pacemaker current in myocytes. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:1138-47. [PMID: 19236845 DOI: 10.1016/j.bbamem.2009.02.011] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/23/2008] [Revised: 02/07/2009] [Accepted: 02/11/2009] [Indexed: 11/18/2022]
Abstract
The time- and voltage-dependent inward current generated by the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contributes to the tissue-specific rhythmic activities in the brain and heart. Four isoforms (HCN1-HCN4) have been identified. Previous studies showed that different HCN isoforms may form functional heteromeric channels. We report here that when HCN2 and HCN4 mRNA were injected into Xenopus oocytes with various ratios of HCN2 over HCN4 at 1:1, 10:1, and 1:10, respectively, the resultant channels showed a depolarized current activation and significantly faster activation kinetics near the midpoint of activation compared with HCN4 homomeric channels. In adult rat myocytes overexpressing HCN4, there was an associated increase in HCN2 mRNA. In neonatal rat myocytes in which HCN2 was knocked down, there was also a simultaneous decrease in HCN4 mRNA. Coimmunoprecipitation experiments showed that HCN2 and HCN4 channel proteins can associate with each other in adult rat ventricles. Finally, in adult myocytes overexpressing HCN4, the hyperpolarization-activated inward current activation, I(f), was shifted to physiological voltages from non-physiological voltages, associated with faster activation kinetics. These data suggested that different ratios of HCN2 and HCN4 transcripts overlapping in different tissues also contribute to the tissue-specific properties of I(f).
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Affiliation(s)
- Qi Zhang
- Center for Cardiovascular and Respiratory Sciences, Department of Physiology, West Virginia University School of Medicine, Morgantown, West Virginia 26506, USA
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25
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Pacemaker activity of the human sinoatrial node: role of the hyperpolarization-activated current, I(f). Int J Cardiol 2009; 132:318-36. [PMID: 19181406 DOI: 10.1016/j.ijcard.2008.12.196] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/02/2008] [Revised: 12/16/2008] [Accepted: 12/22/2008] [Indexed: 11/20/2022]
Abstract
The mechanism of primary, spontaneous cardiac pacemaker activity of the sinoatrial node (SAN) has extensively been studied in several animal species, but is virtually unexplored in man. Understanding the mechanisms of human SAN pacemaker activity is important for developing new therapeutic approaches for controlling the heart rate in the sick sinus syndrome and in diseased myocardium. Here we review the functional role of the hyperpolarization-activated 'funny' current, I(f), in human SAN pacemaker activity. Despite the many animal studies performed over the years, the contribution of I(f) to pacemaker activity is still controversial and not fully established. However, recent clinical data on mutations in the I(f) encoding HCN4 gene, which is thought to be the most abundant isoform of the HCN gene family in SAN, suggest a functional role of I(f) in human pacemaker activity. These clinical findings are supported by recent experimental data from single isolated human SAN cells that provide direct evidence that I(f) contributes to human SAN pacemaker activity. Therefore, controlling heart rate in clinical practice via I(f) blockers offers a valuable approach to lowering heart rate and provides an attractive alternative to conventional treatment for a wide range of patients with confirmed stable angina, while upregulation or artificial expression of I(f) may relieve disease-causing bradycardias.
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26
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Abstract
Cyclic nucleotide-regulated cation channels are ion channels whose activation is regulated by the direct binding of cAMP or cGMP to the channel protein. Two structurally related families of channels regulated by cyclic nucleotides have been identified, the cyclic nucleotide-gated channels and the hyperpolarization-activated cyclic nucleotide-gated channels. Cyclic nucleotide-gated channels play a key role in visual and olfactory transduction. Hyperpolarization-activated cyclic nucleotide-gated channels are present in the conduction system of the heart and are involved in the control of cardiac automaticity. Moreover, these channels are widely expressed in central and peripheral neurons, where they control a variety of fundamental processes.
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Affiliation(s)
- Martin Biel
- Center for Integrated Protein Science Munich and Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13, 81377 Munich, Germany.
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27
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Ramakrishnan NA, Drescher MJ, Barretto RL, Beisel KW, Hatfield JS, Drescher DG. Calcium-dependent binding of HCN1 channel protein to hair cell stereociliary tip link protein protocadherin 15 CD3. J Biol Chem 2008; 284:3227-3238. [PMID: 19008224 DOI: 10.1074/jbc.m806177200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cytoplasmic amino terminus of HCN1, the primary full-length HCN isoform expressed in trout saccular hair cells, was found by yeast two-hybrid protocols to bind the cytoplasmic carboxyl-terminal domain of a protocadherin 15a-like protein. HCN1 was immunolocalized to discrete sites on saccular hair cell stereocilia, consistent with gradated distribution expected for tip link sites of protocadherin 15a. HCN1 message was also detected in cDNA libraries of rat cochlear inner and outer hair cells, and HCN1 protein was immunolocalized to cochlear hair cell stereocilia. As predicted by the trout hair cell model, the amino terminus of rat organ of Corti HCN1 was found by yeast two-hybrid analysis to bind the carboxyl terminus of protocadherin 15 CD3, a tip link protein implicated in mechanosensory transduction. Specific binding between HCN1 and protocadherin 15 CD3 was confirmed with pull-down assays and surface plasmon resonance analysis, both predicting dependence on Ca(2+). In the presence of calcium chelators, binding between HCN1 and protocadherin 15 CD3 was characterized by a K(D) = 2.39 x 10(-7) m. Ca(2+) at 26.5-68.0 microm promoted binding, with K(D) = 5.26 x 10(-8) m (at 61 microm Ca(2+)). Binding by deletion mutants of protocadherin 15 CD3 pointed to amino acids 158-179 (GenBank accession number XP_238200), with homology to the comparable region in trout hair cell protocadherin 15a-like protein, as necessary for binding to HCN1. Amino terminus binding of HCN1 to HCN1, hypothesized to underlie HCN1 channel formation, was also found to be Ca(2+)-dependent, although the binding was skewed toward a lower effective maximum [Ca(2+)] than for the HCN1 interaction with protocadherin 15 CD3. Competition may therefore exist in vivo between the two binding sites for HCN1, with binding of HCN1 to protocadherin 15 CD3 favored between 26.5 and 68 microm Ca(2+). Taken together, the evidence supports a role for HCN1 in mechanosensory transduction of inner ear hair cells.
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Affiliation(s)
- Neeliyath A Ramakrishnan
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Marian J Drescher
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201.
| | - Roberto L Barretto
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201
| | - Kirk W Beisel
- Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska 68178
| | - James S Hatfield
- Electron Microscopy Laboratory, Veterans Affairs Medical Center, Detroit, Michigan 48201
| | - Dennis G Drescher
- Department of Otolaryngology, Wayne State University School of Medicine, Detroit, Michigan 48201; Departments of Biochemistry and Molecular Biology, Wayne State University School of Medicine, Detroit, Michigan 48201
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28
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Abstract
The calcium ion (Ca(2+)) is the simplest and most versatile intracellular messenger known. The discovery of Ca(2+) sparks and a related family of elementary Ca(2+) signaling events has revealed fundamental principles of the Ca(2+) signaling system. A newly appreciated "digital" subsystem consisting of brief, high Ca(2+) concentration over short distances (nanometers to microns) comingles with an "analog" global Ca(2+) signaling subsystem. Over the past 15 years, much has been learned about the theoretical and practical aspects of spark formation and detection. The quest for the spark mechanisms [the activation, coordination, and termination of Ca(2+) release units (CRUs)] has met unexpected challenges, however, and raised vexing questions about CRU operation in situ. Ample evidence shows that Ca(2+) sparks catalyze many high-threshold Ca(2+) processes involved in cardiac and skeletal muscle excitation-contraction coupling, vascular tone regulation, membrane excitability, and neuronal secretion. Investigation of Ca(2+) sparks in diseases has also begun to provide novel insights into hypertension, cardiac arrhythmias, heart failure, and muscular dystrophy. An emerging view is that spatially and temporally patterned activation of the digital subsystem confers on intracellular Ca(2+) signaling an exquisite architecture in space, time, and intensity, which underpins signaling efficiency, stability, specificity, and diversity. These recent advances in "sparkology" thus promise to unify the simplicity and complexity of Ca(2+) signaling in biology.
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Affiliation(s)
- Heping Cheng
- Institute of Molecular Medicine, National Laboratory of Biomembrane and Membrane Biotechnology, Peking University, Beijing, China.
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29
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Huang J, Huang A, Zhang Q, Lin YC, Yu HG. Novel mechanism for suppression of hyperpolarization-activated cyclic nucleotide-gated pacemaker channels by receptor-like tyrosine phosphatase-alpha. J Biol Chem 2008; 283:29912-9. [PMID: 18768480 DOI: 10.1074/jbc.m804205200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We have previously reported an important role of increased tyrosine phosphorylation activity by Src in the modulation of hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. Here we provide evidence showing a novel mechanism of decreased tyrosine phosphorylation on HCN channel properties. We found that the receptor-like protein-tyrosine phosphatase-alpha (RPTPalpha) significantly inhibited or eliminated HCN2 channel expression in HEK293 cells. Biochemical evidence showed that the surface expression of HCN2 was remarkably reduced by RPTPalpha, which was in parallel to the decreased tyrosine phosphorylation of the channel protein. Confocal imaging confirmed that the membrane surface distribution of the HCN2 channel was inhibited by RPTPalpha. Moreover, we detected the presence of RPTPalpha proteins in cardiac ventricles with expression levels changed during development. Inhibition of tyrosine phosphatase activity by phenylarsine oxide or sodium orthovanadate shifted ventricular hyperpolarization-activated current (I(f), generated by HCN channels) activation from nonphysiological voltages into physiological voltages associated with accelerated activation kinetics. In conclusion, we showed a critical role RPTPalpha plays in HCN channel function via tyrosine dephosphorylation. These findings are also important to neurons where HCN and RPTPalpha are richly expressed.
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Affiliation(s)
- Jianying Huang
- Center for Interdisciplinary Research in Cardiovascular Sciences, Department of Physiology and Pharmacology, West Virginia University School of Medicine, Morgantown, West Virginia 26506, USA
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30
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Abstract
The heart automaticity is a fundamental physiological function in higher organisms. The spontaneous activity is initiated by specialized populations of cardiac cells generating periodical electrical oscillations. The exact cascade of steps initiating the pacemaker cycle in automatic cells has not yet been entirely elucidated. Nevertheless, ion channels and intracellular Ca(2+) signaling are necessary for the proper setting of the pacemaker mechanism. Here, we review the current knowledge on the cellular mechanisms underlying the generation and regulation of cardiac automaticity. We discuss evidence on the functional role of different families of ion channels in cardiac pacemaking and review recent results obtained on genetically engineered mouse strains displaying dysfunction in heart automaticity. Beside ion channels, intracellular Ca(2+) release has been indicated as an important mechanism for promoting automaticity at rest as well as for acceleration of the heart rate under sympathetic nerve input. The potential links between the activity of ion channels and Ca(2+) release will be discussed with the aim to propose an integrated framework of the mechanism of automaticity.
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Affiliation(s)
- Matteo E Mangoni
- Institute of Functional Genomics, Department of Physiology, Centre National de la Recherche Scientifique UMR5203, INSERM U661, University of Montpellier I and II, Montpellier, France.
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31
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Abstract
Calcium (Ca) is a universal intracellular second messenger. In muscle, Ca is best known for its role in contractile activation. However, in recent years the critical role of Ca in other myocyte processes has become increasingly clear. This review focuses on Ca signaling in cardiac myocytes as pertaining to electrophysiology (including action potentials and arrhythmias), excitation-contraction coupling, modulation of contractile function, energy supply-demand balance (including mitochondrial function), cell death, and transcription regulation. Importantly, although such diverse Ca-dependent regulations occur simultaneously in a cell, the cell can distinguish distinct signals by local Ca or protein complexes and differential Ca signal integration.
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Affiliation(s)
- Donald M Bers
- Department of Physiology and Cardiovascular Institute, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
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