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Abstract
Cardiac alternans arises from dynamical instabilities in the electrical and calcium cycling systems of the heart, and often precedes ventricular arrhythmias and sudden cardiac death. In this review, we integrate clinical observations with theory and experiment to paint a holistic portrait of cardiac alternans: the underlying mechanisms, arrhythmic manifestations and electrocardiographic signatures. We first summarize the cellular and tissue mechanisms of alternans that have been demonstrated both theoretically and experimentally, including 3 voltage-driven and 2 calcium-driven alternans mechanisms. Based on experimental and simulation results, we describe their relevance to mechanisms of arrhythmogenesis under different disease conditions, and their link to electrocardiographic characteristics of alternans observed in patients. Our major conclusion is that alternans is not only a predictor, but also a causal mechanism of potentially lethal ventricular and atrial arrhythmias across the full spectrum of arrhythmia mechanisms that culminate in functional reentry, although less important for anatomic reentry and focal arrhythmias.
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Affiliation(s)
- Zhilin Qu
- Departments of Medicine (Cardiology), Physiology, and Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA
| | - James N. Weiss
- Departments of Medicine (Cardiology), Physiology, and Computational Medicine, David Geffen School of Medicine, University of California, Los Angeles, CA
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2
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Horváth B, Szentandrássy N, Almássy J, Dienes C, Kovács ZM, Nánási PP, Banyasz T. Late Sodium Current of the Heart: Where Do We Stand and Where Are We Going? Pharmaceuticals (Basel) 2022; 15:ph15020231. [PMID: 35215342 PMCID: PMC8879921 DOI: 10.3390/ph15020231] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 02/07/2022] [Accepted: 02/09/2022] [Indexed: 02/05/2023] Open
Abstract
Late sodium current has long been linked to dysrhythmia and contractile malfunction in the heart. Despite the increasing body of accumulating information on the subject, our understanding of its role in normal or pathologic states is not complete. Even though the role of late sodium current in shaping action potential under physiologic circumstances is debated, it’s unquestioned role in arrhythmogenesis keeps it in the focus of research. Transgenic mouse models and isoform-specific pharmacological tools have proved useful in understanding the mechanism of late sodium current in health and disease. This review will outline the mechanism and function of cardiac late sodium current with special focus on the recent advances of the area.
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Affiliation(s)
- Balázs Horváth
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Norbert Szentandrássy
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
- Department of Basic Medical Sciences, Faculty of Dentistry, University of Debrecen, 4032 Debrecen, Hungary
| | - János Almássy
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Csaba Dienes
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Zsigmond Máté Kovács
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
| | - Péter P. Nánási
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
- Department of Dental Physiology and Pharmacology, University of Debrecen, 4032 Debrecen, Hungary
| | - Tamas Banyasz
- Department of Physiology, University of Debrecen, 4032 Debrecen, Hungary; (B.H.); (N.S.); (J.A.); (C.D.); (Z.M.K.); (P.P.N.)
- Correspondence: ; Tel.: +36-(52)-255-575; Fax: +36-(52)-255-116
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Ranolazine: An Old Drug with Emerging Potential; Lessons from Pre-Clinical and Clinical Investigations for Possible Repositioning. Pharmaceuticals (Basel) 2021; 15:ph15010031. [PMID: 35056088 PMCID: PMC8777683 DOI: 10.3390/ph15010031] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2021] [Revised: 12/16/2021] [Accepted: 12/20/2021] [Indexed: 02/07/2023] Open
Abstract
Ischemic heart disease is a significant public health problem with high mortality and morbidity. Extensive scientific investigations from basic sciences to clinics revealed multilevel alterations from metabolic imbalance, altered electrophysiology, and defective Ca2+/Na+ homeostasis leading to lethal arrhythmias. Despite the recent identification of numerous molecular targets with potential therapeutic interest, a pragmatic observation on the current pharmacological R&D output confirms the lack of new therapeutic offers to patients. By contrast, from recent trials, molecules initially developed for other fields of application have shown cardiovascular benefits, as illustrated with some anti-diabetic agents, regardless of the presence or absence of diabetes, emphasizing the clear advantage of “old” drug repositioning. Ranolazine is approved as an antianginal agent and has a favorable overall safety profile. This drug, developed initially as a metabolic modulator, was also identified as an inhibitor of the cardiac late Na+ current, although it also blocks other ionic currents, including the hERG/Ikr K+ current. The latter actions have been involved in this drug’s antiarrhythmic effects, both on supraventricular and ventricular arrhythmias (VA). However, despite initial enthusiasm and promising development in the cardiovascular field, ranolazine is only authorized as a second-line treatment in patients with chronic angina pectoris, notwithstanding its antiarrhythmic properties. A plausible reason for this is the apparent difficulty in linking the clinical benefits to the multiple molecular actions of this drug. Here, we review ranolazine’s experimental and clinical knowledge on cardiac metabolism and arrhythmias. We also highlight advances in understanding novel effects on neurons, the vascular system, skeletal muscles, blood sugar control, and cancer, which may open the way to reposition this “old” drug alone or in combination with other medications.
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Dalaman U, Özdoğan H, Sircan AK, Şengül SA, Yaraş N. Sulfur Dioxide Derivative Prevents the Prolongation of Action Potential During the Isoproterenol-Induced Hypertrophy of Rat Cardiomyocytes. AN ACAD BRAS CIENC 2021; 93:e20201664. [PMID: 34550202 DOI: 10.1590/0001-3765202120201664] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 02/10/2021] [Indexed: 11/22/2022] Open
Abstract
Exogenous SO2 is toxic especially to the pulmonary and cardiovascular system, similar to nitric-oxide, carbon-monoxide, and hydrogen-sulfide. Endogenous SO2 is produced in many cell types. The SO2 content of the rat heart has been observed to substantially decrease during isoproterenol-induced hypertrophy. This study sought to determine whether an SO2 derivative could inhibit the prolongation of action potentials during the isoproterenol-induced hypertrophy of rat cardiomyocytes and explore the ionic currents. Alongside electrocardiogram recordings, the voltage and current-clamped measurements were conducted in the enzymatically isolated left ventricular cardiomyocytes of Wistar rats. The consistency of the results was evaluated by the novel mathematical electrophysiology model. Our results show that SO2 significantly blocked the prolongation of QT-interval and action potential duration. Furthermore, SO2 did not substantially affect the Na+ currents and did not improve the decreased steady-state and transient outward K+ currents, but it reverted the reduced L-type Ca2+ currents (I CaL) to the physiological levels. Altered inactivation of I CaL was remarkably recovered by SO2. Interestingly, SO2 significantly increased the Ca2+ transients in hypertrophic rat hearts. Our mathematical model also confirmed the mechanism of the SO2 effect. Our findings suggest that the shortening mechanism of SO2 is related to the Ca2+ dependent inactivation kinetics of the Ca2+ current.
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Affiliation(s)
- Uğur Dalaman
- Akdeniz University, Medical Faculty, Department of Biophysics, Dumlupınar Blv., 07070 Antalya, Turkey
| | - Hasan Özdoğan
- Akdeniz University, Medical Faculty, Department of Biophysics, Dumlupınar Blv., 07070 Antalya, Turkey.,Antalya Bilim University, Vocational School of Health Services, Akdeniz Blv. No: 90, 07085 Antalya, Turkey
| | - Ahmed K Sircan
- Antalya Bilim University, Electrical and Computer Engineering, Akdeniz Blv. No: 90, 07085 Antalya, Turkey
| | - Sevgi A Şengül
- Antalya Bilim University, Industrial Engineering, Akdeniz Blv. No: 90, 07085 Antalya, Turkey
| | - Nazmi Yaraş
- Akdeniz University, Medical Faculty, Department of Biophysics, Dumlupınar Blv., 07070 Antalya, Turkey
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Jansen HJ, Bohne LJ, Gillis AM, Rose RA. Atrial remodeling and atrial fibrillation in acquired forms of cardiovascular disease. Heart Rhythm O2 2020; 1:147-159. [PMID: 34113869 PMCID: PMC8183954 DOI: 10.1016/j.hroo.2020.05.002] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Atrial fibrillation (AF) is prevalent in common conditions and acquired forms of heart disease, including diabetes mellitus (DM), hypertension, cardiac hypertrophy, and heart failure. AF is also prevalent in aging. Although acquired heart disease is common in aging individuals, age is also an independent risk factor for AF. Importantly, not all individuals age at the same rate. Rather, individuals of the same chronological age can vary in health status from fit to frail. Frailty can be quantified using a frailty index, which can be used to assess heterogeneity in individuals of the same chronological age. AF is thought to occur in association with electrical remodeling due to changes in ion channel expression or function as well as structural remodeling due to fibrosis, myocyte hypertrophy, or adiposity. These forms of remodeling can lead to triggered activity and electrical re-entry, which are fundamental mechanisms of AF initiation and maintenance. Nevertheless, the underlying determinants of electrical and structural remodeling are distinct in different conditions and disease states. In this focused review, we consider the factors leading to atrial electrical and structural remodeling in human patients and animal models of acquired cardiovascular disease or associated risk factors. Our goal is to identify similarities and differences in the cellular and molecular bases for atrial electrical and structural remodeling in conditions including DM, hypertension, hypertrophy, heart failure, aging, and frailty.
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Affiliation(s)
- Hailey J Jansen
- Department of Cardiac Sciences, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Loryn J Bohne
- Department of Cardiac Sciences, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Anne M Gillis
- Department of Cardiac Sciences, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
| | - Robert A Rose
- Department of Cardiac Sciences, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada.,Department of Physiology and Pharmacology, Libin Cardiovascular Institute, Cumming School of Medicine, University of Calgary, Calgary, Alberta, Canada
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6
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Horváth B, Hézső T, Kiss D, Kistamás K, Magyar J, Nánási PP, Bányász T. Late Sodium Current Inhibitors as Potential Antiarrhythmic Agents. Front Pharmacol 2020; 11:413. [PMID: 32372952 PMCID: PMC7184885 DOI: 10.3389/fphar.2020.00413] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2019] [Accepted: 03/18/2020] [Indexed: 12/19/2022] Open
Abstract
Based on recent findings, an increased late sodium current (INa,late) plays an important pathophysiological role in cardiac diseases, including rhythm disorders. The article first describes what is INa,late and how it functions under physiological circumstances. Next, it shows the wide range of cellular mechanisms that can contribute to an increased INa,late in heart diseases, and also discusses how the upregulated INa,late can play a role in the generation of cardiac arrhythmias. The last part of the article is about INa,late inhibiting drugs as potential antiarrhythmic agents, based on experimental and preclinical data as well as in the light of clinical trials.
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Affiliation(s)
- Balázs Horváth
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Faculty of Pharmacy, University of Debrecen, Debrecen, Hungary
| | - Tamás Hézső
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Dénes Kiss
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - Kornél Kistamás
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
| | - János Magyar
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Division of Sport Physiology, University of Debrecen, Debrecen, Hungary
| | - Péter P. Nánási
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Department of Dental Physiology and Pharmacology, Faculty of Dentistry, University of Debrecen, Debrecen, Hungary
| | - Tamás Bányász
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
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High hydrostatic pressure induces atrial electrical remodeling through angiotensin upregulation mediating FAK/Src pathway activation. J Mol Cell Cardiol 2020; 140:10-21. [PMID: 32006532 DOI: 10.1016/j.yjmcc.2020.01.012] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 01/15/2020] [Accepted: 01/27/2020] [Indexed: 01/02/2023]
Abstract
Hypertension is an independent risk factor for atrial fibrillation (AF), although its specific mechanisms remain unclear. Previous research has been focused on cyclic stretch, ignoring the role of high hydrostatic pressure. The present study aimed to explore the effect of high hydrostatic pressure stimulation on electrical remodeling in atrial myocytes and its potential signaling pathways. Experiments were performed on left atrial appendages from patients with chronic AF or sinus rhythm, spontaneously hypertensive rats (SHRs) treated with or without valsartan (10 mg/kg/day) and HL-1 cells were exposed to high hydrostatic pressure using a self-developed device. Whole-cell patch-clamp recordings and western blots demonstrated that the amplitudes of ICa,L, Ito, and IKur were reduced in AF patients with corresponding changes in protein expression. Angiotensin protein levels increased and Ang1-7 decreased, while focal adhesion kinase (FAK) and Src kinase were enhanced in atrial tissue from AF patients and SHRs. After rapid atrial pacing, AF inducibility in SHR was significantly higher, accompanied by a decrease in ICa,L, upregulation of Ito and IKur, and a shortened action potential duration. Angiotensin upregulation and FAK/Src activation in SHR were inhibited by angiotensin type 1 receptor inhibitor valsartan, thus, preventing electrical remodeling and reducing AF susceptibility. These results were verified in HL-1 cells treated with high hydrostatic pressure, and demonstrated that electrical remodeling regulated by the FAK-Src pathway could be modulated by valsartan. The present study indicated that high hydrostatic pressure stimulation increases AF susceptibility by activating the renin-angiotensin system and FAK-Src pathway in atrial myocytes.
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Kettlewell S, Saxena P, Dempster J, Colman MA, Myles RC, Smith GL, Workman AJ. Dynamic clamping human and rabbit atrial calcium current: narrowing I CaL window abolishes early afterdepolarizations. J Physiol 2019; 597:3619-3638. [PMID: 31093979 PMCID: PMC6767690 DOI: 10.1113/jp277827] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Accepted: 05/13/2019] [Indexed: 11/08/2022] Open
Abstract
Key points Early‐afterdepolarizations (EADs) are abnormal action potential oscillations and a known cause of cardiac arrhythmias. Ventricular EADs involve reactivation of a Ca2+ current (ICaL) in its ‘window region’ voltage range. However, electrical mechanisms of atrial EADs, a potential cause of atrial fibrillation, are poorly understood. Atrial cells were obtained from consenting patients undergoing heart surgery, as well as from rabbits. ICaL was blocked with nifedipine and then a hybrid patch clamp/mathematical‐modelling technique, ‘dynamic clamping’, was used to record action potentials at the same time as injecting an artificial, modifiable, ICaL (ICaL,D‐C). Progressively widening the ICaL,D‐C window region produced EADs of various types, dependent on window width. EAD production was strongest upon moving the activation (vs. inactivation) side of the window. EADs were then induced by a different method: increasing ICaL,D‐C amplitude and/or K+ channel‐blockade (4‐aminopyridine). Narrowing of the ICaL,D‐C window by ∼10 mV abolished these EADs. Atrial ICaL window narrowing is worthy of further testing as a potential anti‐atrial fibrillation drug mechanism.
Abstract Atrial early‐afterdepolarizations (EADs) may contribute to atrial fibrillation (AF), perhaps involving reactivation of L‐type Ca2+ current (ICaL) in its window region voltage range. The present study aimed (i) to validate the dynamic clamp technique for modifying the ICaL contribution to atrial action potential (AP) waveform; (ii) to investigate the effects of widening the window ICaL on EAD‐propensity; and (iii) to test whether EADs from increased ICaL and AP duration are supressed by narrowing the window ICaL. ICaL and APs were recorded from rabbit and human atrial myocytes by whole‐cell‐patch clamp. During AP recording, ICaL was inhibited (3 µm nifedipine) and replaced by a dynamic clamp model current, ICaL,D‐C (tuned to native ICaL characteristics), computed in real‐time (every 50 µs) based on myocyte membrane potential. ICaL,D‐C‐injection restored the nifedipine‐suppressed AP plateau. Widening the window ICaL,D‐C, symmetrically by stepwise simultaneous equal shifts of half‐voltages (V0.5) of ICaL,D‐C activation (negatively) and inactivation (positively), generated EADs (single, multiple or preceding repolarization failure) in a window width‐dependent manner, as well as AP alternans. A stronger EAD‐generating effect resulted from independently shifting activation V0.5 (asymmetrical widening) than inactivation V0.5; for example, a 15 mV activation shift produced EADs in nine of 17 (53%) human atrial myocytes vs. 0 of 18 from inactivation shift (P < 0.05). In 11 rabbit atrial myocytes in which EADs were generated either by increasing the conductance of normal window width ICaL,D‐C or subsequent 4‐aminopyridine (2 mm), window ICaL,D‐C narrowing (10 mV) abolished EADs of all types (P < 0.05). The present study validated the dynamic clamp for ICaL, which is novel in atrial cardiomyocytes, and showed that EADs of various types are generated by widening (particularly asymmetrically) the window ICaL, as well as abolished by narrowing it. Window ICaL narrowing is a potential therapeutic mechanism worth pursuing in the search for improved anti‐AF drugs. Early‐afterdepolarizations (EADs) are abnormal action potential oscillations and a known cause of cardiac arrhythmias. Ventricular EADs involve reactivation of a Ca2+ current (ICaL) in its ‘window region’ voltage range. However, electrical mechanisms of atrial EADs, a potential cause of atrial fibrillation, are poorly understood. Atrial cells were obtained from consenting patients undergoing heart surgery, as well as from rabbits. ICaL was blocked with nifedipine and then a hybrid patch clamp/mathematical‐modelling technique, ‘dynamic clamping’, was used to record action potentials at the same time as injecting an artificial, modifiable, ICaL (ICaL,D‐C). Progressively widening the ICaL,D‐C window region produced EADs of various types, dependent on window width. EAD production was strongest upon moving the activation (vs. inactivation) side of the window. EADs were then induced by a different method: increasing ICaL,D‐C amplitude and/or K+ channel‐blockade (4‐aminopyridine). Narrowing of the ICaL,D‐C window by ∼10 mV abolished these EADs. Atrial ICaL window narrowing is worthy of further testing as a potential anti‐atrial fibrillation drug mechanism.
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Affiliation(s)
- Sarah Kettlewell
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - Priyanka Saxena
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - John Dempster
- Strathclyde Institute of Pharmacy & Biomedical Sciences, University of Strathclyde, Glasgow, UK
| | | | - Rachel C Myles
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - Godfrey L Smith
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
| | - Antony J Workman
- Institute of Cardiovascular & Medical Sciences, University of Glasgow, Glasgow, UK
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Li M, Xu X, Yang X, Kwong JSW, Shang H. The cardioprotective and antiarrhythmic effects of Nardostachys chinensis in animal and cell experiments. Altern Ther Health Med 2017; 17:398. [PMID: 28797251 PMCID: PMC5553922 DOI: 10.1186/s12906-017-1910-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2017] [Accepted: 08/04/2017] [Indexed: 12/13/2022]
Abstract
Background Cardiovascular disease (CVD) is the leading cause of premature death throughout the world. An estimated 17.5 million people died from CVD in 2012, representing 31% of all global deaths. Nardostachys chinensis (NC), a typical traditional Chinese medicine (TCM), plays a crucial role in the management of patients with CVD, especially for those with cardiac arrhythmia. The purpose of this study was to evaluate the cardioprotective and antiarrhythmic effects of NC in animal and cell experiments. Methods To review the cardioprotective and antiarrhythmic effects of NC, studies of NC on cardiovascular diseases in animal and cell experiments were identified from five databases through April 2016. Two investigators independently conducted the literature search, study selection, and data extraction. Results A total of 16 studies were identified, including five animal experiments and eleven cell experiments. Four studies showed significant effects of NC on myocardial protection by inhibiting myocardial apoptosis, inflammation and oxidative stress. Twelve studies indicated significant beneficial effects of NC in cardiac arrhythmia primarily through the modulation of ion channels (Ik, Ik1, INa, ICa-L, Ito). Conclusion The above findings showed the possible efficacy of NC via its cardioprotective and antiarrhythmic effects, but the results should be interpreted with caution due to the limitations and the deficiencies in the studies.
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Zhang Y, Wang HM, Wang YZ, Zhang YY, Jin XX, Zhao Y, Wang J, Sun YL, Xue GL, Li PH, Huang QH, Yang BF, Pan ZW. Increment of late sodium currents in the left atrial myocytes and its potential contribution to increased susceptibility of atrial fibrillation in castrated male mice. Heart Rhythm 2017; 14:1073-1080. [PMID: 28185917 DOI: 10.1016/j.hrthm.2017.01.046] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Indexed: 12/20/2022]
Abstract
BACKGROUND The incidence of atrial fibrillation (AF) is correlated with decreased levels of testosterone in elderly men. Late sodium current may exert a role in AF pathogenesis. OBJECTIVE The purpose of this study was to explore the effect of testosterone deficiency on AF susceptibility and the therapeutic effect of late sodium current inhibitors in mice. METHODS Male ICR mice (5 weeks old) were castrated to establish a testosterone deficiency model. One month after castration, dihydrotestosterone 5 mg/kg was administered subcutaneously for 2 months. Serum total testosterone level was assessed by enzyme-linked immunosorbent assay. High-frequency electrical stimulation was used to induce atrial arrhythmias. Whole-cell patch-clamp technique was used to for single-cell electrophysiologic study. RESULTS Serum dihydrotestosterone levels of castration mice declined significantly but recovered with administration of exogenous dihydrotestosterone. In comparison with sham mice, the number of AF episodes significantly increased by 13.5-fold, AF rate increased by 3.75-fold, and AF duration prolonged in castrated mice. Dihydrotestosterone administration alleviated the occurrence of AF. Action potential duration at both 50% and 90% repolarization were markedly increased in castrated mice compared to sham controls. The late sodium current was enhanced in castrated male mice. These alterations were alleviated by treatment with dihydrotestosterone. Systemic application of the INa-L inhibitors ranolazine, eleclazine, and GS967 inhibited the occurrence of AF in castrated mice. CONCLUSION Testosterone deficiency contributed to the increased late sodium current, prolonged action potential repolarization, and increased susceptibility to AF. Blocking of late sodium current is beneficial against the occurrence of AF in castrated mice.
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Affiliation(s)
- Yang Zhang
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Hui-Min Wang
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Ying-Zhe Wang
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Yi-Yuan Zhang
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Xue-Xin Jin
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Yue Zhao
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Jin Wang
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Yi-Lin Sun
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Gen-Long Xue
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Peng-Hui Li
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Qi-He Huang
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China
| | - Bao-Feng Yang
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China; Department of Pharmacology and Therapeutics, Melbourne School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Melbourne, Australia
| | - Zhen-Wei Pan
- Department of Pharmacology (Key Laboratory of Cardiovascular Medicine Research, Ministry of Education, State-Province Key Laboratories of Biomedicine-Pharmaceutics of China), College of Pharmacy Harbin Medical University, Harbin, Heilongjiang, People's Republic of China.
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Chi L, Belardinelli L, Zeng A, Hirakawa R, Rajamani S, Ling H, Dhalla AK. Inhibition of late Na+ current, a novel target to improve diastolic function and electrical abnormalities in Dahl salt-sensitive rats. Am J Physiol Heart Circ Physiol 2016; 310:H1313-20. [PMID: 26993228 DOI: 10.1152/ajpheart.00863.2015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 03/11/2016] [Indexed: 12/19/2022]
Abstract
Late Na(+) current (INaL) is enhanced in myocytes of animals with chronic heart failure and patients with hypertrophic cardiomyopathy. To define the role of INaL in diastolic heart failure, the effects of GS-458967 (GS-967), a potent INaL inhibitor on mechanical and electrical abnormalities, were determined in an animal model of diastolic dysfunction. Dahl salt-sensitive (DSS) rats fed a high-salt (HS) diet for 8 wk, compared with a normal salt (NS) diet, had increased left ventricular (LV) mass (1,257 ± 96 vs. 891 ± 34 mg) and diastolic dysfunction [isovolumic relaxation time (IVRT): 26.8 ± 0.5 vs. 18.9 ± 0.2 ms; early transmitral flow velocity/early mitral annulus velocity (E/E') ratio: 25.5 ± 1.9 vs. 14.9 ± 0.9]. INaL in LV myocytes from HS rats was significantly increased to 0.41 ± 0.02 from 0.14 ± 0.02 pA/pF in NS rats. The action potential duration (APD) was prolonged to 136 ± 12 from 68 ± 9 ms in NS rats. QTc intervals were longer in HS vs. NS rats (267 ± 8 vs. 212 ± 2 ms). Acute and chronic treatment with GS-967 decreased the enhanced INaL to 0.24 ± 0.01 and 0.17 ± 0.02 pA/pF, respectively, vs. 0.41 ± 0.02 pA/pF in the HS group. Chronic treatment with GS-967 dose-dependently reduced LV mass, the increases in E/E' ratio, and the prolongation of IVRT by 27, 27, and 20%, respectively, at the 1.0 mg·kg(-1)·day(-1) dose without affecting blood pressure or LV systolic function. The prolonged APDs in myocytes and QTc of HS rats were significantly reduced with GS-967 treatment. These results indicate that INaL is a significant contributor to the LV diastolic dysfunction, hypertrophy, and repolarization abnormalities and thus, inhibition of this current is a promising therapeutic target for diastolic heart failure.
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Affiliation(s)
- Liguo Chi
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Luiz Belardinelli
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Aliya Zeng
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Ryoko Hirakawa
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Sridharan Rajamani
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Haiyun Ling
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
| | - Arvinder K Dhalla
- Department of Cardiovascular Biology, Gilead Sciences, Fremont, California
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12
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Horvath B, Bers DM. The late sodium current in heart failure: pathophysiology and clinical relevance. ESC Heart Fail 2014; 1:26-40. [PMID: 28834665 DOI: 10.1002/ehf2.12003] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Revised: 07/13/2014] [Accepted: 07/14/2014] [Indexed: 12/19/2022] Open
Abstract
Large and growing body of data suggest that an increased late sodium current (INa,late ) can have a significant pathophysiological role in heart failure and other heart diseases. The first goal of this article is to describe how INa,late functions under physiological circumstances. The second goal is to show the wide range of cellular mechanisms that can increase INa,late in cardiac disease, and also to describe how the up-regulated INa,late contributes to the pathophysiology of heart failure. The final section of the article discusses the possible use of INa,late -modifying drugs in heart failure, on the basis of experimental and preclinical data.
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Affiliation(s)
- Balazs Horvath
- Department of Physiology, Faculty of Medicine, University of Debrecen, Debrecen, Hungary
- Faculty of Pharmacy, University of Debrecen, Debrecen, Hungary
| | - Donald M Bers
- Department of Pharmacology, School of Medicine, University of California, Davis, CA, USA
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13
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Selective Inhibition of the Late Sodium Current has No Adverse Effect on Electrophysiological or Contractile Function of the Normal Heart. J Cardiovasc Pharmacol 2014; 63:512-9. [DOI: 10.1097/fjc.0000000000000075] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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14
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Guo D, Yu M, Liu Q, Cox RH, Liu T, Yan GX. Ventricular hypertrophy amplifies transmural dispersion of repolarization by preferentially increasing the late sodium current in endocardium. J Electrocardiol 2014; 47:642-8. [PMID: 24813353 DOI: 10.1016/j.jelectrocard.2014.04.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2014] [Indexed: 01/17/2023]
Abstract
BACKGROUND The late sodium current (INa-L) contributes importantly to rate-dependent change in action potential duration (APD) and transmural dispersion of repolarization (TDR). However, little is known about the mechanisms of increased APD rate-dependence and amplified TDR in left ventricular hypertrophy (LVH) and failure. The purpose of this study was to investigate the role of INa-L in rate-adaptation of transmural APD heterogeneity. METHODS APD, its rate-dependence and INa-L current were examined in myocytes isolated from the endocardium and epicardium of the control and LVH rabbits. AP was recorded using the standard microelectrode technique, and INa-L was recorded using the whole-cell patch clamp technique. RESULTS Early afterdepolarizations (EADs) were frequently recorded in the isolated myocytes of the LVH rabbits but not in those of controls. LVH prolonged APD more significantly in the endocardial myocytes than in the epicardium (31.7±3.4 vs. 21.6±1.5% n=6, p<0.05), leading to a marked increase in TDR. LVH endocardial myocytes exhibited a greater rate-dependent change in APD compared to the epicardial myocytes. INa-L densities were significantly increased in both LVH endocardium and epicardium. However, LVH increased the INa-L density preferentially in the endocardial myocytes compared to the epicardial myocytes (54.5±4.8% vs. 39.2±3.3%, n=6, p<0.05). CONCLUSIONS Our results demonstrate that LVH increased the INa-L preferentially in the endocardium over the epicardium, which contributes importantly to the stronger rate-dependent change in repolarization and longer APD in the endocardium. This results in an amplified TDR capable of initiating EAD and ventricular arrhythmias.
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Affiliation(s)
- Donglin Guo
- Lankenau Institute for Medical Research, Wynnewood, PA; College of Life Science, South-Central University for Nationalities, Wuhan, China.
| | - Mengfei Yu
- College of Life Science, South-Central University for Nationalities, Wuhan, China
| | - Qinghua Liu
- College of Life Science, South-Central University for Nationalities, Wuhan, China
| | - Robert H Cox
- Lankenau Institute for Medical Research, Wynnewood, PA
| | - Tengxian Liu
- Lankenau Institute for Medical Research, Wynnewood, PA
| | - Gan-Xin Yan
- Lankenau Institute for Medical Research, Wynnewood, PA; Jefferson Medical College, Philadelphia, PA
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Koskinas KC, Fragakis N, Katritsis D, Skeberis V, Vassilikos V. Ranolazine enhances the efficacy of amiodarone for conversion of recent-onset atrial fibrillation. Europace 2014; 16:973-9. [DOI: 10.1093/europace/eut407] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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16
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Abstract
Late I Na is an integral part of the sodium current, which persists long after the fast-inactivating component. The magnitude of the late I Na is relatively small in all species and in all types of cardiomyocytes as compared with the amplitude of the fast sodium current, but it contributes significantly to the shape and duration of the action potential. This late component had been shown to increase in several acquired or congenital conditions, including hypoxia, oxidative stress, and heart failure, or due to mutations in SCN5A, which encodes the α-subunit of the sodium channel, as well as in channel-interacting proteins, including multiple β subunits and anchoring proteins. Patients with enhanced late I Na exhibit the type-3 long QT syndrome (LQT3) characterized by high propensity for the life-threatening ventricular arrhythmias, such as Torsade de Pointes (TdP), as well as for atrial fibrillation. There are several distinct mechanisms of arrhythmogenesis due to abnormal late I Na, including abnormal automaticity, early and delayed after depolarization-induced triggered activity, and dramatic increase of ventricular dispersion of repolarization. Many local anesthetic and antiarrhythmic agents have a higher potency to block late I Na as compared with fast I Na. Several novel compounds, including ranolazine, GS-458967, and F15845, appear to be the most selective inhibitors of cardiac late I Na reported to date. Selective inhibition of late I Na is expected to be an effective strategy for correcting these acquired and congenital channelopathies.
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Luo A, Ma J, Song Y, Qian C, Wu Y, Zhang P, Wang L, Fu C, Cao Z, Shryock JC. Larger late sodium current density as well as greater sensitivities to ATX II and ranolazine in rabbit left atrial than left ventricular myocytes. Am J Physiol Heart Circ Physiol 2013; 306:H455-61. [PMID: 24322614 DOI: 10.1152/ajpheart.00727.2013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
An increase of cardiac late sodium current (INa.L) is arrhythmogenic in atrial and ventricular tissues, but the densities of INa.L and thus the potential relative contributions of this current to sodium ion (Na(+)) influx and arrhythmogenesis in atria and ventricles are unclear. In this study, whole-cell and cell-attached patch-clamp techniques were used to measure INa.L in rabbit left atrial and ventricular myocytes under identical conditions. The density of INa.L was 67% greater in left atrial (0.50 ± 0.09 pA/pF, n = 20) than in left ventricular cells (0.30 ± 0.07 pA/pF, n = 27, P < 0.01) when elicited by step pulses from -120 to -20 mV at a rate of 0.2 Hz. Similar results were obtained using step pulses from -90 to -20 mV. Anemone toxin II (ATX II) increased INa.L with an EC50 value of 14 ± 2 nM and a Hill slope of 1.4 ± 0.1 (n = 9) in atrial myocytes and with an EC50 of 21 ± 5 nM and a Hill slope of 1.2 ± 0.1 (n = 12) in ventricular myocytes. Na(+) channel open probability (but not mean open time) was greater in atrial than in ventricular cells in the absence and presence of ATX II. The INa.L inhibitor ranolazine (3, 6, and 9 μM) reduced INa.L more in atrial than ventricular myocytes in the presence of 40 nM ATX II. In summary, rabbit left atrial myocytes have a greater density of INa.L and higher sensitivities to ATX II and ranolazine than rabbit left ventricular myocytes.
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Affiliation(s)
- Antao Luo
- Cardio-Electrophysiological Research Laboratory, Medical College of Wuhan University of Science and Technology, Wuhan, China
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Shryock JC, Song Y, Rajamani S, Antzelevitch C, Belardinelli L. The arrhythmogenic consequences of increasing late INa in the cardiomyocyte. Cardiovasc Res 2013; 99:600-11. [PMID: 23752976 DOI: 10.1093/cvr/cvt145] [Citation(s) in RCA: 97] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
This review presents the roles of cardiac sodium channel NaV1.5 late current (late INa) in generation of arrhythmic activity. The assumption of the authors is that proper Na(+) channel function is necessary to the maintenance of the transmembrane electrochemical gradient of Na(+) and regulation of cardiac electrical activity. Myocyte Na(+) channels' openings during the brief action potential upstroke contribute to peak INa and initiate excitation-contraction coupling. Openings of Na(+) channels outside the upstroke contribute to late INa, a depolarizing current that persists throughout the action potential plateau. The small, physiological late INa does not appear to be critical for normal electrical or contractile function in the heart. Late INa does, however, reduce the net repolarizing current, prolongs action potential duration, and increases cellular Na(+) loading. An increase of late INa, due to acquired conditions (e.g. heart failure) or inherited Na(+) channelopathies, facilitates the formation of early and delayed afterpolarizations and triggered arrhythmias, spontaneous diastolic depolarization, and cellular Ca(2+) loading. These in turn increase the spatial and temporal dispersion of repolarization time and may lead to reentrant arrhythmias.
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Affiliation(s)
- John C Shryock
- Department of Biology, Cardiovascular Therapeutic Area, Gilead Sciences, Foster City, CA, USA
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Xue X, Guo D, Sun H, Wang D, Li J, Liu T, Yang L, Shu J, Yan GX. Wenxin Keli suppresses ventricular triggered arrhythmias via selective inhibition of late sodium current. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2013; 36:732-40. [PMID: 23438075 DOI: 10.1111/pace.12109] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/07/2012] [Revised: 12/14/2012] [Accepted: 12/28/2012] [Indexed: 11/28/2022]
Abstract
BACKGROUND Wenxin Keli is a popular Chinese herb extract that approximately five million Asians are currently taking for the treatment of a variety of ventricular arrhythmias. However, its electrophysiological mechanisms remain poorly understood. METHODS AND RESULTS The concentration-dependent electrophysiological effects of Wenxin Keli were evaluated in the isolated rabbit left ventricular myocytes and wedge preparation. Wenxin Keli selectively inhibited late sodium current (INa) with an IC50 of 3.8 ± 0.4 mg/mL, which was significantly lower than the IC50 of 10.6 ± 0.9 mg/mL (n = 6, P < 0.05) for the fast INa. Wenxin Keli produced a small but statistically significant QT prolongation at 0.3 mg/mL, but shortened the QT and Tp-e interval at concentrations ≥ 1 mg/mL. Wenxin Keli increased QRS duration by 10.1% from 34.8 ± 1.0 ms to 38.3 ± 1.1 ms (n = 6, P < 0.01) at 3 mg/mL at a basic cycle length of 2,000 ms. However, its effect on the QRS duration exhibited weak use-dependency, that is, QRS remained less changed at increased pacing rates than other classic sodium channel blockers, such as flecainide, quinidine, and lidocaine. On the other hand, Wenxin Keli at 1-3 mg/mL markedly reduced dofetilide-induced QT and Tp-e prolongation by attenuation of its reverse use-dependence and abolished dofetilide-induced early afterdepolarization (EAD) in four of four left ventricular wedge preparations. It also suppressed digoxin-induced delayed after depolarization (DAD) and ventricular tachycardias without changing the positive staircase pattern in contractility at 1-3 mg/mL in a separate experimental series (four of four). CONCLUSIONS Wenxin Keli suppressed EADs, DADs, and triggered ventricular arrhythmias via selective inhibition of late INa.
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Affiliation(s)
- Xiaolin Xue
- Department of Cardiology, the First Affiliated Hospital, Xi'an Jiaotong University, Xi'an, China
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Abstract
The anti-arrhythmic efficacy of the late sodium channel current (late I(Na)) inhibition has been convincingly demonstrated in the ventricles, particularly under conditions of prolonged ventricular repolarization. The value of late I(Na) block in the setting of atrial fibrillation (AF) remains poorly investigated. All sodium channel blockers inhibit both peak and late I(Na) and are generally more potent in inhibiting late vs. early I(Na). Selective late I(Na) block does not prolong the effective refractory period (ERP), a feature common to practically all anti-AF agents. Although the late I(Na) blocker ranolazine has been shown to be effective in suppression of AF, it is noteworthy that at concentrations at which it blocks late I(Na) in the ventricles, it also potently blocks peak I(Na) in the atria, thus causing rate-dependent prolongation of ERP due to development of post-repolarization refractoriness. Late I(Na) inhibition in atria is thought to suppress intracellular calcium (Ca(i))-mediated triggered activity, secondary to a reduction in intracellular sodium (Na(i)). However, agents that block late I(Na) (ranolazine, amiodarone, vernakalant, etc) are also potent atrial-selective peak I(Na) blockers, so that the reduction of Na(i) loading in atrial cells by these agents can be in large part due to the block of peak I(Na). The impact of late I(Na) inhibition is reduced by the abbreviation of the action potential that occurs in AF patients secondary to electrical remodeling. It stands to reason that selective late I(Na) block may contribute more to inhibition of Ca(i)-mediated triggered activity responsible for initiation of AF in clinical pathologies associated with a prolonged atrial APD (such as long QT syndrome). Additional studies are clearly needed to test this hypothesis.
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Jia S, Lian J, Guo D, Xue X, Patel C, Yang L, Yuan Z, Ma A, Yan GX. Modulation of the late sodium current by ATX-II and ranolazine affects the reverse use-dependence and proarrhythmic liability of IKr blockade. Br J Pharmacol 2012; 164:308-16. [PMID: 21182492 DOI: 10.1111/j.1476-5381.2010.01181.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
BACKGROUND AND PURPOSE Drug-induced torsades de pointes (TdP) often occurs during bradycardia due to reverse use-dependence. We tested the hypothesis that inhibition or enhancement of late sodium current (I(Na,L) ) could modulate the drug-induced reverse use-dependence in QT and T(p-e) (an index of dispersion of repolarization), and therefore the liability for TdP. EXPERIMENTAL APPROACH Arterially perfused rabbit left ventricular wedge preparations were used. Action potentials from the endocardium were recorded simultaneously with a transmural ECG. The effects of Anemonia sulcata toxin (ATX-II) (an I(Na,L) enhancer), d,l-sotalol, clarithromycin and ranolazine (an I(Na,L) blocker) on rate-dependent changes in QT, T(p-e) and proarrhythmic events were tested, either alone or in combination. Rate-dependent QT and T(p-e) slopes and TdP score (a combined index of TdP liability) were calculated at control and during drug infusion. KEY RESULTS ATX-II (30 nM) and sotalol (300 µM) caused a marked increase in QT and T(p-e) intervals, steeper QT-basic cycle length (BCL) and T(p-e) -BCL slopes (i.e. reverse use-dependence), and TdP. Addition of ranolazine (15 µM) to ATX-II or sotalol significantly attenuated QT-BCL, T(p-e) -BCL slopes and the increased TdP scores. In contrast, clarithromycin (100 µM) moderately prolonged QT and T(p-e) without causing R-on-T extrasystole or TdP, but addition of ATX-II (1 nM) to clarithromycin markedly amplified the QT-BCL and T(p-e) -BCL slopes and further increased TdP score. CONCLUSION AND IMPLICATIONS Modulation of I(Na,L) altered drug-induced reverse use-dependence related to QT as well as T(p-e) , indicating that inhibition of I(Na,L) can markedly reduce the TdP liability of agents that prolong QT intervals.
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Affiliation(s)
- Shaobin Jia
- The First Hospital, Xi'An Jiaotong University, Xi'An, China
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