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Sidorenko VS, Cohen I, Dorjee K, Minetti CA, Remeta DP, Gao J, Potapova I, Wang HZ, Hearing J, Yen WY, Kim HK, Hashimoto K, Moriya M, Dickman KG, Yin X, Garcia-Diaz M, Chennamshetti R, Bonala R, Johnson F, Waldeck AL, Gupta R, Li C, Breslauer KJ, Grollman AP, Rosenquist TA. Mechanisms of antiviral action and toxicities of ipecac alkaloids: Emetine and dehydroemetine exhibit anti-coronaviral activities at non-cardiotoxic concentrations. Virus Res 2024; 341:199322. [PMID: 38228190 PMCID: PMC10831786 DOI: 10.1016/j.virusres.2024.199322] [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: 11/29/2023] [Revised: 01/09/2024] [Accepted: 01/13/2024] [Indexed: 01/18/2024]
Abstract
The emergence of highly infectious pathogens with their potential for triggering global pandemics necessitate the development of effective treatment strategies, including broad-spectrum antiviral therapies to safeguard human health. This study investigates the antiviral activity of emetine, dehydroemetine (DHE), and congeneric compounds against SARS-CoV-2 and HCoV-OC43, and evaluates their impact on the host cell. Concurrently, we assess the potential cardiotoxicity of these ipecac alkaloids. Significantly, our data reveal that emetine and the (-)-R,S isomer of 2,3-dehydroemetine (designated in this paper as DHE4) reduce viral growth at nanomolar concentrations (i.e., IC50 ∼ 50-100 nM), paralleling those required for inhibition of protein synthesis, while calcium channel blocking activity occurs at elevated concentrations (i.e., IC50 ∼ 40-60 µM). Our findings suggest that the antiviral mechanisms primarily involve disruption of host cell protein synthesis and is demonstrably stereoisomer specific. The prospect of a therapeutic window in which emetine or DHE4 inhibit viral propagation without cardiotoxicity renders these alkaloids viable candidates in strategies worthy of clinical investigation.
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Affiliation(s)
- Viktoriya S Sidorenko
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Ira Cohen
- Department of Physiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Kunchok Dorjee
- Division of Infectious Diseases, John Hopkins School of Medicine, Baltimore, Maryland 21205, USA
| | - Conceição A Minetti
- Department of Chemistry and Chemical Biology, Rutgers - The State University of New Jersey, Piscataway, New Jersey 08854, USA
| | - David P Remeta
- Department of Chemistry and Chemical Biology, Rutgers - The State University of New Jersey, Piscataway, New Jersey 08854, USA
| | - Junyuan Gao
- Department of Physiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Irina Potapova
- Department of Physiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Hong Zhan Wang
- Department of Physiology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Janet Hearing
- Department of Microbiology and Immunology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Wan-Yi Yen
- Department of Microbiology and Immunology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Hwan Keun Kim
- Department of Microbiology and Immunology, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Keiji Hashimoto
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Masaaki Moriya
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Kathleen G Dickman
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA; Department of Medicine, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Xingyu Yin
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Miguel Garcia-Diaz
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Rajesh Chennamshetti
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Radha Bonala
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA
| | - Francis Johnson
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA; Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, USA
| | - Amanda L Waldeck
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA; Department of Pharmacy, Stony Brook University Hospital, Stony Brook, New York 11794, USA
| | - Ramesh Gupta
- ChemMaster International Inc., Happauge, New York 11788, USA
| | - Chaoping Li
- Chemistry Service Unit of Shanghai Haoyuan Chemexpress Co., Ltd., Shanghai, PR China 201203
| | - Kenneth J Breslauer
- Department of Chemistry and Chemical Biology, Rutgers - The State University of New Jersey, Piscataway, New Jersey 08854, USA; Rutgers Cancer Institute of New Jersey, New Brunswick, NJ 08901, USA
| | - Arthur P Grollman
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA; Department of Medicine, Renaissance School of Medicine, Stony Brook University, Stony Brook, New York 11794, USA
| | - Thomas A Rosenquist
- Department of Pharmacological Sciences, Renaissance School of Medicine, Stony Brook University, Stony Brook, NY 11794, USA.
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Kamkin AG, Kamkina OV, Kazansky VE, Mitrokhin VM, Bilichenko A, Nasedkina EA, Shileiko SA, Rodina AS, Zolotareva AD, Zolotarev VI, Sutyagin PV, Mladenov MI. Identification of RNA reads encoding different channels in isolated rat ventricular myocytes and the effect of cell stretching on L-type Ca 2+current. Biol Direct 2023; 18:70. [PMID: 37899484 PMCID: PMC10614344 DOI: 10.1186/s13062-023-00427-0] [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: 06/19/2023] [Accepted: 10/13/2023] [Indexed: 10/31/2023] Open
Abstract
BACKGROUND The study aimed to identify transcripts of specific ion channels in rat ventricular cardiomyocytes and determine their potential role in the regulation of ionic currents in response to mechanical stimulation. The gene expression levels of various ion channels in freshly isolated rat ventricular cardiomyocytes were investigated using the RNA-seq technique. We also measured changes in current through CaV1.2 channels under cell stretching using the whole-cell patch-clamp method. RESULTS Among channels that showed mechanosensitivity, significant amounts of TRPM7, TRPC1, and TRPM4 transcripts were found. We suppose that the recorded L-type Ca2+ current is probably expressed through CaV1.2. Furthermore, stretching cells by 6, 8, and 10 μm, which increases ISAC through the TRPM7, TRPC1, and TRPM4 channels, also decreased ICa,L through the CaV1.2 channels in K+ in/K+ out, Cs+ in/K+ out, K+ in/Cs+ out, and Cs+ in/Cs+ out solutions. The application of a nonspecific ISAC blocker, Gd3+, during cell stretching eliminated ISAC through nonselective cation channels and ICa,L through CaV1.2 channels. Since the response to Gd3+ was maintained in Cs+ in/Cs+ out solutions, we suggest that voltage-gated CaV1.2 channels in the ventricular myocytes of adult rats also exhibit mechanosensitive properties. CONCLUSIONS Our findings suggest that TRPM7, TRPC1, and TRPM4 channels represent stretch-activated nonselective cation channels in rat ventricular myocytes. Probably the CaV1.2 channels in these cells exhibit mechanosensitive properties. Our results provide insight into the molecular mechanisms underlying stretch-induced responses in rat ventricular myocytes, which may have implications for understanding cardiac physiology and pathophysiology.
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Affiliation(s)
- Andre G Kamkin
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Olga V Kamkina
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Viktor E Kazansky
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Vadim M Mitrokhin
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Andrey Bilichenko
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Elizaveta A Nasedkina
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Stanislav A Shileiko
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Anastasia S Rodina
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Alexandra D Zolotareva
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Valentin I Zolotarev
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Pavel V Sutyagin
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation
| | - Mitko I Mladenov
- Department of Physiology, Pirogov Russian National Research Medical University, Moscow, Russian Federation.
- Faculty of Natural Sciences and Mathematics, Institute of Biology, "Ss. Cyril and Methodius" University, Skopje, North, Macedonia.
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Varró A, Tomek J, Nagy N, Virág L, Passini E, Rodriguez B, Baczkó I. Cardiac transmembrane ion channels and action potentials: cellular physiology and arrhythmogenic behavior. Physiol Rev 2020; 101:1083-1176. [PMID: 33118864 DOI: 10.1152/physrev.00024.2019] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Cardiac arrhythmias are among the leading causes of mortality. They often arise from alterations in the electrophysiological properties of cardiac cells and their underlying ionic mechanisms. It is therefore critical to further unravel the pathophysiology of the ionic basis of human cardiac electrophysiology in health and disease. In the first part of this review, current knowledge on the differences in ion channel expression and properties of the ionic processes that determine the morphology and properties of cardiac action potentials and calcium dynamics from cardiomyocytes in different regions of the heart are described. Then the cellular mechanisms promoting arrhythmias in congenital or acquired conditions of ion channel function (electrical remodeling) are discussed. The focus is on human-relevant findings obtained with clinical, experimental, and computational studies, given that interspecies differences make the extrapolation from animal experiments to human clinical settings difficult. Deepening the understanding of the diverse pathophysiology of human cellular electrophysiology will help in developing novel and effective antiarrhythmic strategies for specific subpopulations and disease conditions.
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Affiliation(s)
- András Varró
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary.,MTA-SZTE Cardiovascular Pharmacology Research Group, Hungarian Academy of Sciences, Szeged, Hungary
| | - Jakub Tomek
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Norbert Nagy
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary.,MTA-SZTE Cardiovascular Pharmacology Research Group, Hungarian Academy of Sciences, Szeged, Hungary
| | - László Virág
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
| | - Elisa Passini
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - Blanca Rodriguez
- Department of Computer Science, British Heart Foundation Centre of Research Excellence, University of Oxford, Oxford, United Kingdom
| | - István Baczkó
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, University of Szeged, Szeged, Hungary
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Haworth RA. Use of Isolated Adult Myocytes to Evaluate Cardiotoxicity. II. Preparation and Properties*. Toxicol Pathol 2020. [DOI: 10.1177/019262339001804a01] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The preparation and properties of isolated adult cardiac myocytes are reviewed, with the goal being to evaluate their usefulness as a model system for measuring cardiotoxicity. Some important factors in cell isolation methodology which impact on the quality of the preparation are identified, along with criteria for assessing the quality of cells after isolation. By all criteria, myocytes isolated by good procedures appear to largely retain their original properties. Moreover, the distinctive behavior of adult myocytes under metabolic stress endows them with a particular usefulness as monitors of toxicity. Overall, we conclude that the art of adult heart cell isolation and culture is now sufficiently advanced for either freshly isolated cells in suspension or cells in culture to be a useful model system for toxicity studies.
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Affiliation(s)
- Robert A. Haworth
- Department of Anesthesiology, University of Wisconsin, Madison, Wisconsin
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Carmeliet E. From Bernstein's rheotome to Neher-Sakmann's patch electrode. The action potential. Physiol Rep 2019; 7:e13861. [PMID: 30604910 PMCID: PMC6316177 DOI: 10.14814/phy2.13861] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2018] [Revised: 07/10/2018] [Accepted: 07/28/2018] [Indexed: 01/08/2023] Open
Abstract
The aim of this review was to provide an overview of the most important stages in the development of cellular electrophysiology. The period covered starts with Bernstein's formulation of the membrane hypothesis and the measurement of the nerve and muscle action potential. Technical innovations make discoveries possible. This was the case with the use of the squid giant axon, allowing the insertion of "large" intracellular electrodes and derivation of transmembrane potentials. Application of the newly developed voltage clamp method for measuring ionic currents, resulted in the formulation of the ionic theory. At the same time transmembrane measurements were made possible in smaller cells by the introduction of the microelectrode. An improvement of this electrode was the next major (r)evolution. The patch electrode made it possible to descend to the molecular level and record single ionic channel activity. The patch technique has been proven to be exceptionally versatile. In its whole-cell configuration it was the solution to measure voltage clamp currents in small cells. See also: https://doi.org/10.14814/phy2.13860 & https://doi.org/10.14814/phy2.13862.
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Xiao Y, Long WQ, Guan KP, Long M, Lu GH, Huang ZB. Role of angiotensin II type 2 receptor during electrophysiological remodeling of left ventricular hypertrophic myocardium in spontaneously hypertensive rats. ACTA ACUST UNITED AC 2017; 12:58-65. [PMID: 29100861 DOI: 10.1016/j.jash.2017.09.014] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2017] [Revised: 08/29/2017] [Accepted: 09/26/2017] [Indexed: 10/18/2022]
Abstract
The objective was to investigate the role of angiotensin II type 2 receptor during electrophysiological remodeling of left ventricular hypertrophic myocardium in spontaneously hypertensive rats (SHRs). A total of 36, aged 10 weeks, male SHRs were divided into three groups: control, valsartan, and valsartan + PD123319 groups (n = 12 in each). The systolic blood pressure, left ventricular mass index, ventricular effective refractory period, and ventricular fibrillation threshold (VFT) were also measured after 8 weeks. At the same time, INa, ICaL, Ito, and membrane capacitance were measured in left ventricular myocytes by whole-cell patch-clamp. The VFT of valsartan was higher than that of control (valsartan vs. CONTROL 17.4 ± 0.6 mA vs. 15.8 ± 0.5 mA, P < .05). The VFT of valsartan was higher than that of valsartan + PD123319 (valsartan vs. valsartan + PD123319: 17.4 ± 0.6 mA vs. 16.6 ± 0.9 mA, P < .05). The density of Ito of valsartan was higher than that of control (valsartan vs. CONTROL 14.7 ± 0.42 pA/pF vs. 11.2 ± 0.15 pA/pF, P < .05). The density of Ito of valsartan was higher than that of valsartan + PD123319 (valsartan vs. valsartan + PD123319: 14.7 ± 0.42 pA/pF vs. 13.6 ± 0.30 pA/pF, P < .05). The density of ICaL of valsartan was lower than that of control (valsartan vs. CONTROL -4.6 ± 0.2 pA/pF vs. -6.9 ± 0.1 pA/pF, P < .05). The density of ICaL of valsartan was lower than that of valsartan + PD123319 (valsartan vs. valsartan + PD123319: -4.6 ± 0.2 pA/pF vs. -5.4 ± 0.1 pA/pF, P < .05). These results demonstrated that the stimulation of angiotensin II type 2 receptor improved electrophysiological remodeling of left ventricular hypertrophic myocardium in SHR.
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Affiliation(s)
- Ying Xiao
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Wei-Qing Long
- Department of Clinical Laboratory, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Kai-Pan Guan
- Department of Respiratory Intensive Care Unit, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Ming Long
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Gui-Hua Lu
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Zhi-Bin Huang
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China.
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López-Dyck E, Andrade-Urzúa F, Elizalde A, Ferrer-Villada T, Dagnino-Acosta A, Huerta M, Osuna-Calleros Z, Rangel-Sandoval C, Sánchez-Pastor E. ACPA and JWH-133 modulate the vascular tone of superior mesenteric arteries through cannabinoid receptors, BK Ca channels, and nitric oxide dependent mechanisms. Pharmacol Rep 2017; 69:1131-1139. [PMID: 29128791 DOI: 10.1016/j.pharep.2017.06.011] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2017] [Revised: 05/26/2017] [Accepted: 06/20/2017] [Indexed: 01/25/2023]
Abstract
BACKGROUND Some cannabinoids, a family of compounds derived from Cannabis sativa (marijuana), have previously shown vasodilator effects in several studies, a feature that makes them suitable for the generation of a potential treatment for hypertension. The mechanism underlying this vasodilator effect in arteries is still controversial. In this report, we explored how the synthetic cannabinoids ACPA (CB1-selective agonist) and JWH-133 (CB2-selective agonist) regulate the vascular tone of rat superior mesenteric arteries. METHODS To screen the expression of CB1 (Cannabinoid receptor 1) and CB2 (Cannabinoid receptor 2) receptors in arterial rings or isolated smooth muscle cells obtained from the artery, immunocytochemistry, immunohistochemistry, and confocal microscopy were performed. In addition, the effects on vascular tone induced by the two cannabinoids were tested in isometric tension experiments in rings obtained from superior mesenteric arteries. The participation of voltage and calcium-activated potassium channel of big conductance (BKCa) and the role of nitric oxide (NO) release on the vascular effects induced by ACPA and JWH-133 were tested. RESULTS CB1 and CB2 receptors were highly expressed in the rat superior mesenteric artery, in both smooth muscle and endothelium. The vasodilation effect shown by ACPA was endothelium-dependent through a mechanism involving CB1 receptors, BKCa channel activation, and NO release; meanwhile, the vasodilator effect of JWH-133 was induced by the activation of CB2 receptors located in smooth muscle and by a CB2 receptor-independent mechanism inducing NO release. CONCLUSIONS CB1 and CB2 receptor activation in superior mesenteric artery causes vasorelaxation by mechanisms involving BKCa channels and NO release.
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Affiliation(s)
- Evelyn López-Dyck
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Mexico
| | | | - Alejandro Elizalde
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Mexico
| | - Tania Ferrer-Villada
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Mexico
| | | | - Miguel Huerta
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Mexico
| | - Zyanya Osuna-Calleros
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Mexico
| | | | - Enrique Sánchez-Pastor
- Centro Universitario de Investigaciones Biomédicas, Universidad de Colima, Colima, Mexico.
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Long-term treatment of spontaneously hypertensive rats with PD123319 and electrophysiological remodeling of left ventricular myocardium. Naunyn Schmiedebergs Arch Pharmacol 2016; 389:1333-1340. [PMID: 27629578 DOI: 10.1007/s00210-016-1300-0] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2016] [Accepted: 09/05/2016] [Indexed: 01/19/2023]
Abstract
To investigate the effects of PD123319, an antagonist of angiotensin II subtype-2 receptor (AT2R), on the electrophysiological characteristics of the left ventricular hypertrophic myocardium in spontaneously hypertensive rats (SHR). A total of twenty-four 10-week-old male SHR were divided into two groups: PD123319 and non-PD123319 groups (n = 12 in each). Twelve 10-week-old Wistar-Kyoto rats served as the control group. Systolic blood pressure, left ventricular mass index (LVMI), ventricular effective refractory period, and ventricular fibrillation threshold were also measured after 8 weeks. I Na, I CaL, I to, and membrane capacitance were measured in the left ventricular myocytes after 8 weeks by whole-cell patch clamp. PD123319 increased LVMI compared with the non-PD123319 group (PD123319 vs. non-PD123319, 3.83 ± 0.11 vs. 3.60 ± 0.19 mg/g; P < 0.01). PD123319 also decreased the ventricular fibrillation threshold compared with the non-PD123319 group (PD123319 vs. non-PD123319, 14.75 ± 0.65 vs. 16.0 ± 0.86 mA; P < 0.01). PD123319 enhanced membrane capacitance compared with the non-PD123319 group (PD123319 vs. non-PD123319, 283.63 ± 5.80 vs. 276.50 ± 4.28 pF; P < 0.05). PD123319 increased the density of I CaL compared with the non-PD123319 group (PD123319 vs. non-PD123319, -6.76 ± 0.48 vs. -6.13 ± 0.30 pA/pF; P < 0.05). PD123319 decreased the density of I to compared with the non-PD123319 group (PD123319 vs. non-PD123319, 11.49 ± 0.50 vs. 12.23 ± 0.36 pA/pF; P < 0.05). Long-term treatment with PD123319 worsened the development of myocyte hypertrophy and associated electrophysiological alterations in spontaneously hypertensive rat.
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9
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Ying X, Weiqing L, Guihua L, Juhong Z, Huang Z. Effect of Valsartan on Sarcoplasmic Reticulum Ca2+-ATPase Pump of the Left Ventricular Myocardium in Rats with Heart Failure with Preserved Ejection Fraction. Biomed Hub 2016; 1:1-9. [PMID: 31988887 PMCID: PMC6945928 DOI: 10.1159/000448132] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2016] [Accepted: 06/30/2016] [Indexed: 11/19/2022] Open
Abstract
Objectives The aim was to investigate the effects of valsartan on the sarcoplasmic reticulum Ca2+-ATPase pump (SERCA) and L-type Ca2+ channel current (I<sub>CaL</sub>) of the left ventricular myocardium in rats with heart failure with preserved ejection fraction. Methods The 30-week-old male spontaneously hypertensive rats (SHRs) are randomly divided into the non-Valsartan and Valsartan groups, and the 30-week-old male Wistar-Kyoto rats served as control rats. The expression of SERCA is measured by Western blot. The I<sub>CaL</sub> is measured by whole-cell patch clamp. The left ventricular end-diastolic pressure and left ventricular relaxation time constant quantity are measured at the same time. Results The left ventricular end-diastolic pressure is much higher in SHRs compared with that in control rats (p < 0.01). The left ventricular relaxation time constant quantity is markedly extended in SHRs compared with control rats (p < 0.01). Valsartan cannot increase the expression of SERCA nor decrease the density of I<sub>CaL</sub> compared with the non-Valsartan group (p > 0.05). Conclusions Valsartan has no effect on SERCA and I<sub>CaL</sub> of the left ventricular myocardium in rats with heart failure with preserved ejection fraction.
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Affiliation(s)
- Xiao Ying
- Department of Anesthesiology, Sun Yat-sen University, Guangzhou, China
| | - Long Weiqing
- Department of Clinical Laboratory, Sun Yat-sen University, Guangzhou, China
| | - Lu Guihua
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Zhang Juhong
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Zhibin Huang
- Department of Cardiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
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Abstract
An electrophysiological analysis of canine single ventricular myocardial (VM) and Purkinje (P) cells was carried out by means of whole cell voltage clamp method. The following results in VM versus P cells were obtained. INa3 was present, had a threshold negative to the fast activating-inactivating INa1, its slow inactivation was cut off by INa1, and contributed to Na+ influx at INa1 threshold. INa1 was smaller and had a less negative threshold. There was no comparable slowly inactivating INa2, accounting for the shorter action potential. Slope conductance at resting potential was about double and decreased to a minimum value at the larger and less negative IK1 peak. The negative slope region of I-V relation was smaller during fast ramps and larger during slow ramps than in P cells, occurred in the voltage range of IK1 block by Mg2+, was not affected by a lower Vh and TTX and was eliminated by Ba2+, in contrast to P cells. ICa was larger, peaked at positive potentials and was eliminated by Ni2+. Ito was much smaller, began at more positive values, was abolished by less negative Vh and by 4-aminopyridine, included a sustained current that 4-aminopyridine decreased but did not eliminate. Steeper ramps increased IK1 peak as well as the fall in outward current during repolarization, consistent with a time-dependent block and unblock of IK1 by polyamines. During repolarization, the positive slope region was consistently present and was similar in amplitude to IK1 peak, whereas it was small or altogether missing in P cells. The total outward current at positive potentials comprised a larger IK1 component whereas it included a larger Ito and sustained current in P cells. These and other results provide a better understanding of the mechanisms underlying the action potential of VM and P cells under normal and some abnormal (arrhythmias) conditions.
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Affiliation(s)
- M Vassalle
- Department of Physiology and Pharmacology, State University of New York, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, U.S.A
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Cavanaugh J, French JA. Post-partum variation in the expression of paternal care is unrelated to urinary steroid metabolites in marmoset fathers. Horm Behav 2013; 63:551-8. [PMID: 23439223 PMCID: PMC3746002 DOI: 10.1016/j.yhbeh.2013.02.006] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/19/2012] [Revised: 02/11/2013] [Accepted: 02/12/2013] [Indexed: 11/17/2022]
Abstract
The organization and activation of maternal care are known to be highly regulated by hormones and there is growing evidence that expression of paternal care is also related to endocrine substrates. We examined the relationship between paternal behavior and steroid hormones in marmoset fathers (Callithrix geoffroyi) and evaluated whether hormone-paternal behavior relationships were altered by previous offspring-care experience in males. Based on previous findings, we predicted that testosterone, estradiol, and cortisol would decrease following the birth of offspring and would be lowest during the period of maximal infant carrying. Furthermore, we predicted that post-partum changes in carrying effort and hormone levels would be influenced by the level of offspring-care experience. Carrying effort and other paternal care behaviors underwent temporal changes over the post-partum period, but these patterns were not related to variation in hormone concentrations over the same period. There was a limited effect of offspring-care experience on hormone concentrations, but experience was found to play a role in the expression of paternal care, with experienced fathers engaging in significantly more infant allogrooming than inexperienced fathers. Furthermore, inexperienced fathers increased the frequency of food sharing in response to infant begging across the post-partum period, while experienced fathers displayed consistently low levels. We posit that a combination of experiential factors and an increased role for alloparents in offspring-care led to these changes. However, it appears that hormonal changes may not influence paternal responsiveness in white-faced marmoset fathers and that hormone-paternal behavior relationships are not critically dependent on a male's previous offspring-care experience.
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Affiliation(s)
- Jon Cavanaugh
- Callitrichid Research Center, Department of Psychology, University of Nebraska, Omaha, NE 68182, USA.
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12
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Saegusa N, Moorhouse E, Vaughan-Jones RD, Spitzer KW. Influence of pH on Ca²⁺ current and its control of electrical and Ca²⁺ signaling in ventricular myocytes. ACTA ACUST UNITED AC 2012; 138:537-59. [PMID: 22042988 PMCID: PMC3206307 DOI: 10.1085/jgp.201110658] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Modulation of L-type Ca(2+) current (I(Ca,L)) by H(+) ions in cardiac myocytes is controversial, with widely discrepant responses reported. The pH sensitivity of I(Ca,L) was investigated (whole cell voltage clamp) while measuring intracellular Ca(2+) (Ca(2+)(i)) or pH(i) (epifluorescence microscopy) in rabbit and guinea pig ventricular myocytes. Selectively reducing extracellular or intracellular pH (pH(o) 6.5 and pH(i) 6.7) had opposite effects on I(Ca,L) gating, shifting the steady-state activation and inactivation curves to the right and left, respectively, along the voltage axis. At low pH(o), this decreased I(Ca,L), whereas at low pH(i), it increased I(Ca,L) at clamp potentials negative to 0 mV, although the current decreased at more positive potentials. When Ca(2+)(i) was buffered with BAPTA, the stimulatory effect of low pH(i) was even more marked, with essentially no inhibition. We conclude that extracellular H(+) ions inhibit whereas intracellular H(+) ions can stimulate I(Ca,L). Low pH(i) and pH(o) effects on I(Ca,L) were additive, tending to cancel when appropriately combined. They persisted after inhibition of calmodulin kinase II (with KN-93). Effects are consistent with H(+) ion screening of fixed negative charge at the sarcolemma, with additional channel block by H(+)(o) and Ca(2+)(i). Action potential duration (APD) was also strongly H(+) sensitive, being shortened by low pH(o), but lengthened by low pH(i), caused mainly by H(+)-induced changes in late Ca(2+) entry through the L-type Ca(2+) channel. Kinetic analyses of pH-sensitive channel gating, when combined with whole cell modeling, successfully predicted the APD changes, plus many of the accompanying changes in Ca(2+) signaling. We conclude that the pH(i)-versus-pH(o) control of I(Ca,L) will exert a major influence on electrical and Ca(2+)-dependent signaling during acid-base disturbances in the heart.
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Affiliation(s)
- Noriko Saegusa
- Department of Physiology, Nora Eccles Harrison Cardiovascular Research and Training Institute, University of Utah, Salt Lake City, UT 84112, USA
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13
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Benitah JP, Alvarez JL, Gómez AM. L-type Ca(2+) current in ventricular cardiomyocytes. J Mol Cell Cardiol 2009; 48:26-36. [PMID: 19660468 DOI: 10.1016/j.yjmcc.2009.07.026] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Revised: 07/09/2009] [Accepted: 07/27/2009] [Indexed: 12/24/2022]
Abstract
L-type Ca(2+) channels are mediators of Ca(2+) influx and the regulatory events accompanying it and are pivotal in the function and dysfunction of ventricular cardiac myocytes. L-type Ca(2+) channels are located in sarcolemma, including the T-tubules facing the sarcoplasmic reticulum junction, and are activated by membrane depolarization, but intracellular Ca(2+)-dependent inactivation limits Ca(2+) influx during action potential. I(CaL) is important in heart function because it triggers excitation-contraction coupling, modulates action potential shape and is involved in cardiac arrhythmia. L-type Ca(2+) channels are multi-subunit complexes that interact with several molecules involved in their regulations, notably by beta-adrenergic signaling. The present review highlights some of the recent findings on L-type Ca(2+) channel function, regulation, and alteration in acquired pathologies such as cardiac hypertrophy, heart failure and diabetic cardiomyopathy, as well as in inherited arrhythmic cardiac diseases such as Timothy and Brugada syndromes.
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JANUARY CRAIGT, SHOROFSKY STEPHEN. Early Afterdepolarizations: Newer Insights into Cellular Mechanisms. J Cardiovasc Electrophysiol 2008. [DOI: 10.1111/j.1540-8167.1990.tb01058.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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15
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Sodi R, Dubuis E, Shenkin A, Hart G. B-type natriuretic peptide (BNP) attenuates the L-type calcium current and regulates ventricular myocyte function. ACTA ACUST UNITED AC 2008; 151:95-105. [PMID: 18616964 DOI: 10.1016/j.regpep.2008.06.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Revised: 05/22/2008] [Accepted: 06/15/2008] [Indexed: 10/21/2022]
Abstract
A fundamental question in physiology is how hormones regulate the functioning of a cell or organ. It was therefore the aim of this study to investigate the effect(s) of BNP-32 on calcium handling by ventricular myocytes obtained from the rat left ventricle. We specifically tested the hypothesis that BNP-32 decreased the L-type calcium current (I(Ca,L)). Perforated patch clamp technique was used to record I(Ca,L) and action potential (AP) in voltage and current clamp mode, respectively. Myocyte shortening was measured using a photodiode array edge-detection system and intracellular calcium transients were measured by fluorescence photometry. Western blotting was used to determine the relative change in the expression of proteins. At the concentrations tested, BNP-32 significantly decreased cell shortening in a dose-dependent manner; increased the phase II slope of the AP by 53.0%; increased the APD(50) by 16.9%; reduced the I(Ca,L) amplitude with a 22.9% decrease in the peak amplitude and reduced Ca(2+)-dependent inactivation; increased the V(1/2) activation of the L-type calcium channel by 51.1% and decreased V(1/2) inactivation by 31.8%; and, intracellular calcium transient amplitude was significantly decreased by 32.0%, whereas the time to peak amplitude and T(1/2) were both significantly increased by 38.7% and 89.4% respectively. Sarcoplasmic reticulum Ca(2+)-ATPase (SERCA2a) protein expression was reduced by BNP-32. These data suggest that BNP-32 regulates ventricular myocyte function by attenuating I(Ca,L), altering the AP and reducing SERCA2a activity and/or expression. This study suggests a novel constitutive mechanism for the autocrine action of BNP on the L-type calcium channel in ventricular myocytes.
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Affiliation(s)
- R Sodi
- Department of Clinical Biochemistry & Metabolic Medicine, Royal Liverpool & Broadgreen University Hospital, Prescot street, Liverpool L7 8XP, United Kingdom.
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16
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Bocchi L, Vassalle M. Characterization of the slowly inactivating sodium current INa2 in canine cardiac single Purkinje cells. Exp Physiol 2007; 93:347-61. [PMID: 17993508 DOI: 10.1113/expphysiol.2007.040881] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The aim of our experiments was to investigate by means of a whole cell patch-clamp technique the characteristics of the slowly inactivating sodium current (I(Na2)) found in the plateau range in canine cardiac Purkinje single cells. The I(Na2) was separated from the fast-activating and -inactivating I(Na) (labelled here I(Na1)) by applying a two-step protocol. The first step, from a holding potential (V(h)) of -90 or -80 mV to -50 mV, led to the quick activation and inactivation of I(Na1). The second step consisted of depolarizations of increasing amplitude from -50 mV to less negative values, which led to the quick activation and slow inactivation of I(Na2). The I(Na2) was fitted with a double exponential function with time constants of tens and hundreds milliseconds, respectively. After the activation and inactivation of I(Na1) at -50 mV, the slope conductance was very small and did not change with time. Instead, during I(Na2), the slope conductance was larger and decreased as a function of time. Progressively longer conditioning steps at -50 mV resulted in a progressive decrease in amplitude of I(Na2) during the subsequent test steps. Gradually longer hyperpolarizing steps (increments of 100 ms up to 600 ms) from V(h) -30 mV to -100 mV were followed on return to -30 mV by a progressively larger I(Na2), as were gradually more negative 500 ms steps from V(h) -30 mV to -90 mV. At the end of a ramp to -20 mV, a sudden repolarization to approximately -35 mV fully deactivated I(Na2). The I(Na2) was markedly reduced by lignocaine (lidocaine) and by low extracellular [Na(+)], but it was little affected by low and high extracellular [Ca(2+)]. At negative potentials, the results indicate that there was little overlap between I(Na2) and the transient outward current, I(to), as well as the calcium current, I(Ca). In the absence of I(to) and I(Ca) (blocked by means of 4-aminopyridine and nickel, respectively), I(Na2) reversed at 60 mV. In conclusion, I(Na2) is a sodium current that can be initiated after the inactivation of I(Na1) and has characteristics that are quite distinct from those of I(Na1). The results have a bearing on the mechanisms underlying the long plateau of Purkinje cell action potential and its modifications in different physiological and pathological conditions.
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Affiliation(s)
- L Bocchi
- Department of Physiology, State University of New York, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA
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López A, Arce H, Guevara MR. Rhythms of high-grade block in an ionic model of a strand of regionally ischemic ventricular muscle. J Theor Biol 2007; 249:29-45. [PMID: 17706682 DOI: 10.1016/j.jtbi.2007.06.015] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2006] [Revised: 06/11/2007] [Accepted: 06/11/2007] [Indexed: 11/15/2022]
Abstract
Electrical alternans, a beat-to-beat alternation in the electrocardiogram or electrogram, is frequently seen during the first few minutes of acute myocardial ischemia, and is often immediately followed by malignant cardiac arrhythmias such as ventricular tachycardia and ventricular fibrillation. As ischemia progresses, higher-order periodic rhythms (e.g., period-4) can replace the period-2 alternans rhythm. This is also seen in modelling work on a two-dimensional (2-D) sheet of regionally ischemic ventricular muscle. In addition, in the experimental work, ventricular arrhythmias are overwhelmingly seen only after the higher-order rhythms arise. We investigate an ionic model of a strand of ischemic ventricular muscle, constructed as a 3-cm-long 1-D cable with a centrally located 1-cm-long segment exposed to an elevated extracellular potassium concentration ([K(+)](o)). As [K(+)](o) is raised in this "ischemic segment" to represent one major effect of ongoing ischemia, the sequence of rhythms {1:1-->2:2 (alternans)-->2:1} is seen. With further increase in [K(+)](o), one sees higher-order periodic 2N:M rhythms {2:1-->4:2-->4:1-->6:2-->6:1-->8:2-->8:1}. In a 2N:M cycle, only M of the 2N action potentials generated at the proximal end of the cable successfully traverse the ischemic segment, with the remaining ones being blocked within the ischemic segment. Finally, there is a transition to complete block {8:1-->2:0-->1:0} (in an n:0 rhythm, all action potentials die out within the ischemic segment). Changing the length of the ischemic segment results in different rhythms and transitions being seen: e.g., when the ischemic segment is 2 cm long, the period-6 rhythms are not seen; when it is 0.5 cm long, there is a 3:1 rhythm interposed between the 2:1 and 1:0 rhythms. We discuss the relevance of our results to the experimental observations on the higher-order rhythms that presage reentrant ischemic ventricular arrhythmias.
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Affiliation(s)
- Alejandro López
- Departamento de Física, Facultad de Ciencias, Universidad Nacional Autónoma de México, Apartado Postal 70-542, 04510 México, Distrito Federal, México
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18
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Vassalle M, Bocchi L, Du F. A slowly inactivating sodium current (INa2) in the plateau range in canine cardiac Purkinje single cells. Exp Physiol 2006; 92:161-73. [PMID: 17053038 DOI: 10.1113/expphysiol.2006.035279] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
The action potential of Purkinje fibres is markedly shortened by tetrodotoxin, suggesting the possibility that a slowly inactivating sodium current might flow during the plateau. The aim of the present experiments was to investigate, in canine cardiac Purkinje single cells by means of a whole cell patch clamp technique, whether a sodium current slowly inactivates at less negative potentials and (if so) some of its distinctive characteristics. The results showed that a 500 ms depolarizing step from a holding potential of -90 mV to -50 mV induced the fast inward current I(Na) (labelled here I(Na1)). With steps to -40 mV or less negative values, a slowly decaying component (tentatively labelled here I(Na2)) appeared, which peaked at -30 to -20 mV and decayed slowly and incompletely during the 500 ms steps. The I(Na2) was present also during steps to -10 mV, but then the transient outward current (I(to)) appeared. When the holding potential (V(h)) was decreased to -60 to -50 mV, I(Na2) disappeared even if a small I(Na1) might still be present. Tetrodotoxin (30 mum), lignocaine (100 mum) and cadmium (0.2 mm; but not manganese, 1 mm) blocked I(Na2). During fast depolarizing ramps, the rapid inactivation of I(Na1) was followed by a negative slope region. During repolarizing ramps, a region of positive slope was present, whereas I(Na1) was absent. At less negative values of V(h), the amplitude of the negative and positive slopes became gradually smaller. Gradually faster ramps increased the magnitude of the negative slope, and tetrodotoxin (30 mum) reduced or abolished it. Thus, Purkinje cells have a slowly decaying inward current owing to Na(+) entry (I(Na2)) that is different in several ways from the fast I(Na1) and that appears important for the duration of the plateau.
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Affiliation(s)
- Mario Vassalle
- Department of Physiology, Box 31, SUNY, Downstate Medical Center, 450 Clarkson Avenue, Brooklyn, NY 11203, USA.
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Cheikh A, Benkhalifa R, Bescond J, El Ayeb M, Raymond G, Cognard C, Potreau D. Depression of cardiac L-type calcium current by a scorpion venom fraction M1 following muscarinic receptors interaction involving adenylate cyclase pathway. Toxicon 2006; 48:373-87. [PMID: 16904145 DOI: 10.1016/j.toxicon.2006.06.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2006] [Revised: 06/20/2006] [Accepted: 06/22/2006] [Indexed: 11/21/2022]
Abstract
The effects of a non-toxic fraction, called M1, from Buthus occitanus tunetanus (Bot) scorpion were studied on rat cardiac contraction and calcium transient and current. A decrease in both rate and tension on isolated intact hearts as well as in calcium transient induced by depolarizing 100 K(+) solution on isolated ventricular cardiomyocytes was firstly observed. Studies with the whole cell patch clamp method showed that M1 decreased the L-type calcium current (ICa(L)) in a dose-dependent manner with an IC50 of 0.36 microg/mL and a Hill coefficient of 0.95. This effect was blocked and reversed by the specific muscarinic receptors antagonist atropine, 1 microM, and was completely prevented when cardiomyocytes were pretreated with Pertussis toxin, 1 microg/mL, to block the alpha subunit of the PTX-sensitive G proteins. These results show that M1 fraction of Bot inhibits basal calcium current by interacting with muscarinic receptors and suggest that this inhibition could be attributed to inhibition of adenylate cyclase activity by a mechanism involving PTX-sensitive G proteins.
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Affiliation(s)
- Amani Cheikh
- Laboratoire Venins et Toxines, Institut Pasteur de Tunis, BP 74-1002, Tunis, Tunisia
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Markevich NI, Pimenov OY, Kokoz YM. Analysis of the modal hypothesis of Ca2+-dependent inactivation of L-type Ca2+ channels. Biophys Chem 2005; 117:173-90. [PMID: 15936868 DOI: 10.1016/j.bpc.2005.04.017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2005] [Revised: 04/28/2005] [Accepted: 04/28/2005] [Indexed: 10/25/2022]
Abstract
A kinetic model of Ca2+-dependent inactivation (CDI) of L-type Ca2+ channels was developed. The model is based on the hypothesis that postulates the existence of four short-lived modes with lifetimes of a few hundreds of milliseconds. Our findings suggest that the transitions between the modes is primarily determined by the binding of Ca2+ to two intracellular allosteric sites located in different motifs of the CI region, which have greatly differing binding rates for Ca2+ (different k(on)). The slow-binding site is controlled by local Ca2+ near a single open channel that is consistent with the "domain" CDI model, and Ca2+ binding to the fast-binding site(s) depends on Ca2+ arising from distant sources that is consistent with the "shell" CDI model. The model helps to explain numerous experimental findings that are poorly understood so far.
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Affiliation(s)
- Nick I Markevich
- Institute of Theoretical and Experimental Biophysics, Russian Academy of Sciences, Pushchino, Moscow 142290, Russia.
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Ashihara T, Trayanova NA. Cell and tissue responses to electric shocks. Europace 2005; 7 Suppl 2:155-65. [PMID: 16102513 DOI: 10.1016/j.eupc.2005.03.020] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2004] [Revised: 03/01/2005] [Accepted: 03/18/2005] [Indexed: 11/19/2022] Open
Abstract
AIM Existing models of myocardial membrane kinetics have not been able to reproduce the experimentally-observed negative bias in the asymmetry of transmembrane potential changes (DeltaV(m)) induced by strong electric shocks. The goals of this study are (1) to demonstrate that this negative bias could be reproduced by the addition, to the membrane model, of electroporation and an outward current, I(a), part of the K(+) flow through the L-type Ca(2+)-channel, and (2) to determine how such modifications in the membrane model affect shock-induced break excitation in a 2D preparation. METHODS AND RESULTS We conducted simulations of shocks in bidomain fibres and sheets with membrane dynamics represented by the Luo-Rudy dynamic model (LRd'2000), to which electroporation (LRd + EP model) and the outward current, I(a), activated upon strong shock-induced depolarization (aLRd model) was added. Assuming I(a) is a part of K(+) flow through the L-type Ca(2+)-channel enabled us to reproduce both the experimentally observed rectangularly-shaped positive DeltaV(m) and the value of near 2 of the negative-to-positive DeltaV(m) ratio. In the sheet, I(a) not only contributed to the negative bias in DeltaV(m) asymmetry at sites polarized by physical and virtual electrodes, but also restricted positive DeltaV(m). Electroporation, in its turn, was responsible for the decrease in cathode-break excitation threshold in the aLRd sheet, compared with the other two cases, as well as for the occurrence of the excitation after the shock-end rather than during the shock. CONCLUSIONS The incorporation of electroporation and I(a) in a membrane model ensures match between simulation results and experimental data. The use of the aLRd model results in a lower threshold for shock-induced break excitation.
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Affiliation(s)
- Takashi Ashihara
- Department of Biomedical Engineering, Tulane University, Boggs Center, New Orleans, LA 70118, USA
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Spencer CI, Sham JSK. Mechanisms underlying the effects of the pyrethroid tefluthrin on action potential duration in isolated rat ventricular myocytes. J Pharmacol Exp Ther 2005; 315:16-23. [PMID: 15980056 DOI: 10.1124/jpet.105.084822] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Due to increased global use, acute exposures to pyrethroid insecticides in humans are of clinical concern. Pyrethroids have a primary mode of action that involves interference with the inactivation of Na+ currents (I(Na)) in excitable cells, which may include cardiac myocytes. To investigate the possible cardiac toxicity of these agents, we have examined the effects of a type-1 pyrethroid, tefluthrin, on isolated rat ventricular myocytes. Under whole-cell current-clamp, tefluthrin prolonged the mean action potential duration at 90% repolarization (APD90) by 216 +/- 34% in 19 myocytes isolated from 14 hearts. About one-third of this prolongation was apparently due to persistent I(Na), with the balance associated with spontaneous cytosolic Ca2+ waves, and Na+-Ca2+ exchange. In some action potentials, tefluthrin also activated early after-depolarizations (EADs). Using a selected EAD-containing action potential clamp, we observed that EADs could evoke a Cd2+-sensitive membrane current (I(EAD)) that triggered secondary sarcoplasmic reticulum (SR) Ca2+ release. The notion that EADs could stimulate Ca2+ current was strengthened by the persistence of I(EAD) in myocytes exposed to extracellular Li+ and Sr2+ ions, used to minimize Na+-Ca2+ exchange and SR Ca2+ release, respectively. Tefluthrin inhibited I(EAD) by approximately 10%. Together, our results support an arrhythmogenic model whereby tefluthrin exposure stimulated Na+ influx, provoking cellular Ca2+ overload by reverse Na+-Ca2+ exchange. During Ca2+ waves, forward Na+-Ca2+ exchange prolonged the action potential markedly and kindled EADs by permitting the reactivation of Ca2+ current. Similar mechanisms may be involved in pyrethroid toxicity in vivo, and also in type 3 long QT syndrome, wherein Na+ channel mutations prolong I(Na).
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Affiliation(s)
- C Ian Spencer
- Division of Pulmonary and Critical Care Medicine, Johns Hopkins Medical Institutions, Baltimore, Maryland, USA.
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Ashihara T, Trayanova NA. Asymmetry in membrane responses to electric shocks: insights from bidomain simulations. Biophys J 2005; 87:2271-82. [PMID: 15454429 PMCID: PMC1304652 DOI: 10.1529/biophysj.104.043091] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Models of myocardial membrane dynamics have not been able to reproduce the experimentally observed negative bias in the asymmetry of transmembrane potential changes (DeltaVm) induced by strong electric shocks delivered during the action potential plateau. The goal of this study is to determine what membrane model modifications can bridge this gap between simulation and experiment. We conducted simulations of shocks in bidomain fibers and sheets with membrane dynamics represented by the LRd'2000 model. We found that in the fiber, the negative bias in DeltaVm asymmetry could not be reproduced by addition of electroporation only, but by further addition of hypothetical outward current, Ia, activated upon strong shock-induced depolarization. Furthermore, the experimentally observed rectangularly shaped positive DeltaVm, negative-to-positive DeltaVm ratio (asymmetry ratio) = approximately 2, electroporation occurring at the anode only, and the increase in positive DeltaVm caused by L-type Ca2+-channel blockade were reproduced in the strand only if Ia was assumed to be a part of K+ flow through the L-type Ca2+-channel. In the sheet, Ia not only contributed to the negative bias in DeltaVm asymmetry at sites polarized by physical and virtual electrodes, but also restricted positive DeltaVm. Inclusion of Ia and electroporation is thus the bridge between experiment and simulation.
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Affiliation(s)
- Takashi Ashihara
- Department of Biomedical Engineering, Tulane University, New Orleans, Louisiana 70118, USA.
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Brette F, Leroy J, Le Guennec JY, Sallé L. Ca2+ currents in cardiac myocytes: Old story, new insights. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2005; 91:1-82. [PMID: 16503439 DOI: 10.1016/j.pbiomolbio.2005.01.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Calcium is a ubiquitous second messenger which plays key roles in numerous physiological functions. In cardiac myocytes, Ca2+ crosses the plasma membrane via specialized voltage-gated Ca2+ channels which have two main functions: (i) carrying depolarizing current by allowing positively charged Ca2+ ions to move into the cell; (ii) triggering Ca2+ release from the sarcoplasmic reticulum. Recently, it has been suggested than Ca2+ channels also participate in excitation-transcription coupling. The purpose of this review is to discuss the physiological roles of Ca2+ currents in cardiac myocytes. Next, we describe local regulation of Ca2+ channels by cyclic nucleotides. We also provide an overview of recent studies investigating the structure-function relationship of Ca2+ channels in cardiac myocytes using heterologous system expression and transgenic mice, with descriptions of the recently discovered Ca2+ channels alpha(1D) and alpha(1E). We finally discuss the potential involvement of Ca2+ currents in cardiac pathologies, such as diseases with autoimmune components, and cardiac remodeling.
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Affiliation(s)
- Fabien Brette
- School of Biomedical Sciences, University of Leeds, Worsley Building Leeds, LS2 9NQ, UK.
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Wray S, Ravens U, Verkhratsky A, Eisner D. Two centuries of excitation-contraction coupling. Cell Calcium 2004; 35:485-9. [PMID: 15110138 DOI: 10.1016/j.ceca.2004.01.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2003] [Accepted: 01/12/2004] [Indexed: 11/25/2022]
Affiliation(s)
- Susan Wray
- Physiological Laboratory, Liverpool University, Crown Street, P.O. Box 147, Liverpool L69 3BX, UK
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Rueckschloss U, Isenberg G. Contraction augments L-type Ca2+ currents in adherent guinea-pig cardiomyocytes. J Physiol 2004; 560:403-11. [PMID: 15297568 PMCID: PMC1665268 DOI: 10.1113/jphysiol.2004.062604] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
As integrins are thought to function as mechanoreceptors, we studied whether they could mediate mechanical modulation of the L-type Ca2+ channel current (ICa) in guinea-pig cardiac ventricular myocytes (CVMs). CVMs were voltage clamped with 280 ms pulses from -45 to 0 mV at 0.5 Hz (1.8 mM [Ca2+]o, 22 degrees C). Five minutes after whole-cell access (designated as 0 min) peak ICa was determined from a current-voltage (I-V) curve. Additional recordings were made after 5, 10 and 15 min. At control, ICa was not stable, but ran down during these periods. This run-down of ICa was attenuated by soluble fibronectin (FN) and was changed to an enhancement of ICa when CVMs were attached to FN-coated coverslips. Soluble peptide containing the integrin binding sequence of FN, Arg-Gly-Asp (RGD motif), did not modulate ICa; however, ICa increased in stimulated CVMs attached to RGD peptide-coated coverslips. The effect was not specific to integrins, because attachment to poly-D-lysine-coated coverslips also augmented ICa in stimulated CVMs. Augmentation of ICa by immobilized FN required rhythmical contraction of attached CVMs, because it was attenuated without electrical stimulation and after cell dialysis with the calcium chelator BAPTA. Furthermore, contraction-induced augmentation of ICa in FN-attached CVMs was sensitive to inhibition of protein kinase C (PKC; by Ro-31-8220), inhibition of tyrosine kinase activity (herbimycin A) and cytoskeletal depolymerization (cytochalasin D or colchicine). We attribute augmentation of ICa to the activation of signalling cascades by shear forces that are generated when CVMs contract against attachment; in vivo similar signals may occur when CVMs contract against attachment of integrins to the extracellular matrix.
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Affiliation(s)
- Uwe Rueckschloss
- Department of Physiology, Martin Luther University, 06097 Halle, Germany.
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Isenberg G. A cell physiologist between East and West Germany. Cell Calcium 2004; 35:491-9. [PMID: 15110139 DOI: 10.1016/j.ceca.2004.01.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2003] [Accepted: 01/12/2004] [Indexed: 11/29/2022]
Affiliation(s)
- Gerrit Isenberg
- Department of Physiology, Julius-Bernstein-Insitut für Physiologie, Martin-Luther-University Halle, Halle 06097, Germany.
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28
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Izumi T, Kihara Y, Sarai N, Yoneda T, Iwanaga Y, Inagaki K, Onozawa Y, Takenaka H, Kita T, Noma A. Reinduction of T-type calcium channels by endothelin-1 in failing hearts in vivo and in adult rat ventricular myocytes in vitro. Circulation 2003; 108:2530-5. [PMID: 14581409 DOI: 10.1161/01.cir.0000096484.03318.ab] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND In ventricular myocardium, the T-type Ca2+ current (ICa,T), which is temporarily observed during fetal and neonatal periods, has been shown to reappear in failing/remodeling hearts. However, its pathophysiological regulation has not been elucidated. METHODS AND RESULTS We utilized Dahl salt-sensitive (DS) rats with hypertension at the stage of concentric left ventricular (LV) hypertrophy (11 weeks old, LVH) and at the heart failure stage (16 to 18 weeks old, CHF). Some were treated with bosentan (100 mg/kg per day) during the period from LVH to CHF. In LVH, neither the presence of ICa,T (measured in the freshly isolated LV myocytes) nor an increase in alpha-1G mRNA expression were detected. This condition was associated with increases in tissue angiotensin II (AII) but not with endothelin (ET)-1 peptides. In contrast, in CHF, when the tissue AII remained elevated and ET-1 de novo increased, ICa,T was recorded in most of the cells (-0.87+/-0.18 pA/pF at -30 mV, P<0.01 versus LVH). This was associated with a significant increase in the alpha-1G mRNA level. The chronic bosentan treatment eliminated both the elevation of alpha-1G mRNA level and ICa,T from the cells, whereas it did not affect the cell size and membrane capacitance. In addition, 48-hour exposure to ET-1 but not AII induced ICa,T in normal adult myocytes in culture from Sprague-Dawley rats. CONCLUSIONS ICa,T channels reappear in failing but not in hypertrophied LV cardiomyocytes in a manner depending on the tissue ET-1 activation.
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Affiliation(s)
- Toshiaki Izumi
- Department of Cardiovascular Medicine, Kyoto University Graduate School of Medicine, 54 Shogoin-Kawaharacho, Sakyo-ku, Kyoto 606-8507, Japan
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29
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Cruz SL, Orta-Salazar G, Gauthereau MY, Millan-Perez Peña L, Salinas-Stefanón EM. Inhibition of cardiac sodium currents by toluene exposure. Br J Pharmacol 2003; 140:653-60. [PMID: 14534149 PMCID: PMC1574070 DOI: 10.1038/sj.bjp.0705481] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2003] [Revised: 07/03/2003] [Accepted: 07/24/2003] [Indexed: 11/09/2022] Open
Abstract
Toluene is an industrial solvent widely used as a drug of abuse, which can produce sudden sniffing death due to cardiac arrhythmias. In this paper, we tested the hypothesis that toluene inhibits cardiac sodium channels in Xenopus laevis oocytes transfected with Nav1.5 cDNA and in isolated rat ventricular myocytes. In oocytes, toluene inhibited sodium currents (INa+) in a concentration-dependent manner, with an IC50 of 274 microm (confidence limits: 141-407 microm). The inhibition was complete, voltage-independent, and slowly reversible. Toluene had no effect on: (i). the shape of the I-V curves; (ii). the reversal potential of Na+; and (iii). the steady-state inactivation. The slow recovery time constant from inactivation of INa+ decreased with toluene exposure, while the fast recovery time constant remained unchanged. Block of INa+ by toluene was use- and frequency-dependent. In rat cardiac myocytes, 300 microm toluene inhibited the sodium current (INa+) by 62%; this inhibition was voltage independent. These results suggest that toluene binds to cardiac Na+ channels in the open state and unbinds either when channels move between inactivated states or from an inactivated to a closed state. The use- and frequency-dependent block of INa+ by toluene might be responsible, at least in part, for its arrhythmogenic effect.
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Affiliation(s)
- Silvia L Cruz
- Departamento de Farmacobiología, Cinvestav, I.P.N. Calzada de los Tenorios, # 235, Col. Granjas Coapa, DF 14330, México
| | - Gerardo Orta-Salazar
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Ave. 14 Sur # 6301, C.U. San Manuel, Puebla 72501, México
| | - Marcia Y Gauthereau
- Departamento de Farmacobiología, Cinvestav, I.P.N. Calzada de los Tenorios, # 235, Col. Granjas Coapa, DF 14330, México
| | - Lourdes Millan-Perez Peña
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Ave. 14 Sur # 6301, C.U. San Manuel, Puebla 72501, México
| | - Eduardo M Salinas-Stefanón
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Ave. 14 Sur # 6301, C.U. San Manuel, Puebla 72501, México
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30
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Isenberg G, Borschke B, Rueckschloss U. Ca2+ transients of cardiomyocytes from senescent mice peak late and decay slowly. Cell Calcium 2003; 34:271-80. [PMID: 12887974 DOI: 10.1016/s0143-4160(03)00121-0] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Ventricular myocytes were isolated from either young (2 months, "young myocytes") or senescent (20-26 months, "senescent myocytes") mice. Ca2+ transients were evoked by 40ms voltage-clamp pulses depolarising at 0.4, 1, 2, 4 or 8Hz. At 8Hz, Ca2+ transients from senescent cells peaked later (39ms versus 23ms) to smaller systolic [Ca2+](c) (667nM versus 1110nM) and decayed at slower rate (16s(-1) versus 33s(-1)) to higher end-diastolic [Ca2+](c) (411nM versus 220nM) than those from young myocytes. These differences were less pronounced at lower frequencies of pulsing and could not be explained by differences of the time integral of Ca2+ inward current. Since concentrations of SERCA2a and SERCA2b proteins were similar in young and senescent cells, slow rate of Ca2+ decay and high diastolic [Ca2+]c are explained on the assumption that the usual Ca2+ stimulation of SERCA2 activity is attenuated in senescent cells. The prolonged time-to-peak [Ca2+]c is discussed to result from insufficient SR Ca2+ filling by SERCA2 and, in context with confocal images, from a shift of the SERCA2b distribution to the subsarcolemmal space. The age-related changes of the Ca2+ transients are discussed to cause systolic and diastolic failure if senescent mouse hearts beat at high frequencies.
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MESH Headings
- Actinin/analysis
- Aging/physiology
- Algorithms
- Analysis of Variance
- Animals
- Blotting, Western
- Calcium/analysis
- Calcium/metabolism
- Calcium Channels, L-Type/physiology
- Calcium Signaling/physiology
- Calcium-Transporting ATPases/metabolism
- Data Interpretation, Statistical
- Electric Stimulation
- Image Processing, Computer-Assisted
- Immunohistochemistry
- Indoles/pharmacology
- Kinetics
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Mice
- Mice, Inbred C57BL
- Microscopy, Confocal
- Microscopy, Fluorescence
- Myocytes, Cardiac/cytology
- Myocytes, Cardiac/metabolism
- Myocytes, Cardiac/physiology
- Patch-Clamp Techniques
- Sarcoplasmic Reticulum/physiology
- Sarcoplasmic Reticulum Calcium-Transporting ATPases
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Affiliation(s)
- G Isenberg
- Department of Physiology, Martin-Luther-University Halle, Halle 06097, Germany.
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Kamkin A, Kiseleva I, Isenberg G. Ion selectivity of stretch-activated cation currents in mouse ventricular myocytes. Pflugers Arch 2003; 446:220-31. [PMID: 12739160 DOI: 10.1007/s00424-003-1018-y] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2002] [Accepted: 01/26/2003] [Indexed: 10/22/2022]
Abstract
Stretch-activated non-selective cation currents ( I(SAC)) constitute a mechanism that can induce cardiac arrhythmias. We studied I(SAC) in mouse ventricular myocytes by stretching part of the cell surface between the patch-pipette and a motor-driven glass stylus. In non-clamped cells, local stretch depolarised and induced after-depolarisations and extrasystoles. In voltage-clamped cells (K(+) currents suppressed) I(SAC) activated by local stretch had a nearly linear voltage dependence and reversed polarity between -12 and 0 mV. Conductance G(SAC) increased with the extent of local stretch. I(SAC) was not a Cl(-) current (insensitivity to replacement of Cl(-) by aspartate(-)). I(SAC) was not a Ca(2+)-activated current (insensitivity to 5 mM intracellular BAPTA). G(SAC) was blocked by 5 micro M GdCl(3) or by 75 mM extracellular (e.c.) CaCl(2). Removal of e.c. CaCl(2) increased G(SAC) 2.5-fold, as if G(SAC) were sensitive to Ca(2+) and Gd(3+). Replacement of 150 mM e.c. Na(+) by 150 mM Cs(+), Li(+), tetraethylammonium (TEA(+)) or N-methyl d-glucosamine (NMDG(+)) yielded currents that suggested for the conductance a selectivity G(Cs)> G(Na)> G(Li)> G(TEA)> G(NMDG). I(SAC) was suppressed by cytochalasin D, as if an intact F-actin cytoskeleton were necessary for activation of I(SAC).
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Affiliation(s)
- Andre Kamkin
- Department of Fundamental and Applied Physiology, Russian States Medical University, Ostrovitjanova 1, 117997, Moscow, Russia
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Alseikhan BA, DeMaria CD, Colecraft HM, Yue DT. Engineered calmodulins reveal the unexpected eminence of Ca2+ channel inactivation in controlling heart excitation. Proc Natl Acad Sci U S A 2002; 99:17185-90. [PMID: 12486220 PMCID: PMC139290 DOI: 10.1073/pnas.262372999] [Citation(s) in RCA: 163] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2002] [Indexed: 11/18/2022] Open
Abstract
Engineered calmodulins (CaMs), rendered Ca2+-insensitive by mutations, function as dominant negatives in heterologous systems, and have revealed mechanisms of ion channel modulation by Ca2+/CaM. The use of these CaMs in native mammalian cells now emerges as a strategy to unmask the biology of such Ca2+ feedback. Here, we developed recombinant adenoviruses bearing engineered CaMs to facilitate their expression in adult heart cells, where Ca2+ regulation may be essential for moment-to-moment control of the heartbeat. Engineered CaMs not only eliminated the Ca2+-dependent inactivation of native calcium channels, but exposed an unexpectedly large impact of removing such feedback: the unprecedented (4- to 5-fold) prolongation of action potentials. This striking result recasts the basic paradigm for action-potential control and illustrates the promise of virally delivered engineered CaM to investigate the biology of numerous other CaM-signaling pathways.
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Affiliation(s)
- Badr A Alseikhan
- Calcium Signals Laboratory, Program in Molecular and Cellular Systems Physiology, Departments of Biomedical Engineering and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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Borg JJ, Yuill KH, Hancox JC, Spencer IC, Kozlowski RZ. Inhibitory effects of the antiestrogen agent clomiphene on cardiac sarcolemmal anionic and cationic currents. J Pharmacol Exp Ther 2002; 303:282-92. [PMID: 12235262 DOI: 10.1124/jpet.102.038901] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The aim of this study was to determine the effects of the antiestrogen agent clomiphene on cardiac anionic and cationic sarcolemmal ion channels. Whole-cell recordings were made from rat and guinea pig ventricular myocytes. Clomiphene inhibited the volume-regulated chloride current [I(Cl,vol), activated by cell swelling after hypotonic shock (approximately 145 mOsM)] with an IC(50) value of approximately 9.4 microM. In contrast, at concentrations up to 100 microM, clomiphene failed to inhibit both the chloride current activated by cyclic AMP (I(Cl,cAMP)) and the anionic background current (I(AB)). At 10 microM, clomiphene blocked the voltage-gated fast sodium current and the L-type calcium current (I(Ca,L)) in both species. The voltage-independent fractional block of I(Ca,L) induced by clomiphene (10 microM) was approximately 82%, this concentration also inhibited the inwardly rectifying K(+) current with a fractional current block of approximately 26% at -90 mV. Fractional block of outward current at +70 mV in rat was approximately 25%, implying that delayed rectifying K(+) channels were also affected by clomiphene. We conclude that clomiphene shows selectivity for I(Cl,vol) over I(Cl,cAMP) and I(AB) and therefore represents a useful tool for studying chloride conductances in isolated ventricular myocytes with interfering currents blocked. However, due to its effects on cation conductances it would be of little value in this regard for other types of in vitro or in vivo experiments.
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Affiliation(s)
- John J Borg
- Department of Pharmacology, School of Medical Sciences, University of Bristol, United Kingdom
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Arce H, Lopez A, Guevara MR. Triggered alternans in an ionic model of ischemic cardiac ventricular muscle. CHAOS (WOODBURY, N.Y.) 2002; 12:807-818. [PMID: 12779609 DOI: 10.1063/1.1499275] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
It has been known for several decades that electrical alternans occurs during myocardial ischemia in both clinical and experimental work. There are a few reports showing that this alternans can be triggered into existence by a premature ventricular contraction. Detriggering of alternans by a premature ventricular contraction, as well as pause-induced triggering and detriggering, have also been reported. We conduct a search for triggered alternans in an ionic model of ischemic ventricular muscle in which alternans has been described recently: a one-dimensional cable of length 3 cm, containing a central ischemic zone 1 cm long, with 1 cm segments of normal (i.e., nonischemic) tissue at each end. We use a modified form of the Luo-Rudy [Circ. Res. 68, 1501-1526 (1991)] ionic model to represent the ventricular tissue, modeling the effect of ischemia by raising the external potassium ion concentration ([K(+)](o)) in the central ischemic zone. As [K(+)](o) is increased at a fixed pacing cycle length of 400 ms, there is first a transition from 1:1 rhythm to alternans or 2:2 rhythm, and then a transition from 2:2 rhythm to 2:1 block. There is a range of [K(+)](o) over which there is coexistence of 1:1 and 2:2 rhythms, so that dropping a stimulus from the periodic drive train during 1:1 rhythm can result in the conversion of 1:1 to 2:2 rhythm. Within the bistable range, the reverse transition from 2:2 to 1:1 rhythm can be produced by injection of a well-timed extrastimulus. Using a stimulation protocol involving delivery of pre- and post-mature stimuli, we derive a one-dimensional map that captures the salient features of the results of the cable simulations, i.e., the {1:1-->2:2-->2:1} transitions with {1:1<-->2:2} bistability. This map uses a new index of the global activity in the cable, the normalized voltage integral. Finally, we put forth a simple piecewise linear map that replicates the {1:1<-->2:2} bistability observed in the cable simulations and in the normalized voltage integral map. (c) 2002 American Institute of Physics.
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Affiliation(s)
- Humberto Arce
- Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-542, 04510 Mexico, Distrito Federal, Mexico
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35
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Orta-Salazar G, Bouchard RA, Morales-Salgado F, Salinas-Stefanon EM. Inhibition of cardiac Na+ current by primaquine. Br J Pharmacol 2002; 135:751-63. [PMID: 11834623 PMCID: PMC1573163 DOI: 10.1038/sj.bjp.0704460] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2001] [Revised: 09/19/2001] [Accepted: 10/26/2001] [Indexed: 11/09/2022] Open
Abstract
The electrophysiological effects of the anti-malarial drug primaquine on cardiac Na(+) channels were examined in isolated rat ventricular muscle and myocytes. In isolated ventricular muscle, primaquine produced a dose-dependent and reversible depression of dV/dt during the upstroke of the action potential. In ventricular myocytes, primaquine blocked I(Na)(+) in a dose-dependent manner, with a K(d) of 8.2 microM. Primaquine (i) increased the time to peak current, (ii) depressed the slow time constant of I(Na)(+) inactivation, and (iii) slowed the fast component for recovery of I(Na)(+) from inactivation. Primaquine had no effect on: (i) the shape of the I - V curve, (ii) the reversal potential for Na(+), (iii) the steady-state inactivation and g(Na)(+) curves, (iv) the fast time constant of inactivation of I(Na)(+), and (v) the slow component of recovery from inactivation. Block of I(Na)(+) by primaquine was use-dependent. Data obtained using a post-rest stimulation protocol suggested that there was no closed channel block of Na(+) channels by primaquine. These results suggest that primaquine blocks cardiac Na(+) channels by binding to open channels and unbinding either when channels move between inactivated states or from an inactivated state to a closed state. Cardiotoxicity observed in patients undergoing malaria therapy with aminoquinolines may therefore be due to block of Na(+) channels, with subsequent disturbances of impulse conductance and contractility.
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Affiliation(s)
- Gerardo Orta-Salazar
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur # 6301, C.U. Puebla, México
| | - Ron A Bouchard
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur # 6301, C.U. Puebla, México
| | - Fernando Morales-Salgado
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur # 6301, C.U. Puebla, México
| | - Eduardo M Salinas-Stefanon
- Instituto de Fisiología, Benemérita Universidad Autónoma de Puebla, Av. 14 Sur # 6301, C.U. Puebla, México
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Rueckschloss U, Isenberg G. Cytochalasin D reduces Ca2+ currents via cofilin-activated depolymerization of F-actin in guinea-pig cardiomyocytes. J Physiol 2001; 537:363-70. [PMID: 11731570 PMCID: PMC2278948 DOI: 10.1111/j.1469-7793.2001.00363.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. L-type Ca2+ channel currents (I(Ca)) were measured in guinea-pig ventricular myocytes (22 degrees C, 300 ms steps from -45 to +10 mV). Pulsing at 0.5 Hz reduced I(Ca) within 5 min to 92 +/- 3% (mean +/- S.E.M., n = 14) and within 10 min to 83 +/- 4 % ('run-down' with reference to I(Ca) after a 5 min equilibration period). 2. Bath-applied cytochalasin D (cytD, 10 microM) reduced I(Ca) to 75 +/- 4% within 5 min and to 61 +/- 4% within 10 min ('cytD reduction of I(Ca)') by reduction of maximal Ca2+ conductance (suggested by fits of time course and of current-potential (I-V) curves). 3. Preincubation with phalloidin (bath applied, 100 microM, 5 h) prevented the cytD reduction of I(Ca). Since phalloidin specifically blocks F-actin depolymerization, cytD reduction of I(Ca) is linked to depolymerization of F-actin. 4. CytD did not attenuate the beta-adrenergic stimulation of I(Ca) (30 nM isoproterenol), suggesting that A kinase anchoring proteins are unlikely to mediate the cytD reduction of I(Ca). The cytD reduction of I(Ca) was abolished by extra-/intracellular acidosis (pH(o) 6.9), by cell dialysis of 5 mM BAPTA, or by serine/threonine protein phosphatase inhibitors. 5. Actin-depolymerizing factor (ADF)/cofilin are proteins that bind to actin, mediate a pH-sensitive depolymerization of F-actin, and are activated by dephosphorylation. Western blots from hearts perfused with solutions containing zero or 10 microM cytD indicated that cytD reduces the ratio of phosphorylated to total ADF/cofilin content by 50%. 6. The data support the concept that cytD mediates dephosphorylation and activation of ADF/cofilin, leading to depolymerization of F-actin with a subsequent reduction of I(Ca).
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Affiliation(s)
- U Rueckschloss
- Department of Physiology, Faculty of Medicine, Martin-Luther-University, 06097 Halle, Germany.
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Hobai IA, O'Rourke B. Decreased sarcoplasmic reticulum calcium content is responsible for defective excitation-contraction coupling in canine heart failure. Circulation 2001; 103:1577-84. [PMID: 11257088 DOI: 10.1161/01.cir.103.11.1577] [Citation(s) in RCA: 184] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Altered excitation-contraction (E-C) coupling in canine pacing-induced heart failure involves decreased sarcoplasmic reticulum (SR) Ca uptake and enhanced Na/Ca exchange, which could be expected to decrease SR Ca content (Ca(SR)) and may explain the reduced intracellular Ca (Ca(i)) transient. Studies in other failure models have suggested that the intrinsic coupling between L-type Ca current (I:(Ca,L)) and SR Ca release is reduced without a change in SR Ca load. The present study investigates whether Ca(SR) and/or coupling is altered in midmyocardial myocytes from failing canine hearts (F). METHODS AND RESULTS Myocytes were indo-1-loaded via patch pipette (37 degrees C), and Ca(i) transients were elicited with voltage-clamp steps applied at various frequencies. I(Ca,L) density was not significantly decreased in F, but steady-state Ca(i) transients were reduced to 20% to 40% of normal myocytes (N). Ca(SR), measured by integrating Na/Ca exchange currents during caffeine-induced release, was profoundly decreased in F, to 15% to 25% of N. When Ca(SR) was normalized in F by preloading in 5 mmol/L external Ca before a test pulse at 2 mmol/L Ca, a normal-amplitude Ca(i) transient was elicited. E-C coupling gain was dependent on Ca(SR) but was affected similarly in both groups, indicating that intrinsic coupling is unaltered in F. CONCLUSIONS A decrease in Ca(SR) is sufficient to explain the diminished Ca(i) transients in F, without a change in the effectiveness of coupling. Therefore, therapeutic approaches that increase Ca(SR) may be able to fully correct the Ca handling deficit in heart failure.
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Affiliation(s)
- I A Hobai
- Institute of Molecular Cardiobiology, Division of Cardiology, Department of Medicine, Johns Hopkins University, Baltimore, Md, USA
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38
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Felix SB, Stangl V, Pietsch P, Bramlage P, Staudt A, Bartel S, Krause EG, Borschke JU, Wernecke KD, Isenberg G, Baumann G. Soluble substances released from postischemic reperfused rat hearts reduce calcium transient and contractility by blocking the L-type calcium channel. J Am Coll Cardiol 2001; 37:668-75. [PMID: 11216995 DOI: 10.1016/s0735-1097(00)01132-3] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
OBJECTIVES This study was designed to investigate the effects of cardiodepressant substances released from postischemic myocardial tissue on myocardial calcium-regulating pathways. BACKGROUND We have recently reported that new cardiodepressant substances are released from isolated hearts during reperfusion after myocardial ischemia. METHODS After 10 min of global ischemia, isolated rat hearts were reperfused, and the coronary effluent was collected for 30 s. We tested the effects of the postischemic coronary effluent on cell contraction, Ca2+ transients and Ca2+ currents of isolated rat cardiomyocytes by applying fluorescence microscopy and the whole-cell, voltage-clamp technique. Changes in intracellular phosphorylation mechanisms were studied by measuring tissue concentrations of cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP), as well as activities of cAMP-dependent protein kinase (cAMP-dPK) and protein kinase C (PKC). RESULTS The postischemic coronary effluent, diluted with experimental buffer, caused a concentration-dependent reduction of cell shortening and Ca2+ transient in the field-stimulated isolated cardiomyocytes of rats, as well as a reduction in peak L-type Ca2+ current in voltage-clamped cardiomyocytes. The current reduction resulted from reduced maximal conductance--not from changes in voltage- and time-dependent gating of the L-type Ca2+ channel. The postischemic coronary effluent modified neither the tissue concentrations of cAMP or cGMP nor the activities of cAMP-dPK and PKC. However, the effluent completely eliminated the activation of glycogen phosphorylase after beta-adrenergic stimulation. CONCLUSIONS Negative inotropic substances released from isolated postischemic hearts reduce Ca2+ transient and cell contraction through cAMP-independent and cGMP-independent blockage of L-type Ca2+ channels.
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Affiliation(s)
- S B Felix
- Klinik für Innere Medizin B, Ernst-Moritz-Arndt-Universität Greifswald, Germany.
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Hu K, Mochly-Rosen D, Boutjdir M. Evidence for functional role of epsilonPKC isozyme in the regulation of cardiac Ca(2+) channels. Am J Physiol Heart Circ Physiol 2000; 279:H2658-64. [PMID: 11087218 DOI: 10.1152/ajpheart.2000.279.6.h2658] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Limited information is available regarding the effects of protein kinase C (PKC) isozyme(s) in the regulation of L-type Ca(2+) channels due to lack of isozyme-selective modulators. To dissect the role of individual PKC isozymes in the regulation of cardiac Ca(2+) channels, we used the recently developed novel peptide activator of the epsilonPKC, epsilonV1-7, to assess the role of epsilonPKC in the modulation of L-type Ca(2+) current (I(Ca,L)). Whole cell I(Ca,L) was recorded using patch-clamp technique from rat ventricular myocytes. Intracellular application of epsilonV1-7 (0.1 microM) resulted in a significant inhibition of I(Ca,L) by 27.9 +/- 2.2% (P < 0.01, n = 8) in a voltage-independent manner. The inhibitory effect of epsilonV1-7 on I(Ca,L) was completely prevented by the peptide inhibitor of epsilonPKC, epsilonV1-2 [5.2 +/- 1.7%, not significant (NS), n = 5] but not by the peptide inhibitors of cPKC, alphaC2-4 (31.3 +/- 2.9%, P < 0.01, n = 6) or betaC2-2 plus betaC2-4 (26.1 +/- 2.9%, P < 0.01, n = 5). In addition, the use of a general inhibitor (GF-109203X, 10 microM) of the catalytic activity of PKC also prevented the inhibitory effect of epsilonV1-7 on I(Ca,L) (7.5 +/- 2.1%, NS, n = 6). In conclusion, we show that selective activation of epsilonPKC inhibits the L-type Ca channel in the heart.
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Affiliation(s)
- K Hu
- Molecular and Cellular Cardiology Program, Veterans Affairs New York Harbor Healthcare System, Brooklyn, New York 11209, USA
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Pignier C, Potreau D. Characterization of nifedipine-resistant calcium current in neonatal rat ventricular cardiomyocytes. Am J Physiol Heart Circ Physiol 2000; 279:H2259-68. [PMID: 11045961 DOI: 10.1152/ajpheart.2000.279.5.h2259] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Calcium current was recorded from ventricular cardiomyocytes of rats at various stages of postnatal development using the whole cell patch-clamp technique. In cultured 3-day-old neonatal cells, the current carried by Ca(2+) or Ba(2+) (5 mM) was not completely inhibited by 2 microM nifedipine. A residual current was activated in the same voltage range as the L-type, nifedipine-sensitive Ca(2+) current, but its steady-state inactivation was negatively shifted by 16 mV. This nifedipine-resistant calcium current was not further inhibited by other organic calcium current antagonists such as PN200-110, verapamil, and diltiazem nor by nickel, omega-conotoxin, or tetrodotoxin. It was completely blocked by cadmium and increased by isoproterenol and forskolin. This current was >20% of total calcium current in ventricular myocytes freshly isolated from neonatal rats, and it decreased during postnatal maturation, disappearing at the adult stage. This suggests that this current could be caused by an isoform of the L-type calcium channel expressed in a way that reflects the developmental stage of the rat heart.
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Affiliation(s)
- C Pignier
- Centre National de la Recherche Scientifique, UMR 6558, Laboratoire des Biomembranes et Signalisation Cellulaire, Faculty of Sciences, University of Poitiers, 86022 Poitiers cedex, France
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Hobai IA, Hancox JC, Levi AJ. Inhibition by nickel of the L-type Ca channel in guinea pig ventricular myocytes and effect of internal cAMP. Am J Physiol Heart Circ Physiol 2000; 279:H692-701. [PMID: 10924068 DOI: 10.1152/ajpheart.2000.279.2.h692] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The characteristics of nickel (Ni) block of L-type Ca current (I(Ca, L)) were studied in whole cell patch-clamped guinea pig cardiac myocytes at 37 degrees C in the absence and presence of 100 microM cAMP in the pipette solution. Ni block of peak I(Ca,L) had a dissociation constant (K(d)) of 0.33 +/- 0.03 mM in the absence of cAMP, whereas in the presence of cAMP, the K(d) was 0.53 +/- 0.05 mM (P = 0.006). Ni blocked Ca entry via Ca channels (measured as I(Ca, L) integral over 50 ms) with similar kinetics (K(d) of 0.35 +/- 0.03 mM in cAMP-free solution and 0.30 +/- 0.02 mM in solution with cAMP, P = not significant). Under both conditions, 5 mM Ni produced a maximal block that was complete for the first pulse after application. Ni block of I(Ca,L) was largely use independent. Ni (0. 5 mM) induced a positive shift (4 to 6 mV) in the activation curve of I(Ca,L). The block of I(Ca,L) by 0.5 mM Ni was independent of prepulse membrane potential (over the range of -120 to -40 mV). Ni (0.5 mM) also induced a significant shift in I(Ca,L) inactivation: by 6 mV negative in cAMP-free solution and by 4 mV positive in cells dialyzed with 100 microM cAMP. These data suggest that, in addition to blocking channel conductance by binding to a site in the channel pore, Ni may bind to a second site that influences the voltage-dependent gating of the L-type Ca channel. They also suggest that Ca channel phosphorylation causes a conformational change that alters some effects of Ni. The results may be relevant to excitation-contraction coupling studies, which have employed internal cAMP dialysis, and where Ni has been used to block I(Ca,L) and Ca entry into cardiac cells.
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Affiliation(s)
- I A Hobai
- Cardiovascular Research Laboratories, Bristol Heart Institute, and Department of Physiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
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Arce H, Xu A, Gonzalez H, Guevara MR. Alternans and higher-order rhythms in an ionic model of a sheet of ischemic ventricular muscle. CHAOS (WOODBURY, N.Y.) 2000; 10:411-426. [PMID: 12779397 DOI: 10.1063/1.166508] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Life-threatening arrhythmias such as ventricular tachycardia and fibrillation often occur during acute myocardial ischemia. During the first few minutes following coronary occlusion, there is a gradual rise in the extracellular concentration of potassium ions ([K(+)](0)) within ischemic tissue. This elevation of [K(+)](0) is one of the main causes of the electrophysiological changes produced by ischemia, and has been implicated in inducing arrhythmias. We investigate an ionic model of a 3 cmx3 cm sheet of normal ventricular myocardium containing an ischemic zone, simulated by elevating [K(+)](0) within a centrally-placed 1 cmx1 cm area of the sheet. As [K(+)](0) is gradually raised within the ischemic zone from the normal value of 5.4 mM, conduction first slows within the ischemic zone and then, at higher [K(+)](0), an arc of block develops within that area. The area distal to the arc of block is activated in a delayed fashion by a retrogradely moving wavefront originating from the distal edge of the ischemic zone. With a further increase in [K(+)](0), the point eventually comes where a very small increase in [K(+)](0) (0.01 mM) results in the abrupt transition from a global period-1 rhythm to a global period-2 rhythm in the sheet. In the peripheral part of the ischemic zone and in the normal area surrounding it, there is an alternation of action potential duration, producing a 2:2 response. Within the core of the ischemic zone, there is an alternation between an action potential and a maintained small-amplitude response ( approximately 30 mV in height). With a further increase of [K(+)](0), the maintained small-amplitude response turns into a decrementing subthreshold response, so that there is 2:1 block in the central part of the ischemic zone. A still further increase of [K(+)](0) leads to a transition in the sheet from a global period-2 to a period-4 rhythm, and then to period-6 and period-8 rhythms, and finally to a complete block of propagation within the ischemic core. When the size of the sheet is increased to 4 cmx4 cm (with a 2 cmx2 cm ischemic area), one observes essentially the same sequence of rhythms, except that the period-6 rhythm is not seen. Very similar sequences of rhythms are seen as [K(+)](0) is increased in the central region (1 or 2 cm long) of a thin strand of tissue (3 or 4 cm long) in which propagation is essentially one-dimensional and in which retrograde propagation does not occur. While reentrant rhythms resembling tachycardia and fibrillation were not encountered in the above simulations, well-known precursors to such rhythms (e.g., delayed activation, arcs of block, two-component upstrokes, retrograde activation, nascent spiral tips, alternans) were seen. We outline how additional modifications to the ischemic model might result in the emergence of reentrant rhythms following alternans. (c) 2000 American Institute of Physics.
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Affiliation(s)
- Humberto Arce
- Departamento de Fisica, Facultad de Ciencias, Universidad Nacional Autonoma de Mexico, Apartado Postal 70-542, 04510 Mexico, Distrito Federal, Mexico
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Yu H, Gao J, Wang H, Wymore R, Steinberg S, McKinnon D, Rosen MR, Cohen IS. Effects of the renin-angiotensin system on the current I(to) in epicardial and endocardial ventricular myocytes from the canine heart. Circ Res 2000; 86:1062-8. [PMID: 10827136 DOI: 10.1161/01.res.86.10.1062] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The Ca(2+)-independent portion of transient outward K(+) current (I(to)) exhibits a transmural gradient in ventricle. To investigate control mechanisms for this gradient, we studied canine epicardial and endocardial ventricular myocytes with use of the whole-cell patch-clamp technique. I(to) was larger in amplitude, had a more negative voltage threshold for activation, and had a more negative midpoint of inactivation in epicardium. Recovery from inactivation was >10-fold slower in endocardium. Incubation of epicardial myocytes with angiotensin II for 2 to 52 hours altered I(to) to resemble unincubated endocardium and reduced the amplitude of the phase 1 notch of the action potential. In contrast, incubation of endocardial myocytes with losartan for 2 to 52 hours altered I(to) to resemble unincubated epicardium and induced a phase 1 notch in the action potential. With RNase protection assays, we determined that incubations with angiotensin II or losartan did not alter mRNA levels for either Kv4.3 or Kv1.4; thus, a change in the alpha subunit for I(to) is unlikely to be responsible. To test whether posttranslational modification produced the effects of angiotensin II, we coexpressed Kv4.3 and the angiotensin II type 1a receptor in Xenopus oocytes. Incubation with angiotensin II increased the time constant for recovery from inactivation of the expressed current by 2-fold with an incubation time constant of 3.7 hours. No effect on activation or inactivation voltage dependence was observed. These results demonstrate that the properties of I(to) in endocardium and epicardium are plastic and likely under the tonic-differing influence of the renin-angiotensin system.
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Affiliation(s)
- H Yu
- Department of Physiology and Biophysics, Institute of Molecular Cardiology, State University of New York at Stony Brook 11794-8661, USA
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Wakkach A, Poea S, Chastre E, Gespach C, Lecerf F, De la Porte S, Tzartos S, Coulombe A, Berrih-Aknin S. Establishment of a human thymic myoid cell line. Phenotypic and functional characteristics. THE AMERICAN JOURNAL OF PATHOLOGY 1999; 155:1229-40. [PMID: 10514405 PMCID: PMC1867031 DOI: 10.1016/s0002-9440(10)65225-x] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
The subset of myoid cells is a normal component of the thymic stroma. To characterize these cells, we immortalized stromal cells from human thymus by using a plasmid vector encoding the SV40 T oncogene. Among the eight cell lines obtained, one had myoid characteristics including desmin and troponin antigens. This new line was designated MITC (myoid immortalized thymic cells). These cells expressed both the fetal and adult forms of muscle acetylcholine receptor (AChR) at the mRNA level, as well as the myogenic transcription factor MyoD1. alpha-Subunit AChR protein expression was detected by flow cytometry and the AChR was functional in patch-clamp studies. In addition, AChR expression was down-modulated by myasthenia gravis sera or by monoclonal antibody anti-AChR on MITC line similarly to TE671 rhabdomyosarcoma cells, making the MITC line an interesting tool for AChR antigenic modulation experiments. Finally, the MITC line expressed LFA-3, produced several cytokines able to act on T cells, and protected total thymocytes from spontaneous apoptosis in vitro. These results are compatible with a role of thymic myoid cells in some steps of thymocyte development. Therefore MITC line appears to be a useful tool to investigate the physiological role of thymic myoid cells.
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Affiliation(s)
- Abdel Wakkach
- Hôpital Marie Lannelongue, Le Plessis-Robinsin, France; INSERM U482, †
| | - Sandrine Poea
- Hôpital Marie Lannelongue, Le Plessis-Robinsin, France; INSERM U482, †
| | - Eric Chastre
- Hôpital St-Antoine, Paris, France; CNRS UPR 9040,‡
| | | | - Florence Lecerf
- Hôpital Marie Lannelongue, Le Plessis-Robinsin, France; INSERM U482, †
| | | | | | - Alain Coulombe
- Hôpital Marie Lannelongue, Le Plessis-Robinsin, France; INSERM U482, †
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Martínez ML, Heredia MP, Delgado C. Expression of T-type Ca(2+) channels in ventricular cells from hypertrophied rat hearts. J Mol Cell Cardiol 1999; 31:1617-25. [PMID: 10471346 DOI: 10.1006/jmcc.1999.0998] [Citation(s) in RCA: 129] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
In this study we examined the existence of T-type Ca(2+) current in ventricular myocytes isolated from rats with pressure-overload hypertrophy. The whole-cell clamp technique was used to record Ca(2+) currents in enzymatically dissociated ventricular cells. T- and L-type Ca(2+) currents were separated by applying voltage steps to different test potentials from a holding potential of -80 mV and -50 mV. T-type Ca(2+) current was defined as the difference between the currents from the two holding potentials. Ventricular myocytes from sham-operated rats showed only L-type Ca(2+) current (maximal density -13.9+/-1.3 pA/pF n=17), whereas ventricular myocytes isolated from rats with aortic stenosis showed both L- and T-type Ca(2+) currents. The average values of T- and L-type Ca(2+) current density were -4.8+/-0.4 pA/pF and -12.4+/-0.9 pA/pF (n=32), respectively. T-type Ca(2+) current was distinguished from L-type Ca(2+) current by its voltage dependence, its kinetics and by its strong blockade by nickel 50 microM. In conclusion, we have demonstrated that hypertrophied ventricular rat cells express T-type Ca(2+) channels and this finding strongly supports a role for this channel in regulating growth processes in cardiac tissue.
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Affiliation(s)
- M L Martínez
- Institute of Pharmacology and Toxicology (CSIC-UCM), Universidad Complutense, Madrid, Spain
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Hirota K, Masuda A, Ito Y. Volatile anesthetics reduce calcium current in parasympathetic neurons from bullfrog hearts. Anesth Analg 1999; 89:225-9. [PMID: 10389809 DOI: 10.1097/00000539-199907000-00041] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
UNLABELLED Although the autonomic nervous system regulates cardiac function, the cellular mechanism(s) of general anesthetics on the activities of parasympathetic neurons have not been directly assessed. We therefore studied the volatile anesthetic actions on the Ca2+ current of parasympathetic neurons isolated from bullfrog hearts. Neurons were enzymatically isolated from the interatrial septum of bullfrog heart and maintained in a short-term tissue culture. The Ca2+ current was recorded with a whole-cell voltage-clamp method under a Na+, K+ -free condition. Isoflurane (2.5 vol%) and sevoflurane (5.0 vol%) reduced the peak amplitude of the Ca2+ current (to 79% and 72% of control, respectively) without changing the reversal potential. The curve-fit analysis of the inactivation kinetics revealed that isoflurane and sevoflurane accelerated the inactivation of the current and that isoflurane shifted the midpoint of the steady-state inactivation curve of the Ca2+ current toward negative by 13.6 mV. The results indicate that volatile anesthetics reduce the Ca2+ current of parasympathetic neurons and modify the inactivation kinetics. IMPLICATIONS The anesthetic reduction of the Ca2+ current of parasympathetic neurons can induce a decrease of acetylcholine release from the post-ganglionic endings. These findings, in part, account for the anesthetic attenuation of the vagal efferent activities observed in humans and experimental animals.
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Affiliation(s)
- K Hirota
- Department of Anesthesiology, Toyama Medical and Pharmaceutical University School of Medicine, Sugitani, Japan
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Hirota K, Masuda A, Ito Y. Volatile Anesthetics Reduce Calcium Current in Parasympathetic Neurons from Bullfrog Hearts. Anesth Analg 1999. [DOI: 10.1213/00000539-199907000-00041] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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48
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Yu H, McKinnon D, Dixon JE, Gao J, Wymore R, Cohen IS, Danilo P, Shvilkin A, Anyukhovsky EP, Sosunov EA, Hara M, Rosen MR. Transient outward current, Ito1, is altered in cardiac memory. Circulation 1999; 99:1898-905. [PMID: 10199889 DOI: 10.1161/01.cir.99.14.1898] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Cardiac memory refers to an altered T-wave morphology induced by ventricular pacing or arrhythmias that persist for variable intervals after resumption of sinus rhythm. METHODS AND RESULTS We induced long-term cardiac memory (LTM) in conscious dogs by pacing the ventricles at 120 bpm for 3 weeks. ECGs were recorded daily for 1 hour, during which time pacing was discontinued. At terminal study, the heart was removed and the electrophysiology of left ventricular epicardial myocytes was investigated. Control (C) and LTM ECG did not differ, except for T-wave amplitude, which decreased from 0.12+/-0.18 to -0.34+/-0.21 mV (+/-SEM, P<0.05), and T-wave vector, which shifted from -37+/-12 degrees to -143+/-4 degrees (P<0.05). Epicardial action potentials revealed loss of the notch and lengthening of duration at 20 days (both P<0.05). Calcium-insensitive transient outward current (Ito) was investigated by whole-cell patch clamp. No difference in capacitance was seen in C and LTM myocytes. Ito activated on membrane depolarization to -25+/-1 mV in C and -7+/-1 mV (P<0.05) in LTM myocytes, indicating a positive voltage shift of activation. Ito density was reduced in LTM myocytes, and a decreased mRNA level for Kv4.3 was observed. Recovery of Ito from inactivation was significantly prolonged: it was 531+/-80 ms (n=10) in LTM and 27+/-6 ms (n=9) in C (P<0.05) at -65 mV. CONCLUSIONS Ito changes are associated with and can provide at least a partial explanation for action-potential and T-wave changes occurring with LTM.
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Affiliation(s)
- H Yu
- Departments of Physiology, State University of New York at Stony Brook, Stony Brook, NY, USA
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Linz KW, Meyer R. Control of L-type calcium current during the action potential of guinea-pig ventricular myocytes. J Physiol 1998; 513 ( Pt 2):425-42. [PMID: 9806993 PMCID: PMC2231304 DOI: 10.1111/j.1469-7793.1998.425bb.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. During an action potential the L-type Ca2+ current (ICa,L) activates rapidly, then partially declines leading to a sustained inward current during the plateau phase. The reason for the sustained part of ICa,L has been investigated here. 2. In the present study the mechanisms controlling the ICa,L during an action potential were investigated quantitatively in isolated guinea-pig ventricular myocytes by whole-cell patch clamp. To measure the actual time courses of ICa,L and the corresponding L-type channel inactivation (fAP) during an action potential, action potential-clamp protocols combined with square pulses were applied. 3. Within the first 10 ms of the action potential the ICa,L rapidly inactivated by about 50 %; during the plateau phase inactivation proceeded to 95 %. Later, during repolarization, the L-type channels recovered up to 25 %. 4. The voltage-dependent component of inactivation during an action potential was determined from measurements of L-type current carried by monovalent cations. This component of inactivation proceeded rather slowly and contributed only a little to fAP. ICa,L during an action potential is thus mainly controlled by Ca2+-dependent inactivation. 5. In order to investigate the source of the Ca2+ controlling fAP, internal Ca2+ homeostasis was manipulated by the use of Ca2+ buffers (EGTA, BAPTA), by blocking Na+-Ca2+ exchange, or by blocking Ca2+ release from the sarcoplasmic reticulum (SR). Internal BAPTA markedly reduced the L-type channel inactivation during the entire action potential, whereas EGTA affected fAP only during the middle and late plateau phases. Inhibition of Na+-Ca2+ exchange markedly increased inactivation of L-type channels. Although blocking SR Ca2+ release decreased the fura-2-measured cytoplasmic Ca2+ concentration ([Ca2+]i) transient by about 90 %, it reduced L-type channel inactivation only during the initial 50 ms of the action potential. Thus, it is Ca2+ entering the cell through the L-type channels that controls the inactivation process for the majority of the action potential. Nevertheless, SR Ca2+-release contributes 40-50 % to L-type channel inactivation during the initial period of the action potential. However, the maximum extent of inactivation reached during the plateau is independent of Ca2+ released from the SR. 6. For the first time, the actual time course of L-type channel inactivation has been directly determined during an action potential under various defined [Ca2+]i conditions. Thereby, the relative contribution to ICa,L inactivation of voltage, Ca2+ entering through L-type channels, and Ca2+ being released from the SR could be directly demonstrated.
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Affiliation(s)
- K W Linz
- Physiological Institute, University of Bonn, Wilhelmstrasse 31, D-53111 Bonn, Germany
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Shepherd N, McDonough HB. Ionic diffusion in transverse tubules of cardiac ventricular myocytes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 275:H852-60. [PMID: 9724289 DOI: 10.1152/ajpheart.1998.275.3.h852] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have estimated the rate of diffusion of calcium ions in the transverse tubules of isolated cardiocytes by recording changes in peak calcium current (ICa) caused by rapid changes of the extracellular calcium concentration ([Ca]o) at various intervals just preceding activation of ICa. Isolated ventricular cells of guinea pig heart and atrial cells from rabbit heart were voltage-clamped (whole cell patch), superfused at a high flow rate, and stimulated continuously with depolarizing pulses (0.5 Hz, 200- or 20-ms pulses from a holding potential of -45 or -75 mV to 0 mV). In ventricular cells, the change in peak ICa following a sudden change of [Ca]o increased rapidly as the delay between the solution change and depolarization was increased, up to a delay of approximately 75 ms [time constant (tau) approximately 20 ms, 30-40% of total current change), and then increased more slowly (tau approximately 200 ms, 60-70% of total current change); 400-500 ms were needed to achieve 90% of the total current increase. In atrial cells, a clear separation into two phases was not possible and 90% of the current change occurred within 85 ms. The slow phase of current change, which was unique to the ventricular cells, presumably reflects the slow equilibration of ions between the bulk perfusate and the lumina of the transverse tubules. If the lengths of the transverse tubules were equal to the cell thickness, the slow rate of change of current would be consistent with an apparent diffusion coefficient for calcium ions of 0.95 x 10(-6) cm2/s, considerably smaller than the value in bulk solution (7.9 x 10(-6) cm2/s). Most likely, this discrepancy is due to a high degree of tortuosity in the transverse tubular system in guinea pig ventricular cells or possibly to ion binding sites within the tubular membranes and glycocalyx.
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Affiliation(s)
- N Shepherd
- Veterans Affairs Medical Center, Durham, North Carolina 27705, USA
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