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Agrawal A, Wang K, Polonchuk L, Cooper J, Hendrix M, Gavaghan DJ, Mirams GR, Clerx M. Models of the cardiac L-type calcium current: A quantitative review. WIREs Mech Dis 2023; 15:e1581. [PMID: 36028219 PMCID: PMC10078428 DOI: 10.1002/wsbm.1581] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2022] [Revised: 06/16/2022] [Accepted: 07/19/2022] [Indexed: 01/31/2023]
Abstract
The L-type calcium current (I CaL ) plays a critical role in cardiac electrophysiology, and models ofI CaL are vital tools to predict arrhythmogenicity of drugs and mutations. Five decades of measuring and modelingI CaL have resulted in several competing theories (encoded in mathematical equations). However, the introduction of new models has not typically been accompanied by a data-driven critical comparison with previous work, so that it is unclear which model is best suited for any particular application. In this review, we describe and compare 73 published mammalianI CaL models and use simulated experiments to show that there is a large variability in their predictions, which is not substantially diminished when grouping by species or other categories. We provide model code for 60 models, list major data sources, and discuss experimental and modeling work that will be required to reduce this huge list of competing theories and ultimately develop a community consensus model ofI CaL . This article is categorized under: Cardiovascular Diseases > Computational Models Cardiovascular Diseases > Molecular and Cellular Physiology.
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Affiliation(s)
- Aditi Agrawal
- Computational Biology & Health Informatics, Department of Computer ScienceUniversity of OxfordOxfordUK
| | - Ken Wang
- Pharma Research and Early Development, Innovation Center BaselF. Hoffmann‐La Roche Ltd.BaselSwitzerland
| | - Liudmila Polonchuk
- Pharma Research and Early Development, Innovation Center BaselF. Hoffmann‐La Roche Ltd.BaselSwitzerland
| | - Jonathan Cooper
- Centre for Advanced Research ComputingUniversity College LondonLondonUK
| | - Maurice Hendrix
- Centre for Mathematical Medicine & Biology, School of Mathematical SciencesUniversity of NottinghamNottinghamUK
- Digital Research Service, Information SciencesUniversity of NottinghamNottinghamUK
| | - David J. Gavaghan
- Computational Biology & Health Informatics, Department of Computer ScienceUniversity of OxfordOxfordUK
| | - Gary R. Mirams
- Centre for Mathematical Medicine & Biology, School of Mathematical SciencesUniversity of NottinghamNottinghamUK
| | - Michael Clerx
- Centre for Mathematical Medicine & Biology, School of Mathematical SciencesUniversity of NottinghamNottinghamUK
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2
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Gonano LA, Mattiazzi A. Targeting late ICaL to close the window to ventricular arrhythmias. J Gen Physiol 2021; 153:212726. [PMID: 34699586 PMCID: PMC8552155 DOI: 10.1085/jgp.202113009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Affiliation(s)
- Luis A Gonano
- Centro de Investigaciones Cardiovasculares Horacio Cingolani, CONICET La Plata, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
| | - Alicia Mattiazzi
- Centro de Investigaciones Cardiovasculares Horacio Cingolani, CONICET La Plata, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, La Plata, Argentina
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3
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Staali L, Colin DA. Bi-component HlgC/HlgB and HlgA/HlgB γ-hemolysins from S. aureus: Modulation of Ca 2+ channels activity through a differential mechanism. Toxicon 2021; 201:74-85. [PMID: 34411591 DOI: 10.1016/j.toxicon.2021.08.007] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2021] [Revised: 07/21/2021] [Accepted: 08/10/2021] [Indexed: 10/20/2022]
Abstract
Staphylococcal bi-component leukotoxins known as *pore-forming toxins* induce upon a specific binding to membrane receptors, two independent cellular events in human neutrophils. First, they provoke the opening of pre-existing specific ionic channels including Ca2+ channels. Then, they form membrane pores specific to monovalent cations leading to immune cells death. Among these leukotoxins, HlgC/HlgB and HlgA/HlgB γ-hemolysins do act in synergy to induce the opening of different types of Ca2+ channels in the absence as in the presence of extracellular Ca2+. Here, we investigate the mechanism underlying the modulation of Ca2+-independent Ca2+ channels in response to both active leukotoxins in human neutrophils. In the absence of extracellular Ca2+, the Mn2+ has been used as a Ca2+ surrogate to determine the activity of Ca2+-independent Ca2+ channels. Our findings provide new insights about different mechanisms involved in the staphylococcal γ-hemolysins activity to regulate three different types of Ca2+-independent Ca2+ channels. We conclude that (i) HlgC/HlgB stimulates the opening of La3+-sensitive Ca2+ channels, through a cholera toxin-sensitive G protein, (ii) HlgA/HlgB stimulates the opening of Ca2+ channels not sensitive to La3+, through a G protein-independent process, and (iii) unlike HlgA/HlgB, HlgC/HlgB toxins prevent the opening of a new type of Ca2+ channels by phosphorylation/de-phosphorylation-dependent mechanisms.
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Affiliation(s)
- Leila Staali
- Bacteriology Institute of Medical Faculty, Louis Pasteur University, 3 rue Koeberlé, F-67000, Strasbourg, France.
| | - Didier A Colin
- Bacteriology Institute of Medical Faculty, Louis Pasteur University, 3 rue Koeberlé, F-67000, Strasbourg, France
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Ahern BM, Sebastian A, Levitan BM, Goh J, Andres DA, Satin J. L-type channel inactivation balances the increased peak calcium current due to absence of Rad in cardiomyocytes. J Gen Physiol 2021; 153:212476. [PMID: 34269819 PMCID: PMC8289690 DOI: 10.1085/jgp.202012854] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2020] [Accepted: 06/25/2021] [Indexed: 12/15/2022] Open
Abstract
The L-type Ca2+ channel (LTCC) provides trigger calcium to initiate cardiac contraction in a graded fashion that is regulated by L-type calcium current (ICa,L) amplitude and kinetics. Inactivation of LTCC is controlled to fine-tune calcium flux and is governed by voltage-dependent inactivation (VDI) and calcium-dependent inactivation (CDI). Rad is a monomeric G protein that regulates ICa,L and has recently been shown to be critical to β-adrenergic receptor (β-AR) modulation of ICa,L. Our previous work showed that cardiomyocyte-specific Rad knockout (cRadKO) resulted in elevated systolic function, underpinned by an increase in peak ICa,L, but without pathological remodeling. Here, we sought to test whether Rad-depleted LTCC contributes to the fight-or-flight response independently of β-AR function, resulting in ICa,L kinetic modifications to homeostatically balance cardiomyocyte function. We recorded whole-cell ICa,L from ventricular cardiomyocytes from inducible cRadKO and control (CTRL) mice. The kinetics of ICa,L stimulated with isoproterenol in CTRL cardiomyocytes were indistinguishable from those of unstimulated cRadKO cardiomyocytes. CDI and VDI are both enhanced in cRadKO cardiomyocytes without differences in action potential duration or QT interval. To confirm that Rad loss modulates LTCC independently of β-AR stimulation, we crossed a β1,β2-AR double-knockout mouse with cRadKO, resulting in a Rad-inducible triple-knockout mouse. Deletion of Rad in cardiomyocytes that do not express β1,β2-AR still yielded modulated ICa,L and elevated basal heart function. Thus, in the absence of Rad, increased Ca2+ influx is homeostatically balanced by accelerated CDI and VDI. Our results indicate that the absence of Rad can modulate the LTCC without contribution of β1,β2-AR signaling and that Rad deletion supersedes β-AR signaling to the LTCC to enhance in vivo heart function.
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Affiliation(s)
- Brooke M Ahern
- Department of Physiology, University of Kentucky, Lexington, KY
| | | | - Bryana M Levitan
- Department of Physiology, University of Kentucky, Lexington, KY.,Gill Heart and Vascular Institute, University of Kentucky, Lexington, KY
| | - Jensen Goh
- Department of Physiology, University of Kentucky, Lexington, KY
| | - Douglas A Andres
- Department of Molecular and Cellular Biochemistry, University of Kentucky, Lexington, KY
| | - Jonathan Satin
- Department of Physiology, University of Kentucky, Lexington, KY
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5
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Bazmi M, Escobar AL. How Ca 2+ influx is attenuated in the heart during a "fight or flight" response. J Gen Physiol 2019; 151:722-726. [PMID: 31004065 PMCID: PMC6572000 DOI: 10.1085/jgp.201912338] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Bazmi and Escobar highlight a recent investigation of the mechanisms that regulate Ca2+ influx during sympathetic stimulation.
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Affiliation(s)
- Maedeh Bazmi
- Quantitative Systems Biology Program, School of Natural Sciences, University of California, Merced, Merced, CA
| | - Ariel L Escobar
- Department of Bioengineering, School of Engineering, University of California, Merced, Merced, CA
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Morales D, Hermosilla T, Varela D. Calcium-dependent inactivation controls cardiac L-type Ca 2+ currents under β-adrenergic stimulation. J Gen Physiol 2019; 151:786-797. [PMID: 30814137 PMCID: PMC6571991 DOI: 10.1085/jgp.201812236] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Accepted: 02/10/2019] [Indexed: 12/18/2022] Open
Abstract
During a cardiac action potential, the activity of L-type Ca2+ channels (LTCCs) is modulated by voltage- and calcium-dependent inactivation processes. Morales et al. show that, in the context of β-adrenergic stimulation, calcium-dependent inactivation directs the regulation of LTCC activity, limiting calcium influx during the action potential. The activity of L-type calcium channels is associated with the duration of the plateau phase of the cardiac action potential (AP) and it is controlled by voltage- and calcium-dependent inactivation (VDI and CDI, respectively). During β-adrenergic stimulation, an increase in the L-type current and parallel changes in VDI and CDI are observed during square pulses stimulation; however, how these modifications impact calcium currents during an AP remains controversial. Here, we examined the role of both inactivation processes on the L-type calcium current activity in newborn rat cardiomyocytes in control conditions and after stimulation with the β-adrenergic agonist isoproterenol. Our approach combines a self-AP clamp (sAP-Clamp) with the independent inhibition of VDI or CDI (by overexpressing CaVβ2a or calmodulin mutants, respectively) to directly record the L-type calcium current during the cardiac AP. We find that at room temperature (20–23°C) and in the absence of β-adrenergic stimulation, the L-type current recapitulates the AP kinetics. Furthermore, under our experimental setting, the activity of the sodium–calcium exchanger (NCX) does not affect the shape of the AP. We find that hindering either VDI or CDI prolongs the L-type current and the AP in parallel, suggesting that both inactivation processes modulate the L-type current during the AP. In the presence of isoproterenol, wild-type and VDI-inhibited cardiomyocytes display mismatched L-type calcium current with respect to their AP. In contrast, CDI-impaired cells maintain L-type current with kinetics similar to its AP, demonstrating that calcium-dependent inactivation governs L-type current kinetics during β-adrenergic stimulation.
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Affiliation(s)
- Danna Morales
- Millennium Nucleus of Ion Channels-Associated Diseases (MiNICAD), Universidad de Chile, Santiago, Chile
| | - Tamara Hermosilla
- Programa de Fisiología y Biofísica, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
| | - Diego Varela
- Millennium Nucleus of Ion Channels-Associated Diseases (MiNICAD), Universidad de Chile, Santiago, Chile .,Programa de Fisiología y Biofísica, Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Santiago, Chile
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7
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Lei M, Xu J, Gao Q, Minobe E, Kameyama M, Hao L. PKA phosphorylation of Cav1.2 channel modulates the interaction of calmodulin with the C terminal tail of the channel. J Pharmacol Sci 2018; 137:187-194. [PMID: 30042022 DOI: 10.1016/j.jphs.2018.05.010] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 05/18/2018] [Accepted: 05/28/2018] [Indexed: 11/16/2022] Open
Abstract
Activity of cardiac Cav1.2 channels is enhanced by cyclic AMP-PKA signaling. In this study, we studied the effects of PKA phosphorylation on the binding of calmodulin to the fragment peptide of the proximal C-terminal tail of α1C subunit (CT1, a.a. 1509-1789 of guinea-pig). In the pull-down assay, in vitro PKA phosphorylation significantly decreased calmodulin binding to CT1 (61%) at high [Ca2+]. The phosphoresistant (CT1SA) and phosphomimetic (CT1SD) CT1 mutants, in which three PKA sites (Ser1574, 1626, 1699) were mutated to Ala and Asp, respectively, bound with calmodulin with 99% and 65% amount, respectively, compared to that of wild-type CT1. In contrast, at low [Ca2+], calmodulin-binding to CT1SD was higher (33-35%) than that to CT1SA. The distal C-terminal region of α1C (CT3, a.a. 1942-2169) is known to interact with CT1 and inhibit channel activity. CT3 bound to CT1SD was also significantly less than that to CT1SA. In inside-out patch, PKA catalytic subunit (PKAc) facilitated Ca2+ channel activity at both high and low Ca2+ condition. Altogether, these results support the hypothesis that PKA phosphorylation may enhance channel activity and attenuate the Ca2+-dependent inactivation, at least partially, by modulating calmodulin-CT1 interaction both directly and indirectly via CT3-CT1 interaction.
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Affiliation(s)
- Ming Lei
- Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, 110122, China; Department of Physiology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima, 890-8544, Japan
| | - Jianjun Xu
- Department of Physiology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima, 890-8544, Japan.
| | - Qinghua Gao
- Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, 110122, China; Department of Physiology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima, 890-8544, Japan
| | - Etsuko Minobe
- Department of Physiology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima, 890-8544, Japan
| | - Masaki Kameyama
- Department of Physiology, Graduate School of Medical and Dental Sciences, Kagoshima University, 8-35-1 Sakuragaoka, Kagoshima, 890-8544, Japan
| | - Liying Hao
- Department of Pharmaceutical Toxicology, School of Pharmacy, China Medical University, Shenyang, 110122, China.
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8
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Zhang Q, Chen J, Qin Y, Wang J, Zhou L. Mutations in voltage-gated L-type calcium channel: implications in cardiac arrhythmia. Channels (Austin) 2018; 12:201-218. [PMID: 30027834 PMCID: PMC6104696 DOI: 10.1080/19336950.2018.1499368] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2018] [Revised: 06/08/2018] [Accepted: 07/05/2018] [Indexed: 02/06/2023] Open
Abstract
The voltage-gated L-type calcium channel (LTCC) is essential for multiple cellular processes. In the heart, calcium influx through LTCC plays an important role in cardiac electrical excitation. Mutations in LTCC genes, including CACNA1C, CACNA1D, CACNB2 and CACNA2D, will induce the dysfunctions of calcium channels, which result in the abnormal excitations of cardiomyocytes, and finally lead to cardiac arrhythmias. Nevertheless, the newly found mutations in LTCC and their functions are continuously being elucidated. This review summarizes recent findings on the mutations of LTCC, which are associated with long QT syndromes, Timothy syndromes, Brugada syndromes, short QT syndromes, and some other cardiac arrhythmias. Indeed, we describe the gain/loss-of-functions of these mutations in LTCC, which can give an explanation for the phenotypes of cardiac arrhythmias. Moreover, we present several challenges in the field at present, and propose some diagnostic or therapeutic approaches to these mutation-associated cardiac diseases in the future.
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Affiliation(s)
- Qing Zhang
- Department of Cardiology, the Second Affiliated Hospital of Nantong University, Nantong First Hospital, Nantong, Jiangsu, China
- Department of Cardiology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
| | - Junjie Chen
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Yao Qin
- Department of Cardiology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
| | - Juejin Wang
- Department of Physiology, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Lei Zhou
- Department of Cardiology, the First Affiliated Hospital of Nanjing Medical University, Nanjing, Jiangsu, China
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9
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Identification of Na+/K+-ATPase inhibition-independent proarrhythmic ionic mechanisms of cardiac glycosides. Sci Rep 2017; 7:2465. [PMID: 28550304 PMCID: PMC5446409 DOI: 10.1038/s41598-017-02496-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 04/13/2017] [Indexed: 12/17/2022] Open
Abstract
The current study explored the Na+/K+-ATPase (NKA) inhibition-independent proarrhythmic mechanisms of cardiac glycosides (CGs) which are well-known NKA inhibitors. With the cytosolic Ca2+ chelated by EGTA and BAPTA or extracellular Ca2+ replaced by Ba2+, effects of bufadienolides (bufalin (BF) and cinobufagin (CBG)) and cardenolides (ouabain (Oua) and pecilocerin A (PEA)) on the L-type calcium current (ICa,L) were recorded in heterologous expression Cav1.2-CHO cells and human embryonic stem cell-derived cardiomyocytes (hESC-CMs). BF and CBG demonstrated a concentration-dependent (0.1 to 100 µM) ICa,L inhibition (maximal ≥50%) without and with the NKA activity blocked by 10 µM Oua. BF significantly shortened the action potential duration at 1.0 µM and shortened the extracellular field potential duration at 0.01~1.0 µM. On the other hand, BF and CBG at 100 µM demonstrated a strong inhibition (≥40%) of the rapidly activating component of the delayed rectifier K+ current (IKr) in heterologous expression HEK293 cells and prolonged the APD of the heart of day-3 Zebrafish larva with disrupted rhythmic contractions. Moreover, hESC-CMs treated with BF (10 nM) for 24 hours showed moderate yet significant prolongation in APD90. In conclusion, our data indicate that CGs particularly bufadienolides possess cytosolic [Ca2+]i- and NKA inhibition- independent proarrhythmic potential through ICa,L and IKr inhibitions.
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Wu J, Wang X, Chung YY, Koh CH, Liu Z, Guo H, Yuan Q, Wang C, Su S, Wei H. L-Type Calcium Channel Inhibition Contributes to the Proarrhythmic Effects of Aconitine in Human Cardiomyocytes. PLoS One 2017; 12:e0168435. [PMID: 28056022 PMCID: PMC5215924 DOI: 10.1371/journal.pone.0168435] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2016] [Accepted: 12/01/2016] [Indexed: 01/17/2023] Open
Abstract
Aconitine (ACO) is well-known for causing lethal ventricular tachyarrhythmias. While cardiac Na+ channel opening during repolarization has long been documented in animal cardiac myocytes, the cellular effects and mechanism of ACO in human remain unexplored. This study aimed to assess the proarrhythmic effects of ACO in human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs). ACO concentration-dependently (0.3 ~ 3.0 μM) shortened the action potentials (AP) durations (APD) in ventricular-like hiPSC-CMs by > 40% and induced delayed after-depolarization. Laser-scanning confocal calcium imaging analysis showed that ACO decreased the duration and amplitude of [Ca2+]i transients and increased in the beating frequencies by over 60%. Moreover, ACO was found to markedly reduce the L-type calcium channel (LTCC) currents (ICa,L) in hiPSC-CMs associated with a positive-shift of activation and a negative shift of inactivation. ACO failed to alter the peak and late Na+ currents (INa) in hiPSC-CMs while it drastically increased the late INa in Guinea-pig ventricular myocytes associated with enhanced activation/delayed inactivation of INa at -55 mV~ -85 mV. Further, the effects of ACO on ICa,L, INa and the rapid delayed rectifier potassium current (Ikr) were validated in heterologous expression systems by automated voltage-clamping assays and a moderate suppression of Ikr was observed in addition to concentration-dependent ICa,L inhibition. Lastly, increased beating frequency, decreased Ca2+ wave and shortened field potential duration were recorded from hiPSC-CMs by microelectrode arrays assay. In summary, our data demonstrated that LTCC inhibition could play a main role in the proarrhythmic action of ACO in human cardiomyocytes.
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Affiliation(s)
- Jianjun Wu
- National Heart Research Institute Singapore, National Heart Centre Singapore, Singapore
| | - Xiangchong Wang
- Department of Pharmacology, Hebei Medical University, Shijiazhuang, Hebei, China
| | - Ying Ying Chung
- National Heart Research Institute Singapore, National Heart Centre Singapore, Singapore
| | - Cai Hong Koh
- National Heart Research Institute Singapore, National Heart Centre Singapore, Singapore
| | - Zhenfeng Liu
- National Heart Research Institute Singapore, National Heart Centre Singapore, Singapore
| | - Huicai Guo
- Department of Toxicology, Hebei Medical University, Shijiazhuang, Hebei, China
| | - Qiang Yuan
- Neuroscience & Behavioral Disorders Program, Duke-NUS Medical School Singapore, Singapore
| | - Chuan Wang
- Department of Pharmacology, Hebei Medical University, Shijiazhuang, Hebei, China
| | - Suwen Su
- Department of Pharmacology, Hebei Medical University, Shijiazhuang, Hebei, China
- * E-mail: (HW); (SS)
| | - Heming Wei
- National Heart Research Institute Singapore, National Heart Centre Singapore, Singapore
- Cardiovascular & Metabolic Disorders Program, Duke-NUS Medical School Singapore, Singapore
- * E-mail: (HW); (SS)
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11
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Markandeya YS, Kamp TJ. Rational strategy to stop arrhythmias: Early afterdepolarizations and L-type Ca2+ current. ACTA ACUST UNITED AC 2016; 145:475-9. [PMID: 26009542 PMCID: PMC4442792 DOI: 10.1085/jgp.201511429] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Affiliation(s)
- Yogananda S Markandeya
- Department of Medicine and Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI 53705 Department of Medicine and Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI 53705
| | - Timothy J Kamp
- Department of Medicine and Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI 53705 Department of Medicine and Department of Cell and Regenerative Biology, University of Wisconsin-Madison, Madison, WI 53705
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12
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Wang Y, Youm JB, Jin CZ, Shin DH, Zhao ZH, Seo EY, Jang JH, Kim SJ, Jin ZH, Zhang YH. Modulation of L-type Ca²⁺ channel activity by neuronal nitric oxide synthase and myofilament Ca²⁺ sensitivity in cardiac myocytes from hypertensive rat. Cell Calcium 2015; 58:264-74. [PMID: 26115836 DOI: 10.1016/j.ceca.2015.06.004] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2015] [Revised: 06/02/2015] [Accepted: 06/06/2015] [Indexed: 10/23/2022]
Abstract
Neuronal nitric oxide synthase (nNOS) is important in cardiac protection in diseased heart. Recently, we have reported that nNOS is associated with myofilament Ca(2+) desensitization in cardiac myocytes from hypertensive rats. So far, the effect of myofilament Ca(2+) desensitization or nNOS on L-type Ca(2+) channel activity (I(Ca)) in cardiac myocyte is unclear. Here, we examined nNOS regulation of I(Ca) in left ventricular (LV) myocytes from sham and angiotensin II (Ang II)-induced hypertensive rats. Our results showed that basal I(Ca) was not different between sham and hypertension (from -60 to +40 mV, 0.1 Hz). S-methyl-L-thiocitrulline (SMTC), a selective nNOS inhibitor, increased peak I(Ca) similarly in both groups. However, chelation of intracellular Ca(2+) [Ca(2+)]i with BAPTA increased I(Ca) and abolished SMTC-augmentation of I(Ca) only in hypertension. Myofilament Ca(2+) desensitization with butanedione monoxime (BDM), a myosin ATPase inhibitor, decreased I(Ca) in both groups but to a greater extent in hypertension. Intracellular BAPTA or nNOS inhibition reinstated I(Ca) in the presence of BDM to the basal level, suggesting Ca(2+)-dependent inactivation of I(Ca) by nNOS and greater vulnerability in hypertension. Increasing stimulation frequencies (2, 4 and 8 Hz) attenuated myofilament Ca(2+) sensitivity in sham and reduced peak ICa in both groups. Nevertheless, SMTC or BAPTA exerted no effect on I(Ca) at high frequencies in either group. These results suggest that nNOS attenuates I(Ca) via Ca(2+)-dependent mechanism and the vulnerability is greater in hypertension subject to myofilament Ca(2+) desensitization. nNOS or [Ca(2+)]i does not affect I(Ca) at high stimulation frequencies. The results were recapitulated with computer simulation.
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Affiliation(s)
- Yue Wang
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University, College of Medicine, South Korea
| | - Jae Boum Youm
- Department of Physiology, Inje University, College of Medicine, Busan, South Korea
| | - Chun Zi Jin
- Yanbian University Hospital, Yanji, Jilin Province, China
| | - Dong Hoon Shin
- Department of Premedical Program, College of Medicine, Chosun University, Gwangju, South Korea
| | - Zai Hao Zhao
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University, College of Medicine, South Korea
| | - Eun Yeong Seo
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University, College of Medicine, South Korea
| | - Ji Hyun Jang
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University, College of Medicine, South Korea
| | - Sung Joon Kim
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University, College of Medicine, South Korea
| | - Zhe Hu Jin
- Yanbian University Hospital, Yanji, Jilin Province, China.
| | - Yin Hua Zhang
- Department of Physiology, Ischemic/Hypoxic Disease Institute, Seoul National University, College of Medicine, South Korea; Yanbian University Hospital, Yanji, Jilin Province, China; Institute of Cardiovascular Sciences, University of Manchester, UK.
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13
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Lu Y, Hou S, Huang D, Luo X, Zhang J, Chen J, Xu W. Expression profile analysis of circulating microRNAs and their effects on ion channels in Chinese atrial fibrillation patients. Int J Clin Exp Med 2015; 8:845-853. [PMID: 25785065 PMCID: PMC4358520] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2014] [Accepted: 01/09/2015] [Indexed: 06/04/2023]
Abstract
OBJECTIVE To investigate the changes in expression profile of circulating microRNAs (miRNAs) and the regulatory effect of atrial fibrilation (AF)-related miRNAs on ion channels. METHODS 112 patients with AF were assigned into observation group, and another 112 non-AF people were assigned into control group. Total plasma RNAs were extracted from patients' blood samples. Differentially expressed miRNA-1s were transfected into primary-cultured neonatal rat cardiac myocytes. RESULTS Compared with control group, significant differences were observed in 15 kinds of miRNAs in observation group. Down-regulation of the expression of miRNAs included hsa-miR-328, hsa-miR-145, hsa-miR-222, hsa-miR-1, hsa-miR-162, hsa-miR-432, and hsa-miR-493b; Up-regulation of the expression included hsa-miR634, hsa-miR-664, hsa-miR-9, hsa-miR-152, hsa-miR-19, hsa-miR-454, hsa-miR-146, and hsa-miR-374a. The expression level of CACNB2 protein in miRNA-1 group was significantly lower than that in blank control group, negative control group, MTmiRNA-1 group, AMO-1 group and miRNA-1+AMO-1 cotransfection group (P < 0.05), while in AMO-1 group, the expression level of CACNB2 protein was significantly higher than that in other groups (P < 0.05). These results indicated that transfected miRNA-1 could significantly inhibit the expression of CACNB2 protein. CONCLUSIONS Circulating miRNAs can be used in studies concerning on the regulation mechanism of the occurrence and development of AF. MiRNA-1 can decrease the intracellular Ca(2+) concentration and prevent the AF.
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Affiliation(s)
- Yingmin Lu
- Department of Cardiology, Xinhua (Chongming) Hospital, School of Medicine, Shanghai Jiaotong University Shanghai 202150, China
| | - Shuxin Hou
- Department of Cardiology, Xinhua (Chongming) Hospital, School of Medicine, Shanghai Jiaotong University Shanghai 202150, China
| | - Damin Huang
- Department of Cardiology, Xinhua (Chongming) Hospital, School of Medicine, Shanghai Jiaotong University Shanghai 202150, China
| | - Xiaohan Luo
- Department of Cardiology, Xinhua (Chongming) Hospital, School of Medicine, Shanghai Jiaotong University Shanghai 202150, China
| | - Jinchun Zhang
- Department of Cardiology, Xinhua (Chongming) Hospital, School of Medicine, Shanghai Jiaotong University Shanghai 202150, China
| | - Jian Chen
- Department of Cardiology, Xinhua (Chongming) Hospital, School of Medicine, Shanghai Jiaotong University Shanghai 202150, China
| | - Weiping Xu
- Department of Cardiology, Xinhua (Chongming) Hospital, School of Medicine, Shanghai Jiaotong University Shanghai 202150, China
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14
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Weiss S, Oz S, Benmocha A, Dascal N. Regulation of cardiac L-type Ca²⁺ channel CaV1.2 via the β-adrenergic-cAMP-protein kinase A pathway: old dogmas, advances, and new uncertainties. Circ Res 2013; 113:617-31. [PMID: 23948586 DOI: 10.1161/circresaha.113.301781] [Citation(s) in RCA: 78] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In the heart, adrenergic stimulation activates the β-adrenergic receptors coupled to the heterotrimeric stimulatory Gs protein, followed by subsequent activation of adenylyl cyclase, elevation of cyclic AMP levels, and protein kinase A (PKA) activation. One of the main targets for PKA modulation is the cardiac L-type Ca²⁺ channel (CaV1.2) located in the plasma membrane and along the T-tubules, which mediates Ca²⁺ entry into cardiomyocytes. β-Adrenergic receptor activation increases the Ca²⁺ current via CaV1.2 channels and is responsible for the positive ionotropic effect of adrenergic stimulation. Despite decades of research, the molecular mechanism underlying this modulation has not been fully resolved. On the contrary, initial reports of identification of key components in this modulation were later refuted using advanced model systems, especially transgenic animals. Some of the cardinal debated issues include details of specific subunits and residues in CaV1.2 phosphorylated by PKA, the nature, extent, and role of post-translational processing of CaV1.2, and the role of auxiliary proteins (such as A kinase anchoring proteins) involved in PKA regulation. In addition, the previously proposed crucial role of PKA in modulation of unstimulated Ca²⁺ current in the absence of β-adrenergic receptor stimulation and in voltage-dependent facilitation of CaV1.2 remains uncertain. Full reconstitution of the β-adrenergic receptor signaling pathway in heterologous expression systems remains an unmet challenge. This review summarizes the past and new findings, the mechanisms proposed and later proven, rejected or disputed, and emphasizes the essential issues that remain unresolved.
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Affiliation(s)
- Sharon Weiss
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Tel-Aviv, Israel.
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15
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Membrane channels as integrators of G-protein-mediated signaling. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2013; 1838:521-31. [PMID: 24028827 DOI: 10.1016/j.bbamem.2013.08.018] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2013] [Revised: 08/14/2013] [Accepted: 08/21/2013] [Indexed: 01/03/2023]
Abstract
A variety of extracellular stimuli regulate cellular responses via membrane receptors. A well-known group of seven-transmembrane domain-containing proteins referred to as G protein-coupled receptors, directly couple with the intracellular GTP-binding proteins (G proteins) across cell membranes and trigger various cellular responses by regulating the activity of several enzymes as well as ion channels. Many specific populations of ion channels are directly controlled by G proteins; however, indirect modulation of some channels by G protein-dependent phosphorylation events and lipid metabolism is also observed. G protein-mediated diverse modifications affect the ion channel activities and spatio-temporally regulate membrane potentials as well as of intracellular Ca(2+) concentrations in both excitatory and non-excitatory cells. This article is part of a Special Issue entitled: Reciprocal influences between cell cytoskeleton and membrane channels, receptors and transporters. Guest Editor: Jean Claude Hervé.
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16
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Lee P, Sobie EA, Peskin CS. Computer simulation of voltage sensitive calcium ion channels in a dendritic spine. J Theor Biol 2013; 338:87-93. [PMID: 23999286 DOI: 10.1016/j.jtbi.2013.08.019] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2013] [Revised: 08/16/2013] [Accepted: 08/20/2013] [Indexed: 11/27/2022]
Abstract
Membrane current through voltage-sensitive calcium ion channels at the postsynaptic density of a dendritic spine is investigated. To simulate the ion channels that carry such current and the resulting temporal and spatial distribution of concentration, current, and voltage within the dendritic spine, the immersed boundary method with electrodiffusion is applied. In this simulation method a spatially continuous chemical potential barrier is used to simulate the influence of the membrane on each species of ion. The amplitudes of these barriers can be regulated to simulate channel gating. Here we introduce this methodology in a one-dimensional setting. First, we study the current-voltage relationship obtained with fixed chemical potential barriers. Next, we simulate stochastic ion-channel gating in a calcium channel with multiple subunits, and observe the diffusive wave of calcium entry within the dendritic spine that follows channel opening. This work lays the foundation for future three-dimensional studies of electrodiffusion and advection electrodiffusion in dendritic spines.
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Affiliation(s)
- Pilhwa Lee
- Department of Physiology and Biotechnology and Bioengineering Center, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
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17
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Cardiac ion channels and mechanisms for protection against atrial fibrillation. Rev Physiol Biochem Pharmacol 2013; 162:1-58. [PMID: 21987061 DOI: 10.1007/112_2011_3] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/10/2023]
Abstract
Atrial fibrillation (AF) is recognised as the most common sustained cardiac arrhythmia in clinical practice. Ongoing drug development is aiming at obtaining atrial specific effects in order to prevent pro-arrhythmic, devastating ventricular effects. In principle, this is possible due to a different ion channel composition in the atria and ventricles. The present text will review the aetiology of arrhythmias with focus on AF and include a description of cardiac ion channels. Channels that constitute potentially atria-selective targets will be described in details. Specific focus is addressed to the recent discovery that Ca(2+)-activated small conductance K(+) channels (SK channels) are important for the repolarisation of atrial action potentials. Finally, an overview of current pharmacological treatment of AF is included.
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18
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N-acetylcysteine prevents electrical remodeling and attenuates cellular hypertrophy in epicardial myocytes of rats with ascending aortic stenosis. Basic Res Cardiol 2012; 107:290. [PMID: 22855324 DOI: 10.1007/s00395-012-0290-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/15/2011] [Revised: 05/22/2012] [Accepted: 07/18/2012] [Indexed: 02/07/2023]
Abstract
Pressure overload is associated with cardiac hypertrophy and electrical remodeling. Here, we investigate the effects of the antioxidant N-acetylcysteine (NAC) on the cellular cardiac electrophysiology of female Sprague-Dawley rats with ascending aortic stenosis (AS). Rats were treated with NAC (1 g/kg body weight) or control solution 1 week before the intervention and in the week following AS or sham operation. Seven days after the operation, blood pressure and left ventricular pressure were measured before the heart was excised. Single cells were isolated from epicardial and endocardial layers of the left ventricular free wall and investigated using the whole-cell patch-clamp technique. Systolic blood pressure and left ventricular peak pressure were not significantly altered in the NAC group. NAC reduced the increase (p < 0.001) in the relative left ventricular weight (p < 0.05) as well as the increase (p < 0.001) in cell capacitance in epicardial (p < 0.05), but not in endocardial myocytes of AS animals. The L-type Ca(2+) current (I (CaL)) was significantly increased by AS in epicardial (+19 % at 0 mV, p < 0.01) but not in endocardial myocytes. NAC completely prevented this increase in I (CaL) (p < 0.01). The current density of the transient outward K(+) current (I (to)) was not affected by AS or NAC. Action potential duration to 90 % repolarization was significantly prolonged in epicardial (p < 0.01) as well as in endocardial (p < 0.001) cells of AS animals. NAC prevented the AP prolongation in epicardial myocytes only (p < 0.05). We conclude that reducing oxidative stress in pressure overload can prevent electrical remodeling and ameliorate hypertrophy in epicardial but not in endocardial myocytes.
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19
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Cohen-Kutner M, Yahalom Y, Trus M, Atlas D. Calcineurin Controls Voltage-Dependent-Inactivation (VDI) of the Normal and Timothy Cardiac Channels. Sci Rep 2012; 2:366. [PMID: 22511998 PMCID: PMC3328044 DOI: 10.1038/srep00366] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 03/22/2012] [Indexed: 12/25/2022] Open
Abstract
Ca2+-entry in the heart is tightly controlled by Cav1.2 inactivation, which involves Ca2+-dependent inactivation (CDI) and voltage-dependent inactivation (VDI) components. Timothy syndrome, a subtype-form of congenital long-QT syndrome, results from a nearly complete elimination of VDI by the G406R mutation in the α11.2 subunit of Cav1.2. Here, we show that a single (A1929P) or a double mutation (H1926A-H1927A) within the CaN-binding site at the human C-terminal tail of α11.2, accelerate the inactivation rate and enhances VDI of both wt and Timothy channels. These results identify the CaN-binding site as the long-sought VDI-regulatory motif of the cardiac channel. The substantial increase in VDI and the accelerated inactivation caused by the selective inhibitors of CaN, cyclosporine A and FK-506, which act at the same CaN-binding site, further support this conclusion. A reversal of enhanced-sympathetic tone by VDI-enhancing CaN inhibitors could be beneficial for improving Timothy syndrome complications such as long-QT and autism.
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20
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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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21
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Lin YC, Huang J, Kan H, Castranova V, Frisbee JC, Yu HG. Defective calcium inactivation causes long QT in obese insulin-resistant rat. Am J Physiol Heart Circ Physiol 2011; 302:H1013-22. [PMID: 22198168 DOI: 10.1152/ajpheart.00837.2011] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The majority of diabetic patients who are overweight or obese die of heart disease. We suspect that the obesity-induced insulin resistance may lead to abnormal cardiac electrophysiology. We tested this hypothesis by studying an obese insulin-resistant rat model, the obese Zucker rat (OZR). Compared with the age-matched control, lean Zucker rat (LZR), OZR of 16-17 wk old exhibited an increase in QTc interval, action potential duration, and cell capacitance. Furthermore, the L-type calcium current (I(CaL)) in OZR exhibited defective inactivation and lost the complete inactivation back to the closed state, leading to increased Ca(2+) influx. The current density of I(CaL) was reduced in OZR, whereas the threshold activation and the current-voltage relationship of I(CaL) were not significantly altered. L-type Ba(2+) current (I(BaL)) in OZR also exhibited defective inactivation, and steady-state inactivation was not significantly altered. However, the current-voltage relationship and activation threshold of I(BaL) in OZR exhibited a depolarized shift compared with LZR. The total and membrane protein expression levels of Cav1.2 [pore-forming subunit of L-type calcium channels (LTCC)], but not the insulin receptors, were decreased in OZR. The insulin receptor was found to be associated with the Cav1.2, which was weakened in OZR. The total protein expression of calmodulin was reduced, but that of Cavβ2 subunit was not altered in OZR. Together, these results suggested that the 16- to 17-wk-old OZR has 1) developed cardiac hypertrophy, 2) exhibited altered electrophysiology manifested by the prolonged QTc interval, 3) increased duration of action potential in isolated ventricular myocytes, 4) defective inactivation of I(CaL) and I(BaL), 5) weakened the association of LTCC with the insulin receptor, and 6) decreased protein expression of Cav1.2 and calmodulin. These results also provided mechanistic insights into a remodeled cardiac electrophysiology under the condition of insulin resistance, enhancing our understanding of long QT associated with obese type 2 diabetic patients.
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Affiliation(s)
- Yen-Chang Lin
- Center for Cardiovascular and Respiratory Sciences, Department of Physiology and Pharmacology, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, WV 26056, USA.
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22
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Jons C, O-Uchi J, Moss AJ, Reumann M, Rice JJ, Goldenberg I, Zareba W, Wilde AAM, Shimizu W, Kanters JK, McNitt S, Hofman N, Robinson JL, Lopes CMB. Use of mutant-specific ion channel characteristics for risk stratification of long QT syndrome patients. Sci Transl Med 2011; 3:76ra28. [PMID: 21451124 DOI: 10.1126/scitranslmed.3001551] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Inherited long QT syndrome (LQTS) is caused by mutations in ion channels that delay cardiac repolarization, increasing the risk of sudden death from ventricular arrhythmias. Currently, the risk of sudden death in individuals with LQTS is estimated from clinical parameters such as age, gender, and the QT interval, measured from the electrocardiogram. Even though a number of different mutations can cause LQTS, mutation-specific information is rarely used clinically. LQTS type 1 (LQT1), one of the most common forms of LQTS, is caused by mutations in the slow potassium current (I(Ks)) channel α subunit KCNQ1. We investigated whether mutation-specific changes in I(Ks) function can predict cardiac risk in LQT1. By correlating the clinical phenotype of 387 LQT1 patients with the cellular electrophysiological characteristics caused by an array of mutations in KCNQ1, we found that channels with a decreased rate of current activation are associated with increased risk of cardiac events (hazard ratio=2.02), independent of the clinical parameters usually used for risk stratification. In patients with moderate QT prolongation (a QT interval less than 500 ms), slower activation was an independent predictor for cardiac events (syncope, aborted cardiac arrest, and sudden death) (hazard ratio = 2.10), whereas the length of the QT interval itself was not. Our results indicate that genotype and biophysical phenotype analysis may be useful for risk stratification of LQT1 patients and suggest that slow channel activation is associated with an increased risk of cardiac events.
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Affiliation(s)
- Christian Jons
- Cardiology Division, Department of Medicine, University of Rochester School of Medicine and Dentistry, Rochester, NY 14642, USA
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23
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Kurusu T, Hamada H, Sugiyama Y, Yagala T, Kadota Y, Furuichi T, Hayashi T, Umemura K, Komatsu S, Miyao A, Hirochika H, Kuchitsu K. Negative feedback regulation of microbe-associated molecular pattern-induced cytosolic Ca2+ transients by protein phosphorylation. JOURNAL OF PLANT RESEARCH 2011; 124:415-24. [PMID: 21063744 DOI: 10.1007/s10265-010-0388-4] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Accepted: 10/11/2010] [Indexed: 05/24/2023]
Abstract
Microbe/pathogen-associated molecular patterns (MAMPs/PAMPs) often induce rises in cytosolic free Ca(2+) concentration ([Ca(2+)](cyt)) and protein phosphorylation. Though they are postulated to play pivotal roles in plant innate immunity, their molecular links and the regulatory mechanisms remain largely unknown. To investigate the regulatory mechanisms for MAMP-induced Ca(2+) mobilization, we have established a transgenic rice (Oryza sativa) cell line stably expressing apoaequorin, and characterized the interrelationship among MAMP-induced changes in [Ca(2+)](cyt), production of reactive oxygen species (ROS) and protein phosphorylation. Oligosaccharide and sphingolipid MAMPs induced Ca(2+) transients mainly due to plasma membrane Ca(2+) influx, which were dramatically suppressed by a protein phosphatase inhibitor, calyculin A (CA). Hydrogen peroxide and hypo-osmotic shock triggered similar [Ca(2+)](cyt) elevations, which were not affected by CA. MAMP-induced protein phosphorylation, which is promoted by CA, has been shown to be required for ROS production and MAPK activation, while it negatively regulates MAMPs-induced Ca(2+) mobilization and may play a crucial role in temporal regulation of [Ca(2+)](cyt) signature.
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Affiliation(s)
- Takamitsu Kurusu
- Department of Applied Biological Science, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba, 278-8510, Japan
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24
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Cordeiro JM, Gonçalves PP, Dunant Y. Synaptic vesicles control the time course of neurotransmitter secretion via a Ca²+/H+ antiport. J Physiol 2011; 589:149-67. [PMID: 21059764 DOI: 10.1113/jphysiol.2010.199224] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We investigated the physiological role of the vesicular Ca2+/H+ antiport in rapid synaptic transmission using the Torpedo electric organ (a modified neuromuscular system). By inhibiting V-type H+-transporting ATPase (V-ATPase), bafilomycin A1 dissipates the H+ gradient of synaptic vesicles, thereby abolishing the Ca2+/H+ antiport driving force. In electrophysiology experiments, bafilomycin A1 significantly prolonged the duration of the evoked electroplaque potential. A biochemical assay for acetylcholine (ACh) release showed that the effect of bafilomycin A1 was presynaptic. Indeed, bafilomycin A1 increased the amount of radio-labelled ACh released in response to paired-pulse stimulation. Bafilomycin A1 also enhanced Ca2+-dependent ACh release from isolated nerve terminals (synaptosomes). The bafilomycin-induced electroplaque potential lengthening did not arise from cholinesterase inhibition, since eserine (which also prolonged the electroplaque potential) strongly decreased evoked ACh release. Bafilomycin A1 augmented the amount of calcium accumulating in nerve terminals following a short tetanic stimulation and delayed subsequent calcium extrusion. By reducing stimulation-dependent calcium accumulation in synaptic vesicles, bafilomycin A1 diminished the corresponding depletion of vesicular ACh, as tested using both intact tissue and isolated synaptic vesicles. Strontium ions inhibit the vesicular Ca2+/H+ antiport, while activating transmitter release at concentrations one order of magnitude higher than Ca2+ does. In the presence of Sr2+ the time course of the electroplaque potential was also prolonged but, unlike bafilomycin A1, Sr2+ enhanced facilitation in paired-pulse experiments. It is therefore proposed that the vesicular Ca2+/H+ antiport function is to shorten 'phasic' transmitter release, allowing the synapse to transmit briefer impulses and so to work at higher frequencies.
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Affiliation(s)
- J Miguel Cordeiro
- Department of Fundamental Neurosciences, Faculty of Medicine, University of Geneva, CH-1211-Geneva 4, Switzerland
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25
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Oz S, Tsemakhovich V, Christel CJ, Lee A, Dascal N. CaBP1 regulates voltage-dependent inactivation and activation of Ca(V)1.2 (L-type) calcium channels. J Biol Chem 2011; 286:13945-53. [PMID: 21383011 DOI: 10.1074/jbc.m110.198424] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
CaBP1 is a Ca(2+)-binding protein that regulates the gating of voltage-gated (Ca(V)) Ca(2+) channels. In the Ca(V)1.2 channel α(1)-subunit (α(1C)), CaBP1 interacts with cytosolic N- and C-terminal domains and blunts Ca(2+)-dependent inactivation. To clarify the role of the α(1C) N-terminal domain in CaBP1 regulation, we compared the effects of CaBP1 on two alternatively spliced variants of α(1C) containing a long or short N-terminal domain. In both isoforms, CaBP1 inhibited Ca(2+)-dependent inactivation but also caused a depolarizing shift in voltage-dependent activation and enhanced voltage-dependent inactivation (VDI). In binding assays, CaBP1 interacted with the distal third of the N-terminal domain in a Ca(2+)-independent manner. This segment is distinct from the previously identified calmodulin-binding site in the N terminus. However, deletion of a segment in the proximal N-terminal domain of both α(1C) isoforms, which spared the CaBP1-binding site, inhibited the effect of CaBP1 on VDI. This result suggests a modular organization of the α(1C) N-terminal domain, with separate determinants for CaBP1 binding and transduction of the effect on VDI. Our findings expand the diversity and mechanisms of Ca(V) channel regulation by CaBP1 and define a novel modulatory function for the initial segment of the N terminus of α(1C).
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Affiliation(s)
- Shimrit Oz
- Department of Physiology and Pharmacology, Sackler School of Medicine, Tel Aviv University, Tel Aviv 69978, Israel
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Satin J, Schroder EA, Crump SM. L-type calcium channel auto-regulation of transcription. Cell Calcium 2011; 49:306-13. [PMID: 21295347 DOI: 10.1016/j.ceca.2011.01.001] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2010] [Revised: 01/06/2011] [Accepted: 01/07/2011] [Indexed: 01/24/2023]
Abstract
L-type calcium channels (LTCC) impact the function of nearly all excitable cells. The classical LTCC function is to mediate trans-sarcolemmal Ca(2+) flux. This review focuses on the contribution of a mobile segment of the LTCC that regulates ion channel function, and also serves as a regulator of transcription in the nucleus. Specifically we highlight recent work demonstrating an auto-feedback regulatory pathway whereby the LTCC transcription factor regulates the LTCC. Also discussed is acute and long-term regulation of function by the LTCC-transcription regulator.
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Affiliation(s)
- Jonathan Satin
- Department of Physiology, MS-508, University of Kentucky College of Medicine, 800 Rose Street, Lexington, KY 40536-0298, USA.
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27
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Zhang Z, Lin H, Cao C, Khurana S, Pallone TL. Voltage-gated divalent currents in descending vasa recta pericytes. Am J Physiol Renal Physiol 2010; 299:F862-71. [PMID: 20630935 DOI: 10.1152/ajprenal.00321.2010] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Multiple voltage-gated Ca(2+) channel (Ca(V)) subtypes have been reported to participate in control of the juxtamedullary glomerular arterioles of the kidney. Using the patch-clamp technique, we examined whole cell Ca(V) currents of pericytes that contract descending vasa recta (DVR). The dihydropyridine Ca(V) agonist FPL64176 (FPL) stimulated inward Ca(2+) and Ba(2+) currents that activated with threshold depolarizations to -40 mV and maximized between -20 and -10 mV. These currents were blocked by nifedipine (1 μM) and Ni(2+) (100 and 1,000 μM), exhibited slow inactivation, and conducted Ba(2+) > Ca(2+) at a ratio of 2.3:1, consistent with "long-lasting" L-type Ca(V). In FPL, with 1 mM Ca(2+) as charge carrier, Boltzmann fits yielded half-maximal activation potential (V(1/2)) and slope factors of -57.9 mV and 11.0 for inactivation and -33.3 mV and 4.4 for activation. In the absence of FPL stimulation, higher concentrations of divalent charge carriers were needed to measure basal currents. In 10 mM Ba(2+), pericyte Ca(V) currents activated with threshold depolarizations to -30 mV, were blocked by nifedipine, exhibited voltage-dependent block by diltiazem (10 μM), and conducted Ba(2+) > Ca(2+) at a ratio of ∼2:1. In Ca(2+), Boltzmann fits to the data yielded V(1/2) and slope factors of -39.6 mV and 10.0 for inactivation and 2.8 mV and 7.7 for activation. In Ba(2+), V(1/2) and slope factors were -29.2 mV and 9.2 for inactivation and -5.6 mV and 6.1 for activation. Neither calciseptine (10 nM), mibefradil (1 μM), nor ω-agatoxin IVA (20 and 100 nM) blocked basal Ba(2+) currents. Calciseptine (10 nM) and mibefradil (1 μM) also failed to reverse ANG II-induced DVR vasoconstriction, although raising mibefradil concentration to 10 μM was partially effective. We conclude that DVR pericytes predominantly express voltage-gated divalent currents that are carried by L-type channels.
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Affiliation(s)
- Zhong Zhang
- Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, USA
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Alvarez JL, Petzhold D, Pankonien I, Behlke J, Kouno M, Vassort G, Morano I, Haase H. Ahnak1 modulates L-type Ca2+ channel inactivation of rodent cardiomyocytes. Pflugers Arch 2010; 460:719-30. [DOI: 10.1007/s00424-010-0853-x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 05/28/2010] [Accepted: 06/02/2010] [Indexed: 01/21/2023]
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Grunnet M. Repolarization of the cardiac action potential. Does an increase in repolarization capacity constitute a new anti-arrhythmic principle? Acta Physiol (Oxf) 2010; 198 Suppl 676:1-48. [PMID: 20132149 DOI: 10.1111/j.1748-1716.2009.02072.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The cardiac action potential can be divided into five distinct phases designated phases 0-4. The exact shape of the action potential comes about primarily as an orchestrated function of ion channels. The present review will give an overview of ion channels involved in generating the cardiac action potential with special emphasis on potassium channels involved in phase 3 repolarization. In humans, these channels are primarily K(v)11.1 (hERG1), K(v)7.1 (KCNQ1) and K(ir)2.1 (KCNJ2) being the responsible alpha-subunits for conducting I(Kr), I(Ks) and I(K1). An account will be given about molecular components, biophysical properties, regulation, interaction with other proteins and involvement in diseases. Both loss and gain of function of these currents are associated with different arrhythmogenic diseases. The second part of this review will therefore elucidate arrhythmias and subsequently focus on newly developed chemical entities having the ability to increase the activity of I(Kr), I(Ks) and I(K1). An evaluation will be given addressing the possibility that this novel class of compounds have the ability to constitute a new anti-arrhythmic principle. Experimental evidence from in vitro, ex vivo and in vivo settings will be included. Furthermore, conceptual differences between the short QT syndrome and I(Kr) activation will be accounted for.
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Affiliation(s)
- M Grunnet
- NeuroSearch A/S, Ballerup, and Danish National Research Foundation Centre for Cardiac Arrhythmia, University of Copenhagen, Denmark.
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Teng J, Iida K, Ito M, Izumi-Nakaseko H, Kojima I, Adachi-Akahane S, Iida H. Role of glycine residues highly conserved in the S2-S3 linkers of domains I and II of voltage-gated calcium channel alpha(1) subunits. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2010; 1798:966-74. [PMID: 20067760 DOI: 10.1016/j.bbamem.2010.01.004] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/21/2009] [Revised: 12/19/2009] [Accepted: 01/04/2010] [Indexed: 11/24/2022]
Abstract
The pore-forming component of voltage-gated calcium channels, alpha(1) subunit, contains four structurally conserved domains (I-IV), each of which contains six transmembrane segments (S1-S6). We have shown previously that a Gly residue in the S2-S3 linker of domain III is completely conserved from yeasts to humans and important for channel activity. The Gly residues in the S2-S3 linkers of domains I and II, which correspond positionally to the Gly in the S2-S3 linker of domain III, are also highly conserved. Here, we investigated the role of the Gly residues in the S2-S3 linkers of domains I and II of Ca(v)1.2. Each of the Gly residues was replaced with Glu or Gln to produce mutant Ca(v)1.2s; G182E, G182Q, G579E, G579Q, and the resulting mutants were transfected into BHK6 cells. Whole-cell patch-clamp recordings showed that current-voltage relationships of the four mutants were the same as those of wild-type Ca(v)1.2. However, G182E and G182Q showed significantly smaller current densities because of mislocalization of the mutant proteins, suggesting that Gly(182) in domain I is involved in the membrane trafficking or surface expression of alpha(1) subunit. On the other hand, G579E showed a slower voltage-dependent current inactivation (VDI) compared to Ca(v)1.2, although G579Q showed a normal VDI, implying that Gly(579) in domain II is involved in the regulation of VDI and that the incorporation of a negative charge alters the VDI kinetics. Our findings indicate that the two conserved Gly residues are important for alpha(1) subunit to become functional.
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Affiliation(s)
- Jinfeng Teng
- Department of Biology, Tokyo Gakugei University, 4-1-1 Nukui kita-machi, Koganei-shi, Tokyo 184-8501, Japan
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Warren DE, Galli GLJ, Patrick SM, Shiels HA. The cellular force-frequency response in ventricular myocytes from the varanid lizard, Varanus exanthematicus. Am J Physiol Regul Integr Comp Physiol 2010; 298:R567-74. [PMID: 20053961 DOI: 10.1152/ajpregu.00650.2009] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
To investigate the cellular mechanisms underlying the negative force-frequency relationship (FFR) in the ventricle of the varanid lizard, Varanus exanthematicus, we measured sarcomere and cell shortening, intracellular Ca(2+) ([Ca(2+)](i)), action potentials (APs), and K(+) currents in isolated ventricular myocytes. Experiments were conducted between 0.2 and 1.0 Hz, which spans the physiological range of in vivo heart rates at 20-22 degrees C for this species. As stimulation frequency increased, diastolic length, percent change in sarcomere length, and relaxation time all decreased significantly. Shortening velocity was unaffected. These changes corresponded to a faster rate of rise of [Ca(2+)](i), a decrease in [Ca(2+)](i) transient amplitude, and a seven-fold increase in diastolic [Ca(2+)](i). The time constant for the decay of the Ca(2+) transient (tau) decreased at higher frequencies, indicating a frequency-dependent acceleration of relaxation (FDAR) but then reached a plateau at moderate frequencies and did not change above 0.5 Hz. The rate of rise of the AP was unaffected, but the AP duration (APD) decreased with increasing frequency. Peak depolarization tended to decrease, but it was only significant at 1.0 Hz. The decrease in APD was not due to frequency-dependent changes in the delayed inward rectifier (I(Kr)) or the transient outward (I(to)) current, as neither appeared to be present in varanid ventricular myocytes. Our results suggest that a negative FFR relationship in varanid lizard ventricle is caused by decreased amplitude of the Ca(2+) transient coupled with an increase in diastolic Ca(2+), which leads to incomplete relaxation between beats at high frequencies. This coincides with shortened APD at higher frequencies.
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Affiliation(s)
- Daniel E Warren
- Department of Anesthesia and Perioperative Care, University of California, San Francisco, San Francisco, CA 94143, USA.
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Matthes J, Herzig S. Less is more, or enough is enough? Ca(2+)-dependent inactivation revisited. J Physiol 2010; 588:15-6. [PMID: 19948660 DOI: 10.1113/jphysiol.2009.184846] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Affiliation(s)
- Jan Matthes
- Department of Pharmacology, University of Cologne
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Kamkin A, Kiseleva I, Theres H, Eulert-Grehn JJ, Wagner KD, Scholz H, Vetter R. Enhanced L-type calcium currents in cardiomyocytes from transgenic rats overexpressing SERCA2a. Exp Clin Cardiol 2010; 15:e109-e115. [PMID: 21264068 PMCID: PMC3016070] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
BACKGROUND Previous research reported that transgenic rats overexpressing the sarco(endo)plasmic reticulum Ca(2+)-ATPase SERCA2a exhibit improved contractile function of the myocardium. Furthermore, impaired Ca(2+) uptake and reduced relaxation rates in rats with diabetic cardiomyopathy were partially rescued by transgenic expression of SERCA2a in the heart. OBJECTIVE To explore whether enhanced Ca(2+) cycling in the cardiomyocytes of SERCA2a transgenic rats is associated with changes in L-type Ca(2+) (I(Ca-L)) currents. METHODS The patch-clamp technique was used to measure whole-cell currents in cardiomyocytes from transgenic rats overexpressing SERCA2a and from wild-type (nontransgenic) animals. RESULTS The amplitudes of I(Ca-L) currents at depolarizing pulses ranging from -45 mV to 0 mV (350 ms duration, 1 Hz) were significantly higher in cardiomyocytes of SERCA2a transgenic rats than in nontransgenic rats (1985±48 pA [n=32] versus 1612±55 pA [n=28], respectively). The inactivation kinetics of I(Ca-L) showed subtle differences with increased tau fast and tau slow decay constants in cardiomyocytes of SERCA2a transgenic animals. Beta-adrenergic stimulation with 50 nM isoproterenol reduced tau fast and tau slow decay constants in cardiomyocytes of transgenic rats to values that were not significantly different from those in normal cardiomyocytes. Furthermore, isoproterenol enhanced I(Ca-L) currents 3.2-fold and 2.3-fold in cardiomyocytes with and without the SERCA2a transgene, respectively, and this effect was abolished by buffering intracellular Ca(2+) with BAPTA. CONCLUSIONS These findings indicate that enhanced Ca(2+) cycling in the hearts of SERCA2a transgenic rats, both under normal conditions and during beta-adrenergic stimulation, involves changes in I(Ca-L) currents. Modified I(Ca-L) kinetics may contribute, to some extent, to the improved contractile function of the myocardium of transgenic rats.
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Affiliation(s)
- Andre Kamkin
- Institut für Vegetative Physiologie
- Department of Fundamental and Applied Physiology, Russian States Medical University, Moscow, Russia
| | - Irina Kiseleva
- Institut für Vegetative Physiologie
- Department of Fundamental and Applied Physiology, Russian States Medical University, Moscow, Russia
| | - Heinz Theres
- Medizinische Klinik mit Schwerpunkt Kardiologie, Pulmologie und Angiologie
| | - Jaime-Jürgen Eulert-Grehn
- Institut für Klinische Pharmakologie und Toxikologie, Charité-Universitätsmedizin Berlin, Berlin, Germany
| | - Kay-Dietrich Wagner
- Institut für Vegetative Physiologie
- INSERM U907
- Université de Nice-Sophia Antipolis, Nice, France
| | | | - Roland Vetter
- Institut für Klinische Pharmakologie und Toxikologie, Charité-Universitätsmedizin Berlin, Berlin, Germany
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Josephson IR, Guia A, Lakatta EG, Lederer WJ, Stern MD. Ca(2+)-dependent components of inactivation of unitary cardiac L-type Ca(2+) channels. J Physiol 2009; 588:213-23. [PMID: 19917566 DOI: 10.1113/jphysiol.2009.178343] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A Ca(2+) ion-dependent inactivation (CDI) of L-type Ca(2+) channels (LCC) is vital in limiting and shaping local Ca(2+) ion signalling in a variety of excitable cell types. However, under physiological conditions the unitary LCC properties that underlie macroscopic inactivation are unclear. Towards this end, we have probed the gating kinetics of individual cardiac LCCs recorded with a physiological Ca(2+) ion concentration (2 mM) permeating the channel, and in the absence of channel agonists. Upon depolarization the ensemble-averaged LCC current decayed with a fast and a slow exponential component. We analysed the unitary behaviour responsible for this biphasic decay by means of a novel kinetic dissection of LCC gating parameters. We found that inactivation was caused by a rapid decrease in the frequency of LCC reopening, and a slower decline in mean open time of the LCC. In contrast, with barium ions permeating the channel ensemble-averaged currents displayed only a single, slow exponential decay and little time dependence of the LCC open time. Our results demonstrate that the fast and slow phases of macroscopic inactivation reflect the distinct time courses for the decline in the frequency of LCC reopening and the open dwell time, both of which are modulated by Ca(2+) influx. Analysis of the evolution of CDI in individual LCC episodes was employed to examine the stochastic nature of the underlying molecular switch, and revealed that influx on the order of a thousand Ca(2+) ions may be sufficient to trigger CDI. This is the first study to characterize both the unitary kinetics and the stoichiometry of CDI of LCCs with a physiological Ca(2+) concentration. These novel findings may provide a basis for understanding the mechanisms regulating unitary LCC gating, which is a pivotal element in the local control of Ca(2+)-dependent signalling processes.
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Affiliation(s)
- Ira R Josephson
- Department of Physiology and Pharmacology, CUNY Medical School, City College of New York, New York, NY 10031, USA.
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Mason SA, MacLeod KT. Cardiac action potential duration and calcium regulation in males and females. Biochem Biophys Res Commun 2009; 388:565-70. [PMID: 19682977 DOI: 10.1016/j.bbrc.2009.08.050] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2009] [Accepted: 08/07/2009] [Indexed: 11/19/2022]
Abstract
Adult women have longer QT intervals compared with men of a similar age, indicating differences in the speed of repolarisation of the ventricles. We investigate the influences of gender on ventricular electrophysiology and intracellular Ca(2+) regulation of the guinea pig heart. Comparing sexually mature animals, females exhibited a significantly longer APD. Peak L-type Ca(2+) current (I(CaL)) was larger in females and when this current was inhibited with nifedipine the gender differences in APD were removed. APD differences also disappeared when the SR was depleted of Ca(2+). Inactivation of I(CaL) during a clamp step is faster in females but slower during an action potential and SR Ca(2+) content is larger. We suggest that gender differences in APD result from variation in the kinetics of I(CaL) stemming from alterations to Ca(2+) release.
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Affiliation(s)
- Sammy A Mason
- Department of Cardiology, School of Medicine, Cardiff University, Wales Heart Research Institute, Heath Park, Cardiff CF14 4XN, UK
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Findeisen F, Minor DL. Disruption of the IS6-AID linker affects voltage-gated calcium channel inactivation and facilitation. ACTA ACUST UNITED AC 2009; 133:327-43. [PMID: 19237593 PMCID: PMC2654080 DOI: 10.1085/jgp.200810143] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Two processes dominate voltage-gated calcium channel (CaV) inactivation: voltage-dependent inactivation (VDI) and calcium-dependent inactivation (CDI). The CaVβ/CaVα1-I-II loop and Ca2+/calmodulin (CaM)/CaVα1–C-terminal tail complexes have been shown to modulate each, respectively. Nevertheless, how each complex couples to the pore and whether each affects inactivation independently have remained unresolved. Here, we demonstrate that the IS6–α-interaction domain (AID) linker provides a rigid connection between the pore and CaVβ/I-II loop complex by showing that IS6-AID linker polyglycine mutations accelerate CaV1.2 (L-type) and CaV2.1 (P/Q-type) VDI. Remarkably, mutations that either break the rigid IS6-AID linker connection or disrupt CaVβ/I-II association sharply decelerate CDI and reduce a second Ca2+/CaM/CaVα1–C-terminal–mediated process known as calcium-dependent facilitation. Collectively, the data strongly suggest that components traditionally associated solely with VDI, CaVβ and the IS6-AID linker, are essential for calcium-dependent modulation, and that both CaVβ-dependent and CaM-dependent components couple to the pore by a common mechanism requiring CaVβ and an intact IS6-AID linker.
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Affiliation(s)
- Felix Findeisen
- Cardiovascular Research Institute, Department of Biochemistry and Biophysics, California Institute for Quantitative Biosciences, University of California, San Francisco, CA 94158, USA
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Modulation of L-type Ca2+ channel current density and inactivation by β-adrenergic stimulation during murine cardiac embryogenesis. Basic Res Cardiol 2008; 104:295-306. [DOI: 10.1007/s00395-008-0755-7] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/13/2008] [Accepted: 09/22/2008] [Indexed: 10/21/2022]
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hERG1 channel activators: A new anti-arrhythmic principle. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 98:347-62. [DOI: 10.1016/j.pbiomolbio.2009.01.002] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Tikhonov DB, Zhorov BS. Molecular modeling of benzothiazepine binding in the L-type calcium channel. J Biol Chem 2008; 283:17594-604. [PMID: 18397890 DOI: 10.1074/jbc.m800141200] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Benz(othi)azepine (BTZ) derivatives constitute one of three major classes of L-type Ca(2+) channel ligands. Despite intensive experimental studies, no three-dimensional model of BTZ binding is available. Here we have built KvAP- and KcsA-based models of the Ca(v)1.2 pore domain in the open and closed states and used multiple Monte Carlo minimizations to dock representative ligands. In our open channel model, key functional groups of BTZs interact with BTZ-sensing residues, which were identified in previous mutational experiments. The bulky tricyclic moiety occupies interface between domains III and IV, while the ammonium group protrudes into the inner pore, where it is stabilized by nucleophilic C-ends of the pore helices. In the closed channel model, contacts with several ligand-sensing residues in the inner helices are lost, which weakens ligand-channel interactions. An important feature of the ligand-binding mode in both open and closed channels is an interaction between the BTZ carbonyl group and a Ca(2+) ion chelated by the selectivity filter glutamates in domains III and IV. In the absence of Ca(2+), the tricyclic BTZ moiety remains in the domain interface, while the ammonium group directly interacts with a glutamate residue in the selectivity filter. Our model suggests that the Ca(2+) potentiation involves a direct electrostatic interaction between aCa(2+) ion and the ligand rather than an allosteric mechanism. Energy profiles indicate that BTZs can reach the binding site from the domain interface, whereas access through the open activation gate is unlikely, because reorientation of the bulky molecule in the pore is hindered.
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Affiliation(s)
- Denis B Tikhonov
- Department of Biochemistry and Biomedical Sciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada
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40
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The Timothy syndrome mutation differentially affects voltage- and calcium-dependent inactivation of CaV1.2 L-type calcium channels. Proc Natl Acad Sci U S A 2008; 105:2157-62. [PMID: 18250309 DOI: 10.1073/pnas.0710501105] [Citation(s) in RCA: 131] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Calcium entry into excitable cells is an important physiological signal, supported by and highly sensitive to the activity of voltage-gated Ca2+ channels. After membrane depolarization, Ca2+ channels first open but then undergo various forms of negative feedback regulation including voltage- and calcium-dependent inactivation (VDI and CDI, respectively). Inactivation of Ca2+ channel activity is perturbed in a rare yet devastating disorder known as Timothy syndrome (TS), whose features include autism or autism spectrum disorder along with severe cardiac arrhythmia and developmental abnormalities. Most cases of TS arise from a sporadic single nucleotide change that generates a mutation (G406R) in the pore-forming subunit of the L-type Ca2+ channel Ca(V)1.2. We found that the TS mutation powerfully and selectively slows VDI while sparing or possibly speeding the kinetics of CDI. The deceleration of VDI was observed when the L-type channels were expressed with beta1 subunits prominent in brain, as well as beta2 subunits of importance for the heart. Dissociation of VDI and CDI was further substantiated by measurements of Ca2+ channel gating currents and by analysis of another channel mutation (I1624A) that hastens VDI, acting upstream of the step involving Gly406. As highlighted by the TS mutation, CDI does not proceed to completeness but levels off at approximately 50%, consistent with a change in gating modes and not an absorbing inactivation process. Thus, the TS mutation offers a unique perspective on mechanisms of inactivation as well as a promising starting point for exploring the underlying pathophysiology of autism.
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Zhang H, Inoue R, Shi J, Jin XH, Li YQ. Synergistic actions of diacylglycerol and inositol 1,4,5 trisphosphate for Ca2+-dependent inactivation of TRPC7 channel. Acta Pharmacol Sin 2008; 29:90-7. [PMID: 18158870 DOI: 10.1111/j.1745-7254.2008.00721.x] [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] [Indexed: 11/29/2022] Open
Abstract
AIM The aim of the present study was to explore the mechanism for the Ca2+- dependent inactivation of the canonical transient receptor potential (TRPC) 7 channel expressed in human embryonic kidney 293 cells. METHOD The whole-cell patch-clamp technique was used in the study. RESULTS With Ca2+-free external solution, the perfusion of 100 micromol/L carbachol to, or dialysis of the cell with 100 micromol/L guanosine 5'-3-O-(thio)triphosphate (GTPgammaS), induced large inward currents, respectively. These currents were rapidly inhibited by the addition of 1 mmol/L Ca2+ into the bath, and recovery from this inhibition was only partial after the Ca2+ removal, unless vigorous intracellular Ca2+ buffering with 10 mmol/L 1,2 bis(2- aminophenoxy)ethane-N,N,No,No-tetraacetic acid (BAPTA) (plus 4 mmol/L Ca2+) was employed. In contrast, the current induced by a membrane-permeable analog of diacylglycerol (DAG), 1-oleoyl-2-acetyl-sn-glycerol (OAG; 100 micromol/L) did not undergo the inhibition persisting after Ca2+ removal. Interestingly, the inclusion of inositol 1,4,5 trisphosphate (IP3; 100 micromol/L) in the patch pipette rendered the OAG-induced current susceptible to the persistent Ca2+-mediated inhibition independent of the IP3 receptor in the majority of the tested cells, as evidenced by the inability of heparin and thapsigargin in reversing the effect of IP3. CONCLUSION The present results suggest that Ca2+ entry via the activated TRPC7 channel plays a critical role in inactivating the channel where the cooperative actions of DAG and IP3 are essentially involved.
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Affiliation(s)
- Hua Zhang
- Department of Anatomy and KK Leung Brain Research Centre, The Fourth Military Medical University, Xi'an, China
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Abstract
Beta2 adrenergic receptors were identified in keratinocytes more than 30 years ago, but their function in the epidermis continues to be elucidated. Abnormalities in their expression, signaling pathway, or in the generation of endogenous catecholamine agonists by keratinocytes have been implicated in the pathogenesis of cutaneous diseases such as atopic dermatitis, vitiligo, and psoriasis. New studies also indicate that the beta2AR also modulates keratinocyte migration, and thus can function to regulate wound reepithelialization. This review focuses on the function of these receptors in keratinocytes and their contribution to cutaneous physiology and disease.
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Affiliation(s)
- Raja K. Sivamani
- Medical Student, Department of Dermatology, University of California, Davis, CA 95616
| | - Susanne T. Lam
- Medical Student, Department of Dermatology, University of California, Davis, CA 95616
| | - R. Rivkah Isseroff
- Professor of Dermatology, Department of Dermatology, University of California, Davis, CA 95616 and Dermatology Service, Department of Veterans Affairs, Northern California Health Care System, Mather, CA 95655
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Liu SJ. Inhibition of L-type Ca2+channel current and negative inotropy induced by arachidonic acid in adult rat ventricular myocytes. Am J Physiol Cell Physiol 2007; 293:C1594-604. [PMID: 17804608 DOI: 10.1152/ajpcell.00284.2007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have previously shown an increase in arachidonic acid (AA) release in response to proinflammatory cytokines in adult rat ventricular myocytes (ARVM). AA is known to alter channel activities; however, its effects on cardiac L-type Ca2+channel current ( ICa,L) and excitation-contraction coupling remain unclear. The present study examined effects of AA on ICa,L, using the whole cell patch-clamp technique, and on cell shortening (CS) and the Ca2+transient of ARVM. ICa,Lwas monitored in myocytes held at −70 mV and internally equilibrated and externally perfused with Na+- and K+-free solutions. Exposure to AA caused a voltage-dependent block of ICa,Lconcentration dependently (IC508.5 μM). The AA-induced inhibition of ICa,Lis consistent with its hyperpolarizing shift in the voltage-dependent properties and reduction in maximum slope conductance. In the presence of AA, BSA completely blocked the AA-induced suppression of ICa,Land CS. Intracellular load with AA had no effect on the current density but caused a small depolarizing shift in the ICa,Lactivation curve, suggesting a site-specific action of AA. Moreover, intracellular AA had no effect on the extracellular AA-induced decrease in ICa,L. Pretreatment with indomethacin, an inhibitor of cyclooxygenase, or addition of nordihydroguaiaretic acid, an inhibitor of lipoxygenase, had no effect on AA-induced changes in ICa,L. Furthermore, AA suppressed CS and Ca2+transients of intact ARVM with no significant effect on SR function and myofilament Ca2+sensitivity. Therefore, these results suggest that AA inhibits contractile function of ARVM, primarily due to its direct inhibition of ICa,Lat an extracellular site.
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Affiliation(s)
- Shi J Liu
- Dept. of Pharmaceutical Sciences and Dept. of Pharmacology & Toxicology, Univ. of Arkansas for Medical Sciences, 4301 West Markham St. MS 522-3, Little Rock, AR 72205, USA.
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Zhu ZI, Clancy CE. L-type Ca2+ channel mutations and T-wave alternans: a model study. Am J Physiol Heart Circ Physiol 2007; 293:H3480-9. [PMID: 17933974 DOI: 10.1152/ajpheart.00476.2007] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A number of mutations have been linked to diseases for which the underlying mechanisms are poorly understood. An example is Timothy Syndrome (TS), a multisystem disorder that includes severe cardiac arrhythmias. Here we employ theoretical simulations to examine the effects of a TS mutation in the L-type Ca(2+) channel on cardiac dynamics over multiple scales, from a gene mutation to protein, cell, tissue, and finally the ECG, to connect a defective Ca(2+) channel to arrhythmia susceptibility. Our results indicate that 1) the TS mutation disrupts the rate-dependent dynamics in a single cardiac cell and promotes the development of alternans; 2) in coupled tissue, concordant alternans is observed at slower heart rates in mutant tissue than in normal tissue and, once initiated, rapidly degenerates into discordant alternans and conduction block; and 3) the ECG computed from mutant-simulated tissue exhibits prolonged QT intervals at physiological rates and with small increases in pacing rate, T-wave alternans, and alternating T-wave inversion. At the cellular level, enhanced Ca(2+) influx due to the TS mutation causes electrical instabilities. In tissue, the interplay between faulty Ca(2+) influx and steep action potential duration restitution causes arrhythmogenic discordant alternans. The prolongation of action potentials causes spatial dispersion of the Na(+) channel excitability, leading to inhomogeneous conduction velocity and large action potential spatial gradients. Our model simulations are consistent with the ECG patterns from TS patients, which suggest that the TS mutation is sufficient to cause the clinical phenotype and allows for the revelation of the complex interactions of currents underlying it.
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Affiliation(s)
- Zheng I Zhu
- Department of Physiology and Biophysics, Weill Medical College of Cornell University, 1300 York Avenue, New York, NY 10021, USA
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Acsai K, Kun A, Farkas AS, Fülöp F, Nagy N, Balázs M, Szentandrássy N, Nánási PP, Papp JG, Varró A, Tóth A. Effect of partial blockade of the Na(+)/Ca(2+)-exchanger on Ca(2+) handling in isolated rat ventricular myocytes. Eur J Pharmacol 2007; 576:1-6. [PMID: 17727839 DOI: 10.1016/j.ejphar.2007.07.047] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2007] [Revised: 07/19/2007] [Accepted: 07/23/2007] [Indexed: 11/30/2022]
Abstract
SEA0400 is a selective inhibitor of the Na(+)/Ca(2+) exchanger having equal potencies to suppress both the forward and reverse mode operation of the Na(+)/Ca(2+) exchanger. Present experiments were designed to study the effect of partial blockade of Na(+)/Ca(2+) exchanger on Ca(2+) handling in isolated rat ventricular myocytes. Intracellular Ca(2+) transient and cell shortening were measured in ventricular myocytes loaded with Fura-2-AM fluorescent dye. Partial blockade of Na(+)/Ca(2+) exchanger was induced by superfusion of the cells with SEA0400 at a concentration of 0.3 microM. Amplitude of the intracellular Ca(2+) transient and cell shortening was significantly increased by SEA0400 in both field stimulated and voltage clamped myocytes, without significant elevation of diastolic Ca(2+) level and the decay time constant of the Ca(2+) transient. In patch clamped myocytes the SEA0400 induced increase in the Ca(2+) transient and cell shortening was accompanied by significant reduction of peak L-type Ca(2+) current. These effects can be explained by the autoregulative nature of cardiac Ca(2+) handling, as the reduced Ca(2+) efflux from the cell results in an increased Ca(2+) load to the sarcoplasmic reticulum leading to increased Ca(2+) release, which in turn may decrease the L-type Ca(2+) current by accelaration of Ca(2+) dependent inactivation of L-type Ca(2+) current. Our results suggest that complex changes in the Ca(2+) cycling can occur after selective pharmacological inhibition of the Na(+)/Ca(2+) exchanger.
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Affiliation(s)
- Károly Acsai
- Division of Cardiovascular Pharmacology, Hungarian Academy of Sciences, Szeged, Hungary.
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Faber GM, Rudy Y. Calsequestrin mutation and catecholaminergic polymorphic ventricular tachycardia: a simulation study of cellular mechanism. Cardiovasc Res 2007; 75:79-88. [PMID: 17531962 PMCID: PMC2030636 DOI: 10.1016/j.cardiores.2007.04.010] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2007] [Revised: 03/15/2007] [Accepted: 04/13/2007] [Indexed: 11/19/2022] Open
Abstract
OBJECTIVES Patients with a missense mutation of the calsequestrin 2 gene (CASQ2) are at risk for catecholaminergic polymorphic ventricular tachycardia. This mutation (CASQ2(D307H)) results in decreased ability of CASQ2 to bind Ca2+ in the sarcoplasmic reticulum (SR). In this theoretical study, we investigate a potential mechanism by which CASQ2(D307H) manifests its pro-arrhythmic consequences in patients. METHODS Using simulations in a model of the guinea pig ventricular myocyte, we investigate the mutation's effect on SR Ca2+ storage, the Ca2+ transient (CaT), and its indirect effect on ionic currents and membrane potential. We model the effects of isoproterenol (ISO) on Ca(V)1.2 (the L-type Ca2+ current, I(Ca(L))) and other targets of beta-adrenergic stimulation. RESULTS ISO increases I(Ca(L)), prolonging action potential (AP) duration (Control: 172 ms, +ISO: 207 ms, at cycle length of 1500 ms) and increasing CaT (Control: 0.79 microM, +ISO: 1.61 microM). ISO increases I(Ca(L)) by reducing the fraction of channels which undergo voltage-dependent inactivation and increasing transitions from a non-conducting to conducting mode of channel gating. CASQ2(D307H) reduces SR storage capacity, thereby reducing the magnitude of CaT (Control: 0.79 microM, CASQ2(D307H): 0.52 microM, at cycle length of 1500 ms). The combined effect of CASQ2(D307H) and ISO elevates SR free Ca2+ at a rapid rate, leading to store-overload-induced Ca2+ release and delayed afterdepolarization (DAD). If resting membrane potential is sufficiently elevated, the Na+-Ca2+ exchange-driven DAD can trigger I(Na) and I(Ca(L)) activation, generating a triggered arrhythmogenic AP. CONCLUSIONS The CASQ2(D307H) mutation manifests its pro-arrhythmic consequences due to store-overload-induced Ca2+ release and DAD formation due to excess free SR Ca2+ following rapid pacing and beta-adrenergic stimulation.
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Affiliation(s)
- Gregory M. Faber
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106-7207
| | - Yoram Rudy
- Cardiac Bioelectricity and Arrhythmia Center and Department of Biomedical Engineering, Washington University, St. Louis, MO 63130-4899
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Inui T, Mori Y, Watanabe M, Takamaki A, Yamaji J, Sohma Y, Yoshida R, Takenaka H, Kubota T. Physiological Role of L-Type Ca2+ Channels in Marginal Cells in the Stria Vascularis of Guinea Pigs. J Physiol Sci 2007; 57:287-98. [DOI: 10.2170/physiolsci.rp006807] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Accepted: 10/25/2007] [Indexed: 11/05/2022]
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Faber GM, Silva J, Livshitz L, Rudy Y. Kinetic properties of the cardiac L-type Ca2+ channel and its role in myocyte electrophysiology: a theoretical investigation. Biophys J 2006; 92:1522-43. [PMID: 17158566 PMCID: PMC1796810 DOI: 10.1529/biophysj.106.088807] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The L-type Ca(2+) channel (Ca(V)1.2) plays an important role in action potential (AP) generation, morphology, and duration (APD) and is the primary source of triggering Ca(2+) for the initiation of Ca(2+)-induced Ca(2+)-release in cardiac myocytes. In this article we present: 1), a detailed kinetic model of Ca(V)1.2, which is incorporated into a model of the ventricular mycoyte where it interacts with a kinetic model of the ryanodine receptor in a restricted subcellular space; 2), evaluation of the contribution of voltage-dependent inactivation (VDI) and Ca(2+)-dependent inactivation (CDI) to total inactivation of Ca(V)1.2; and 3), description of dynamic Ca(V)1.2 and ryanodine receptor channel-state occupancy during the AP. Results are: 1), the Ca(V)1.2 model reproduces experimental single-channel and macroscopic-current data; 2), the model reproduces rate dependence of APD, [Na(+)](i), and the Ca(2+)-transient (CaT), and restitution of APD and CaT during premature stimuli; 3), CDI of Ca(V)1.2 is sensitive to Ca(2+) that enters the subspace through the channel and from SR release. The relative contributions of these Ca(2+) sources to total CDI during the AP vary with time after depolarization, switching from early SR dominance to late Ca(V)1.2 dominance. 4), The relative contribution of CDI to total inactivation of Ca(V)1.2 is greater at negative potentials, when VDI is weak; and 5), loss of VDI due to the Ca(V)1.2 mutation G406R (linked to the Timothy syndrome) results in APD prolongation and increased CaT.
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Affiliation(s)
- Gregory M Faber
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio, USA
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Oheim M, Kirchhoff F, Stühmer W. Calcium microdomains in regulated exocytosis. Cell Calcium 2006; 40:423-39. [PMID: 17067670 DOI: 10.1016/j.ceca.2006.08.007] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2006] [Accepted: 08/23/2006] [Indexed: 11/19/2022]
Abstract
Katz and co-workers showed that Ca(2+) triggers exocytosis. The existence of sub-micrometer domains of greater than 100 microM [Ca(2+)](i) was postulated on theoretical grounds. Using a modified, low-affinity aequorin, Llinas et al. were the first to demonstrate the existence of Ca(2+) 'microdomains' in squid presynaptic terminals. Over the past several years, it has become clear that individual Ca(2+) nano- and microdomains forming around the mouth of voltage-gated Ca(2+) channels ascertain the tight coupling of fast synaptic vesicle release to membrane depolarization by action potentials. Recent work has established different geometric arrangements of vesicles and Ca(2+) channels at different central synapses and pointed out the role of Ca(2+) syntillas - localized, store operated Ca(2+) signals - in facilitation and spontaneous release. The coupling between Ca(2+) increase and evoked exocytosis is more sluggish in peripheral terminals and neuroendocrine cells, where channels are less clustered and Ca(2+) comes from different sources, including Ca(2+) influx via the plasma membrane and the mobilization of Ca(2+) from intracellular stores. Finally, also non- (electrically) excitable cells display highly localized Ca(2+) signaling domains. We discuss in particular the organization of structural microdomains of Bergmann glia, specialized astrocytes of the cerebellum that have only recently been considered as secretory cells. Glial microdomains are the spatial substrate for functionally segregated Ca(2+) signals upon metabotropic activation. Our review emphasizes the large diversity of different geometric arrangements of vesicles and Ca(2+) sources, leading to a wide spectrum of Ca(2+) signals triggering release.
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Affiliation(s)
- Martin Oheim
- Molecular and Cellular Biophysics of Synaptic Transmission, INSERM, U603, Paris, France.
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Olypher A, Cymbalyuk G, Calabrese RL. Hybrid systems analysis of the control of burst duration by low-voltage-activated calcium current in leech heart interneurons. J Neurophysiol 2006; 96:2857-67. [PMID: 16943313 DOI: 10.1152/jn.00582.2006] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The leech heartbeat CPG is paced by the alternating bursting of pairs of mutually inhibitory heart interneurons that form elemental half-center oscillators. We explore the control of burst duration in heart interneurons using a hybrid system, where a living, pharmacologically isolated, heart interneuron is connected with artificial synapses to a model heart interneuron running in real-time, by focusing on a low-voltage-activated (LVA) calcium current I(CaS). The transition from silence to bursting in this half-center oscillator occurs when the spike frequency of the bursting interneuron declines to a critical level, f(Final), at which the inhibited interneuron escapes owing to a build-up of the hyperpolarization-activated cation current, I(h). We varied I(CaS) inactivation time constant either in the living heart interneuron or in the model heart interneuron. In both cases, varying I(CaS) inactivation time constant did not affect f(Final) of either interneuron, but in the varied interneuron, the time constant of decline of spike frequency during bursts to f(Final) and thus the burst duration varied directly and nearly linearly with I(CaS) inactivation time constant. Bursts of the opposite, nonvaried interneuron did not change. We show also that control of burst duration by I(CaS) inactivation does not require synaptic interaction by reconstituting autonomous bursting in synaptically isolated living interneurons with injected I(CaS). Therefore inactivation of LVA calcium current is critically important for setting burst duration and thus period in a heart interneuron half-center oscillator and is potentially a general intrinsic mechanism for regulating burst duration in neurons.
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Affiliation(s)
- Andrey Olypher
- Department of Biology, Emory University, 1510 Clifton Road N.E., Atlanta, GA 30322, USA
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