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Kim JG, Sung DJ, Kim HJ, Park SW, Won KJ, Kim B, Shin HC, Kim KS, Leem CH, Zhang YH, Cho H, Bae YM. Impaired Inactivation of L-Type Ca2+ Current as a Potential Mechanism for Variable Arrhythmogenic Liability of HERG K+ Channel Blocking Drugs. PLoS One 2016; 11:e0149198. [PMID: 26930604 PMCID: PMC4772914 DOI: 10.1371/journal.pone.0149198] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 01/28/2016] [Indexed: 01/06/2023] Open
Abstract
The proarrhythmic effects of new drugs have been assessed by measuring rapidly activating delayed-rectifier K+ current (IKr) antagonist potency. However, recent data suggest that even drugs thought to be highly specific IKr blockers can be arrhythmogenic via a separate, time-dependent pathway such as late Na+ current augmentation. Here, we report a mechanism for a quinolone antibiotic, sparfloxacin-induced action potential duration (APD) prolongation that involves increase in late L-type Ca2+ current (ICaL) caused by a decrease in Ca2+-dependent inactivation (CDI). Acute exposure to sparfloxacin, an IKr blocker with prolongation of QT interval and torsades de pointes (TdP) produced a significant APD prolongation in rat ventricular myocytes, which lack IKr due to E4031 pretreatment. Sparfloxacin reduced peak ICaL but increased late ICaL by slowing its inactivation. In contrast, ketoconazole, an IKr blocker without prolongation of QT interval and TdP produced reduction of both peak and late ICaL, suggesting the role of increased late ICaL in arrhythmogenic effect. Further analysis showed that sparfloxacin reduced CDI. Consistently, replacement of extracellular Ca2+ with Ba2+ abolished the sparfloxacin effects on ICaL. In addition, sparfloxacin modulated ICaL in a use-dependent manner. Cardiomyocytes from adult mouse, which is lack of native IKr, demonstrated similar increase in late ICaL and afterdepolarizations. The present findings show that sparfloxacin can prolong APD by augmenting late ICaL. Thus, drugs that cause delayed ICaL inactivation and IKr blockage may have more adverse effects than those that selectively block IKr. This mechanism may explain the reason for discrepancies between clinically reported proarrhythmic effects and IKr antagonist potencies.
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Affiliation(s)
- Jae Gon Kim
- Department of Physiology and the Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, South Korea
- Next-Generation Pharmaceutical Research Center, Korea Institute of Toxicology, Korea Research Institute of Chemical Technology, Daejeon, South Korea
| | - Dong Jun Sung
- Division of Sport Science, College of Science and Technology, Konkuk University, Choongju, South Korea
| | - Hyun-ji Kim
- Department of Physiology and the Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, South Korea
| | - Sang Woong Park
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, South Korea
| | - Kyung Jong Won
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, South Korea
| | - Bokyung Kim
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, South Korea
| | - Ho Chul Shin
- Department of Veterinary Pharmacology and Toxicology, College of Veterinary Medicine, Konkuk University, Seoul, South Korea
| | - Ki-Suk Kim
- Next-Generation Pharmaceutical Research Center, Korea Institute of Toxicology, Korea Research Institute of Chemical Technology, Daejeon, South Korea
- Human and Environmental Toxicology Program, University of Science and Technology, Daejeon, South Korea
| | - Chae Hun Leem
- Department of Physiology, University of Ulsan College of Medicine, Seoul, South Korea
| | - Yin Hua Zhang
- Department of Physiology, Seoul National University College of Medicine, Seoul, South Korea
| | - Hana Cho
- Department of Physiology and the Samsung Biomedical Research Institute, Sungkyunkwan University School of Medicine, Suwon, South Korea
- * E-mail: ;
| | - Young Min Bae
- Department of Physiology, KU Open Innovation Center, Research Institute of Medical Science, Konkuk University School of Medicine, Chungju, South Korea
- * E-mail: ;
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Ryu JS, Kim WT, Lee JH, Kwon JH, Kim HA, Shim EB, Youm JB, Leem CH. Analysis of factors affecting Ca(2+)-dependent inactivation dynamics of L-type Ca(2+) current of cardiac myocytes in pulmonary vein of rabbit. J Physiol 2012; 590:4447-63. [PMID: 22674726 DOI: 10.1113/jphysiol.2012.229203] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
L-type Ca(2+) channels (ICaLs) are inactivated by an increase in intracellular [Ca(2+)], known as Ca(2+)-dependent inactivation (CDI). CDI is also induced by Ca(2+) released from the sarcoplasmic reticulum (SR), known as release-dependent inhibition (RDI). As both CDI and RDI occur in the junctional subsarcolemmal nanospace (JSS), we investigated which factors are involved within the JSS using isolated cardiac myocytes from the main pulmonary vein of the rabbit. Using the whole-cell patch clamp technique, RDI was readily observed with the application of a pre-pulse followed by a test pulse, during which the ICaLs exhibited a decrease in peak current amplitude and a slower inactivation. A fast acting Ca(2+) chelator, 1,2-bis(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA), abolished this effect. As the time interval between the pre-pulse and test pulse increased, the ICaLs exhibited greater recovery and the RDI was relieved. Inhibition of the ryanodine receptor (RyR) or the SR Ca(2+)-ATPase (SERCA) greatly attenuated RDI and facilitated ICaL recovery. Removal of extracellular Na(+),which inhibits the Na(+)-Ca(2+) exchange (Incx), greatly enhanced RDI and slowed ICaL recovery, suggesting that Incx critically controls the [Ca(2+)] in the JSS. We incorporated the Ca(2+)-binding kinetics of the ICaL into a previously published computational model. By assuming two Ca(2+)-binding sites in the ICaL, of which one is of low-affinity with fast kinetics and the other is of high-affinity with slower kinetics, the new model was able to successfully reproduce RDI and its regulation by Incx. The model suggests that Incx accelerates Ca(2+) removal from the JSS to downregulate CDI and attenuates SR Ca(2+) refilling. The model may be useful to elucidate complex mechanisms involved in excitation–contraction coupling in myocytes.
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Affiliation(s)
- Ju Seok Ryu
- Department of Physiology, University of Ulsan College of Medicine, Seoul, Korea
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