Hydrogen Peroxide Modifies the Kinetics of HERG Channel Expressed in a Mammalian Cell Line
- Department of Medicine, Faculty of Medicine and Faculty of Pharmacy, Laval University and Quebec Heart Institute, Laval Hospital, Sainte-Foy, Quebec, Canada
Abstract
Reactive oxygen species such as H2O2 were shown to influence both electrical and contractile properties of the heart. H2O2 modulates action potential duration and leads to reperfusion-induced arrhythmias. As these effects could involve the modulation of repolarizing currents, we assessed effects of H2O2 on HERG (which encodes the cardiac potassium channel IKr) expressed in Chinese hamster ovary cells. HERG currents were recorded using the whole-cell patch-clamp technique. HERG activation and deactivation were accelerated when cells were superfused with 30 μM, 100 μM, or 1 mM H2O2. For example, at 1 mM H2O2, τact was decreased from 862 ± 178 to 633 ± 151 ms (P < 0.05;n = 6), and fast τdeact was reduced from 286 ± 47 to 151 ± 18 ms (P < 0.05; n = 6). A negative shift ofV½ was also observed (from −1.9 to −13.7 mV with 30 μM H2O2; P < 0.05), reflecting the acceleration of the activating current. Effects of H2O2 superfusion were prevented by intracellular application of catalase but superoxide dismutase prevented only H2O2-induced acceleration of activation. This indicates that H2O2 diffuses intracellularly before acting on HERG and that its effects on activation but not deactivation are mediated by the superoxide anion. Moreover, τact decrease preceded fast τdeact decrease by about 4 min, suggesting that these effects were not produced by the same intracellular pathway or at the same site on HERG protein. Acceleration of HERG activation kinetics leads to an increase of outward current during the plateau phase of the action potential. This could suggest a reason for H2O2-induced shortening of the action potential. The faster HERG deactivation could be involved in reperfusion-induced arrhythmias by reducing K+ conductance in the early diastole, thus increasing the risks of premature beats.
Footnotes
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Send reprint requests to: Dr. Pascal Daleau, Laval Hospital, Research Center, 2725, Chemin Ste-Foy, Ste-Foy, QC, Canada, G1V 4G5. E-mail:Pascal.Daleau{at}phc.ulaval.ca
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This work was supported by a grant from the Medical Research Council of Canada (MT 12883) and by an operating grant from the Heart and Stroke Foundation of Canada. Dr. Daleau is the recipient of a scholarship from the Fonds de la Recherche en Santé du Québec (J2, 980123).
- Abbreviations:
- ROS
- reactive oxygen species
- HERG
- humanether-a-gogo-related gene
- CHO cells
- Chinese hamster ovary cells
- AP
- action potential
- APD
- action potential duration
- SOD
- superoxide dismutase
- V½
- voltage at which the current was half-activated
- I-V
- current-voltage
- τact
- time constant of activation
- τdeact
- time constant of deactivation
- PAS domain
- Per,Arnt, Sim domain
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- Received August 29, 2000.
- Accepted December 19, 2000.
- The American Society for Pharmacology and Experimental Therapeutics
