Vol. 297, Issue 1, 96-102, April 2001

Hydrogen Peroxide Modifies the Kinetics of HERG Channel Expressed in a Mammalian Cell Line

Jocelyn Bérubé, David Caouette and Pascal Daleau

Department of Medicine, Faculty of Medicine and Faculty of Pharmacy, Laval University and Quebec Heart Institute, Laval Hospital, Sainte-Foy, Quebec, Canada

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 I_Kr) 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, _act was decreased from 862 ± 178 to 633 ± 151 ms (P < 0.05; n = 6), and fast _deact was reduced from 286 ± 47 to 151 ± 18 ms (P < 0.05; n = 6). A negative shift of V1/2 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, _act decrease preceded fast _deact 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.