Hydrogen peroxide modifies the kinetics of HERG channel expressed in a mammalian cell line

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 microM, 100 microM, or 1 mM H2O2. For example, at 1 mM H2O2, tau(act) was decreased from 862 +/- 178 to 633 +/- 151 ms (P < 0.05; n = 6), and fast tau(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 microM 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, tau(act) decrease preceded fast tau(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.