Effects of hydroxyl radicals on KATP channels in guinea-pig ventricular myocytes

We studied the effects of oxygen free radicals on the ATP-sensitive potassium channel (K-ATP channel) of guinea-pig ventricular myocytes. Single K-ATP channel currents were recorded from inside-out patches in the presence of symmetrical K+ concentrations (140 mM in both bath and pipette solutions). Reaction of xanthine oxidase (0.1 U/ml) on hypoxanthine (0.5 mM) produced superoxide anions (. O-2(-)) and hydrogen perdxide (H2O2). Exposure of the patch membrane to . O-2(-) and H2O2 increased the opening of K-ATP channels, but this activation was prevented by adding 1 mu M glibenclamide to the bath solution. In the presence of ferric iron (Fe3+: 0.1 mM), the same procedure produced hydroxyl radicals ( OH) via the iron-catalysed Haber-Weiss reaction. . OH also activated K-ATP channels; however, this activation could not be prevented by, even very high concentrations of glibenclamide (10 mu M). These different effects of glibenclamide suggest that the mode of action of these oxygen free radicals on K-ATP channels is different and that . OH is more potent than . O-2(-)/H2O2 in activating K-ATP channels in the heart.