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

Abstract

 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 (·O₂ ^-) and hydrogen peroxide (H₂O₂). Exposure of the patch membrane to ·O₂ ^- and H₂O₂ increased the opening of K_ATP channels, but this activation was prevented by adding 1 µM 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 µM). 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 ·O₂ ^-/H₂O₂ in activating K_ATP channels in the heart.