Oxygen-derived free radicals (OFRs), produced as myocardium is reperfused after ischemic injury, contribute to reversible and irreversible cellular injury. KATP channels, activated by ischemia, have been reported to participate in the arrhythmogenic response to acute myocardial ischemia. Therefore, we examined the effects of OFRs on the regulation of KATP channel activity.

Isolated mice (ICR) hearts were perfused with Tyrode's solution on a Langendorff apparatus. Single ventricular myocytes were isolated using enzymatic digestion with collagenase and protease. Single channel currents in the inside-out patch mode were recorded. OFRs were applied by mixing hypoxanthine and xanthine oxidase. The currents were recorded in the patch membrane at a holding potential of -60 mV.

OFRs generated by 0.1 U/mL xanthine oxidase and 0.5 mM hypoxanthine had no effects on the activities of KATP channels before and after treatment with 200 micrometer ATP. OFRs generated with 0.2 U/mL xanthine oxidase and 1.0 mM hypoxanthine reactivated the channel activities which had been attenuated by 100 micrometer ATP. In the presence of 100 U/mL superoxide dismutase and 122 U/mL catalase, which are OFRs scavengers, OFRs did not affect the KATP channels activities.

OFRs generated by the reaction of hypoxanthine and xanthine oxidase increased the KATP channel activities in the inside-out patch.