FREE-RADICALS IRREVERSIBLY DECREASE CA2+ CURRENTS IN ISOLATED GUINEA-PIG VENTRICULAR MYOCYTES

The effects of free radicals on voltage-gated Ca2+ currents (I-Ca) were investigated in single guinea-pig ventricular myocytes using the whole-cell clamp technique. I-Ca was measured in the baseline state and after the application of free radicals from cumene hydroperoxide or generated from the addition of purine to xanthine oxidase. I-Ca decreased from 846 +/- 533 (S.D.) pA to 688 +/- 444 pA (n = 7, P < 0.05) in the presence of 100 mu M cumene hydroperoxide and from 708 +/- 157 pA to 457 +/- 163 pA (n = 5, P < 0.0001) in the presence of 500 mu M cumene hydroperoxide. I-Ca also decreased from 1303 +/- 560 pA to 965 +/- 360 pA in the presence of the free radical generating system (2.3 mM purine plus 20 U/l xanthine oxidase). The reduced I-Ca could not be restored by washing for up to 5 min using normal recording solution. We conclude that I-Ca is decreased in the presence of cumene hydroperoxide and an oxygen-derived free radical generating system in single guinea-pig ventricular myocytes. The cellular Ca2+ overload observed in free radical mediated reperfusion injury is therefore unlikely to result from an increase in sarcolemmal Ca2+ entry via voltage-gated Ca2+ channels.