Free radicals irreversibly decrease Ca2+ currents in isolated guinea-pig ventricular myocytes.

The effects of free radicals on voltage-gated Ca2+ currents (ICa) were investigated in single guinea-pig ventricular myocytes using the whole-cell clamp technique. ICa 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. ICa decreased from 846 +/- 533 (S.D.) pA to 688 +/- 444 pA (n = 7, P < 0.05) in the presence of 100 microM cumene hydroperoxide and from 708 +/- 157 pA to 457 +/- 163 pA (n = 5, P < 0.0001) in the presence of 500 microM cumene hydroperoxide. ICa 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 ICa could not be restored by washing for up to 5 min using normal recording solution. We conclude that ICa 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.