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

The effects of free radicals on voltage-gates 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 μM cumene hydroperoxide and from 708 ± 157 pA to 457 ± 163 pA(n = 5, P < 0.0001) in the presence of 500 μM 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 sacrolemmal Ca²⁺ entry via voltage-gated Ca²⁺ channels.