Effects of anoxia on K and Ca currents in isolated guinea pig cardiocytes

Whole cell currents were measured in isolated cardiocytes of guinea pig under anoxic conditions (pO2 less than 0.5 torr). After 2 to 32 (mean 11.2) minutes of anoxia, time independent outward currents developed gradually which had a linear current-voltage relation between -100 and +20 mV and reversed at the resting potential of the cells (-82 to -90 mV). After 20 to 170 (mean 38) seconds, the amplitude of these outward currents saturated (3.6 +/- 0.5 nA at +10 mV, n = 23). Reoxygenation within one minute after the appearance of the first extra outward currents led in most cells (greater than 90%) to their complete disappearance in 2 to 4 (mean 2.87, n = 15) seconds. Ca currents were not affected at the time when the first extra outward currents occurred. It is concluded that (i) the anoxia-induced outward current is carried by K+ ions probably through KATP channels which open at intracellular ATP concentrations below 1 mmol/l (Noma and Shibasaki 1985) and (ii) this degree of ATP depletion does not affect normal Ca channel function.