Alterations of ionic currents after reoxygenation in isolated cardiocytes of guinea-pigs

Single myocytes were isolated from ventricles of adult guinea-pig hearts. The patch-clamp technique in the whole-cell configuration was used to study ionic currents. Experiments were performed in an experimental chamber that allowed the cells to be exposed to a sufficiently low O₂ pressure to cause metabolic inhibition after 4–35 min (mean 14.1 min, n=20), which was indicated by the appearance of a large time-independent K current. Reoxygenation about 1 min after the first extra outward current was observed caused this current to vanish completely within 2–6 s if the calcium inside the pipette was buffered to negligible values with 20 mmol/l EGTA. With only 10 M EGTA in the pipette, reoxygenation was followed by an arrhythmogenic period of 10–150 s duration, which was dominated by three types of event: (a) transient inward currents (I_ti) developed during the first 5–10 s (26 cells); (b) the net current was increased by a factor of 1.9±0.4 (mean±SD, n=17) yielding a reversal potential for the increased component of –77±4 mV (mean±SD, n=4); and (c) the Ca current decreased by 20%–100% within the first 5–10 s. At the end of the arrhythmogenic period, I_ti vanished, the net current recovered completely, and the Ca current recovered partially. At –45 mV, increasing preceding depolarization enlarged the amplitude of both the I_ti and the net current, I_ti being about four times more increased than the net current. The suppression of the Ca current was independent of the phase of the preceding I_ti. We conclude that in isolated cardiocytes, after the induction of an anoxia-induced K current, reoxygenation causes a period of up to 150 s of cytosolic Ca overload, during which I_ti is triggered, the net current is enhanced, and the Ca current is suppressed.This work was supported by the Deutsche Forschungsgemeinschaft, Hi 137/10-1