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

Abstract

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 microM 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 (Iti) 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, Iti vanished, the net current recovered completely, and the Ca current recovered partially. At -45 mV, increasing preceding depolarization enlarged the amplitude of both the Iti and the net current, Iti being about four times more increased than the net current. The suppression of the Ca current was independent of the phase of the preceding Iti. 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 Iti is triggered, the net current is enhanced, and the Ca current is suppressed.