ROLE OF INWARD AND DELAYED RECTIFIER CURRENTS IN GENERATION OF EARLY AFTERDEPOLARIZATION IN GUINEA-PIG VENTRICULAR MYOCYTES UNDER K-FREE ORLOW K+ SUPERFUSION()

Early afterdepolarization (EAD) was studied in isolated ventricular my ocytes of guinea pig heart. Under K+-free's treatment most of the myoc ytes showed hyperpolarization in resting potential and the duration of action potential was prolonged, eventually lending to the appearance of EAD with the second plateau of -76 +/- 3 mV. TTX (10 mu M) and vera pamil (10 mu M) or normal Tyrode's solution abolished the EAD. The bac kground I-V curve showed inward rectifying with a crossover in the lev el of -80 to -30 mV and the reversal potential shifted from -80 to -12 0 mV when normal Tyrode's solution was changed to K+-free solution. Th e changes of I-V relationship of inward current I-K) were similar to t he background ones except without crossover The delayed rectifier curr ent (I-K) was inhibited significantly under K+-free treatment. Low K(2.7 mM) superfusion was able to induce EAD in only a few cases (4/15) . Adding Cs+ (5.0 mM) into low K+ solution, EAD was induced in almost every case. The background I-V curve was inhibited slightly under low K+ superfusion, but was inhibited significantly with a remarkable cros sover under low K+ and Cs+ treatment. The changes of I-V curve I-Kl un der low K+ or low K+ and Cs+ treatment were similar to the changes of background ones. There were no significant changes in the I-K under lo w K+ superfusion while a remarkable inhibition occurred under low K+ a nd Cs+ treatment It was suggested that both I-Kl and I-K were involved in the induction of EAD under K+-free or Cs+ treatment in guinea pig ventricular myocytes.