Developmental Changes in Action Potential Prolongation by K⁺-Channel Blockers in Chick Myocardium

The effects of K⁺-channel blockers on the action potential duration of the myocardium were examined in isolated right ventricles from the 7 - 10-day-old, 11 - 13-day-old, and 14 - 20-day-old embryo and 1 - 7-day-old hatched chicks. E-4031 significantly prolonged action potential duration at all developmental stages examined; the prolongation was largest in the 11 - 13-day-old embryo and was accompanied by early after-depolarizations. Chromanol 293B showed smaller prolongation at all stages examined. Terfenadine prolonged action potential duration in the 11 - 13-day-old embryo, but not in other stages. Thus, the chick ventricular myocardium changes its repolarization properties during development.