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

Abstract

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.