Electrophysiological Development of Chick Embryo Heart Cells

Electrophysiological properties of chick embryo heart cells were studied in the ages of 2-4 days (in vivo), 7-1- days (excised) and 13-15 days (excised and cut into fragments). Cells were impaled at random at as many loci of the preparations as possible. In the early stage nearly half of the cells impaled showed slow diastolic depolarization in both atrium and ventricle, which, however, occurred less frequently in later stage and finaly disappeared at 13-15 day old in both atrium and ventricle. Action potential overshoot increased as development proceeded in both atrium and ventricle. On the contrary, action potential duration was decreased in atrium and increased in ventricle. On the contrary, action potential duration was decreased in atrium and increased in ventricle. Sensibility to high potassium was similar to that of adult in all stages examined, i. e., shortening of duration occurred in an overwhelming number of impaled cells. Low Na+ affected overshoot with older wmbryos, but not with younger ones up to 4 day old. It was concluded that a )