Abstract
The differences of the property in rat myocardium between newborn and adult were investigated. It was the most obvious alterations of rat ECG with age that Q-T interval became short and S-T segment disappeared. In accordance with these alterations, the alterations of ventricular action potential (AP) configuration were recognized, too: the duration of AP became short and the plateau phase disappeared with age. These alterations with age were independent of the stimulation frequency. The effect of Ca antagonist on the AP configuration was different between newborn and adult: the plateau phase of newborn's AP was reduced by it, but little effect was seen in adult AP. But the plateau phase was appeared and the duration of AP was prolonged even in adult under the condition of low temperature Tyrode solution, and this plateau phase, was reduced by Ca antagonist. Moreover, in each preparation the slow response induced by the activity of slow channel, which was obtained by elevated potassium concentration, was recognized. From these results, it was suggested that more rapid appearance of repolarization in adult than in newborn deprived of the opportunity of the activation of slow channel, so that no plateau phase was observed in adult AP.
