title: Postnatal development of electrophysiological manifestations of the working ventricular myocardium of albino rats.
abstract: To elucidate the postnatal development of electrogenesis in the rat ventricular myocardium, we investigated specimens of the right ventricles of rats of different ages (newborn, 2 days, 5 days, 10 days and adult) by means of glass microelectrodes and a programmable stimulator. The resting membrane potential rose from -82 mV (newborn) to -89.6 mV (adult). During the first 10 postnatal days the plateau phase of the action potential (AP) shortened from 46 ms to 16 ms; in adulthood its duration was 9.6 ms. An increase in the stimulation frequency from 2 Hz to 10 Hz led to pronounced shortening of the myocardial AP of newborn and 2-day-old rats; with advancing age the influence of a mounting frequency diminished and the myocardium of adult rats was frequency-insensitive. The first AP evoked after a rest interval in the myocardium of newborn animals was prolonged proportionally to the logarithm of the duration of the interval; the AP of adult rats was unaffected by the length of the interval. During the rest interval diastolic depolarization appeared on the myocardium of newborn rats; with advancing age it slowed down and the decrease in membrane voltage was smaller. In the adult rats myocardium there was no diastolic depolarization.
mesh_terms: D000200:Action Potentials; D000375:Aging; D000818:Animals; D000831:Animals, Newborn / Q000502:physiology; D004594:Electrophysiology; D006321:Heart / Q000502:physiology*; D066298:In Vitro Techniques; D008564:Membrane Potentials; D051381:Rats