CHANGES IN ACTION-POTENTIALS AND ION CURRENTS IN LONG-TERM CULTURED NEONATAL RAT VENTRICULAR CELLS

A primary culture of neonatal ventricular myocytes isolated from day-o ld rats was established for investigating the changes in action potent ials and ion currents over long periods. Cells at days 5 and 15 in cul ture were studied. These changes in vitro were compared with those in situ derived from the age-matched freshly isolated cells. During prima ry culture, quiescent cells demonstrated shortening of action potentia l durations (APD) resembling the developmental changes observed in sit u. The beating cultured cells were not associated with APD shortening. Despite constant current amplitudes, the densities of Ca2+ currents ( I-Ca) decreased in the quiescent cultures at later ages as a result of cell enlargement. I-Ca densities were maintained in the beating cultu red and freshly isolated cells. Acceleration in the inactivation of I- Ca was observed during developments both in vitro and in situ. In addi tion, the densities of transient outward currents (I-to) tripled and d oubled in the quiescent and beating cells during 15-day cultures. Howe ver, I-to in beating cultured cells made less contribution to APD in c ontrast to the quiescent cultured and freshly isolated myocytes. These findings demonstrate that electrophysiological properties differ betw een two types of long-term cultured cells. I-Ca densities remained con stant in the beating cultures, suggesting that cell beating may be req uired for the maintenance of I-Ca density in developing cardiomyocytes .