Developmental Changes in Ca2+ Currents from Newborn Rat Cardiomyocytes in Primary Culture

Electrophysiological characteristics of neonatal rat ventricular cardiomyocytes in primary culture were studied using the whole-cell patch-clamp recording technique. Cell size, estimated by measurement of membrane capacitance, was significantly increased throughout the culture from 22.4 +/- 5.4 pF at day 2 to 55.0 +/- 16.1 pF at day 7, reflecting the hypertrophic process which characterises postnatal cell development. The Ca2+ current was investigated at day 2 and 7 of the culture which constituted the early postnatal and maximally developed stages, respectively, of isolated cells in our experimental conditions. At 2 days of culture, two types of Ca2+ current could be distinguished, as also observed in freshly dissociated newborn ventricular cells. From their potential dependence and pharmacological characteristics, they could be attributed to the T- (ICa-T) and L-type (ICa-L) Ca2+ current components. After 7 days of culture, only the latter ICa-L was present and its density was significantly increased when compared to the density in 2-day-old cells, but lower than that obtained in freshly dissociated adult cells. As the age of the culture progressed, the steady-state inactivation curve was shifted toward negative potentials, in the direction of the inactivation curve obtained for adult cells. Compared to the serum-free control conditions, the density of ICa-L was significantly increased in the presence of fetal calf serum throughout the culture. Consequently, the density of ICa-L obtained in 7-day-old cells was similar to the density of ICa-L obtained in freshly dissociated adult cardiac cells.(ABSTRACT TRUNCATED AT 250 WORDS)