DEVELOPMENTAL-CHANGES IN CA2+ CURRENTS FROM NEWBORN RAT CARDIOMYOCYTES IN PRIMARY CULTURE

Electrophysiological characteristics of neonatal rat ventricular cardi omyocytes in primary culture were studied using the whole-cell patch-c lamp recording technique. Cell size, estimated by measurement of membr ane capacitance, was significantly increased throughout the culture fr om 22.4 +/- 5.4 pF at day 2 to 55.0 +/- 16.1 pF at day 7, reflecting t he hypertrophic process which characterises postnatal cell development . The Ca2+ current was investigated at day 2 and 7 of the culture whic h constituted the early postnatal and maximally developed stages, resp ectively, 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 b e attributed to the T- (I-Ca-T) and L-type (I-Ca-L) Ca2+ current compo nents. After 7 days of culture, only the latter I-Ca-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 dissociate d adult cells. As the age of the culture progressed, the steady-state inactivation curve was shifted toward negative potentials, in the dire ction of the inactivation curve obtained for adult cells. Compared to the serum-free control conditions, the density of I-Ca-L was significa ntly increased in the presence of fetal calf serum throughout the cult ure. Consequently, the density of I-Ca-L obtained in 7-day-old cells w as similar to the density of I-Ca-L obtained in freshly dissociated ad ult cardiac cells. These results show that in rat neonatal ventricular cardiomyocytes, the changes in Ca2+ current during development in pri mary culture can be compared to that observed in vivo during the first weeks of the postnatal period. The data suggest that the composition of the culture medium is a conditioning factor in the development of c ardiac cells in culture. However, the determination and the role of sp ecific factors contained also discussed in terms of a possible correla tion between the expression and maturation of the Ca2+ current compone nts and the capabilities of the neonatal cardiac cells to proliferate and/or to hypertrophy. For these reasons primary cultures of neonatal rat cardiac cells could constitute a valuable in vitro model for studi es of postnatal development.