Cell Cycle-related Changes in the Voltage-gated Ca2+Currents in Cultured Newborn Rat Ventricular Myocytes

The expression of T-type Ca2+current (ICa,T) has been reported to change during postnatal heart development and myocardial hypertrophy, which are characterized respectively by the arrest of the cell cycle soon after birth and a switching on of DNA synthesis in the terminally differentiated cardiac myocytes. The hypothesis that there are cell cycle-related changes in cardiac Ca2+channel expression was tested by performing whole-cell voltage-clamp recording and BromodeoxyUridine (BrdU) immunolabeling to determine the S phase of the cell cycle in the same single cultured newborn rat ventricular cells. Myocytes were isolated from 1-day-old Wistar rats and cultured for 15 days. ICa,Twas detected in 27% of the 5-day cultured myocytes. The progressive loss of ICa,Tduring the period of 15-day incubation, which resembles the developmental changesin vivo, paralleled the decrease in the percentage of cells showing BrdU labeling. At day 5 of cell culture, the fraction of myocytes expressing ICa,Twas significantly higher in the BrdU-labeled population (95%) as compared with the non-labeled cells (19%). In addition, a 72-h treatment with 20μmnickel, an ICa,Tblocker, revealed no effect on the percentage of BrdU-positive cells. -type Ca2+current (ICa,L) was constantly expressed throughout the 15-day cell culture. The frequency of ICa,Lexpression was identical between the BrdU-labeled and the non-labeled myocytes, although the latter cell population demonstrated a relatively greater current density. No differences in the inactivating kinetics of ICa,Land their reaction toβ-adrenoceptor stimulation were observed between the two groups. These findings provide convincing evidence for the cell cycle-related expression of cardiac Ca2+channel. Cardiomyocytes at the S phase of the cell cycle predominantly express ICa,T, while the major properties of ICa,Lare unchanged during the cell cycle. Such a cell cycle-related channel expression may play a critical role in regulating the cardiac electrophysiological properties during heart development and myocardial remodeling.