Reexpression of the nifedipine-resistant calcium channel during dedifferentiation of adult rat ventricular cardiomyocytes

INTRODUCTION: Using an adult rat ventricular culture model and whole-cell patch-clamp technique, we investigated whether the nifedipine-resistant calcium current observed at the neonatal stage but not at the adult stage could be reobserved under dedifferentiating conditions. METHODS AND RESULTS: Application of 2 microM nifedipine totally inhibited the inward calcium current (carried by 5 mM Ba2+) in freshly isolated cells from adult rat heart, but it failed to block it completely when cells are cultured for 8 to 12 days. Dose-response curves of nifedipine in the range from 2 to 50 microM showed a residual current that represented, in the presence of 2 microM nifedipine, 16.4%+/-1.8% (n = 10) and 20.4%+/-1.5% (n = 10) of the total current in 8- and 12-day-old cultured cells, respectively. In these conditions, its density at 0 mV increased slightly during culture (-2.1+/-0.2 pA/pF, n = 7, and -3.2+/-0.4 pA/pF, n = 8, after 8 and 12 days in culture, respectively), without modification in the current-to-voltage curve, as well as in kinetics properties. CONCLUSION: These results show that nifedipine-resistant calcium current, which has been shown to be developmentally regulated in rat ventricular cardiomyocytes, can be reexpressed in cultured-dedifferentiated cells. Its possible expression and implication in physiopathologic function are suggested.