APs and L-type calcium currents in CDI-impaired cardiomyocytes. (A) Representative AP waveforms from a newborn rat cardiomyocyte overexpressing CaMwt (solid black line) or CaM34 (dashed blue line). APs were elicited by 2–5 ms depolarizing current injections (100–200 pA) at 1 Hz. The horizontal line indicates zero level. (B) Bar graph of APD estimated at 20% (APD20), 50% (APD50), and 90% (APD90) of the repolarization phase. (C) Phase plot of the normalized first derivative of membrane potential (dV/dt) against membrane potential (Vm) for the APs shown in A. Empty symbols correspond to data from cardiomyocytes overexpressing CaMwt and blue symbols for cardiomyocytes overexpressing CaM34. (D) Bar graph of overshoot, threshold potentials, and mean DMPs. (E) Representative nifedipine-sensitive current (solid line) elicited by the AP (dashed line) prerecorded from the same cardiomyocyte overexpressing CaM34. (F) Bar graph of maximal current normalized by cell capacitance (pA/pF), total time of nifedipine-sensitive current normalized by its APD (TTCnorm), and the total current integral normalized by cell capacitance (Qtotal). Data are shown as percentages with respect to CaMwt-overexpressing cardiomyocytes. Bar graphs are mean ± SEM; empty bars represent cardiomyocytes overexpressing CaMwt, and blue bars correspond to those overexpressing CaM34 (n = 7; *, P < 0.01 with respect to CaMwt).