Reopening of L‐type calcium channels in human ventricular myocytes during applied epicardial action potentials

Aims: Present study was performed to compare the dynamics of human L‐type calcium current (I_Ca,L) flowing during rectangular voltage pulses, voltage ramps, and action potentials (APs) recorded from epicardiac and endocardiac canine ventricular cells. Methods: I _Ca,L was recorded in single myocytes isolated from undiseased human hearts using the whole cell voltage clamp technique. Results: The decay of I_Ca,L was monotonic when using rectangular pulses or endocardial APs as voltage commands, whereas the current became double‐peaked (displaying a second rise and fall) during epicardial (EPI) APs or voltage ramps used to mimic EPI APs. These I_Ca,L profiles were associated with single‐hooked and double‐hooked phase‐plane trajectories, respectively. No sustained current was observed during the AP commands. Kinetics of deactivation and recovery from inactivation of human I_Ca,L were determined using twin‐pulse voltage protocols and voltage ramps, and the results were similar to those obtained previously in canine cells under identical experimental conditions. Conclusions: I _Ca,L can inactivate partially before and deactivate during the phase‐1 repolarization of the epicardiac AP, and reopening of these channels seems to be associated with formation of the dome.