Fig. 6. Effect of dihydropyridines, verapamil and NiCl₂ on the low-voltage activated calcium current of muscle cells. Sr²⁺ was used as the charge carrier. Unmarked traces are those recorded before the drug was applied while traces marked with an asterisk indicate those recorded with the drug applied, and traces marked by an arrow indicate those recorded after washing with bath solution. The stimulus protocol used was a single 20 ms voltage step to -30 mV from a holding potential of -80 mV. The early large phasic negative-going current excursion is the uncompensated capacitative current while the transients at the end of the traces are the ‘off’ capacitative transients.