Separation of membrane currents using a Paramecium mutant.

The net membrane current of the electrically excitable membrane of Paramecium during step depolarisations was measured using voltage-clamp techniques. The mutant, pawn B, lacks a functional Ca channel. Thus the difference between the total current measured in the wild type and the leakage and rectification currents measured in the pawn mutant is the Ca current. These findings were confirmed by ion substitution experiments. The possibility that inactivation may be apparent only, and caused by a hypothetical, superposed, Ca-induced, rectifying K+ current was eliminated.