Fig. 6. Characterisation of action potentials recorded from muscle 214 from mature females. (A) The application of tetrodotoxin (TTX) (0.5 µmol l^–1) had no effect on the generation or the shape of the action potential. (B) Application of Cd²⁺ (50 µmol l^–1) completely blocked action potentials. Even increasing the injected current (from 24 to 40 nA) was not effective in generating potentials when Cd²⁺ was present in the bath. After washing in normal saline (10 min), action potentials reappeared. (C) Nifedipine (50 µmol l^–1), which is known to modulate L-type Ca²⁺ channels, blocked the generation of action potentials even when the amount of current was increased (from 27.5 to 49 nA). Washing with normal saline reversed the blocking effect of nifedipine. The examples shown in A, B, C are from two different preparations.