POSTSYNAPTIC EFFECTS OF HC-3 AT THE NEUROMUSCULAR JUNCTION OF THE FROG

Abstract

Intracellular recording from single muscle fibers has been used to study the effects of hemicholinium No. 3 (HC-3) on neuromuscular transmission in the excised m. ext. l. dig. IV of the frog. Concentrations of HC-3 greater than 10⁻⁵ M decreased the amplitude of the end-plate potentials (e.p.p.'s) and the magnitude of the depolarization produced by iontophoretic application of acetylcholine. Neither a decrease in e.p.p. quantum content nor depolarization of the end plate accompanied the decreased e.p.p. amplitude. The duration of the potential produced by the application of ACh was increased and the falling phase of the e.p.p. prolonged. 10⁻⁴ M HC-3 produced a marked change in the shape of the e.p.p., the effect being similar to that produced by procaine.