Properties of postsynaptic channels induced by acetylcholine in different frog muscle fibres

Abstract

Skeletal muscles in the frog are composed of 2 distinct classes of muscle fiber: fast muscle fibers capable of propagating action potentials and twitches, and slow muscle fibers normally unable to generate action potentials or twitches. Amphibian muscles also contain a spectrum of intermediate fibers whose structural and functional properties lie between those of fast and slow fibers. Much is now known about the characteristics of the channels opened by the transmitter acetylcholine (ACh) acting on the membrane of fast fibers, but the molecular action of ACh on the other fiber types is only poorly understood . The existence of a muscle in the mandibular arch of the frog is reported in which most, if not all, the fibers are multiply innervated and are capable of eliciting action potentials. The channels induced by the transmitter on the synaptic membrane of fast, slow and submaxillaris muscle fibers differ in their lifetimes and conductances.