Synaptic channel gating differences at snake twitch and slow neuromuscular junctions

Abstract

Two readily distinguishable skeletal muscle fibre types are found in the muscles of lower vertebrates, including amphibians, birds, fishes and reptiles¹: twitch and slow fibres. In response to membrane depolarisation the twitch fibre contracts briefly, whereas the slow fibre can develop and maintain tension for long periods. The slow fibres each have several endplates which differ anatomically from the twitch fibre's single endplate^1,2 and may have a direct role in the maintained contractile behaviour. We report here studies of the synaptic conductance change mediated by acetylcholine (ACh, the natural chemical agonist) in these fibres and document a difference in the voltage dependence of endplate channel lifetime which correlates with muscle type. This difference may be mediated by an altered expression of the gating mechanism of the synaptic channel.