Effects of surfactants on the twitch tension of frog sartorius muscle

Abstract

Many types of cells show permeability increases to ions and to various uncharged molecules when exposed to surface-active agents (surfactants). Nonionic surfactants are less effective than ionic surfactants in increasing permeability and in depolarizing nerve and muscle cells. In the present experiments the strength of isometric twitch responses of directly stimulated frog sartorius muscles was measured. Ionic surfactants generally produced an irreversible decrease in the twitch response, whereas nonionic surfactants (at equimolar concentrations) had little effect. Aerosol OT conditioned muscles so that curare or neostigmine appeared to produce a decrease in the twitch tension of directly stimulated fibers. Possibly the Aerosol OT treatment increased the permeability of the conducting membrane, allowing curare and neostigmine to interact with the acetylcholine system proposed by Nachmansohn. The above observations could be accounted for by increases in permeability caused by the ionic surfactants. Two observations suggested additional actions of ionic surfactants: low concentrations of cetyltrimethylammonium produced a reversible decrease in twitch tension; low concentrations of anionic surfactants caused an increase in contractile tension.