Contractile activities of mammalian smooth muscles in chloride-deficient media

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Abstract
When the chloride ion of the medium around uterine or intestinal smooth muscles was replaced by nitrate, bromide, iodide or thiocyanate, the phasic contractions were potentiated, and marked tonic contractions were induced. The changes in the phasic contractions resembled those in skeletal muscle in having stronger and longer-lasting ‘twitch’ contractions, in exhibiting some dependence of these changes on the concentration of the substituting anions, and in having some changes in electrical excitability. The tonic contractions were accompanied by markedly increased spike discharges, which occurred with a slight increase rather than a decrease of the resting potential. Tonic contraction could be elicited in sodium-free medium by using sucrose or by using sequentially choline chloride and choline nitrate as substitutes. Distinct roles of sodium and chloride in the contractile activities were recognizable upon resupplying these two ions separately to preparations deprived of both. It was concluded that presence of external sodium was necessary for phasic contractions, and presence of external chloride necessary for relaxation from tonic contractions.

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