POTENTIATION OF TWITCH TENSION AND PROLONGATION OF ACTION POTENTIAL INDUCED BY REDUCTION OF TEMPERATURE IN RAT AND FROG MUSCLE

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Abstract
Observations were made on the modification of twitch response induced by cooling the rat triceps surae in situ and cooling isolated frog muscle. The rat muscles were cooled by refrigeration of the whole animal or by placing the leg in a cooling chamber. The frog muscles were cooled by placing the leg or the isolated muscle in cool Ringer''s soln. Cooling the rat triceps surae from 37[degree]C to 24[degree]C by refrigeration increased twitch tension about 80-90% and increased the duration of the action potential about 300%. The time course of the twitch was increased about 350%. Reduction of the temp. Of the bathing fluid from 27.5[degree]C to 14.5[degree]C induced changes in the twitch response and action potential of the in situ gastrocnemius muscle of summer frogs similar to those observed in rat muscle. The same change of temp. usually produced a decrease of twitch tension of in situ muscle of winter frogs and of isolated frog muscle. A causal relation between increased duration of membrane ''breakdown'' and increased twitch contraction of muscle fibers is suggested.