Muscle Twitch Tension - Influence of Electrical Stimulating Conditions at Different Temperatures I. Results for Chloride Ringer's

Abstract

An attempt was made to resolve experimentally the conflicting data on the variation of the amplitude of isometric twitch tension with temperature for frog skeletal muscle. It was shown that the use of mass electrodes, to provide "supermaximal" stimuli for excised, uncurarized frog sartorius muscle can lead to low values of "peak" twitch tension at temperatures above 18[degree]C, if the stimulating current amplitude is the only variable parameter. In order to determine the peak tension, two parameters, amplitude and duration must be varied. The application of different durations of "supermaximal" stimuli, and the use of widely differing types of mechanical attachments between muscle and transducers by previous investigators, may account for the conflicting results. The effect of pulse duration of a single stimulus on the amplitude of elicited tension was found to be temperature dependent, with a minimal effect at 0[degree]C. The maximum amplitude of isometric tension in response to a single stimulus for uncurarized frog sartorius muscle was shown to increase with increasing temperature. The maximum amplitudes of isometric tetanus tension at temperatures above 18[degree]C are considerably greater than those reported by previous investigators. This is attributed primarily to improved measurement methods, in particular to arrangements which prevent loss of tension due to the compliance of attachments between muscle and transducer. Values of the ratio of the twitch to tetanus tension as high as 0.8 have been obtained, as compared with the generally reported range of values 0.1 to 0.3. The maximum amplitude of tension developed by a curarized muscle in chloride Ringer''s, at temperatures above 18oC, in response to a single pulse delivered by a mass electrode is considerably less than that of an uncurarized muscle adequately stimulated at the same temperature. Increasing the duration of the stimulus does not overcome the barrier of the curarization.