Measurement of Heat Production during the Summation of Isometric Contraction in Frog Skeletal Muscle withan Infrared Radiometer

Abstract

The heat production of frog skeletal muscle during isometriccontraction was measured with an infrared radiometer at room temperature (23-26°C), attention being focused on the heat produced duringthe summation of twitches by two successive stimuli.When the amountof heat produced by the second stimulus was plotted against the cor-responding tension increment, the data points fell on two regressionlines of approximately the same slope except for the intermediate stimulusintervals.One regression line started from the origin, while the otherintersected the ordinate at about 1mcal/g.If a twitch was produced atvarious times after a 0.5 sec tetanus, all the data points on the heat versustension increment plot distributed around a single regression line startingfrom the origin.These results are explained by assuming that therelation between the tension-dependent heat and the tension incrementin a twitch produced after a preceding mechanical response remainsnearly constant irrespective of the stimulus interval, while the amountof tension-independent heat production varies depending on the timeafter the preceding stimulation.