Measurement of heat production during the summation of isometric contraction in frog skeletal muscle with an infrared radiometer.

Abstract

The heat production of frog skeletal muscle during isometric contraction was measured with an infrared radiometer at room temperature (23--26 degrees C), attention being focused on the heat produced during the summation of twitches by two successive stimuli. When the amount of heat produced by the second stimulus was plotted against the corresponding tension increment, the data points fell on two regression lines of approximately the same slope except for the intermediate stimulus intervals. One regression line started from the origin, while the other intersected the ordinate at about 1 mcal/g. If a twitch was produced at various times after a 0.5 sec tetanus, all the data points on the heat versus tension increment plot distributed around a single regression line starting from the origin. These results are explained by assuming that the relation between the tension-dependent heat and the tension increment in a twitch produced after a preceding mechanical response remains nearly constant irrespective of the stimulus interval, while the amount of tension-independent heat production varies depending on the time after the preceding stimulation.