Recovery heat production of isolated rabbit papillary muscle at 20 degrees C

Using metal-film thermopiles, heat production of isolated rabbit papillary muscles was measured under aerobic conditions at 20 degrees C. The time course of total heat production resulting from a single contraction (average of 10) and a twitch train of 10 contractions (0.2 Hz) was separated into initial (I) and recovery heat (R). The time course of recovery heat production of single twitches was characterized by a time constant of 25.4 +/- 1.7 s (mean +/- SE; n = 10). The recovery ratio, R/I, was 1.18 +/- 0.08 (mean +/- SE; n = 7). Total heat produced 25.2 +/- 2.9 mJ.gdw-1 (mean +/- SE; n = 11). After trains of 10 contractions a time constant of 25.2 +/- 1.6 s (mean +/- SE; n = 9) was found. The recovery ratio was 1.14 +/- 0.09 (mean +/-SE; n = 9). Total heat produced was 489 +/- 41 mJ.gdw-1 (mean +/- SE; n = 9). Time constants and recovery ratios for 1 and 10 twitches were not significantly different. This suggests that only the extent but not the nature of the chemical processes after contraction changes when the preparation produces about 20 times more heat. Since the recovery ratio values did not differ largely from the value derived theoretically the conclusion is justified that, under normal aerobic conditions, PCr splitting and its oxidative resynthesis are the major metabolic processes responsible for the energy supply of isolated cardiac muscle.