Abstract
The time course of oxygen uptake following isometric twitch contractions of isolated rabbit papillary muscles was measured using a polarographic oxygen electrode. Using a diffusion model we eliminated the effect of oxygen storage on the measured time course of oxygen uptake to determine the time constant of mitochondrial "off" kinetics. Two different approaches were followed. In Method 1, two steady-state levels were compared, whereas in Method 2, the time course of mitochondrial "off" kinetics was studied. Using Method 1 we found tau = 20 +/- 8 seconds (n = 7), whereas Method 2 yielded tau = 26 +/- 9 seconds (n = 11). These findings were compared with preliminary measurements of recovery heat production of the same preparation and at the same temperature. Heat produced after a train of 10 twitch contractions appeared to follow a monoexponential time course with a time constant of 24.9 +/- 9.5 seconds (n = 9). These results suggest that aerobic metabolism in isolated rabbit papillary muscle constitutes the only recovery process.
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