AJP - Heart and Circulatory Physiology, Vol 253, Issue 2 325-H332, Copyright © 1987 by American Physiological Society
Time course of aerobic recovery after contraction of rabbit papillary muscle
F. Mast and G. Elzinga
The time course of oxygen uptake after isometric twitch contractions of
isolated rabbit papillary muscles was determined at 20 degrees C by
continuous polarographic measurement of the partial pressure of oxygen in a
219-microliters glass chamber in which the fluid circulated rapidly. The
response time of the oxygen-measuring system was characterized by a delay
of 1.1 s and a time constant of 2.1 s after that delay. Depending on the
stimulation frequency (0.125-1.0 Hz) the total amount of oxygen uptake for
120 twitches varied from 5.3 to 32.7 nmol/mg dry wt, and the steady-state
oxygen consumption rate varied from 0.4 to 8.5 nmol X min-1 X mg dry wt-1.
On the basis of a diffusion model we eliminated the effect of oxygen
storage on the measured time course of oxygen consumption to determine the
mitochondrial kinetics. We found a time constant of an average 19-22 s of
mitochondrial off kinetics. By use of this time constant for the change in
oxygen consumption rate after contraction, it can be estimated that 9-10%
of the oxygen required to restore ATP levels is already taken up by the
mitochondria during the twitch.
