title: Time course of aerobic recovery after contraction of rabbit papillary muscle.
abstract: 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.
mesh_terms: D000818:Animals; D066298:In Vitro Techniques; D008929:Mitochondria, Heart / Q000378:metabolism; D009200:Myocardial Contraction; D010101:Oxygen Consumption; D010210:Papillary Muscles / Q000378:metabolism / Q000502:physiology*; D011817:Rabbits; D012146:Rest; D013997:Time Factors