Kinetics of oxygen consumption after a single isometric tetanus of frog sartorius muscle at 20°C

Abstract

The time-course of the rate of oxygen consumption (Q02) has been measured in the excised frog sartorius muscle after single isometric tetani of 0.11.0 s at 20°C. To measure AQo2(t), the change in Q02 from its basal level, a novel method was devised, based on the validity in this tissue of the one-dimensional diffusion equation for oxygen, established in the preceding paper. After a tetanus, AQ02 reached a peak within 45-90 s, then declined exponentially, and could be well fit by AQo2(t) = Qo + Q1(e -k1t - e-k2t) T2 (= 1/k2). which characterized the rise of 02, was a decreasing function of tetanus duration (range: from 1.1 ± 0.28 min [n = 5] for a 0.1-s tetanus, to 0.34 ± 0.05 min [n = 8] for a 1.0-sec tetanus), t, (= 1/ki), which characterized the decline of AQ02. was not dependent on tetanus duration, with mean 3.68 ± 0.24 min (n = 46). A forthcoming paper in this series shows that these kinetics of AQ02 are the responses to impulse-like changes in the rate of ATP hydrolysis. The variation ofr2 with tetanus duration thus indicates the involvement of a nonlinear process in the coupling of O2 consumption to ATP hydrolysis. However, the monoexponential decline of AQ_ojj), with time constant independent of tetanus duration, suggests that during this phase, the coupling is rate-limited by a single reaction with apparent first order kinetics. © 1978, Rockefeller University Press., All rights reserved.