The Journal of General Physiology, Vol 73, 159-174, Copyright © 1979 by The Rockefeller University Press
The relationship between initial creatine phosphate breakdown and recovery oxygen consumption for a single isometric tetanus of the frog sartorius muscle at 20 degrees C
M Mahler
A previous paper (Mahler, M. 1978 J. Gen. Physiol. 71:559--580) describes
the time-course of the suprabasal rate of oxygen consumption (delta QO2) in
the sartorius muscle of R. pipiens after isometric tetani of 0.1--1.0 s at
20 degrees C. To test whether these were the responses to impulse changes
in the rate of ATP hydrolysis, we compared the total suprabasal oxygen
consumption during recovery (delta[O2]) with the amount of ATP hydrolyzed
during a contraction, measured indirectly as the decrease in creatine
phosphate (delta[CP]O). If suprabasal ATP hydrolysis during recovery is
negligible in comparison with that during contraction, delta[CP]0/delta[O2]
should approximate the P:O2 ratio for oxidative metabolism, which has an
expected value of 6.1--6.5. We found: formula; see text. We conclude that
in this muscle at 20 degrees C: (a) after a tetanus of 0.2--1.0 s, delta
QO2(t) can be considered the response to an impulse increase in the rate of
ATP hydrolysis; (b) the reversal during recovery of unidentified exothermic
reactions occurring during the contraction (Woledge, R. C. 1971. Prog.
Biophys. Mol. Biol. 22:39--74) can be coupled to an ATP hydrolysis that is
at most a small fraction of delta[CP]0; (c) the pooled mean for
delta[CP]0/delta[O2], 6.58 +/- 0.55, sets an experimental lower bound for
the P:O2 ratio in vivo.
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