RELATIONSHIP BETWEEN INITIAL CREATINE-PHOSPHATE BREAKDOWN AND RECOVERY OXYGEN-CONSUMPTION FOR A SINGLE ISOMETRIC TETANUS OF THE FROG SARTORIUS MUSCLE AT 20-DEGREES-C

A previous paper (Mahler, M. 1978. J. Gen. Physiol. 71:559-580) describes the time-course of the suprabasal rate of oxygen consumption (ΔQo2) in the sartorius muscle of R. pipiens after isometric tetani of 0.1-1.0 s at 20°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 (Δ[CP]o) with the amount of ATP hydrolyzed during a contraction, measured indirecdy as the decrease in creatine phosphate (Δ[CP]o). If suprabasal ATP hydrolysis during recovery is negligible in comparison with that during contraction, (Δ[CP]o)/Δ[O2] should approximate the P:02 ratio for oxidative metabolism, which has an expected value of 6.1-6.5. We found: All values are ± SEM. Number in parentheses is number of measurements. We conclude that in this muscle at 20°C: (a) after a tetanus of 0.2-1.0 s, ΔQo2(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 A[CP]0; (c) the pooled mean for (Δ[CP]o)/Δ[O2], 6.58 ± 0.55, sets an experimental lower bound for the P: 02 ratio in vivo. © 1979, Rockefeller University Press., All rights reserved.