Reappraisal of diffusion, solubility, and consumption of oxygen in frog skeletal muscle, with applications to muscle energy balance

Abstract

Previously we tested the validity of the one-dimensional diffusion equation for 02 in the excised frog sartorius muscle and used it to measure the diffusion coefficient (D) for O2 in this muscle and the time course of its rate of 02 consumption (QO2) after a tetanus (Mahler, 1978, 1979, J. Gen. Physiol., 71:533-557, 559-580, 73:159-174). A transverse section of the frog sartorius is in fact well fit by a hemi-ellipse with width divided by maximum thickness averaging 5.1 ± 0.2. Using the previous techniques with the two-dimensional diffusion equation and this hemi-elliptical boundary yields a value for D that is 30% smaller than reported previously; the revised values at 0, 10, and 22. 8°C are 6.2, 7.9, and 10.8 × 10-6 cm2/s, respectively. After a tetanus at 20°C, Qos rose quickly to a peak and then declined exponentially, with a time constant (τ) ~15% faster than that reported previously; τ averaged 2.1 min in Rana temporaria and 2.6 min in Rana pipiens. A technique was devised to measure the solubility (α) of O2 in intact, respiring muscles, and yielded α(muscle)/α(H20) = 1.26 ± 0.04. With these modifications, the values for 02 consumption obtained with the diffusion method were in agreement with those measured by the direct method of Kushmerick and Paul (1976, J. Physiol. [Loud.]., 254:693- 709). Using results from both methods, at 20°C the ratio of phosphorylcreatine split during a tetanus to 02 consumption during recovery ranged from 5.2 to 6.2 µmol/µmol, and postcontractile ATP hydrolysis was estimated to be 13.6 ± 4.1 (n = 3) µmol/umol total creatine. © 1985, Rockefeller University Press., All rights reserved.