Krogh' s diffusion coefficient for oxygen in isolated Xenopus skeletal muscle fibers and rat myocardial trabeculae at maximum rates of oxygen consumption.

The value of the diffusion coefficient for oxygen in muscle is uncertain. The diffusion coefficient is important because it is a determinant of the extracellular oxygen tension at which the core of muscle fibers becomes anoxic (Po_2crit). Anoxic cores in muscle fibers impair muscular function and may limit adaptation of muscle cells to increased load and/or activity. We used Hill's diffusion equations to determine Krogh's diffusion coefficient (Dα) for oxygen in single skeletal muscle fibers from Xenopus laevis at 20°C (n = 6) and in myocardial trabeculae from the rat at 37°C (n = 9). The trabeculae were dissected from the right ventricular myocardium of control (n = 4) and 'monocrotaline-treated, pulmonary hypertensive rats (n = 5). The cross-sectional area of the preparations, the maximum rate of oxygen consumption (Vo_{2 max}), and Po_2crit were determined. Dα increased in the following order: Xenopus muscle fibers Dα = 1.23 nM·mm²·mmHg^-1·s^-1 (SD 0.12), control rat trabeculae Dα = 2.29 nM·mm²·mmHg^-1·s^-1 (SD 0.24) (P = 0.0012 vs. Xenopus), and hypertrophied rat trabeculae Dα = 6.0 nM·mm²·mmHg^-1·s^-1 (SD 2.8) (P = 0.039 vs. control rat trabeculae). Dα increased with extracellular space in the preparation (Spearman's rank correlation coefficient = 0.92, P < 0.001). The values for Dα indicate that Xenopus muscle fibers cannot reach Vo_{2 max} in vivo because Po_2crit can be higher than arterial Po₂ and that hypertrophied rat cardiomyocytes can become hypoxic at the maximum heart rate. [ABSTRACT FROM AUTHOR]