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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 ( D α) 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 ( O 2 max ), and P O 2crit were determined. D α increased in the following order: Xenopus muscle fibers D α = 1.23 nM·mm 2 ·mmHg –1 ·s –1 (SD 0.12), control rat trabeculae D α = 2.29 nM·mm 2 ·mmHg –1 ·s –1 (SD 0.24) ( P = 0.0012 vs. Xenopus ), and hypertrophied rat trabeculae D α = 6.0 nM·mm 2 ·mmHg –1 ·s –1 (SD 2.8) ( P = 0.039 vs. control rat trabeculae). D α increased with extracellular space in the preparation (Spearman’s rank correlation coefficient = 0.92, P < 0.001). The values for D α indicate that Xenopus muscle fibers cannot reach O 2 max in vivo because P O 2crit can be higher than arterial P O 2 and that hypertrophied rat cardiomyocytes can become hypoxic at the maximum heart rate. heart muscle; critical oxygen tension; maximum rate of oxygen consumption Address for reprint requests and other correspondence: W. J. van der Laarse, Dept. of Physiology, Institute for Cardiovascular Research, Van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands (e-mail: wj.vanderlaarse@vumc.nl ) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of Applied Physiology The American Physiological Society

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