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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

¹Department of Physiology, Institute for Cardiovascular Research, VU University Medical Center, and ²Institute for Fundamental and Clinical Human Movement Sciences, Vrije Universiteit, Amsterdam, The Netherlands

Submitted 25 April 2005 ; accepted in final form 22 July 2005

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) 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 PO_2crit were determined. D increased in the following order: Xenopus muscle fibers D = 1.23 nM·mm²·mmHg^–1·s^–1 (SD 0.12), control rat trabeculae D = 2.29 nM·mm²·mmHg^–1·s^–1 (SD 0.24) (P = 0.0012 vs. Xenopus), and hypertrophied rat trabeculae D = 6.0 nM·mm²·mmHg^–1·s^–1 (SD 2.8) (P = 0.039 vs. control rat trabeculae). D increased with extracellular space in the preparation (Spearman’s rank correlation coefficient = 0.92, P < 0.001). The values for D indicate that Xenopus muscle fibers cannot reach O_{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.

heart muscle; critical oxygen tension; maximum rate of oxygen consumption

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