Determination of diffusivity of oxygen and carbon dioxide in respiring tissue: Results in rat skeletal muscle

Gas transfer rates for O₂ and CO₂ through freshly excised respiring rat abdominal muscle were measured. The tissue separated as a thin membrane two chambers, one of which was ventilated with a constant gas mixture. The other chamber was closed and the time course of changes ofP_O2andP_CO2, initially set at varied levels, was followed by electrodes. A plot of rate of change ofP_O2 andP_CO2 in the closed chamber against the partial pressure difference across the tissue yielded both Krogh's diffusion constant,K_O2 andK_CO2, and metabolic rate of tissue, i. e. specific O₂ consumption and CO₂ production,\(\dot m_{{\text{O}}_{\text{2}} } \) and\(\dot m_{{\text{CO}}_{\text{2}} } \). The mean values at 37°C,K_O2=1.31×10⁻⁹ mMol·cm⁻¹·min⁻¹·torr⁻¹ andK_CO2=28.0×10⁻⁹ mMol·cm⁻¹·min⁻¹·torr⁻¹, did not differ significantly from values determined by other authors in various tissue preparations in which metabolism had been suppressed. Average O₂ consumption,\(\dot m_{{\text{O}}_{\text{2}} } \), was not different from the values obtained in the same tissue by the Warbung manometric method, 0.74 mMol·min⁻¹·L⁻¹. The mean respiratory quotient, calculated as the ratio of mean CO₂ production and mean O₂ consumption, was 0.85.