Measurement of Krogh's diffusion constant of CO₂ in respiring muscle at various CO₂ levels: Evidence for facilitated diffusion

Summary

Krogh's diffusion constant for CO₂, K_CO2, was determined in respiring muscle tissue at various levels of tissueP _CO2, between 10 and 160 torr, using a technique described previously (Kawashiro et al., 1975).

With increasing mean tissueP _CO2, K_CO2 declined towards an apparently asymptotic value. The relationship between K_CO2 (10⁻⁹ mmol·cm⁻¹·min⁻¹·torr⁻¹) andP _CO2 (torr) at 37° C could be approximated by the equation K_CO2=17.3 {1+1.72·exp(-0.027{P _CO2)}AtP _CO2=0 toor K_CO2 exceeded the asymptotic value, which was virtually attained atP _CO2=100 torr, by more than a factor of two. Thus CO₂ diffusion in muscle appears to be facilitated in the lowP _CO2 range.

Specific CO₂ production rate of tissue, which was determined simultaneously, did not vary with CO₂ in theP _CO2 range studied.

Effects of facilitated CO₂ transport on CO₂ exchange in muscle are assessed using simple models. In the presence of CO₂ facilitation muscleP _CO2 is reduced, particularly during exercise.