Photocolorimetric Determination of Rate of Uptake of CO and O₂ By Reduced Human Red Cell Suspensions at 37°C

¹ From the Department of Physiology and Pharmacology, Graduate School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, and the Department of Colloid Science, University of Cambridge, Cambridge, England

The over-all velocity constants, k_c' and l_c' (in mm^–1 x sec.^–1), for the combination of O₂ and CO, respectively, with reduced hemoglobin in 1:80 human red cell suspensions at 37°C have been measured in a Hartridge-Roughton continuous flow apparatus. Relative pigment concentration in the flowing cell suspension was estimated from the difference in light transmission at two different colors in order to reduce the influence of light scattering. The average value of k_c' was 92; that for l_c' was 79. Values for corresponding velocity constants for the uptake of O₂ and CO by a membrane free layer of concentrated hemoglobin solution, comparable in dimensions to the erythrocyte, have been calculated from previously reported values for the rates of reaction and diffusion in hemoglobin solutions, and are, respectively, 3.6 and 2.3 times greater than k_c' and l_c'. We assume that this difference reflects the additional resistance to gas diffusion into the erythrocyte imposed by the cell membrane, and on this basis we have calculated values for the ratio of the permeability of the red cell membrane to the permeability of the red cell interior (). For human red cells at 37°C, the value of is about 1.5, both for O₂ and for CO penetration.