Kinetics of O2 uptake and release by red cells in stopped-flow apparatus: effects of unstirred layer

Using a stopped-flow apparatus, measurements were made of the velocity of uptake and release of oxygen by red cells of man, sheep and goat, three species of widely differing red cell size. The results were used to calculate resistances to O2 uptake provided by: (1) any unstirred layer (USL) outside the cells; (2) the cell membrane; and (3) the cell substance, in which the process of simultaneous diffusion and chemical reaction occurs. For O2 release, the USL was virtually abolished by using sufficient dithionite in the reactant buffer for it to diffuse up to the cell membrane and mop up O2 as it passes out of the cell. Hence, differences in the rate of O2 uptake and release allowed estimation of the resistance and thickness of the USL. Its thickness in the three species was between 0.7 and 0.9 micron; it provided at least 70% of the resistance to O2 uptake located outside the cell interior (cell membrane plus USL). Existence of the USL slows the uptake of O2 in the stopped-flow apparatus by a factor of at least 1.8 to 2.0.