Kinetics of O 2 uptake and release by red cells in stopped-flow apparatus: Effects of unstirred layer

Abstract

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 resistance to O 2 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 simulataneous diffusion and chemical reaction occurs. For O 2 release, the USL was virtually abolished by using sufficient dilthionite in the reactant buffer for it to diffuse up to the cell membrane and mop up O 2 as it passes out of the cell. Hence, differences in the rate of O 2 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 μm; it provided at least 70% of the resistance to O 2 uptake located outside the cell interior (cell membrane plus USL). Existence of the USL slows the uptake of O 2 in the stopped-flow apparatus by a factor of at least 1.8 to 2.0.