The kinetics of O2 release by human red blood cells in the presence of external sodium dithionite.

Oxygen release by human erythrocytes in the presence of external sodium dithionite was examined by stopped-flow, rapid mixing techniques. The resultant time courses were analyzed quantitatively using a three-dimensional disc model which had been developed previously to describe oxygen uptake (Vandegriff, K. D., and Olson, J. S. (1984) Biophys. J. 45, 825-835). This scheme takes into account diffusion of oxygen through external unstirred solvent layers and intracellular oxygen diffusion and chemical reaction with hemoglobin. Application of this model to deoxygenation time courses required three additional considerations: the reaction of free oxygen with external sodium dithionite, cooperative oxygen binding to intracellular hemoglobin, and the alkaline Bohr effect. The resultant theoretical treatment described accurately both the observed dependence of the deoxygenation rate on dithionite concentration and pH and the exact shapes of the corresponding time courses. Membrane resistance to oxygen diffusion was not required to simulate the observed data as had been suggested previously (Lawson, W. H., Jr., Holland, R. A. B., and Forster, R. E. (1965). J. Appl. Physiol. 20, 912-918). The final, three-dimensional model is general and allows, for the first time, analysis of both oxygen uptake and release kinetics (Vandegriff, K. D., and Olson, J. S. (1984) J. Biol. Chem. 259, 12619-12627).