Morphological and physiological factors affecting oxygen uptake and release by red blood cells

The kinetics of oxygen uptake and release by human, salamander (Amphiuma means), and artificially constructed red cells were measured under a variety of physiological conditions using stopped-flow, rapid mixing techniques. The results were analyzed quantitatively using the generalized, three-dimensional disc model that was developed in two previous publications (Vandegriff, K. D., and Olson, J. S. (1984) Biophys. J. 45, 825-835 and Vandegriff, K. D., and Olson, J. S. (1984) J. Biol. Chem. 259, 12609-12618). The apparent rate of gas exchange is governed primarily by the oxygen flux at the red cell surface. In the case of uptake, this flux is roughly independent of intracellular chemical reaction parameters and inversely proportional to the thickness of the unstirred solvent layer which is adjacent to the red cell surface. For release experiments in the presence of high concentrations of sodium dithionite, the flux at the cell surface is inversely proportional to the oxygen affinity of the intracellular hemoglobin and roughly independent of the thickness of the external unstirred solvent layer. As a result, the effects of cell size, internal heme concentration, and pH are expressed differently in the two types of kinetic experiments. The rate of oxygen uptake depends on roughly the second power of the surface area to volume ratio of the erythrocyte, whereas the rate of release is much less dependent on the size and shape of the red cell. The half-time of oxygen uptake is directly proportional to intracellular heme concentration for cells of equivalent geometries; the half-time of oxygen release is linearly dependent on internal heme concentration but, at low heme concentrations, is determined primarily by the rate of oxygen dissociation from hemoglobin. The rate of cellular oxygenation is roughly independent of pH and internal 2,3-diphosphoglycerate concentration; in contrast, the rate of deoxygenation depends markedly on these conditions. As the pH is lowered or the internal diphosphoglycerate concentration is raised, the overall oxygen affinity of the cell suspension decreases severalfold, and the rate of oxygen release increases by roughly the same extent.