The effect of the red cell membrane and a diffusion boundary layer on the rate of oxygen uptake by human erythrocytes

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Abstract
Contributions of the red cell membrane and an external diffusion boundary layer (unstirred layer) to the resistance to O2 entry into the red cell are dealt with. Bovine serum albumin (BSA) was added to the extracellular fluid to enhance the effect of the diffusion boundary layer by diminishing both the solubility and the diffusivity of O2. The rate of O2 uptake by human red cells at various extracellular BSA concentrations was determined with a stopped-flow rapid-reaction apparatus. The initial rate of O2 uptake by the red cells was directly proportional to the diffusion coefficient of O2 in the extracellular fluid. If the diffusion boundary layer and the plasma membrane are considered as resistors in series, 82-100% of the total resistance to O2 entering the cell is due to the diffusion boundary layer. The best estimate is that 95% of the resistance resides in the diffusion boundary layer. The best estimate of O2 permeability of the red cell membrane is 3.15 .times. 10-6 mmol/(cm2 s mmHg). With this permeability the membrane would account for only 5% of the total resistance to O2 entering the cell. Partly because the membrane O2 diffusion resistance is a small fraction of the total resistance this estimate of the membrane resistance has a large SD. The membrane may account for 0-18% of the total resistance to O2 entering the cell. The effective thickness of the diffusion boundary layer immediately after mixing is about 1.93 .mu.m according to this analysis.