Abstract
1. This paper deals with the contributions of the red cell membrane and an external diffusion boundary layer (;unstirred layer') to the resistance to O(2) entry into the red cell. 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 O(2). The rate of O(2) uptake by human red cells at various extracellular BSA concentrations was determined with a stopped-flow rapid-reaction apparatus.2. The initial rate of O(2) uptake by the red cells was directly proportional to the diffusion coefficient of O(2) in the extracellular fluid.3. If the diffusion boundary layer and the plasma membrane are considered as resistors in series, we estimate that 82-100% of the total resistance to O(2) entering the cell is due to the diffusion boundary layer. Our best estimate is that 95% of the resistance resides in the diffusion boundary layer.4. Our best estimate of the O(2) permeability of the red cell membrane is 3.15 x 10(-6) m-mole/(cm(2) sec mmHg). With this permeability the membrane would account for only 5% of the total resistance to O(2) entering the cell. Partly because the membrane O(2) diffusion resistance is a small fraction of the total resistance our estimate of the membrane resistance has a large standard deviation. Taking our estimate of the membrane resistance plus and minus its standard deviation we find that the membrane may account for 0-18% of the total resistance to O(2) entering the cell.5. The effective thickness of the diffusion boundary layer immediately after mixing is about 1.93 mum according to our analysis.