Secondary CO2 Diffusion Following HCO3- Shift Across the Red Cell Membrane
In order to elucidate the effect of CO2 diffusion in the red blood cell (RBC) on the Bohr shift, it is absolutely necessary to evaluate the diffusivity of CO2 and HCO3 within the RBC as well as across the RBC membrane. Uchida et al.(1) measured the diffusion coefficients of CO2 and HCO 3 - ions in hemoglobin solution (Hb) in a Hb layer with a constant thickness by varying Hb concentration. Extrapolating the relation between the diffusion coefficient and Hb concentration, the coefficients of CO2 and HCO 3 - within the RBC were estimated as follows: D(CO2) = 3.4 × 10-6, and D(HCO 3 - ) = 1.4 × 10-6 cm2/sec, respectively. Furthermore, Niizeki et al. (2) measured the diffusion rate of CO2 into the RBC by using a stopped flow method, where the HCO 3 - shift was suppressed by contrplling intracellular Cl- concentration preliminarily. The half-time, being about 77 msec, was longer than the values measured by a rapid flow method by Pilper (3), and Constantine et al.(4). From Niizeki’s data the diffusivity across the boundary layer, or the transfer coefficient of CO2, η(CO2) was estimated to be; η(CO2) = 2 × 10-6 cm/sec • Torr, on an average. From our microphotometric observation it was confirmed that the Bohr shift does not occur in a buffer solution.
KeywordsTransfer Coefficient Diffusion Equation Outward Diffusion Hemoglobin Solution Alternate Direction Implicit Method
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