Estimation of the Rate of CO2 Diffusion Into the Red Cell Through the Bohr Shift

When the reactions of the red blood cell with O2 and CO2 are observed in a reaction chamber of a micro-photometric apparatus, the plasma layer around the cell tends to be superfluously thick and usually becomes highly resistive to the O2 and CO2 diffusions. Nevertheless, since the diffusivity of CO2 through aqueous solution, in general, is about 20 times as high as that of O2, the rates of the Bohr-on- and off-shifts have been thought to be almost the same as those of the oxygenation and deoxygenation. In our observation, however, the Bohr-on-shift was constantly slower than the oxygenation, while the Bohr-off-shift was comparable with the deoxygenation rate. The half-time of the Bohr-on-shift was about 60% longer than that of the oxygenation. This fact suggested that the diffusion rates of CO2 and/or HCO3 ions were comparable with that of O2 and they could even be evaluated quantitatively by comparing the Bohr-shifts with the oxygenation and deoxygenation rates. Thus, in the present study the estimation of the CO2 diffusion rate into and out of the red cell was attempted from the measured rates of the simple O2 reactions and the Bohr shift.