抄録
The diffusion rate of CO2, into and out of the red cell, was measured by using a stopped flow method with pH-sensitive fluorescence of 4-methylumbelliferone. A red cell suspension of 15% hematocrit with the PCO2 of 8Torr (or 65Torr) was mixed with the same amount of saline solution having 65Torr (or 8Torr). Carbonic anhydrase was added to the external solution at a concentration of 20mg/100ml in order to accelerate the hydration and dehydration reactions, so that the PCO2 change in the fluid could be observed instantaneously through pH. In the inward diffusion PCO2 showed a large change, suggesting a lack of HCO3- shift across the red cell membrane. In the outward diffusion, however, the PCO2, change was smaller, suggesting that H+ ions produced in the external solution by CO2 hydration were rapidly buffered by the red cell. The half-times of the inward and outward diffusions were, on an average, 0.08 and 0.13sec, respectively. The results of the simulation revealed that the above difference in half-times was attributed to the difference in slope between the two dissociation curves with and without the HCO3--shift. The diffusion rate was almost constant and remained independent of the direction of CO2 flux. That is, at a low pH range the permeation of H+ ions across the red cell membrane was much faster than the diffusion rate of CO2.
