Rate of CO2 diffusion in the human red blood cell measured with pH-sensitive fluorescence.

Abstract

The diffusion rate of C02, 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 8 Torr (or 65 Torr) was mixed with the same amount of saline solution having 65 Torr (or 8 Torr). Carbonic anhydrase was added to the external solution at a concentration of 20 mg/100 ml in order to accelerate the hydration and dehydration reactions, so that the Pcoz change in the fluid could be observed instantaneously through pH. In the inward diffusion Pcoz showed a large change, suggesting a lack of HC03-shift across the red cell membrane. In the outward diffusion, however, the PC0, change was smaller, suggesting that H+ ions produced in the external solution by C02 hydration were rapidly buffered by the red cell. The half times of the inward and outward diffusions were, on an average, 0.08 and 0.13 sec, 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 HC03--shift. The diffusion rate was almost constant and remained independent of the direction of C02 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 C02.

Theoretical analyses for arterial-venous O2 content difference and Haldane effect during rebreathing.

“…The transfer coefficient of C02 (,(C02)) was also estimated from the numerical solution of the diffusion equation accompanying the HC03 -shift , and from the experimental data on the C02 diffusion and HC03 -shift (NIIZEKI et al, 1983. It was determined to be 2.5 x 10-6 cm • s-1 • Torr-1 similar to the ?J(02).…”

Numerical solution of partial differential equations for CO2 diffusion accompanying HCO3- shift in red blood cells.

“…His value is apparently short, compared with the value measured by NIIZEKI et al (1983) at the hematocrit of 0.075. This difference may be ascribed to the difference in hematocrit, referring to the computed data of Fig.…”

“…(11) (12) 7) Computation of the final extracellular Pco2 and HC03-. The extracellular fluid in the RBC suspension used by NIIzEKI et al (1983) contained carbonic anhydrase of 20 mg/ dl, and therefore, the hydration and dehydration reactions proceeded fairly fast in the fluid, with the equilibrium being established in a short time. Thus, extracellular Pco 2 and HC03-were corrected at each end of the increment time by using the following equation derived from two Henderson-Hasselbalch equations before and after both the C02 diffusion and HC03-shift:…”

“…Therefore, because the intracellular Pco2 change is mainly limited by the C02 and HC03-diffusions, we attempted to solve the differential equations for the diffusion numerically in a disc RBC model. In an effort to obtain a numerical solution, NIIZEKI et al (1983) measured the diffusion rate of C02 in the RBC in a closed RBC suspension. In their experiment on the inward C02 diffusion, the final extracellular HC03-content unexpectedly coincided with the initial value.…”

Relationship between the transfer rate and the gap in partial pressure of gas molecules at a heterogeneous interface.

“…UCHIDA et al [31] measured the C02 diffusion rate in a thin layer of hemoglobin solution, and found that the inward and outward diffusions were equally retarded at the gas-liquid interface. NIIZEKI et al [23,24] measured the C02 diffusion rate in the RBC under lowered convective conditions and found that the value of tj for C02, being 2.5 x 10-6 cm • s-1 • Torr-1, was identical to that for 02 [9,10,16].Oxygenation and deoxygenation reactions of hemoglobin are very fast [20] and hydration and dehydration reactions of C02 are also highly accelerated by carbonic anhydrase in RBC [23]. Thus, the rates of 02 and C02 reactions with RBC are limited by the transfer rates of these gases and HC03 -ion across the RBC interface as well as by the intracellular diffusion rate.…”