Interrelation of pH, temperature, and oxygen on deoxygenation rate of red cells.

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Abstract
Rates of red cell deoxygenation were measured in-vitro via differential photocolorimetry in a stopped-flow rapid reaction apparatus using a relative excess of sodium dithionite to maintain PO2 outside the red cell near zero. Deoxygenation half-times are 4 times slower than those reported by other investigators for continuous flow systems using oxygen electrodes, and this difference may be due to stagnant flow adjacent to the electrode. Deoxygenation rate decreased approximately 5% for each increase of 0.1 pH unit between pH 6.5 and 7.9 at 37 and 22 C. The deoxygenation rate constant, kc, was inversely related to the percent saturation oxyhemoglobin so that Kc increased as deoxygenation proceeded. These effects of pH and saturation can be explained on the basis of the changes in chemical kinetics of hemoglobin with oxygen without invoking other factors such as altered membrane permeability. Step increases in PCO2 at 37 C, accomplished by deoxy-genating red cell suspensions (PCO2 5 mm Hg, pH 8.8) with sodium dithionite in buffer having greater PCO2 (PCO2 143, pH 6.9), resulted in a rate that was greater than when dithionite had PCO2 and pH similar to that of red cells; and calculations suggest that this effect can be explained by the dual action that decreasing red cell pH has in displacing O2 from oxyhemoglobin via the Bohr shift and increasing the deoxygenation rate.