Influence of 2,3-diphosphoglycerate on the buffering properties of human blood

Abstract

The effect of the concentration of red cell 2,3-diphosphoglycerate (2,3-DPG, 0.5–21 μmoles/g cells) on the buffering properties and on the slope of the relation between the extracellular and intracellular pH (ΔpH_i/ΔpH_e) of human blood was studied. The results were evaluated in connection with previous findings concerning the effect of 2,3-DPG on the Donnan ratior _H ⁺=H _e ⁺ /H _i ⁺ . ΔpH_i/ΔpH_e decreases with rising red cell 2,3-DPG content as well as with rising extracellular pH. ΔpH_i/ΔpH_e andr _H ⁺ can be related to each other by the empirical equation $$\Delta {\text{pH}}_{\text{i}} /\Delta {\text{pH}}_{\text{e}} = 1 + \log \user2{ }r_{{\text{H}}^{\text{ + }} } = 1 + {\text{pH}}_{\text{i}} - {\text{pH}}_{\text{e}} .$$ The validity of this equation appears to be restricted to conditions where the Donnan ratior _H ⁺ is altered between 0.3 and 1 either by changes of the red cell concentration of buffering anions such as 2,3-DPG or by changes of the extracellular pH. As determined in suspensions of red cells with intact membranes, the 2,3-DPG- and pH-induced changes of ΔpH_i/ΔpH_e lead to proportional changes in the buffering power of the non-bicarbonate buffers of erythrocytes. Due to this effect the buffering power of suspensions of cells containing 5 times the normal concentration of the buffer 2,3-DPG islower than that of cells with normal 2,3-DPG content (at extracellular pH values above 7). These findings demonstrate that the action of intracellular nonbicarbonate buffers in blood is effectively modulated by the physico-chemical properties of the red cell membrane.