Influence of 2,3-diphosphoglycerate on the buffering properties of human blood: role of the red cell membrane.

The effect of the concentration of red cell 2,3-diphosphoglycerate (2,3-DPG, 0.5-21 mumoles/g cells) on the buffering properties and on the slope of the relation between the extracellular and intracellular pH (deltapHi/deltapHe) of human blood was studied. The results were evaluated in connection with previous findings concerning the effect of 2,3-DPG on the Donnan ratio rH+ = H+e/H+i. deltapHi/deltapHe decreases with rising red cell 2,3-DPG content as well as with rising extracellular pH. deltapHi/deltapHe and rH+ can be related to each other by the empirical equation deltapHi/deltapHe = 1 + log rH+ = 1 + pHi - pHe. The validity of this equation appears to be restricted to conditions where the Donnan ratio rH+ 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 deltapHi/deltapHe 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 is lower than that of cells with normal 2,3-DPG content (at extracellular pH values above 7). These findings demonstrate that the action of intracellular non-bicarbonate buffers in blood is effectively modulated by the physico-chemical properties of the red cell membrane.