Erythrocyte phosphate metabolism and pH in vitro: a model for clinical phosphate disorders in acidosis and alkalosis.

When whole blood from 9 normal donors was incubated at 37 degrees C for 90 min under 95%, O2/5% CO2, over a range of pH from 7.1 to 7.9, the concentrations of orthophosphate (Pi) in plasma, in whole blood and in the cells decreased with increasing pH. At all pHs the ratio of cell to plasma concentrations of Pi was higher than that predicted from the cell to plasma distribution ratio for chloride, on the assumption that the mono- and di-anionic forms of Pi distributed passively in response to the membrane potential. Both the observed and predicted distribution ratios for Pi, and the difference between them, decreased with increasing pH. It is concluded that the observed distribution of Pi between erythrocytes and plasma is not consistent with a steady-state passive distribution, and that small changes of pH in vitro can lead to marked alterations in cellular Pi concentration. These measurements provide a direct example of the redistribution of Pi between cells and plasma, which has been postulated to occur in glycolyzing cells, leading to Pi depletion, during pH disturbances in vivo.