The effect of inorganic phosphate on sodium fluxes in dog red blood cells

The effect of extracellular inorganic phosphate on Na⁺ movements in dog red blood cells has been studied. As the phosphate concentration is increased from 0 to 30 mM, Na⁺ efflux increases by 2- to 3-fold and Na⁺ influx increases approximately 2-fold. This enhancement of Na⁺ fluxes by phosphate can be prevented by the addition of iodoacetate (1 mM), an inhibitor of glycolysis, or 4-acetamido-4′-iso-thiocyantostilbene-2,2′-disulfonic acid (0.01 mM), which blocks anion transport, to the medium. The increases in Na⁺ movements are not caused by changes in cell volumes. These results suggest that phosphate must enter the cell to enhance Na⁺ fluxes and that the mechanism of action may be via a stimulatory effect on glycolysis.