The Na+/H+ exchanger in immature and mature granulocytic HL-60 cells. Property changes induced by intracellular acidification and cell maturation.

We have compared the properties of the Na+/H+ exchanger in two cell populations: growing promyelocytic HL-60 cells (immature) and HL-60 cells induced to mature into granulocytes by dimethyl sulfoxide. The exchanger was activated by intracellular acidification from pH 7.25 to pH 5.5. In both immature and mature granulocytic cells, this type of activation resulted in the expected increase in Vmax for Na+ uptake but also in an increase in KmNa. Maximum acidification caused an increase in Vmax of approximately 10-fold in both types of cells. The increase in KmNa was influenced by cell maturation. In immature cells, the KmNa was higher than in mature cells at all pH values tested, and this difference increased with acidification. Maximum acidification increased the KmNa from 15 +/- 4 to 124 +/- 17 mM in immature cells and from 10 +/- 3 to 43 +/- 20 mM in mature cells. Intracellular pH also influenced the pattern of inhibition of 22Na uptake by dimethylamiloride, a specific inhibitor of the exchanger. At intracellular pH 7.0 dimethylamiloride inhibition was mostly competitive in immature and competitive in mature cells. At lower intracellular pH, 5.9, the inhibition was mixed in both types of cells. Thus, the properties of the exchanger in granulocytic cells are influenced by the cell maturation stage and the intracellular pH.