Abstract
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.
Highlights
We have compared the properties of the Na+/H+ex- physiologicmode of activation
The exchanger is actichanger in two cellpopulations:growing promyelocy- vated in a rapid and transient manner by osmotic shrinkage tic HL-60 cells(immature)and HL-60 cellsinduced to mature into granulocytes by dimethyl sulfoxide
We have previously reported that during granulocytic maturation of promyelocytic HL-60 cells the kinetic properties of the Na+/H+ exchanger are altered [10].After the first day of cell maturation, the exchanger had lower K, for sodium uptake and a different pattern of activation by intracellular H’
Summary
From the Departments of Medicine, Pediatrics, and Biophysics, University of Rochester MedicalCenter, Rochester, New York 14642. 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 V,,, for Na+ uptake and in an increase in K,,,,,. We have previously reported that during granulocytic maturation of promyelocytic HL-60 cells the kinetic properties of the Na+/H+ exchanger are altered [10].After the first day of cell maturation, the exchanger had lower K,,, for sodium uptake and a different pattern of activation by intracellular H’. Activation of the exchanger by intracellular H’ has been found in all cell systems testedand is presumed to be a common response to phorbol myristate acetate as measured by the nitro blue tetrazolium assay (LO).
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