Changes in Na+-H+ exchange regulation upon granulocytic differentiation of HL60 cells.

The changes in activation of Na+-H+ exchange on granulocytic differentiation of human leukemic promyelocytic HL60 cells have been studied by measuring changes in intracellular pH with the fluorescent pH indicator 2,7-biscarboxyethyl-5(6)-carboxyfluorescein (BCECF). It was found that the Na+-H+ exchanger is activated by stimulation of protein kinase C in the dimethyl sulfoxide (DMSO)-differentiated (neutrophil-like) HL60 cell, but not in the undifferentiated (promyelocyte-like) cell. In contrast, osmotic shrinkage of the cells triggers the exchanger in the undifferentiated cells, but not in the DMSO-differentiated cells. The data suggest that activation of Na+-H+ exchange by osmotic shock does not occur exclusively through stimulation of kinase C.