Leukotriene D4-induced increases in the cytoplasmic pH of human myelocytic leukocytes

The effects of leukotriene D4 on the intracellular pH of human myelocytes, derived from cultured HL-60 cells by dimethylsulfoxide-induced differentiation, were quantified with the fluorescent indicator 2',7'-bis-(2-carboxy-ethyl)-5,6-carboxyfluorescein. Leukotriene D4, but not C4 or E4, increased intracellular pH optimally by 3 min with a half-maximal effect at 1-2 nM. The increases in intracellular pH stimulated by leukotriene D4 were prevented by pretreatment of myelocytes with leukotriene D4 but not peptide chemotactic factors. Analogs of amiloride that inhibit selectively the Na+/H+ antiport also prevented the intracellular alkalinization induced by leukotriene D4. The rate of recovery of intracellular pH after an acid load with 30 mM sodium propionate was approximately 30% higher at each level of intracellular pH for myelocytes exposed to leukotriene D4 than for those challenged in buffer alone. The increase elicited by leukotriene D4 in the adherence of myelocytic leukocytes to surfaces thus is associated with an enhanced sensitivity of the Na+/H+ antiport to intracellular pH, that is, not coupled to an earlier rise in the cytosolic level of Ca+2.