Cytoplasmic pH change induced by leukotriene B4 in human neutrophils

Leukotriene B₄ induced a biphasic change in the cytoplasmic pH of human neutrophils: an initial rapid acidification followed by an alkalinization. The acidification was slightly reduced by the removal of extracellular Ca²⁺, but the subsequent alkalinization was not. The leukotriene B₄-induced alkalinization was dependent on extracellular Na⁺ and pH, and was inhibited by amiloride and its more potent analogue, 5-(N,N-hexamethylene)amiloride. These characteristics indicate that the cytoplasmic alkalinization is mediated by the Na⁺-H⁺ exchange. Oxidation products of leukotriene B₄, 20-hydroxyleukotriene B₄, 20-carboxyleukotriene B₄, and (5S)-hydroxy-6,8,11,14-eicosatetraenoic acid (5-HETE) also stimulated the Na⁺-H⁺ exchange, but higher concentrations were required. Treatment of the cells with pertussis toxin inhibited both phases of the leukotriene B₄ induced pH_i change, while cholera toxin did not affect the pH_i change. The alkalinization induced by leukotriene B₄ was inhibited by 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), an inhibitor of protein kinase C, but was not inhibited by N-(2-guanidinoethyl)-5-isoquinolinesulfonamide which has a less inhibitory effect on protein kinase C. Acidification was not affected by the drugs. These findings suggest that a GTP-binding protein sensitive to pertussis toxin and protein kinase C are involved in the activation of the Na⁺-H ⁺ exchange stimulated by leukotriene B₄.