Na+/H+ exchange modulates the production of leukotriene B4 by human neutrophils.
Human neutrophils produce various compounds of the 5-lipoxygenase pathway, including (5S)-hydroxyeicosatetraenoic acid, leukotriene B4, its 6-trans isomers and omega-oxidation metabolites of LTB4, when the cells are stimulated with the Ca2+ ionophore A23187. The elevation in the extracellular pH (pHo) facilitated the cytoplasmic alkalinization induced by the ionophore as determined fluorometrically using 2',7'-bis(carboxyethyl)carboxyfluorescein and enhanced the production of all the 5-lipoxygenase metabolites. The production decreased when the alkalinization was blocked by the decrease in the pHo, the removal of the extracellular Na+ or the addition of specific inhibitors of the Na+/H+ exchange, such as 5-(NN-hexamethylene)amiloride, 5-(N-methyl-N-isobutyl)amiloride and 5-(N-ethyl-N-isopropyl)amiloride. The alkalinization of the cytoplasm with methylamine completely restored the production suppressed by the removal of Na+ from the medium. These findings suggest that the change in the cytoplasmic pH (pHi) mediated by the Na+/H+ exchange regulates the production of the lipoxygenase metabolites. The site of the metabolism controlled by the pHi change seemed to be the 5-lipoxygenase, because the production of all the metabolites decreased in parallel and the release of [3H]arachidonic acid from the neutrophils in response to the ionophore was not affected by the pHi change. Furthermore, the production of the 5-lipoxygenase metabolites stimulated by A23187 with or without exogenous arachidonic acid showed a similar pHo-dependence and the production induced by N-formylmethionyl-leucylphenylalanine (chemotactic peptide) with exogenous arachidonic acid also decreased when the cytoplasmic alkalinization was inhibited.
Osaki
M
M
Department of Dermatology, Kyushu University School of Medicine, Fukuoka, Japan.
Sumimoto
H
H
Takeshige
K
K
Cragoe
E J
EJ
Hori
Y
Y
Minakami
S
S
D001094:Arachidonate 5-Lipoxygenase / Q000378:metabolism; D016718:Arachidonic Acid; D001095:Arachidonic Acids / Q000378:metabolism; D000001:Calcimycin / Q000494:pharmacology; D006801:Humans; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007975:Leukotriene B4 / Q000096:biosynthesis*; D008744:Methylamines / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D012964:Sodium / Q000378:metabolism*
D001095:Arachidonic Acids; D008744:Methylamines; D007975:Leukotriene B4; D016718:Arachidonic Acid; D000001:Calcimycin; D006859:Hydrogen; D012964:Sodium; C027451:methylamine; D001094:Arachidonate 5-Lipoxygenase