Mediation by platelet-activating factor of 12-hydroxyeicosatetraenoic acid-induced cytosolic free calcium concentration elevation in neutrophils

12(R)-hydroxyeicosatetraenoic acid (HETE) shows biphasic increase in cytosolic free calcium concentration ([Ca2+](i)) in rabbit and human neutrophils; the initial transient phase and the continuous falling phase. 12(S)-HETE was less potent in both species. BN50739, a platelet-activating factor (PAF) receptor antagonist, inhibited both phases of 12(R)-HETE-induced [Ca2+](i) rise but did not affect leukotriene B-4 (LTB4)-induced [Ca2+](i) rise. N-tosyl-L-phenylalanine chloromethyl ketone (TPCK), a PAF synthesis inhibitor, and manoalide, a phospholipase A(2) inhibitor, reduced 12(R)-HETE-induced [Ca2+](i) rise; These blockers inhibited the continuous phase of [Ca2+](i) rise induced by N-formyl-methionyl-leucyl-phenylalanine (FMLP) with little effect on the initial phase. It had no significant effect on LTB4-induced [Ca2+](i) rise. SC-41930, a LTB4-receptor antagonist, did not block 12-HETE-induced [Ca2+](i) rise. In 12(R)-HETE-, FMLP- and LTB4-stimulated cells, accumulations of cell-associated PAF and released PAF were detected but not in unstimulated cells. BN50739 did not affect the accumulation of cell-associated PAF and release of PAF in 12(R)-HETE-stimulated cells. These results suggest that 12(R)-HETE-induced and partially, FMLP-induced, but not LTB4-induced [Ca2+](i) rise are mediated by PAF, which is produced and released by stimulation of the cells by 12(R)-HETE and FMLP, respectively. (C) 2000 Elsevier Science Inc. All rights reserved.