Using a mortar and pestle and working in a glove bag under an atmosphere of dry nitrogen, lumps of potassium superoxide, purchased from K & K Chemicals, were ground to a fine consistency before use. (9) G.

ABSTRACT15(S)-Hydroxy-(5Z,8Z,11Z,13E)-eicosatetraenoic acid (15-HETE) exerted a time-and concentrationdependent inhibition of superoxide anion (O°) production and exocytosis of both azurophil and specific granule constituents from human polymorphonuclear neutrophils (PMN) stimulated with the receptor-specific agonists, N-formylmethionylleucylphenylalanine (FMLP), platelet-activating factor, and leukotriene B4, but not that elicited by phorbol 12-myristate 13-acetate. 15-HETE did not alter the binding of FMLP to its specific receptors on PMN but, rather, appeared to interfere with a subsequent process in signal transduction. Receptorcoupled production of inositol 1,4,5-trisphosphate (InsP3) and increases in cytosolic free calcium elicited with FMLP, plateletactivating factor, and leukotriene B4 were suppressed by 15-HETE. 15--HETE did not, however, inhibit the mobilization of45Ca from intracellular stores elicited by the addition ofInsP3 to permeabilized PMN. 15-HETE suppressed 0-production and increases in intracellular [Ca2+] induced when cell-surface receptors were bypassed and the PMN were activated directly by the guanine nucleotide-binding protein (G protein) activators aluminum fluoride (AIF ) and mastoparan. 15-HETE, however, did not perturb all G protein functions because cAMP production in FMLP-activated PMN was essentially unaffected by 15-HETE. These data support the proposition that 15-HETE modulates receptor-triggered activation of PMN either by uncoupling G protein stimulation of phospholipase C or by directly inhibiting phospholipase C, thus inhibiting the InsP3-dependent rise in intracellular [Ca2+] that is prerequisite for PMN responsiveness to receptor agonists.

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