RELATIONSHIP BETWEEN ARACHIDONATE RELEASE AND EXOCYTOSIS IN PERMEABILIZED HUMAN NEUTROPHILS STIMULATED WITH FORMYLMETHIONYL-LEUCYL-PHENYLALANINE (FMETLEUPHE), GUANOSINE 5'-[GAMMA-THIO]TRIPHOSPHATE (GTP[S]) AND CA2+

The role of two G-proteins, G(p) and G(e), in the stimulus-secretion pathway has been proposed on the basis of studies where GTP analogues have been introduced into permeabilized cell preparations. In this study, evidence is provided that two G-proteins are also involved when a receptor-directed agonist is used. Intact human neutrophils were made refractory to formylmethionyl-leucyl-phenylalanine (fMetLeuPhe) stimulation by metabolic inhibition and then permeabilized with streptolysin O to compare the intracellular requirements for exocytosis from specific and azurophilic granules and arachidonate release. In the presence of 1-mu-M-Ca2+ and 1 mM-MgATP, fMetLeuPhe or guanosine 5'-[gamma-thio]triphosphate (GTP[S]) induce secretion from both granule types as well as arachidonate release. Secretion and arachidonate release owing to fMetLeuPhe can occur in the absence of ATP, conditions under which G-protein-mediated activation of phospholipase C is suppressed. GTP[S]-induced secretion can also occur in the absence of MgATP, but GTP[S]-induced arachidonate release cannot. It is concluded that fMetLeuPhe, like GTP[S], stimulates secretion by interacting with another G-protein-mediated reaction apart from G(p). Evidence is provided that a possible target for the second G-protein-mediated reaction involved in fMetLeuPhe-induced secretion (but not GTP[S]-induced secretion) is phospholipase A2.