PERTUSSIS TOXIN-SENSITIVE ACTIVATION OF PHOSPHOLIPASE-A(2) CAN BE RESOLVED FROM PHOSPHOINOSITIDASE-C IN PRIMARY CULTURES OF MOUSE OSTEOBLASTS USING INDOMETHACIN

Recent work has established that various bone-resorbing hormones are a ble to activate phosphoinositide metabolism as well as eicosanoid prod uction in osteoblast-like cells, although the relationship between the se pathways is unclear. We used pertussis toxin and indomethacin to in hibit the stimulation of [H-3]arachidonic acid release and [H-3]phosph oinositide turnover caused by treating primary cultures of mouse osteo blasts with fetal calf serum. We found (1) that pertussis toxin and in domethacin each inhibited both pathways and (2) that although pertussi s toxin inhibited [H-3]arachidonic acid release to a greater extent th an indomethacin, [H-3]inositol phosphate accumulation was inhibited ra ther more effectively by indomethacin. These data suggest that whereas ligands in fetal calf serum activate [H-3]arachidonic acid release la rgely directly via the action of a pertussis-sensitive G protein, acti vation of phosphoinositidase C is indirect, being substantially depend ent upon eicosanoid production. These experiments suggest that serial activation of phospholipase A2 and phosphoinositidase C may occur in o steoblasts and that only the former enzyme is regulated by a pertussis toxin-sensitive G protein.