Agonist-specific alterations in receptor–phospholipase coupling following inactivation of Gi2α gene1 Available to Purchase

Different forms of phospholipase A₂, together with pertussis toxin-sensitive G-proteins, [Ca²⁺]_i (intracellular Ca²⁺ concentration), protein kinase C, calmodulin, protein tyrosine kinases, mitogen-activated protein kinases and Ca²⁺/calmodulin-dependent protein kinase appear to play a role in agonist-mediated release of arachidonic acid. Here we report that fibroblasts from 14-day-old mouse embryos with inactivated G_i2α (α-subunit of the heterotrimeric G-protein G_i2) gene display a marked decrease in the ability of lysophosphatidic acid, thrombin and Ca²⁺ ionophores to release arachidonic acid compared with their normal counterparts. The requirement for G_i2α in the release of arachidonic acid following increased [Ca²⁺]_i may be explained by the incomplete translocation of cytosolic phospholipase A₂ observed in G_i2α-deficient cells. Paradoxically, inactivation of the G_i2α gene resulted in up-regulation of bradykinin receptors and their coupling to increased arachidonic acid release, phospholipase C activity and [Ca²⁺]_i. A concomitant increase in basal phospholipase C activity was also observed in the G_i2α-deficient cells. These observations establish a pleiotropic and essential role for G_i2α in receptor-phospholipase coupling that contrasts with its less obligatory participation in agonist-mediated inhibition of adenylate cyclase.