Evidence for coupling of bradykinin receptors to a guanine-nucleotide binding protein to stimulate arachidonate liberation in the osteoblast-like cell line, MC3T3-E1

The effect of bradykinin on the activation production of inositol 1,4,5-triphosphate and prostaglandin E₂(PGE₂) was examined in the murine osteoblastic cell line, MC3T3-E1. Bradykinin, at concentrations ranging from 1 to 1000 nM, stimulated the production of inositol 1,4,5-triphosphate 2.5- to 3-fold within 10 s, and elevated cytosolic-free Ca²⁺, even in the absence of external Ca²⁺. This process is mediated through the activation of phospholipase C. Bradykinin at the same concentration also stimulated the production of PGE₂ and caused a release of ³H radioactivity of the cells prelabeled with [³H]arachidonic acid, probably via the activation of phospholipase A₂. Pretreatment of the cells with pertussis toxin inhibited the stimulation of PGE₂ production and ³H radioactivity release, while the elevation in cytosolic Ca²⁺ and the production of inositol 1,4,5-triphosphate were not altered by toxin-pretreatment. The addition of an unhydrolyzable analog of GTP, guanosine 5′-[γ-thio]triphosphate (GTPγS) to the β-escin-permeabilized cells prelabeled with [³H]arachidonic acid enhanced the release of ³H radioactivity. The simultaneous presence of bradykinin with GTPγS further activated the ³H radioactivity release in the β-escin-permeabilized cells. These results provide evidence that receptors for bradykinin in the MC3T3-E1 couple, stimulating arachidonate release, probably via the activation of phospholipase A₂, through a guanine nucleotide binding protein sensitive to pertussis toxin.