Second messenger systems stimulated by bradykinin in osteoblastic cells: evidence for B₂ receptors

The effects of bradykinin, analogs and inhibitors on the human osteoblastic osteosarcoma cell lines Saos 2 and G292 and on normal rat calvarial osteoblastic cells were investigated. In all cell types, bradykinin (1 nM-100μM) caused significant time- and dose-dependent changes in the levels of inositol phosphates. Neomycin inhibited the inositol phosphate response to bradykinin, while indomethacin had no effect. Bradykinin also elicited a dose-dependent increase in free cytosolic calcium concentration. Bradykinin and T-kinin did not affect cyclic AMP levels in these cells. Doses of des-Arg⁹-bradykinin, a B₁ receptor agonist, up to 100 nM did not stimulate the osteoblastic inositol phosphate response. In addition, the bradykinin-stimulated inositol phosphate response was unaffected by des-Arg⁹-[Leu⁸]-bradykinin, a B₁ receptor antagonist, while it was inhibited by D-Arg-[Hyp³-[β-(2-thienyl)-Ala]^5,8-D-Phe⁷]-bradykinin, a B₂ receptor antagonist. These results suggest that in osteoblastic cells the mechanism of action of bradykinin involves stimulation of the phosphoinositide metabolism and increases in cytosolic calcium levels through activation of B₂ receptors.