Bradykinin stimulates production of inositol (1,4,5) trisphosphate in cultured mesangial cells of the rat via a BK2‐kinin receptor

Abstract

1 Using [¹²⁵I-Tyr⁰]-BK, as radiolabelled ligand, and various agonists and antagonists of bradykinin (BK) we identified a single class of specific BK₂-binding sites in mesangial cell membranes (B_max = 73 fmol mg⁻¹ protein and K_d = 3.7 nm). 2 Following the addition of 0.1 μm BK, inositol (1,4,5) trisphosphate (IP3) formation increased within 20 s from a basal level of 64 to a maximal value of 175 pmol mg⁻¹ protein. 3 Incubation in a Ca²⁺-free medium did not change IP3 production but a 5 min preincubation with 1 mm EGTA completely prevented the BK-induced IP3 formation, suggesting that IP3 formation is partly dependent on extracellular calcium. 4 The BK₂ antagonist d-Arg-Hyp³-d-Phe⁷-BK (10 μm) but not the BK₁ antagonist (des-Arg⁹-Leu⁸-BK) abolished IP3 production in response to 0.1 μm BK. Pretreatment of mesangial cells with pertussis toxin was without effect on BK-induced IP3 formation, whereas phorbol 12-myristate 13-acetate significantly enhanced (by 25%) BK-induced IP3 formation. 5 The present data demonstrate that inositol phosphate breakdown in rat mesangial cells can be mediated via activation of a BK₂-kinin receptor and is under negative control of protein-kinase C.