BRADYKININ STIMULATES PRODUCTION OF INOSITOL (1,4,5) TRISPHOSPHATE IN CULTURED MESANGIAL CELLS OF THE RAT VIA A BK2-KININ RECEPTOR

1 Using [I-125-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-mu-M 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-mu-M) but not the BK1 antagonist (des-Arg9-Leu8-BK) abolished IP3 production in response to 0.1-mu-M 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.