The native and heterologously expressed kinin b2 receptor is coupled to two different g proteins

Bradykinin (BK) is a potent proinflammatory and vasoactive peptide that binds specifically to a kinin 82 receptor expressed ubiquitously in human tissues. Recently cloned, the kinin B2 receptor is predicted to be a member of the G protein coupled receptor family. The aim of this study was to identify the signal transduction event(s) activated by the 82 receptor and the heterotrimeric G protein(s) that mediates this event. In both human synovial cells (which express the native kinin B2 receptor), and a stable clone of CHO cells expressing the wild type human kinin B2 receptor, BK proved to be a potent stimulus for elevating cytosolic Ca2+ ([Ca2+]i), inositol phosphates (InsP), and arachidonic acid. (AA), levels (EDso's, 1-5 nM), indicating activation of phospholipase C and, possibly of phospholipase A2, via the kinin 82 receptor. Coupling of the receptor to PLC activation was mediated via a pertussis toxin (PTX)insensitive G protein (probably Goq/Gan). BK-induced elevations in AA levels were enhanced by PTX pretreatment, indicating possible dual regulation by a PTX-insensitive stimulatory protein and a PTX-sensitive inhibitory protein. BK did not elevate cyclic AMP levels in either untreated or PTX pretreated cells, indicating lack of coupling of the kinin 62 receptor to Gccs. Immunoprecipitation of photoaffinity labeled G proteins confirmed that the 82 receptor is coupled to G