High affinity bradykinin binding to human inflammatory cells

Specific direct bradykinin (BK) binding and competitive inhibition was detected in human neutrophil and peripheral blood mononuclear cell (PBMC) detergent solubilized extracts and purified plasma membranes using in vitro radioreceptor ligand binding. Scatchard analyses of [125I]-BK binding revealed an equilibrium dissociation constant (Kd) of 2.9 x 10(-11) M for neutrophils and 5.6 x 10(-11) M for PBMC using [des-arg9]-BK a B1 agonist; 2.6 x 10(-11) M for neutrophils, 6.2 x 10(-11) M for PBMC with BK a B2 agonist; 5.4 x 10(-11) M for PBMC using Lys-BK a B2 agonist. The number of binding sites (Bmax) was calculated to be 0.113 fM/microgram protein (720 receptors per cell) for neutrophils and 0.200 fM/microgram protein (1289 receptors per cell) for PBMC with the B1 agonist while with the B2 agonists the values were 0.128 fM/microgram protein (818 receptors per cell) for neutrophils and 0.157 fM/microgram protein (1005 receptors per cell) for PBMC with BK, and 0.293 fM/microgram protein (1870 receptors per cell) with Lys-BK for PBMC. In a competitive binding inhibition assay using neutrophil and PBMC glycerol purified plasma membranes, high affinity binding in the nanomolar range was detected to Lys-BK and BK but with [des-arg9]-BK a 10-100 fold lower order affinity was observed this being indicative of pharmacologically defined B2 characteristics.