High agonist-independent clearance of rabbit kinin B1 receptors in cultured cells

We hypothesized that the inducible kinin B(1) receptor (B(1)R) is rapidly cleared from cells when its synthesis subsides. The agonist-independent degradation of the rabbit B(1)Rs and related B(2) receptors (B(2)Rs) was investigated. Endocytosis of the B(1)R-yellow fluorescent protein (YFP) conjugate was more intense than that of B(2)R-green fluorescent protein (GFP) based on fluorescence accumulation in HEK 293 cells treated with a lysosomal inhibitor. The cells expressing B(1)R-YFP contained more GFP/YFP-sized degradation product(s) than those expressing B(2)R-GFP (immunoblot, antibodies equally reacting with both fluorescent proteins). The binding site density of B(1)R-YFP decreased in the presence of protein synthesis or maturation inhibitors (anisomycin, brefeldin A), whereas that of B(2)R-GFP remained constant. Wild-type B(1)Rs were also cleared faster than B(2)Rs in rabbit smooth muscle cells treated with metabolic inhibitors. Contractility experiments based on brefeldin A-treated isolated rabbit blood vessels also functionally support that B(1)Rs are more rapidly eliminated than B(2)Rs (decreased maximal effect of agonist over 2 h). The highly regulated B(1)R is rapidly degraded, relative to the constitutive B(2)R.