Ligand-mediated regulation of kinin receptors in the rabbit

The kinin B1 receptors (B1Rs), stimulated by des-Arg9-kinins, are completely inducible, notably following treatment of animals with bacterial lipopolysaccharide. Several studies based on cultured cells have suggested a form of autoregulation of kinin receptors, because B2 receptor (B2R) or B1R stimulation could transcriptionally upregulate B1R expression. The B2R may rather be downregulated in inflammatory conditions. A rabbit B2R-green fluorescent protein (GFP) conjugate stably expressed in HEK 293 cells was rapidly internalized in response to the agonist bradykinin. Ligand-induced receptor cycling was documented applying confocal microscopy. The results confirm agonist-induced B2R endocytosis, but extensive recycling to the cell membrane does not support agonist-induced downregulation.