Kinin receptors: functional aspects.

Two types of receptors (B1R, B2R) for kinins are defined in mammalian species. Comparative experiments involving recombinant fusion proteins consisting of rabbit B1R or B2R fused to GFP-related proteins are exploited to study the regulation of the response to kinins at the receptor level. The following points will be briefly reviewed and supported by some novel data. (1) The constitutive B2Rs are internalized upon agonist stimulation, but completely recycled to the cell surface; however, B2R destruction can be achieved following limited proteolysis (extracellular trypsin, neutrophil proteases), a plausible down-regulation mechanism in pathology. (2) The inducible B1Rs, stimulated by des-Arg9-kinins, are not phosphorylated nor internalized upon agonist stimulation, but rather undergo a reversible redistribution to caveolae-related rafts. B2Rs are also subjected to this translocation, but only transiently (before endocytosis). (3) Based on the analysis of rabbit aortic smooth muscle cells, B1R induction by cytokines is dependent on nuclear factor KB in rabbit vascular tissue, but exogenous kinins acting on either receptor type do not induce B1R expression.