The kallikrein-kinin system, activated during inflammatory conditions and the regulation of specific cardiovascular and renal functions, includes two G protein-coupled receptors for bradykinin (BK)-related peptides. 9 -BK (1-100 nM) rapidly concentrated the receptor-associated fluorescence into multiple aggregates that remained associated with the plasma membrane (no significant internalization) and colocalized with caveolin-1. This reaction was slowly reversible upon agonist washing at 37°C and prevented pretreatment with a B 1 R antagonist. ␤-Cyclodextrin treatment, which extracts cholesterol from membranes and disrupts caveolae-related rafts, prevented agonist-induced redistribution of B 1 R-YFP but not the PLA 2 activation mediated by this receptor. The agonist radioligand copurified with caveolin-1 to a greater extent than the tritiated antagonist in buoyant fractions of HEK 293 cells treated with the ligands. Agonistinduced cellular translocation of the kinin B 1 R to caveolaerelated rafts without endocytosis is a novel variation on the theme of G protein-coupled receptor adaptation.

Kinin B1receptor (B1R) expression and the importance of the transcription factor nuclear factor (NF)-κB in this process were evaluated in models based on the rabbit aorta: freshly isolated tissue (postisolation induction) and cultured smooth muscle cells (SMCs). A 3-h incubation of freshly isolated tissues determined a sharp B1R mRNA increase (RT-PCR). Coincubation of tissues with a stimulus (interleukin-1β, fetal bovine serum, epidermal growth factor, or cycloheximide) further increased mRNA levels. Cultured SMCs possessed a basal population of surface B1Rs ([3H]Lys-des-Arg9-bradykinin binding) that was upregulated by treatments with the same set of stimuli (binding, mRNA, nuclear runon). Pharmacological inhibitors of NF-κB (MG-132, BAY 11-7082, dexamethasone) or actinomycin D reduced the postisolation induction of B1Rs in fresh aortic tissue (contractility or mRNA) and the cytokine effect on cells (mRNA, binding). NF-κB may be a common mediator of various stimuli that increase B1R gene transcription in the rabbit aorta, including tissue isolation, but cycloheximide also stabilizes B1R mRNA. The SMC models faithfully mimic the in vivo situation with regard to B1R regulation.

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