Regulation of bradykinin action at the receptor level

Intact cultured human foreskin fibroblasts can be used as an in vitro system to study the regulatory events related to kinin receptor function. Specific bradykinin (BK) receptor sites (B2 subtype) were measured by direct binding study and correlated with BK-induced biological effects such as the release of inositol phosphates, formation of prostacyclin (PGI2), and accumulation of cyclic 3'5' adenosine monophosphate (cAMP). Depending on the ambient concentration of BK in the culture medium, homologous receptor downregulation accompanied by a reduction in BK-stimulated PGI2 release occurred. These events were transient and followed by the recovery of both BK binding sites and BK responsiveness that was related to destruction of BK by highly active degradation systems. The fate of receptor-bound [3H]BK was studied by the acetic acid "stripping technique" that completely removes surface-bound [3H]BK while leaving internalized material with the remaining cells. Kinetic analysis of inside/surface ratios of 3H radioactivity revealed data consistent with the hypothesis of internalization of BK-receptor complexes. High-performance liquid chromatography (HPLC) analysis of internalized 3H counts showed significant quantities of intact [3H]BK occurring in an intracellular compartment. Compounds or drugs that enhance intracellular cAMP levels or inhibit generation of eicosanoids were shown to modify the BK response by indirect means. BK-receptor binding sites appear to be under tight regulatory control by both the mechanisms influencing the ambient concentration of BK and the interaction between multiple mediators.