Autoregulation of Bradykinin Receptors

As bstract. The interaction of bradykinin (BK) with its specific receptors on intact cultured human fibroblasts results in production ofprostaglandins, including prostacyclin (PG12), and accumulation of cyclic AMP. Incubation of cells with 1 ,tM BK for 5 min at 37°C led to a marked reduction (75-90%) in BK-induced PGI2 release and in total number of [3H]BK-binding sites with no change in dissociation constant (6.1 and 7.6 nM for control and BK-treated cells, respectively). The decrease in receptor number did not result from BK transferred from the first incubation into the binding assay. BK-induced receptor loss was temperature dependent; exposure of cells to BK at 40C had little or no effect on receptor number. After incubation with BK for _ 15 min, further incubation in the absence of BK for 30 min at 370C almost completely restored both receptor number and BK-induced PGI2 release. With more prolonged exposure to BK (>1 h), restoration of receptors was inversely related to the length of exposure and the concentration ofBK. Recovery was unaffected by cycloheximide. During prolonged incubation without removal ofBK, cells began to recover receptors by 5 h; >99% of the bradykinin initially present disappeared by 3 h. Bacitracin greatly retarded BK disappearance and totally prevented recovery. These observations provide direct evidence that the number of BK receptors on cultured human fibroblasts can be regulated by BK itself. In addition, it appears that BKdegrading systems, by influencing local concentrations of the peptide, may play an important role in the autoregulation of BK receptors. The presence of highly active