THE MECHANISM FOR THE RAPID DESENSITIZATION IN BRADYKININ-STIMULATED INOSITOL MONOPHOSPHATE PRODUCTION IN NG108-15 CELLS INVOLVES INTERACTION OF A SINGLE RECEPTOR WITH MULTIPLE SIGNALING PATHWAYS

We have previously shown that the mechanism for the rapid desensitizat ion in bradykinin (BDK)-stimulated inositol monophosphate (IP) product ion in NG108-15 cells involves both a rapid loss of receptors from the cell surface and an uncoupling of the receptor:G-protein:phospholipas e C (PLC) signaling process, with protein kinase C (PKC) activation pl aying a role only at a postreceptor level (Wolsing and Rosenbaum, 1991 ). In contrast to BDK, a 5-min pretreatment with the BDK receptor ''an tagonist'' NPC-567 is sufficient to cause a substantial decrease in th e subsequent BDK maximal response (E(max)) without altering either the BDK potency (EC50) or the BDK receptor number. An 18-hr pretreatment of the cells with 200 ng/ml pertussis toxin (PT) does not alter the BD K response (Fold stim = 2.36 +/- 0.1 8 vs. 2.00 +/- 0.25 in controls, N = 4), reiterating previous observations that BDK-stimulated IP produ ction in this cell line is mediated by a pertussis toxin (PT)-insensit ive G-protein. However, PT pretreatment significantly (P < .05) attenu ates the receptor loss that accompanies the desensitization process. T aken together, these data imply that the BDK receptor in NG108-15 cell s interacts with both PT-sensitive and PT-insensitive G-proteins. Beca use NPC-567 pretreatment results in a desensitization that is not acco mpanied by receptor loss, it appears that NPC-567 is able to facilitat e an agonistic interaction with only the PT-insensitive G-proteins tha t are available to the receptor.