Abstract

We have previously shown that the mechanism for the rapid desensitization in bradykinin (BDK)-stimulated inositol monophosphate (IP) production in NG108-15 cells involves both a rapid loss of receptors from the cell surface and an uncoupling of the receptor:G-protein:phospholipase C (PLC) signaling process, with protein kinase C (PKC) activation playing a role only at a postreceptor level (Wolsing and Rosenbaum, 1991). In contrast to BDK, a 5-min pretreatment with the BDK receptor "antagonist" NPC-567 is sufficient to cause a substantial decrease in the subsequent BDK maximal response (Emax) 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 BDK response (Fold stim = 2.36 +/- 0.18 vs. 2.00 +/- 0.25 in controls, N = 4), reiterating previous observations that BDK-stimulated IP production in this cell line is mediated by a pertussis toxin (PT)-insensitive G-protein. However, PT pretreatment significantly (P < .05) attenuates the receptor loss that accompanies the desensitization process. Taken together, these data imply that the BDK receptor in NG108-15 cells interacts with both PT-sensitive and PT-insensitive G-proteins. Because NPC-567 pretreatment results in a desensitization that is not accompanied by receptor loss, it appears that NPC-567 is able to facilitate an agonistic interaction with only the PT-insensitive G-proteins that are available to the receptor.