TY - JOUR
T1 - Antagonists of bradykinin that stabilize a G-protein-uncoupled state of the B2 receptor act as inverse agonists in rat myometrial cells
AU - Leeb-Lundberg, L. M.Fredrik
AU - Mathis, Sandra A.
AU - Herzig, Maryanne C.S.
PY - 1994/10/21
Y1 - 1994/10/21
N2 - Several B2 bradykinin (BK) receptor-specific antagonists including HOE140, NPC17731, and NPC567 exhibited negative intrinsic activity, which was observed as a decrease in basal phosphoinositide hydrolysis in primary cultures of rat myometrial cells, and this response was opposite to that elicited by the agonist BK. The order of potency of the antagonists in attenuating basal activity was essentially the same as that in competing both [3H]BK and [3H]NPC17731 for binding to B2 receptors on both intact rat myometrial cells and bovine myometrial membranes. We previously proposed a three-state model for the binding of agonists to G-protein-coupled B2 receptors in bovine myometrial membranes (Leeb-Lundberg, L. M. F. and Mathis, S. A. (1990) J. Biol. Chem. 265, 9621-9627). This model was based on the ability of BK to promote the sequential formation of three receptor binding states where formation of the third, equilibrium state was blocked by Gpp(NH)p (guanyl-5'-yl imidodiphosphate) identifying it as the G-protein- coupled state of the receptor. Here, we show that, in contrast to BK, these antagonists bound preferentially to a G-protein-uncoupled state of the receptor. These results indicate that B2 receptor antagonists that stabilize a G-protein-uncoupled state of the receptor act as inverse agonists. Furthermore, these results provide strong evidence that endogenous G-protein- coupled receptors exhibit spontaneous activity in their natural environment in the absence of agonist occupancy.
AB - Several B2 bradykinin (BK) receptor-specific antagonists including HOE140, NPC17731, and NPC567 exhibited negative intrinsic activity, which was observed as a decrease in basal phosphoinositide hydrolysis in primary cultures of rat myometrial cells, and this response was opposite to that elicited by the agonist BK. The order of potency of the antagonists in attenuating basal activity was essentially the same as that in competing both [3H]BK and [3H]NPC17731 for binding to B2 receptors on both intact rat myometrial cells and bovine myometrial membranes. We previously proposed a three-state model for the binding of agonists to G-protein-coupled B2 receptors in bovine myometrial membranes (Leeb-Lundberg, L. M. F. and Mathis, S. A. (1990) J. Biol. Chem. 265, 9621-9627). This model was based on the ability of BK to promote the sequential formation of three receptor binding states where formation of the third, equilibrium state was blocked by Gpp(NH)p (guanyl-5'-yl imidodiphosphate) identifying it as the G-protein- coupled state of the receptor. Here, we show that, in contrast to BK, these antagonists bound preferentially to a G-protein-uncoupled state of the receptor. These results indicate that B2 receptor antagonists that stabilize a G-protein-uncoupled state of the receptor act as inverse agonists. Furthermore, these results provide strong evidence that endogenous G-protein- coupled receptors exhibit spontaneous activity in their natural environment in the absence of agonist occupancy.
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M3 - Article
C2 - 7929307
AN - SCOPUS:0028113891
VL - 269
SP - 25970
EP - 25973
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 42
ER -