Leeb-Lundberg L M, Mathis S A, Herzig M C
Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284-7760.
J Biol Chem. 1994 Oct 21;269(42):25970-3.
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.
几种B2缓激肽（BK）受体特异性拮抗剂，包括HOE140、NPC17731和NPC567，表现出负性内在活性，这在大鼠子宫肌层细胞原代培养物中表现为基础磷酸肌醇水解的降低，且这种反应与激动剂BK引发的反应相反。拮抗剂减弱基础活性的效力顺序与在完整大鼠子宫肌层细胞和牛子宫肌层膜上竞争[3H]BK和[3H]NPC17731与B2受体结合的效力顺序基本相同。我们之前提出了一个激动剂与牛子宫肌层膜中G蛋白偶联B2受体结合的三态模型（Leeb-Lundberg，L.M.F.和Mathis，S.A.（1990）J.Biol.Chem.265，9621 - 9627）。该模型基于BK促进三种受体结合状态顺序形成的能力，其中第三种平衡状态的形成被Gpp(NH)p（鸟苷 - 5'-基亚氨二磷酸）阻断，这将其确定为受体的G蛋白偶联状态。在此，我们表明，与BK相反，这些拮抗剂优先结合受体的G蛋白非偶联状态。这些结果表明，稳定受体G蛋白非偶联状态的B2受体拮抗剂作为反向激动剂起作用。此外，这些结果提供了有力证据，表明内源性G蛋白偶联受体在没有激动剂占据的自然环境中表现出自发活性。
