Bruns R F, Fergus J H
Department of Pharmacology, Parke-Davis Pharmaceutical Research Division, Warner-Lambert Company, Ann Arbor, Michigan 48105.
Mol Pharmacol. 1990 Dec;38(6):939-49.
Several 2-amino-3-benzoylthiophenes were found to increase the binding of [3H]N6-cyclohexyladenosine to A1 adenosine receptors in rat brain membranes. Concentration-response curves were bell-shaped, with up to 45% stimulation of binding at 10 microM followed by inhibition at higher concentrations. Because these compounds originated from a series of nonxanthine adenosine antagonists, the inhibition of binding was attributed to the presence of interfering adenosine antagonist activity. The compounds stimulated binding of several A1 agonist ligands but only inhibited binding of the A1 antagonist ligand [3H]8-cyclopentyl-1,3-dipropylxanthine, indicating that enhancement was specific for the agonist conformation of the receptor. The enhancement was also specific for the A1 receptor, because agonist binding to A2 adenosine, M2 muscarinic, alpha 2 adrenergic, and delta opiate receptors showed little or no enhancement. Uncoupling of the A1 receptor from the inhibitory guanine nucleotide-binding protein did not prevent enhancement. The enhancers slowed the dissociation of [3H]N6-cyclohexyladenosine from the A1 receptor, implying an allosteric mechanism of action. The inhibition of forskolin-stimulated cyclic AMP accumulation in FRTL-5 cells was employed as a functional index of A1 receptor activation. The enhancers caused up to 19-fold leftward shifts in the concentration-response curve for N6-cyclopentyladenosine and also caused up to 55% inhibition of cyclic AMP accumulation in the absence of agonist. The binding and functional results are consistent with a model in which the enhancers bind preferentially to the agonist conformation of the A1 receptor, thereby shifting the receptor equilibrium in favor of agonist binding. Adenosine enhancers may be useful for ischemia and other conditions involving local energy deficits. More generally, allosteric enhancers may provide a means for strengthening physiological control circuits in a variety of receptor systems.
研究发现，几种2-氨基-3-苯甲酰基噻吩可增强大鼠脑膜中[3H]N6-环己基腺苷与A1腺苷受体的结合。浓度-效应曲线呈钟形，在10微摩尔时结合增强高达45%，更高浓度时则出现抑制。由于这些化合物源自一系列非黄嘌呤腺苷拮抗剂，结合抑制被归因于干扰性腺苷拮抗剂活性的存在。这些化合物可增强几种A1激动剂配体的结合，但仅抑制A1拮抗剂配体[3H]8-环戊基-1,3-二丙基黄嘌呤的结合，表明增强作用对受体的激动剂构象具有特异性。这种增强作用对A1受体也具有特异性，因为激动剂与A2腺苷、M2毒蕈碱、α2肾上腺素能和δ阿片受体的结合几乎没有增强或没有增强。A1受体与抑制性鸟嘌呤核苷酸结合蛋白的解偶联并不能阻止增强作用。增强剂减缓了[3H]N6-环己基腺苷从A1受体的解离，这意味着其作用机制为变构机制。在FRTL-5细胞中，抑制福斯可林刺激的环磷酸腺苷积累被用作A1受体激活的功能指标。增强剂使N6-环戊基腺苷的浓度-效应曲线向左移动高达19倍，并且在没有激动剂的情况下，还可导致环磷酸腺苷积累抑制高达55%。结合和功能结果与一个模型一致，即增强剂优先结合A1受体的激动剂构象，从而使受体平衡向有利于激动剂结合的方向移动。腺苷增强剂可能对缺血及其他涉及局部能量缺乏的病症有用。更普遍地说，变构增强剂可能为加强各种受体系统中的生理控制回路提供一种手段。
