Cardiac muscarinic receptors. Cooperativity as the basis for multiple states of affinity
Cardiac muscarinic receptors. Cooperativity as the basis for multiple states of affinity
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DOI：
10.1021/bi961939t
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发表时间：
1997-06-17
期刊：
影响因子：
2.9
通讯作者：
Wells, JW
中科院分区：
文献类型：
--
作者：
Chidiac, P;Green, MA;Wells, JW
已将合作性研究为在叙利亚仓鼠洗涤的膜中观察到的效果的机理基础，特别是N- [H-3]甲基科泊胺仅标记为66-75％的甲基核酸基质氨基苯二甲酸酯，仅标记为66-75％。显然每个放射性物的饱和浓度。同样，由N- [H-3]标记的甲基质丙胺标记的受体揭示了在天然膜中对激动剂的三种亲和力，并随后通过丙基苯甲酰胆碱芥末酱对约80％的地点的不可逆封锁。在这两种制剂中，鸟叶藻次磷酸盐（GMP-PNP）造成了明显的位点相互转换，从对激动剂的较高亲和力到较低的亲和力，从对拮抗剂的较低亲和力到更高的亲和力。根据包括受体的合作和非合作形式的模型获得了对数据的出色和机械一致的描述。前者用ADAIR方程的变体描述了前者，而后者则包括在于与芥末的治疗中幸存下来的低亲和力位点，如果明显能力的差异来自N-的结合中的负合作性[H-3 [H-3] ]甲基科泊胺，受体的合作形式至少在天然膜中是三价。否则，GMP-PNP在测定中使用的放射性物体浓度所施加的约束表明，相反，受体的合作形式至少是四载体，相比之下，二价受体与烷基化膜的数据足以充分随着寡聚阵列中功能位点之间相互作用的可能性降低，呈现了一个模型，其中所述受体在其合作特性不同的两个或多个州之间自发互动。 GMP-PNP的效果可以合理化为不同状态之间平衡的变化。
Cooperativity has been investigated as the mechanistic basis for effects observed with cardiac muscarinic receptors in washed membranes from Syrian hamsters, Specifically, N-[H-3]methylscopolamine labeled only 66-75% of the sites labeled by [H-3]quinuclidinylbenzilate at apparently saturating concentrations of each radioligand. Also, receptors labeled by N-[H-3]methylscopolamine revealed three states of affinity for agonists, both in native membranes and following irreversible blockade of about 80% of the sites by propylbenzilylcholine mustard; in both preparations, guanylylimidodiphosphate (GMP-PNP) effected an apparent interconversion of sites from higher to lower affinity for agonists and from lower to higher affinity for the antagonist. Excellent and mechanistically consistent descriptions of the data were obtained in terms of a model comprising cooperative and noncooperative forms of the receptor; the former was described by a variant of the Adair equation, and the latter was included to account for low-affinity sites that survived treatment with the mustard, If differences in apparent capacity derive from negative cooperativity in the binding of N-[H-3]methylscopolamine, the cooperative form of the receptor was at least trivalent in native membranes; otherwise, constraints imposed by the effects of GMP-PNP at the concentrations of radioligand used in the assays dictate that the cooperative form of the receptor was at least tetravalent, In contrast, a divalent receptor is sufficient with the data from alkylated membranes, in accord with the reduced likelihood of interactions between functional sites within an oligomeric array, A model is presented wherein the receptor interconverts spontaneously between two or more states differing in their cooperative properties. The effects of GMP-PNP can be rationalized as a shift in the equilibrium between the different states.