Bolger G T, Luchowski E M, Triggle D J
Department of Biochemical Pharmacology, School of Pharmacy, State University of New York, Buffalo 14260.
Can J Physiol Pharmacol. 1989 Apr;67(4):331-43. doi: 10.1139/y89-054.
The relationship between ion movements (sodium uptake and potassium release) and agonist-induced contractile responses or muscarinic receptor binding was investigated in the guinea pig ileal longitudinal muscle (GPLM). Sodium uptake and potassium release were agonist-dependent, concentration-dependent, and stereoselective, with the following rank order of maximum ion movement: muscarinic agonists greater than histamine greater than substance P = serotonin. Potassium depolarization did not initiate sodium uptake or potassium release. Sodium uptake was rapid and monophasic, preceding potassium release which was biphasic in nature. Full muscarinic agonists produced equal maximal increases in sodium uptake, while maximal potassium release varied for all muscarinic agonists and in addition differed from sodium uptake in the following ways: time course, stereoselectivity, sensitivity to calcium antagonists, modulation by the guanylyl nucleotide derivative, 5'-guanylylimidodiphosphate (Gpp(NH)p), and inhibition by muscarinic receptor blockade with benzilylcholine mustard. The calcium ionophores A23187 and ionomycin (SQ23377) did not produce any sodium uptake; A23187 but not ionomycin produced potassium release comparable to that evoked by muscarinic agonists. Ion movement in response to combinations of agonists were not additive. Muscarinic agonist binding as measured by competition for [3H]quinuclidinyl benzilate ([3H]QNB) binding, was best described by multiple sites and was regulated by Gpp(NH)p. Excellent correlations were observed between the dissociation constants for binding and sodium uptake, potassium release, and contraction. The best correlations were those between the pharmacologic responses and the high affinity binding site in the absence, and the low affinity site in the presence, of Gpp(NH)p, respectively. Furthermore, the potencies of muscarinic agonists to evoke ion movements and to inhibit [3H]QNB binding were similar, and from one to two orders of magnitude less than those for contraction. It is suggested that contraction and potassium release were mediated by the high affinity, and sodium uptake by the low and average affinity muscarinic agonist binding sites, respectively. These findings suggest an agonist-activated receptor-effector coupling model in GPLM that leads to the activation of sodium uptake, potassium release, and subsequently, contraction.
在豚鼠回肠纵肌（GPLM）中研究了离子运动（钠摄取和钾释放）与激动剂诱导的收缩反应或毒蕈碱受体结合之间的关系。钠摄取和钾释放依赖于激动剂、具有浓度依赖性且具有立体选择性，最大离子运动的顺序如下：毒蕈碱激动剂大于组胺大于P物质 = 5-羟色胺。钾去极化不会引发钠摄取或钾释放。钠摄取迅速且呈单相，先于本质上呈双相的钾释放。完全毒蕈碱激动剂在钠摄取方面产生相等的最大增加，而所有毒蕈碱激动剂的最大钾释放各不相同，并且在以下方面也与钠摄取不同：时间进程、立体选择性、对钙拮抗剂的敏感性、鸟苷酸衍生物5'-鸟苷酰亚胺二磷酸（Gpp(NH)p）的调节以及苯甲酰胆碱氮芥对毒蕈碱受体的阻断抑制作用。钙离子载体A23187和离子霉素（SQ23377）不会产生任何钠摄取；A23187但不是离子霉素产生的钾释放与毒蕈碱激动剂诱发的钾释放相当。对激动剂组合的离子运动反应不是相加的。通过对[3H]喹核醇基苯甲酸酯（[3H]QNB）结合的竞争来测量的毒蕈碱激动剂结合，最好用多个位点来描述并且受Gpp(NH)p调节。在结合的解离常数与钠摄取、钾释放和收缩之间观察到极好的相关性。最佳相关性分别是在不存在Gpp(NH)p时药理反应与高亲和力结合位点之间以及在存在Gpp(NH)p时与低亲和力位点之间的相关性。此外，毒蕈碱激动剂诱发离子运动和抑制[3H]QNB结合的效力相似，并且比收缩的效力小一到两个数量级。提示收缩和钾释放分别由高亲和力介导，而钠摄取由低亲和力和平均亲和力的毒蕈碱激动剂结合位点介导。这些发现提示了GPLM中一种激动剂激活的受体 - 效应器偶联模型，该模型导致钠摄取、钾释放以及随后的收缩的激活。
