Brunner F, Kühberger E, Schloos J, Kukovetz W R
Institut für Pharmakodynamik und Toxikologie, Universität Graz, Austria.
Eur J Pharmacol. 1991 Apr 24;196(3):247-55. doi: 10.1016/0014-2999(91)90437-u.
The nature of the muscarinic receptor subtype mediating contraction of the endothelium-denuded bovine coronary artery was investigated in vitro by functional measurements and radioligand binding studies. The acetylcholine (ACh)-induced isotonic contraction of circularly cut muscle strips was recorded and expressed as a percentage of the maximum contraction obtained with 80 mM K+. In order to distinguish between M1, M2 and M3 receptors, the potency of the five subtype-selective antagonists, 4-diphenylacetoxy-N-methyl-piperidine methobromide (4-DAMP), parafluor-hexahydro-siladifenidol (pFHHSiD), pirenzepine, AF-DX 116 and methoctramine, to block the ACh-induced contraction was estimated. All the antagonists competitively inhibited the responses induced by ACh, with one exception, namely, 4-DAMP, whose Schild plot had a slope greater than one. The low affinity of pirenzepine (pA2 7.14 +/- 0.14) excluded an action at the M1 subtype. The low affinity of AF-DX 116 (pA2 6.49 +/- 0.18) and methoctramine (pA2 5.88 +/- 0.07) suggest that the bovine coronary artery smooth muscle receptor is not of the M2 (cardiac) subtype. In contrast, 4-DAMP (pA2 9.04 +/- 0.03) and pFHHSiD (pA2 7.64 +/- 0.04) potently inhibited the ACh-induced contraction with affinities similar to those reported for the M3 (glandular) receptor. In addition, the muscarinic receptors mediating coronary artery contraction were characterized in antagonist/[3H]N-methyl-scopolamine ([3H]NMS) competition binding studies. With the exception of AF-DX 116, all antagonists bound to a homogeneous population of receptors with pseudo-Hill slopes not different from unity. The pKi values, albeit somewhat lower, essentially substantiated the functional affinity estimates.(ABSTRACT TRUNCATED AT 250 WORDS)
通过功能测量和放射性配体结合研究，在体外研究了介导去内皮牛冠状动脉收缩的毒蕈碱受体亚型的性质。记录乙酰胆碱（ACh）诱导的圆形切割肌条的等张收缩，并表示为用80 mM K+获得的最大收缩的百分比。为了区分M1、M2和M3受体，评估了五种亚型选择性拮抗剂4-二苯基乙酰氧基-N-甲基哌啶甲溴化物（4-DAMP）、对氟六氢硅二苯胺（pFHHSiD）、哌仑西平、AF-DX 116和甲奥克明阻断ACh诱导收缩的效力。所有拮抗剂均竞争性抑制ACh诱导的反应，但4-DAMP除外，其Schild图的斜率大于1。哌仑西平的低亲和力（pA2 7.14±0.14）排除了其对M1亚型的作用。AF-DX 116（pA2 6.49±0.18）和甲奥克明（pA2 5.88±0.07）的低亲和力表明牛冠状动脉平滑肌受体不是M2（心脏）亚型。相比之下，4-DAMP（pA2 9.04±0.03）和pFHHSiD（pA2 7.64±0.04）有效抑制ACh诱导的收缩，其亲和力与报道的M3（腺体）受体相似。此外，在拮抗剂/[3H]N-甲基东莨菪碱（[3H]NMS）竞争结合研究中对介导冠状动脉收缩的毒蕈碱受体进行了表征。除AF-DX 116外，所有拮抗剂均与同质受体群体结合，其伪希尔斜率与1无差异。pKi值虽然略低，但基本上证实了功能亲和力估计值。（摘要截断于250字）
