Kostka P, Ahmad S, Kwan C Y, Daniel E E, Gordon R K, Chiang P K
Department of Applied Biochemistry, Walter Reed Army Institute of Research, Washington, DC.
J Pharmacol Exp Ther. 1992 Oct;263(1):226-31.
Prejunctional muscarinic receptors from the deep muscular plexus of canine ileum were studied, and their properties were compared with those of the postjunctional receptors of the circular smooth muscle. In the purified synaptosomal fraction (a fraction containing primarily the axonal varicosities of deep muscular plexus), the muscarinic ligand N-[3H]methylscopolamine labeled an apparently homogenous population of receptors (nH = 1) with a Kd of 2.7 nM and a Bmax of 195 +/- 44 fmol/mg protein (mean +/- S.D., n = 4). These receptors showed a high affinity for the M3/M1-selective antagonist 4-diphenylacetoxy-N-methylpiperidine methiodide (pKi = 7.41); in contrast, the pKi values of pirenzepine (5.60), methoctramine (5.65) and AF-DX 116 (5.21) implied little selectivity for these subtypes. The binding properties of muscarinic receptors in the synaptosomal fraction were different from the binding properties of muscarinic receptors in the purified circular smooth muscle plasma membranes. Most notably, the circular smooth muscle receptors had significantly lower affinity for N-[3H]methylscopolamine (Kd = 16 nM) with a Bmax value of 2088 +/- 276 fmol/mg. The affinities of the M2 subtype-selective muscarinic antagonists methoctramine and AF-DX 116 were similar in both membrane preparations. The receptor population associated with the deep muscular plexus synaptosomal fraction was linked to the inhibition of adenylate cyclase activity, as demonstrated by a concentration-dependent, atropine-sensitive inhibition of the forskolin-stimulated enzyme in the presence of muscarinic agonists carbachol and oxotremorine. Based on the pharmacological observations presented here, the prejunctional muscarinic receptors in the axonal varicosities of deep muscular plexus are different from the postjunctional receptors present in the circular smooth muscle.
对犬回肠深层肌丛的接头前毒蕈碱受体进行了研究，并将其特性与环形平滑肌的接头后受体特性进行了比较。在纯化的突触体组分（主要包含深层肌丛轴突膨体的组分）中，毒蕈碱配体N-[3H]甲基东莨菪碱标记了一个明显均一的受体群体（nH = 1），其解离常数（Kd）为2.7 nM，最大结合量（Bmax）为195±44 fmol/mg蛋白质（平均值±标准差，n = 4）。这些受体对M3/M1选择性拮抗剂碘化4-二苯乙酰氧基-N-甲基哌啶（pKi = 7.41）表现出高亲和力；相比之下，哌仑西平（5.60）、甲奥克溴铵（5.65）和AF-DX 116（5.21）的pKi值表明对这些亚型几乎没有选择性。突触体组分中毒蕈碱受体的结合特性与纯化的环形平滑肌质膜中毒蕈碱受体的结合特性不同。最值得注意的是，环形平滑肌受体对N-[3H]甲基东莨菪碱的亲和力显著较低（Kd = 16 nM），最大结合量为2088±276 fmol/mg。M2亚型选择性毒蕈碱拮抗剂甲奥克溴铵和AF-DX 116在两种膜制剂中的亲和力相似。与深层肌丛突触体组分相关的受体群体与腺苷酸环化酶活性的抑制有关，这在毒蕈碱激动剂卡巴胆碱和氧化震颤素存在的情况下，通过对福斯高林刺激的酶的浓度依赖性、阿托品敏感抑制得以证明。基于此处给出的药理学观察结果，深层肌丛轴突膨体中的接头前毒蕈碱受体与环形平滑肌中存在的接头后受体不同。
