Araujo D M, Lapchak P A, Quirion R
Douglas Hospital Research Center, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
Synapse. 1991 Nov;9(3):165-76. doi: 10.1002/syn.890090303.
The present study shows that [3H]4-DAMP binds specifically, saturably, and with high affinity to muscarinic receptor sites in the rat brain. In homogenates of hippocampus, cerebral cortex, striatum, and thalamus, [3H]4-DAMP appears to bind two sub-populations of muscarinic sites: one class of high-affinity, low capacity sites (Kd less than 1 nM; Bmax = 45-152 fmol/mg protein) and a second class of lower-affinity, high capacity sites (Kd greater than 50 nM; Bmax = 263-929 fmol/mg protein). In cerebellar homogenates, the Bmax of [3H]4-DAMP binding sites was 20 +/- 2 and 141 +/- 21 fmol/mg protein for the high- and the lower-affinity site, respectively. The ligand selectivity profile for [3H]4-DAMP binding to its sites was similar for both the high- and lower-affinity sites; atropine = (-)QNB = 4-DAMP much greater than pirenzepine greater than AF-DX 116, although pirenzepine was more potent (16-fold) at the lower- than at the high-affinity sites. The autoradiographic distribution of [3H]4-DAMP sites revealed a discrete pattern of labeling in the rat brain, with the highest densities of [3H]4-DAMP sites present in the CA1 sub-field of Ammon's horn of the hippocampus, the dentate gyrus, the olfactory tubercle, the external plexiform layer of the olfactory bulb and layers I-II of the frontoparietal cortex. Although the distribution of [3H]pirenzepine sites was similar to that of [3H]4-DAMP sites in many brain regions, significant distinctions were apparent. Thus, both the ligand selectivity pattern of [3H]4-DAMP binding and the autoradiographic distribution of sites suggest that although the high-affinity [3H]4-DAMP sites may consist primarily of muscarinic-M3 receptors, the lower-affinity [3H]4-DAMP sites may be composed of a large proportion of muscarinic-M1 receptors.
本研究表明，[3H]4-DAMP能特异性、饱和性且高亲和力地结合大鼠脑中的毒蕈碱受体位点。在海马、大脑皮层、纹状体和丘脑的匀浆中，[3H]4-DAMP似乎能结合两类毒蕈碱位点：一类是高亲和力、低容量位点（解离常数Kd小于1 nM；最大结合量Bmax = 45 - 152 fmol/mg蛋白质），另一类是低亲和力、高容量位点（Kd大于50 nM；Bmax = 263 - 929 fmol/mg蛋白质）。在小脑匀浆中，[3H]4-DAMP结合位点的高亲和力和低亲和力位点的Bmax分别为20±2和141±21 fmol/mg蛋白质。[3H]4-DAMP与其位点结合的配体选择性谱在高亲和力和低亲和力位点上相似；阿托品=（-）QNB = 4-DAMP远大于哌仑西平大于AF-DX 116，尽管哌仑西平在低亲和力位点上的效力比高亲和力位点高16倍。[3H]4-DAMP位点的放射自显影分布揭示了大鼠脑中离散的标记模式，海马阿蒙角的CA1亚区、齿状回、嗅结节、嗅球的外丛状层以及额顶叶皮层的I-II层中[3H]4-DAMP位点密度最高。尽管在许多脑区[3H]哌仑西平位点的分布与[3H]4-DAMP位点相似，但明显存在显著差异。因此，[3H]4-DAMP结合的配体选择性模式和位点的放射自显影分布均表明，虽然高亲和力的[3H]4-DAMP位点可能主要由毒蕈碱-M3受体组成，但低亲和力的[3H]4-DAMP位点可能很大一部分由毒蕈碱-M1受体组成。
