Flamez A, de Backer J P, Wilczak N, Vauquelin G, de Keyser J
Department of Neurology, Academisch Ziekenhuis, Brussels, Belgium.
Neurosci Lett. 1994 Jul 4;175(1-2):17-20. doi: 10.1016/0304-3940(94)91067-7.
Clozapine displays nanomolar affinity for cloned human D4-type dopamine receptors expressed in tissue culture cells. Therefore, [3H]clozapine has been introduced as a radioligand for the labelling of the D4 dopamine receptors. We found that, in membranes of postmortem human striatum, amygdala, frontal cortex and substantia nigra, neither dopamine nor the dopamine agonist apomorphine displaced the binding of [3H]clozapine (5-20 nM). [3H]Clozapine competition curves with clozapine and loxapine revealed the presence of two binding sites. The high-affinity site was displaced by atropine and pirenzepine with nanomolar affinity. The low-affinity site did not correspond to a serotonin, adrenergic, gamma-amino butyric acid, N-methyl-D-aspartate, benzodiazepine, histamine, sigma, imidazoline receptor-binding site, or catecholamine uptake site. Our results suggest that [3H]clozapine in postmortem human brain binds to M1-type muscarinic cholinergic receptors and to a low-affinity binding site but is not a suitable radioligand for investigating the D4 dopamine receptors.
氯氮平对在组织培养细胞中表达的克隆人 D4 型多巴胺受体表现出纳摩尔级亲和力。因此，[3H]氯氮平已被用作标记 D4 多巴胺受体的放射性配体。我们发现，在人死后纹状体、杏仁核、额叶皮质和黑质的膜中，多巴胺和多巴胺激动剂阿扑吗啡均不能取代 [3H]氯氮平（5 - 20 nM）的结合。[3H]氯氮平与氯氮平和洛沙平的竞争曲线显示存在两个结合位点。高亲和力位点可被阿托品和哌仑西平以纳摩尔亲和力取代。低亲和力位点与血清素、肾上腺素能、γ-氨基丁酸、N-甲基-D-天冬氨酸、苯二氮䓬、组胺、σ、咪唑啉受体结合位点或儿茶酚胺摄取位点均不对应。我们的结果表明，人死后大脑中的 [3H]氯氮平与 M1 型毒蕈碱胆碱能受体以及一个低亲和力结合位点结合，但不是研究 D4 多巴胺受体的合适放射性配体。
