Yum L, Wolf K M, Chiappinelli V A
Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, MO 63104, USA.
Neuroscience. 1996 May;72(2):545-55. doi: 10.1016/0306-4522(95)00531-5.
The family of nicotinic acetylcholine receptors contains numerous subtypes. Since the subunit compositions of most native neuronal nicotinic receptors are unknown, an important method for distinguishing subtypes of functional neuronal receptors is based on pharmacological criteria, such as affinity for snake toxins. We have now examined the affinities of native chick nicotinic receptors for methyllycaconitine, a toxin purified from Delphinium. We find that methyllycaconitine is a potent antagonist at central nicotinic receptors located on Edinger-Westphal neurons, producing nearly complete functional blockade of nicotinic responses at 10 nM. In marked contrast, methyllycaconitine is 1000-fold less potent at blocking nicotinic responses in the lateral spiriform nucleus. Methyllycaconitine inhibits kappa-bungarotoxin-sensitive nicotinic receptors in ciliary ganglia at 0.5-1.0 microM. Radioligand binding studies also reveal heterogeneity in the affinity of the toxin for nicotinic receptors. Methyllycaconitine binds most avidly to [125I] alpha-bungarotoxin sites in brain (Ki = 5.4 nM), and is 200-fold less potent at muscle nicotinic receptors (IC50 = 1.1 microM). The least potent binding of the toxin is to [3H]nicotine sites in brain (Ki = 3.7 microM). Methyllycaconitine is thus a useful pharmacological tool for distinguishing certain subtypes of native nicotinic receptors. The relatively low affinity of the toxin for nicotinic receptors in the lateral spiriform nucleus is consistent with the known properties of these receptors, which include a high affinity for [3H]nicotine and a lack of sensitivity to alpha- and kappa-bungarotoxin. On the basis of high affinity for methyllycaconitine and insensitivity to alpha-bungarotoxin, the nicotinic receptors in the Edinger-Westphal nucleus are unlike any previously described nicotinic receptor subtype.
烟碱型乙酰胆碱受体家族包含众多亚型。由于大多数天然神经元烟碱型受体的亚基组成尚不清楚，区分功能性神经元受体亚型的一种重要方法是基于药理学标准，例如对蛇毒素的亲和力。我们现在研究了天然鸡烟碱型受体对甲基lycaconitine（一种从翠雀属植物中纯化的毒素）的亲和力。我们发现甲基lycaconitine是位于动眼神经副核的中枢烟碱型受体的强效拮抗剂，在10 nM时几乎能完全功能性阻断烟碱型反应。与之形成鲜明对比的是，甲基lycaconitine在阻断外侧螺旋状核中的烟碱型反应方面效力要低1000倍。甲基lycaconitine在0.5 - 1.0 microM时抑制睫状神经节中对κ-银环蛇毒素敏感的烟碱型受体。放射性配体结合研究也揭示了该毒素对烟碱型受体亲和力的异质性。甲基lycaconitine与脑中的[125I]α-银环蛇毒素位点结合最紧密（Ki = 5.4 nM），而在肌肉烟碱型受体上的效力低200倍（IC50 = 1.1 microM）。该毒素与脑中[3H]尼古丁位点的结合效力最低（Ki = 3.7 microM）。因此，甲基lycaconitine是区分某些天然烟碱型受体亚型的有用药理学工具。该毒素对外侧螺旋状核中烟碱型受体的相对低亲和力与这些受体的已知特性一致，这些特性包括对[3H]尼古丁的高亲和力以及对α-和κ-银环蛇毒素不敏感。基于对甲基lycaconitine的高亲和力和对α-银环蛇毒素不敏感，动眼神经副核中的烟碱型受体不同于任何先前描述的烟碱型受体亚型。
