Storch A, Schrattenholz A, Cooper J C, Abdel Ghani E M, Gutbrod O, Weber K H, Reinhardt S, Lobron C, Hermsen B, Soskiç V
Laboratory of Molecular Neurobiology, Johannes Gutenberg University Medical School, Mainz, Germany.
Eur J Pharmacol. 1995 Aug 15;290(3):207-19. doi: 10.1016/0922-4106(95)00080-1.
The acetylcholine esterase inhibitor (-)-physostigmine has been shown to act as agonist on nicotinic acetylcholine receptors from muscle and brain, by binding to sites on the alpha-polypeptide that are distinct from those for the natural transmitter acetylcholine (Schröder et al., 1994). In the present report we show that (-)-physostigmine, galanthamine, and the morphine derivative codeine activate single-channel currents in outside-out patches excised from clonal rat pheochromocytoma (PC12) cells. Although several lines of evidence demonstrate that the three alkaloids act on the same channels as acetylcholine, the competitive nicotinic antagonist methyllycaconitine only inhibited channel activation by acetylcholine but not by (-)-physostigmine, galanthamine or codeine. In contrast, the monoclonal antibody FK1, which competitively inhibits (-)-physostigmine binding to nicotinic acetylcholine receptors, did not affect channel activation by acetylcholine but inhibited activation by (-)-physostigmine, galanthamine and codeine. The three alkaloids therefore act via binding sites distinct from those for acetylcholine, in a 'noncompetitive' fashion. The potency of (-)-physostigmine and related compounds to act as a noncompetitive agonist is unrelated to the level of acetylcholine esterase inhibition induced by these drugs. (-)-Physostigmine, galanthamine and codeine do not evoke sizable whole-cell currents, which is due to the combined effects of low open-channel probability, slow onset and slow inactivation of response. In contrast, they sensitize PC12 cell nicotinic receptors in their submaximal response to acetylcholine. While the abundance of nicotinic acetylcholine receptor isoforms expressed in PC12 cells excludes identification of specific nicotinic acetylcholine receptor subtypes that interact with noncompetitive agonists, the identical patterns of single-channel current amplitudes observed with acetylcholine and with noncompetitive agonists suggested that all PC12 cell nicotinic acetylcholine receptor subtypes that respond to acetylcholine also respond to noncompetitive agonist. The action of noncompetitive agonists therefore seems to be highly conserved between nicotinic acetylcholine receptor subtypes, in agreement with the high level of structural conservation in the sequence region harboring major elements of this site.
乙酰胆碱酯酶抑制剂（-）-毒扁豆碱已被证明可作为肌肉和脑烟碱型乙酰胆碱受体的激动剂，通过与α-多肽上与天然递质乙酰胆碱不同的位点结合（施罗德等人，1994年）。在本报告中，我们表明（-）-毒扁豆碱、加兰他敏和吗啡衍生物可待因能激活从克隆大鼠嗜铬细胞瘤（PC12）细胞上切下的外向型膜片钳中的单通道电流。尽管有几条证据表明这三种生物碱与乙酰胆碱作用于相同的通道，但竞争性烟碱拮抗剂甲基lycaconitine仅抑制乙酰胆碱引起的通道激活，而不抑制（-）-毒扁豆碱、加兰他敏或可待因引起的通道激活。相反，竞争性抑制（-）-毒扁豆碱与烟碱型乙酰胆碱受体结合的单克隆抗体FK1不影响乙酰胆碱引起的通道激活，但抑制（-）-毒扁豆碱、加兰他敏和可待因引起的通道激活。因此，这三种生物碱通过与乙酰胆碱不同的结合位点以“非竞争性”方式起作用。（-）-毒扁豆碱及相关化合物作为非竞争性激动剂的效力与这些药物诱导的乙酰胆碱酯酶抑制水平无关。（-）-毒扁豆碱、加兰他敏和可待因不会引起可观的全细胞电流，这是由于低开放通道概率、反应起始缓慢和失活缓慢的综合作用。相反，它们使PC12细胞烟碱受体对乙酰胆碱的亚最大反应敏感化。虽然PC12细胞中表达的烟碱型乙酰胆碱受体亚型的丰度排除了鉴定与非竞争性激动剂相互作用的特定烟碱型乙酰胆碱受体亚型的可能性，但观察到的乙酰胆碱和非竞争性激动剂的单通道电流幅度相同模式表明，所有对乙酰胆碱有反应的PC12细胞烟碱型乙酰胆碱受体亚型也对非竞争性激动剂有反应。因此，非竞争性激动剂的作用在烟碱型乙酰胆碱受体亚型之间似乎高度保守，这与该位点主要元件所在序列区域的高度结构保守性一致。
