Berry-Kravis E, Dawson G
J Neurochem. 1985 Dec;45(6):1731-8. doi: 10.1111/j.1471-4159.1985.tb10528.x.
A neuroblastoma X Chinese hamster embryonic brain explant hybrid cell line (NCB-20) expressed 5-hydroxytryptamine (5-HT1) receptors, linked to adenylate cyclase, which closely resembled 5-HT1 receptors previously characterized in central nervous tissue. However, the affinity of the receptors for 5-HT was only 150 nM compared to 5 nM in membranes prepared from cerebral cortex. The elevation of cyclic AMP levels in NCB-20 cells produced by 5-HT was found additive to that produced by cholera toxin but synergistic with that produced by either prostaglandin E1 (PGE1) or forskolin, suggesting that these latter two agents elevate cyclic AMP levels by a different mechanism than 5-HT. The elevation of cyclic AMP levels by either 5-HT or PGE1 was reversed by [D-Ala2,D-Leu5]enkephalin (DADLE), morphine, clonidine, and 3,4-dihydroxyphenylethylamine (dopamine) on a short (30 min) time scale. However, continued exposure to DADLE resulted in loss of the initial inhibitory effects of DADLE after 6 h and return of cyclic AMP levels to that seen with either 5-HT or PGE1 alone. When the DADLE exposure time was increased to 48 h, 5-HT produced a further twofold increase in cyclic AMP levels, but there was no increase in the responsiveness of the cells to PGE1 unless naloxone was added 1 h prior to treatment with PGE1. Scatchard analysis showed that the increased potency of 5-HT resulted from an increase in receptor affinity for 5-HT (from a KD of 150 +/- 20 nM to one of 20 +/- 7 nM), with a reduction in the number of apparent binding sites. The 5-HT supersensitivity observed in NCB-20 cells may be a good model for neurotransmitter interactions that produce desensitization or facilitation in the intact nervous system.
一种神经母细胞瘤与中国仓鼠胚胎脑外植体的杂交细胞系（NCB - 20）表达与腺苷酸环化酶偶联的5 - 羟色胺（5 - HT1）受体，该受体与先前在中枢神经组织中鉴定的5 - HT1受体极为相似。然而，该受体对5 - HT的亲和力为150 nM，而从大脑皮层制备的膜中该亲和力为5 nM。5 - HT引起的NCB - 20细胞中环磷酸腺苷（cAMP）水平升高被发现与霍乱毒素引起的升高具有相加性，但与前列腺素E1（PGE1）或福斯高林引起的升高具有协同性，这表明后两种试剂升高cAMP水平的机制与5 - HT不同。在短时间（30分钟）内，[D - Ala2，D - Leu5]脑啡肽（DADLE）、吗啡、可乐定和3,4 - 二羟基苯乙胺（多巴胺）可逆转5 - HT或PGE1引起的cAMP水平升高。然而，持续暴露于DADLE 6小时后，DADLE的初始抑制作用消失，cAMP水平恢复到单独使用5 - HT或PGE1时的水平。当DADLE暴露时间增加到48小时时，5 - HT使cAMP水平进一步增加两倍，但除非在PGE1处理前1小时加入纳洛酮，否则细胞对PGE1的反应性不会增加。Scatchard分析表明，5 - HT效力的增加是由于受体对5 - HT的亲和力增加（从KD为150±20 nM增加到20±7 nM），同时表观结合位点数量减少。在NCB - 20细胞中观察到的5 - HT超敏感性可能是完整神经系统中产生脱敏或易化作用的神经递质相互作用的良好模型。
