Klein R L, Sanna E, McQuilkin S J, Whiting P J, Harris R A
Department of Pharmacology, University of Colorado Health Sciences Center, Denver 80262.
Eur J Pharmacol. 1994 Jul 15;268(2):237-46. doi: 10.1016/0922-4106(94)90194-5.
Both 5-HT3 receptor antagonists and benzodiazepine receptor ligands have effects on anxiety, and alter the behavioral action of ethanol. For these reasons, we tested the ability of several 5-HT3 receptor antagonists to inhibit the ligand binding and function of the gamma-aminobutyric acidA/benzodiazepine receptor Cl- channel complex of mouse brain membranes. MDL 72222 (1-a-H-3-a-5-aH-optropan-3yl-3,5-dichlorobenzoate) and LY 278584 (1-methyl-N-(8-methyl-8-azabicyclo[3.2.1.]oct-3-yl)-1H-indazole-3- carboxamide) inhibited [3H]flunitrazepam binding with Ki values of approximately 20 microM; ICS 205-930 (3 alpha-tropanyl-1H-indole-3-carboxylic acid ester) was more potent with a Ki of 0.8 microM. ICS 205-930 (50 microM) had no effect on [3H]muscimol binding. ICS 205-930, MDL 72222, and LY 278584 all inhibited the binding of [35S]TBPS (tert-butylbicyclophosphorothionate) with Ki values of approximately 10 microM and reduced muscimol-dependent 36Cl- flux into mouse cortical microsacs by 30-45% at a concentration of 10 microM. ICS 205-930, MDL 72222, and LY 278584 (at micromolar concentrations) reduced GABA-gated chloride currents studied in Xenopus oocytes expressing human alpha 1 beta 1 gamma 2S GABAA receptor subunits. ICS 205-930 differed from the other two 5-HT3 receptor antagonists in that it induced a biphasic effect on GABA-gated currents: at concentrations from 0.1 to 5 microM it potentiated GABA responses, whereas at higher concentrations (50-100 microM) it produced inhibition. The stimulatory action induced by ICS 205-930 was due to interaction at the benzodiazepine recognition site because expression of the gamma 2 subunit was required and Ro 15-1788 (1 microM) completely prevented the potentiation caused by ICS 205-930. Thus, several 5-HT3 receptor antagonists inhibit benzodiazepine binding and affect GABAA receptor function. These actions are most pronounced for ICS 205-930 and likely involve direct affects on the GABA/benzodiazepine complex rather than interactions with 5-HT3 receptors.
5-羟色胺3（5-HT3）受体拮抗剂和苯二氮䓬受体配体均对焦虑有影响，并能改变乙醇的行为作用。基于这些原因，我们测试了几种5-HT3受体拮抗剂抑制小鼠脑膜γ-氨基丁酸A/苯二氮䓬受体氯离子通道复合物的配体结合及功能的能力。MDL 72222（1-α-H-3-α-5-αH-奥普托烷-3-基-3,5-二氯苯甲酸酯）和LY 278584（1-甲基-N-（8-甲基-8-氮杂双环[3.2.1]辛-3-基）-1H-吲唑-3-甲酰胺）抑制[3H]氟硝西泮结合，其抑制常数（Ki）值约为20微摩尔；ICS 205-930（3-α-托烷-1H-吲哚-3-羧酸酯）的效力更强，Ki为0.8微摩尔。ICS 205-930（50微摩尔）对[3H]蝇蕈醇结合无影响。ICS 205-930、MDL 72222和LY 278584均抑制[35S]叔丁基双环磷硫代酸盐（TBPS）的结合，Ki值约为10微摩尔，并在10微摩尔浓度时使蝇蕈醇依赖的36Cl-流入小鼠皮质微囊减少30%-45%。ICS 205-930、MDL 72222和LY 278584（微摩尔浓度）可降低在表达人α1β1γ2S GABAA受体亚基的非洲爪蟾卵母细胞中研究的GABA门控氯离子电流。ICS 205-930与其他两种5-HT3受体拮抗剂不同，它对GABA门控电流产生双相效应：在0.1至5微摩尔浓度时增强GABA反应，而在较高浓度（50-100微摩尔）时产生抑制作用。ICS 205-930诱导的刺激作用是由于在苯二氮䓬识别位点的相互作用，因为需要γ2亚基的表达，且Ro 15-1788（1微摩尔）可完全阻止ICS 205-930引起的增强作用。因此，几种5-HT3受体拮抗剂抑制苯二氮䓬结合并影响GABAA受体功能。这些作用在ICS 205-930中最为明显，可能涉及对GABA/苯二氮䓬复合物的直接影响，而非与5-HT3受体的相互作用。
