Allen M C, Gale P A, Hunter A C, Lloyd A, Hardy S P
School of Pharmacy and Biomolecular Sciences, University of Brighton, Lewes Road, BN2 4GJ, Brighton, UK.
Biochim Biophys Acta. 2000 Dec 20;1509(1-2):229-36. doi: 10.1016/s0005-2736(00)00297-2.
Native 5-HT(3) and AChR ligand-gated cation channels can be inhibited (blocked) by the non-steroidal antioestrogen tamoxifen. However, the exact site and mechanism of inhibition by tamoxifen on these channels remain unclear. We have investigated the action of the membrane impermeant quaternary derivative, ethylbromide tamoxifen (EBT), on native ligand-gated 5-HT(3) receptor channels and voltage-gated K(+) channels in NG108-15 cells using whole cell patch clamp. Extracellular EBT inhibited whole cell cationic currents of 5-HT(3) receptors with IC(50) of 0.22+/-0.4 microM (n(H)=1.05+/-0.2). The channel block was characterised by voltage independent and use independent behaviour (similar to that of tamoxifen). EBT was unable to inhibit voltage-gated K(+) currents in NG108-15 cells. This was in contrast to the inhibition by tamoxifen which, at similar concentrations, accelerated the apparent inactivation of these outward K(+) currents. The inhibition of 5-HT(3) receptors by a membrane impermeant derivative of tamoxifen supports the view that the binding site for antioestrogens is extracellular and the inhibition is not mediated through genomic/transcriptional activity.
天然的5-羟色胺3（5-HT(3)）和乙酰胆碱受体配体门控阳离子通道可被非甾体抗雌激素他莫昔芬抑制（阻断）。然而，他莫昔芬对这些通道的具体抑制位点和机制仍不清楚。我们使用全细胞膜片钳技术，研究了膜不透性季铵衍生物溴化乙他莫昔芬（EBT）对NG108-15细胞中天然配体门控5-HT(3)受体通道和电压门控钾（K(+)）通道的作用。细胞外EBT以0.22±0.4微摩尔的半数抑制浓度（IC(50)）抑制5-HT(3)受体的全细胞阳离子电流（n(H)=1.05±0.2）。通道阻断的特征是电压非依赖性和使用非依赖性行为（类似于他莫昔芬）。EBT不能抑制NG108-15细胞中的电压门控K(+)电流。这与他莫昔芬的抑制作用形成对比，在相似浓度下，他莫昔芬会加速这些外向K(+)电流的明显失活。他莫昔芬的膜不透性衍生物对5-HT(3)受体的抑制作用支持了抗雌激素的结合位点在细胞外且抑制作用不是通过基因组/转录活性介导的这一观点。
