Sahebgharani M, Hardy S P, Lloyd A W, Hunter A C, Allen M C
Department of Pharmacy and Biomolecular Sciences, University of Brighton, Brighton, UK.
Cell Physiol Biochem. 2001;11(2):99-104. doi: 10.1159/000047797.
BACKGROUND/AIMS: Tamoxifen has been shown to inhibit volume activated chloride currents in many cell types. Tamoxifen has also been reported to inhibit a number of cation channels as well as cytosolic proteins such as calmodulin. The mechanism of channel block by tamoxifen is not known but three hypotheses can be proposed: i) a direct effect following binding to the channel protein from the aqueous environment or ii) a direct effect on the channel protein after partitioning into the lipid membrane or iii) an indirect mechanism via binding to intracellular regulatory proteins after diffusion across the lipid membrane. The aim of these experiments was to distinguish between these hypotheses using membrane permeant and impermeant antioestrogens.
Volume activated chloride currents were recorded from single HeLa cells using whole cell patch clamp technique. The ability of tamoxifen and its membrane impermeant quaternary derivative ethyl bromide tamoxifen (EBT) to inhibit these currents was examined.
Extracellular tamoxifen at 3 microM inhibited volume activated chloride currents in HeLa cells whereas EBT had no effect up to 10 microM when applied either to the extracellular bathing solution or the intracellular solution via the patch pipette.
Eliminating the ability of tamoxifen to cross the plasma membrane abolishes its channel blocking activity against volume activated chloride channels in HeLa cells.
背景/目的：已证实他莫昔芬可抑制多种细胞类型中的容积激活氯电流。也有报道称他莫昔芬可抑制多种阳离子通道以及诸如钙调蛋白等胞质蛋白。他莫昔芬阻断通道的机制尚不清楚，但可提出三种假说：i）从水性环境与通道蛋白结合后的直接效应；ii）在分配到脂质膜后对通道蛋白的直接效应；iii）在穿过脂质膜扩散后通过与细胞内调节蛋白结合的间接机制。这些实验的目的是使用膜通透性和非通透性抗雌激素来区分这些假说。
使用全细胞膜片钳技术从单个HeLa细胞记录容积激活氯电流。研究了他莫昔芬及其膜不通透的季铵衍生物乙基溴化他莫昔芬（EBT）抑制这些电流的能力。
3 microM的细胞外他莫昔芬可抑制HeLa细胞中的容积激活氯电流，而当通过膜片吸管应用于细胞外浴液或细胞内溶液时，高达10 microM的EBT没有作用。
消除他莫昔芬穿过质膜的能力可消除其对HeLa细胞中容积激活氯通道的通道阻断活性。
