Effects of submicellar bile salt concentrations on biological membrane permeability to low molecular weight non-ionic solutes
Effects of submicellar bile salt concentrations on biological membrane permeability to low molecular weight non-ionic solutes
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DOI：
10.1021/bi960497i
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发表时间：
1996-06-18
期刊：
影响因子：
2.9
通讯作者：
Donovan, JM
中科院分区：
文献类型：
--
作者：
Albalak, A;Zeidel, ML;Donovan, JM
假设胆盐通过增加膜对水溶性溶质的渗透性介导细胞毒性。我们研究了亚胶束胆盐浓度是否影响模型和天然膜对不带电小分子（如水、尿素和氨）的渗透性。通过监测包埋的羧基荧光素（CF）的自猝灭，测定了由蛋黄磷脂酰胆碱（EYPC）+/-胆固醇（Ch）或大鼠肝微粒体膜组成的大单层囊泡的渗透水渗透性（P-f）和尿素渗透性。利用CF荧光的pH依赖性测定氨渗透性。亚胶束胆盐浓度没有显着改变P-f的EYPC +/- Ch或大鼠肝微粒体膜。在牛磺脱氧胆酸盐（TDC）或牛磺熊脱氧胆酸盐浓度接近那些溶解膜脂质，CF泄漏发生从囊泡，但P-F保持不变。较高的胆盐浓度（0.5-2 mM TDC）不改变等摩尔EYPC/Ch膜的P-f。尽管在一个或两个膜半叶中存在胆汁盐，但跨膜水通量的活化能不变（EYPC为12.1 +/- 1.2 kcal/mol），这强烈表明胆汁盐不会形成促进水通量的跨膜孔。此外，亚胶束胆盐浓度并没有增加膜的渗透性尿素或氨。我们的结论是，在亚胶束浓度，胆汁盐不形成非选择性对流通道，促进跨膜运输的小不带电分子。这些结果表明，胆盐介导的特定底物的运输，而不是非选择性的膜通透性增强，是胆盐对肠细胞和肝细胞的细胞毒性的基础。
Bile salts have been hypothesized to mediate cytotoxicity by increasing membrane permeability to aqueous solutes. We examined whether submicellar bile salt concentrations affect model and native membrane permeability to small uncharged molecules such as water, urea, and ammonia. Osmotic water permeability (P-f) and urea permeability were measured in large unilamellar vesicles composed with egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) or rat liver microsomal membranes by monitoring self-quenching of entrapped carboxyfluorescein (CF). Ammonia permeability was determined utilizing the pH dependence of CF fluorescence. Submicellar bile salt concentrations did not significantly alter P-f of EYPC +/- Ch or rat liver microsomal membranes. At taurodeoxycholate (TDC) or tauroursodeoxycholate concentrations approaching those that solubilized membrane lipids, CF leakage occurred from vesicles, but P-f remained unchanged. Higher bile salt concentrations (0.5-2 mM TDC) did not alter P-f of equimolar EYPC/Ch membranes. The activation energy for transmembrane water flux was unchanged (12.1 +/- 1.2 kcal/mol for EYPC) despite the presence of bile salts in one or both membrane hemileaflets, suggesting strongly that bile salts do not form transmembrane pores that facilitate water flux. Furthermore, submicellar bile salt concentrations did not increase membrane permeability to urea or ammonia. We conclude that at submicellar concentrations, bile salts do not form nonselective convective channels that facilitate transmembrane transport of small uncharged molecules. These results suggest that bile salt-mediated transport of specific substrates, rather than nonselective enhancement of membrane permeability, underlies bile salt cytotoxicity for enterocytes and hepatocytes.