The cholesterol (Chol) content in the fiber cell plasma membranes of the eye lens is extremely high, exceeding the solubility threshold in the lenses of old humans. This high Chol content forms pure Chol bilayer domains (CBDs) and Chol crystals in model membranes and membranes formed from the total lipid extracts from human lenses. CBDs have been detected using electron paramagnetic resonance (EPR) spin-labeling approaches. Here, we confirm the presence of CBDs in giant unilamellar vesicles prepared using the electroformation method from Chol/1-palmitoyl-2-oleoylphosphocholine and Chol/distearoylphosphatidylcholine mixtures. Confocal microscopy experiments using phospholipid (PL) analog (1,1′-dioctadecyl-3,3,3′,3′-tetramethylindocarbocyanine-5,5′-disulfonic acid) and cholesterol analog fluorescent probes (23-(dipyrrometheneboron difluoride)-24-norcholesterol) were performed, allowing us to make three major conclusions: (1) In all membranes with a Chol/PL mixing ratio (expressed as a molar ratio) >2, pure CBDs were formed within the bulk PL bilayer saturated with Chol. (2) CBDs were present as the pure Chol bilayer and not as separate patches of Chol monolayers in each leaflet of the PL bilayer. (3) CBDs, presented as single large domains, were always located at the top of giant unilamellar vesicles, independent of the change in sample orientation (right-side-up/upside-down). Results obtained with confocal microscopy and fluorescent Chol and PL analogs, combined with those obtained using EPR and spin-labeled Chol and PL analogs, contribute to the understanding of the organization of lipids in the fiber cell plasma membranes of the human eye lens.

中文翻译：

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共聚焦显微镜证实，在磷脂酰胆碱中，胆固醇含量非常高的巨型单层囊泡会形成纯胆固醇双层结构域。

眼晶状体的纤维细胞质膜中的胆固醇（Chol）含量极高，超过了老年人晶状体中的溶解度阈值。这种高的Chol含量会在模型膜和由人晶状体的总脂质提取物形成的膜中形成纯Chol双层结构域（CBD）和Chol晶体。已使用电子顺磁共振（EPR）自旋标记方法检测到CBD。在这里，我们确认使用电形成方法由Chol / 1-棕榈酰基-2-油酰基磷酸胆碱和Chol /二硬脂酰基磷脂酰胆碱混合物制备的巨大单层囊泡中存在CBD。使用磷脂（PL）类似物（1,1'-dioctadecyl-3,3,3'，3'-tetramethylindocarbocyanine-5，进行了5'-二磺酸）和胆固醇类似物荧光探针（23-（二氟亚甲基二硼化硼）-24-降胆固醇）的荧光探针，这使我们得出三个主要结论：（1）在所有具有Chol / PL混合比的膜中（表示为摩尔比> 2），在用Chol饱和的本体PL双层中形成纯CBD。（2）CBD以纯Chol双层的形式存在，而不是以PL双层的每个小叶中单独的Chol单层的形式存在。（3）CBD呈现为单个大区域，始终位于巨大的单层囊泡顶部，而与样品方向的变化无关（右侧-上/下-倒置）。通过共聚焦显微镜和荧光Chol和PL类似物获得的结果，再结合使用EPR和自旋标记的Chol和PL类似物获得的结果，