Borchman D, Byrdwell W C, Yappert M C
Department of Chemistry, Kentucky Lions Eye Research Institute, University of Louisville 40292.
Invest Ophthalmol Vis Sci. 1994 Oct;35(11):3938-42.
The long-term purpose of this research was to establish the relationships between composition, structure, and function that affect human lens membranes. The authors hypothesized that the functional differences of epithelial, cortical, and nuclear lens membranes are related to compositional differences. Furthermore, age-dependent alterations in membrane function and structure can also be related to variations in the phospholipid composition. To explore these possibilities, the authors determined the phospholipid composition of epithelial, cortical, and nuclear membranes from pools of human lenses of different ages.
Membranes were extracted from pools of clear human lenses of different ages using a monophasic methanolic extraction that minimizes the interfacial fluff produced with biphasic extractions. The phospholipid composition was determined by 31P NMR:
Only minor differences were detected between cortical and nuclear fractions. All phospholipids, except sphingomyelin, phosphatidylethanolamine, and the phospholipid with a shift of 0.12 parts per million (ppm) in the 31P NMR spectrum, showed significant differences in the epithelial fractions of all age groups compared to the fiber fractions; the percentage of phosphatidylcholine was considerably higher than that in the cortical and nuclear membranes of the same age. Conversely, the percentage of phosphatidylglycerol and lysophosphatidylglycerol was significantly smaller in the epithelial membranes than in the fiber membranes. The age-related changes in the composition of cortical and nuclear membranes were identical. These membranes showed a steady increase with age in the percentage of sphingomyelin and of an unidentified component with a shift of 1.2 ppm. The percentage of phosphatidylcholine decreased with age in both epithelial and fiber membranes. The rate of decrease was greater in the epithelial membranes than in the fiber membranes. Epithelial membranes contained approximately five times more phosphatidylcholine than fiber membranes of corresponding age.
Regardless of age, the composition of epithelial cell membranes was different than that of cortical and nuclear membranes, which showed similar phospholipid content. This suggests that significant compositional changes occur when epithelial cells become elongated to form fiber cells.
本研究的长期目的是确定影响人晶状体膜的组成、结构和功能之间的关系。作者假设上皮、皮质和核晶状体膜的功能差异与组成差异有关。此外，膜功能和结构的年龄依赖性变化也可能与磷脂组成的变化有关。为了探索这些可能性，作者测定了不同年龄人晶状体池的上皮、皮质和核膜的磷脂组成。
使用单相甲醇提取法从不同年龄的透明人晶状体池中提取膜，该方法可最大限度减少双相提取产生的界面绒毛。通过31P核磁共振测定磷脂组成。
皮质和核部分之间仅检测到微小差异。除鞘磷脂、磷脂酰乙醇胺和在31P核磁共振谱中化学位移为百万分之0.12（ppm）的磷脂外，所有年龄组的上皮部分与纤维部分相比，所有磷脂均显示出显著差异；磷脂酰胆碱的百分比明显高于同年龄的皮质和核膜。相反，上皮膜中磷脂酰甘油和溶血磷脂酰甘油的百分比明显低于纤维膜。皮质和核膜组成的年龄相关变化是相同的。这些膜中鞘磷脂和化学位移为1.2 ppm的未鉴定成分的百分比随年龄稳步增加。上皮膜和纤维膜中磷脂酰胆碱的百分比均随年龄下降。上皮膜中的下降速率大于纤维膜。上皮膜中的磷脂酰胆碱含量约为相应年龄纤维膜的五倍。
无论年龄如何，上皮细胞膜的组成与皮质和核膜不同，后两者显示出相似的磷脂含量。这表明上皮细胞伸长形成纤维细胞时会发生显著的组成变化。
