Vrensen G, Van Marle J, Van Veen H, Willekens B
Department of Morphology, The Netherlands Ophthalmic Research Institute, Amsterdam.
Exp Eye Res. 1992 Mar;54(3):433-46. doi: 10.1016/0014-4835(92)90055-w.
The ultrastructure of fibre membranes in human lenses, varying in age from premature to 40 years, was investigated using a strict protocol regarding their localization within the lens. The ultrastructural approaches used were scanning electron microscopy (SEM), and transmission electron microscopy (TEM) of ultrathin sections and freeze-fracture replicas. Irrespective of the age of the lens, superficial fibre membranes are characterized by a high density of intramembrane particles (IMPs) and numerous gap junctions (GJs). In contrast deep cortical fibres, at the SEM-level characterized by grooves and ridges, are largely free of IMPs but still contain numerous GJs. In between these regions a transitional zone was observed. At the SEM-level the transitional fibres are characterized by wrinkled membranes and formation of grooves and ridges. In freeze-fracture replicas the presence of numerous square arrays (SAs) associated with GJs is most remarkable. It is concluded that at all ages studied, the maturation and compaction of lens fibres results in a transformation of membrane architecture leading to clear-cut ultrastructural differences between superficial and deep cortical membranes. It is argued that this ultrastructural heterogeneity parallels the gradients observed biochemically for intrinsic membrane proteins and cholesterol:phospholipid ratios. The observations confirm the electrophysiological view that superficial membranes have an 'average' permeability and that deep cortical membranes are 'degenerate' or 'non-leaky'.
利用一套关于纤维膜在晶状体中定位的严格方案，研究了年龄从早产儿到40岁不等的人类晶状体中纤维膜的超微结构。所采用的超微结构方法包括扫描电子显微镜（SEM）、超薄切片的透射电子显微镜（TEM）以及冷冻蚀刻复型。无论晶状体的年龄如何，表层纤维膜的特征都是膜内颗粒（IMP）密度高且有大量缝隙连接（GJ）。相比之下，深层皮质纤维在SEM水平上以沟槽和脊为特征，基本上没有IMP，但仍含有大量GJ。在这些区域之间观察到一个过渡带。在SEM水平上，过渡纤维的特征是膜起皱以及形成沟槽和脊。在冷冻蚀刻复型中，与GJ相关的大量方形阵列（SA）的存在最为显著。得出的结论是，在所研究的所有年龄段，晶状体纤维的成熟和压实导致膜结构的转变，从而在表层和深层皮质膜之间产生明显的超微结构差异。有人认为这种超微结构的异质性与内在膜蛋白和胆固醇：磷脂比率的生化梯度相似。这些观察结果证实了电生理学观点，即表层膜具有“平均”通透性，而深层皮质膜是“退化的”或“无渗漏的”。
