The structure of the lens epithelium and its basement membrane in the diabetic state.

The basement membrane of the crystalline lens of the diabetic rat was found to have a similar elasticity modulus at high stress to that of normal membrane. However, at low stress and extension Young's modulus of elasticity was 0.36 (Mean) +/- 0.15 (SD) X 10(6) Nm-2 and about 30 per cent lower than that of normal membrane. Diabetic membrane was significantly more extensible since it extended a further 7.5% as compared with normal membrane before it ruptured. These changes in the elastic properties of the membrane was accompanied by characteristic changes in the epithelial cells. The cells become round and swollen containing cytoplasm rich in rough and smooth endoplasmic reticulum. The changes suggest increased metabolic activity while the presence of intra-cellular membrane whorls indicate phagocytic activity. Plaques of epithelial cells were sometimes found at the anterior poles of diabetic lenses. Electron microscopic observations of ultrasonicated fragments of diabetic membrane showed that the filaments had no difference in periodicity (3.7 nm) from those found in normal membrane, but their spacing was significantly increased by 0.2 nm. The increased extensibility and decreased Young's modulus of elasticity at low stress, together with the increase spacing of the filaments, were shown to be consistent with the view that the helical macromolecules forming the filaments of diabetic basement membrane may be increased in length.