title: Thickness and volume constants and ultrastructural organization of basement membrane (lens capsule).
abstract: 1. The basement membrane of the crystalline lens of the rat has been found to have the following elastic constants: a Young's Modulus of elasticity of 0.56 +/- 0.38 x 10(6) Nm-2 at low stress and 11.3 +/- 1.9 x 10(6) Nm-2 at rupture, an ultimate stress of 28.8 +/- 4.5 x 10(5) Nm-2, and a maximum percentage elongation of 41.3 +/- 5.8. 2. The ratio of initial thickness of the membrane to the thickness at the point of rupture is 0.271 +/- 0.02 while the similar ratio for volume is 0.461 +/- 0.031. 3. Electron microscopic observations of ultrasonicated fragments of the entire membrane show long filaments in parallel arrays and sheets. The filaments show a periodicity of 3.7 nm and a spacing of 3.5 nm. 4. Electron microscopic observations of collagenase-treated membrane show a poorly staining matrix associated with separate short straight non-periodic filaments some 2.5 nm in diameter. In addition strands project from the ends of the filaments with a diameter of between 0.5 and 1.0 nm. 5. A model is proposed which consists of these filaments, composed of between three and five parallel strands, some 0.8 nm in diameter, wound in a superhelix. 6. The model predicts satisfactorily thickness and volume changes in the membrane when subjected to stress, and also indicates that the filaments would have a similar Young's Modulus of elasticity and ultimate stress to those of collagen. 7. If the basement membrane of the smallest retinal capillaries is subjected to a change of pressure of only 5 mmHg within the vessel lumen, then the membrane is likely to undergo some 30% reduction in thickness.
mesh_terms: D000818:Animals; D001485:Basement Membrane / Q000502:physiology / Q000648:ultrastructure; D003094:Collagen / Q000502:physiology; D004548:Elasticity; D066298:In Vitro Techniques; D007908:Lens, Crystalline / Q000502:physiology* / Q000648:ultrastructure; D046911:Macromolecular Substances; D008854:Microscopy, Electron; D008954:Models, Biological; D051381:Rats; D013314:Stress, Mechanical
chemical_list: D046911:Macromolecular Substances; D003094:Collagen