THICKNESS AND VOLUME CONSTANTS AND ULTRASTRUCTURAL ORGANIZATION OF BASEMENT-MEMBRANE (LENS CAPSULE)

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. © 1979 The Physiological Society