Uneven distribution and size of rabbit lens capsule proteoglycans

To document the ultrastructural distribution of lens capsule proteoglycans, rabbit lens capsules were fixed and stained overnight in 50 mM sodium acet ate, pH 5.6, containing 2.5% glutaraldehyde, 0.2% Cuprolinic Blue and 0.2 M MgCl2. They were rinsed, stained with 1% aqueous sodium tungstate, embedde d in Epon, sectioned (60 nm), and examined with an electron microscope at 6 0 kV. Proteoglycan-Cuprolinic Blue complexes mainly appeared as networks of small electron-dense filaments throughout the posterior and anterior capsules. T he posterior capsule was a single layer with a network of small proteoglyca n filaments gradually decreasing in size from the humoral side (90x10 nm) t o the lenticular side (30x8 nm). The humoral side of the anterior capsule h ad a thin lamina (400 nm) containing large (180x40 nm), very electron-dense proteoglycan-Cuprolinic Blue complexes plus small proteoglycans. Below thi s lamina, the complexes were only seen as filaments slightly smaller than t hose in the corresponding area of the posterior capsule. Cuprolinic Blue binding of the anterior and posterior lens capsules reveale d differences in the size and distribution of their sulphated proteoglycans which do not correspond to the patterns of their immunoreactivity with ant i-heparan sulphate proteoglycan. The humoral lamina in the anterior capsule s, with large proteoglycan structures, might be a distinct structural and f unctional compartment.