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 acetate, 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, embedded in Epon, sectioned (60 nm), and examined with an electron microscope at 60 kV. Proteoglycan-Cuprolinic Blue complexes mainly appeared as networks of small electron-dense filaments throughout the posterior and anterior capsules. The posterior capsule was a single layer with a network of small proteoglycan filaments gradually decreasing in size from the humoral side (90 x 10 nm) to the lenticular side (30 x 8 nm). The humoral side of the anterior capsule had a thin lamina (400 nm) containing large (180 x 40 nm), very electron-dense proteoglycan-Cuprolinic Blue complexes plus small proteoglycans. Below this lamina, the complexes were only seen as filaments slightly smaller than those in the corresponding area of the posterior capsule. Cuprolinic Blue binding of the anterior and posterior lens capsules revealed differences in the size and distribution of their sulphated proteoglycans which do not correspond to the patterns of their immunoreactivity with anti-heparan sulphate proteoglycan. The humoral lamina in the anterior capsules, with large proteoglycan structures, might be a distinct structural and functional compartment.