Ultrastructural distribution of hyaluronan in rat cornea

The ultrastructural distribution of hyaluronan (hyaluronic acid) in rat cornea was investigated using tissue processed by osmium tetroxide/microwave fixation and epoxy resin embedding or by glutaraldehyde/microwave fixation and lowicryl K4M embedding. Hyaluronan-binding proteins (HABP) and link proteins (LP) coupled to 15-20 nm gold particles were used as novel ultrastructural markers in a one-step post-embedding procedure. These probes labelled the intra- and extracellular aspects of corneal epithelial and endothelial plasma membranes, as well as those of stromal keratocytes. In the corneal epithelium, wing and superficial cell plasma membranes were intensely stained, whereas basal cells exhibited a weak reaction on their stromal-facing surfaces and an intermediate one on their lateroapical aspects. In the corneal endothelium labelling was associated primarily with the apical and lateral plasma membranes. The labelling intensity associated with keratocyte plasma membranes was weak.