Observations on the collagen and proteinpolysaccharide complex of rabbit corneal stroma

Abstract

The form and interrelationship of the collagen fibrils and proteinpolysaccharide complex of rabbit corneal stroma were studied by electron microscopy. The intact tissue was examined as Araldite sections stained with alkaline lead citrate and uranyl acetate, and the mechanically disintegrated cornea after positive or negative staining with phosphotungstic acid or after treatment with 0.5% bismuth nitrate in 0.1 M nitric acid. The corneal collagen fibrils vary in cross-sectional area from 4.6 to 9.6 x 10⁴ sq. Å and do not exhibit a regular hexagonal distribution. Like tendon fibrils they consist of longitudinal filaments, but their appearance suggests that they lack some of the interfilament cross-links present in tendon. In sections of intact cornea and in negatively stained disintegrated cornea, filaments which are considered to be the protein cores of proteinpolysaccharide macromolecules are evident. They are about 40 Å wide and 2000 Å long. They appear to run an angular course, orthogonal to the collagen fibrils, and to be tangentially attached to several fibrils in the region of the a band. After treatment with bismuth nitrate disintegrated cornea contains coarsely beaded filaments. The filaments are about 2000 Å long and the beads about 70 Å in diameter. It is considered that these are again proteinpolysaccharide macromolecules and that each bead represents one or more polysaccharide chains in coiled configuration.