Vitreous structure. V. The morphology and thermal stability of vitreous collagen fibers and comparison to articular cartilage (type II) collagen.

Vitreous samples from bovine, ovine, human, canine, and lapine unfrozen eyes were found to contain fine fibrils which displayed no clearly discernible banding pattern when negatively stained with either phosphotungstic acid (pH 8.9) or silicotungstic acid (pH 7.0). The fibrils from the different species were found to be of similar width (10.5 to 12.5 nm) with the exception of the lapine samples which contained narrower fibrils (7 nm). In vitreous samples positively stained with uranyl acetate, cross-striations were observed to occur along the length of the vitreous fibrils of all species studied. These cross-striations represent a repeating band pattern with the major period having an axial repeat distance of 62 nm and containing alternating light and dark bands with 10.5 nm spacings between like bands. This banding was found to closely resemble that of collagen fibrils isolated from articular cartilage. Uranyl acetate-stained segment long-spacing monomers prepared from pepsin-solubilized bovine vitreous and. articular cartilage collagens were also found to be very similar in length and banding pattern. The shrinkage temperatures obtained with bundles of vitreous fibrils were comparable for all species studied (59° to 60°), with the exception of the lapine samples which were lower (56° to 57°). Markedly different behavior was observed with thin full-depth slices of articular cartilage. However, the melting temperatures of bovine, ovine, and lapine vitreous and bovine articular cartilage solubilized collagens were found, to be the same. These studies further illustrate the similarity in properties of the helical regions of the type II collagens of these two tissues.