An analysis by rotary shadowing of the structure of the mammalian vitreous humor and zonular apparatus.

An electron microscopic analysis of human and bovine vitreous humor after rotary shadowing showed the presence of both collagen fibrils and an extensive loose network of hyaluronan molecules. No interaction between the collagen fibrils and the hyaluronan molecules was observed under the conditions used for rotary shadowing. Periodic "struts" were present on the surface of the collagen fibrils. These struts showed an organization the same as that previously observed for type IX collagen on the surface of collagen fibrils from chicken cartilage and vitreous. However, the knob of the noncollagenous NC4 domain of cartilage type IX collagen was not observed at the ends of the struts in a manner identical to that of chicken vitreous humor. Zonular fibrils were dissected out from bovine eyes and shown by rotary shadowing to contain a beaded fibril which is similar in morphology to the "elastin-associated" microfibrils of many connective tissues. Experiments in which the zonular fibrils were stretched and fixed prior to rotary shadowing showed that the distance between each bead is variable and can be accounted for by the bowing out of overlapping filaments which connect each bead.