Differences in the microfibrillar arrangement of collagen fibrils. Distribution and possible significance.

The microfibrillar arrangement of collagen fibrils has been studied on replicas of freeze-fractured specimens and on thin sections of specimens treated with a 4.0 M guanidinium chloride solution. Collagen fibrils with straight arrangement of their microfibrils usually have a variable diameter and correspond in their distribution to genetical type I and type II collagens. Collagen fibrils with helicoidal arrangement of their microfibrils present a relatively small and uniform diameter and show a tissue distribution similar to that of the genetical type III collagen. The corneal stroma, although predominantly composed of type I collagen, displays collagen fibrils with a helicoidal microfibrillar arrangement, and small uniform diameter. This exception can be explained in consideration of the function of the collagen of the corneal stroma. A close correlation between all the different microfibrillar patterns of the collagen fibrils and their function in the anatomical sites we examined is evident.