Histochemical studies of the colonic epithelial glycoproteins of the normal rabbit

Two general classes of glycoproteins have been identified in the colonic epithelial cells of New Zealand white rabbits. Each is associated with an ultrastructurally distinct secretory cell. The first of these classes is found in cells, termed vesiculated columnar cells, characterized by electron-translucent vesicles, a small rough endoplasmic reticulum-Golgi complex and prominent microvilli. The glycoproteins of the vesiculated cells contain abundant O-sulphate ester, sialic acids with ester substituents at positions C-8 or C-9 (or with two or three side chain substituents) and neutral sugars with vicinal diols whose periodate oxidation is prevented by an O-acyl ester substituent(s). The second class of glycoproteins occurs in goblet cells characterized by electron-dense vesicles, an abundant rough endoplasmic reticulum, a well-developed Golgi apparatus and few, if any, microvilli. Goblet cells along the entire length of the crypts contain neutral sugars with periodate-oxidisable vicinal diols and a ferriferricyanide-reactive component. Cells in the upper halves of the crypts also contain components that are sulphated, Schiff-reactive and acid-fast. In the lower halves of the crypts, the goblet cells contain smaller quantities of the above components plus sialic acids, some of which possibly have an O-acyl substituent located at position C-8 or C-9 (or which have two or three side chain O-acyl substituents). It is suggested that the function of the glycoproteins from the vesiculated columnar cells is protective and that from the goblet cells is lubricative.