Carbohydrate content of the endolymphatic sac. A histochemical and lectin-labelling study in the Mongolian gerbil

A secretory activity has recently been attributed to the endolymphatic sac (ES), as a possible way to contribute to the fluid balance of the entire endolymphatic compartment. Previous histochemical studies have indicated the existence of carbohydrate complexes in the secretory product, both neutral and acidic in nature. A thorough analysis of these compounds in the gerbilline ES was carried out using both transmission electron microscopic (TEM) histochemistry, using dialyzed iron and periodic acid--chromic--silver staining techniques, as well as immunoflourescence with fluorescein-labelled lectins (FITC-lectins). N-acetylglucosamine was found to be one of the major carbohydrate components both of the epithelial layer of the ES and of the luminal precipitate. Proofs for a local secretory activity and its intracellular pathway are presented, suggesting to be involved in the regulation of pressure and volume of inner ear fluids.