Localization of anionic sulfate groups in the tectorial membrane

Colloidal iron hydroxide (CIH) staining demonstrates the existence of anionic sulfate groups of glycoconjugates associated with several constituents of the tectorial membrane (TM). In the adult animal, labelling in the main body of the TM appears as long, electron-dense patches surrounding type A fibrils which show alternating stained and unstained zones. On the other hand, labelling of the fibrils of the matrix of the TM appears as single, CIH particles with no special arrangement. Some of the structurally distinct regions of the TM are also labelled (limbal zone, Hensen's stripe and inner portions of the cover net), while others are not (marginal band and outer portions of the cover net). Staining of type A fibrils in the major TM is already present in newborn animals; while, both the outermost region of the TM closest to the cells of the organ of Kölliker and the minor TM are not labelled. The implications of these distributions of sulfated glycoconjugates for the electrochemical properties of the TM are discussed.