Developmental aspects of glycoprotein secretion and migration in the endolymphatic space

Secretion and migration of sulphated glycoproteins during the early postnatal development of the rat inner ear was studied autoradiographically with the use of 35SO4. This isotope was found to be selectively incorporated into the embryonal sulcus cells and subsequently expelled into the tectorial membrane. This process decreased simultaneously with the replacement of the tall sulcus cells by cuboidal cells and the detachment of the tectorial membrane from these cells. A two stage development of the tectorial membrane is postulated: formation of filaments followed by incorporation of glycoproteins. Incorporation of isotope was also observed in the sensory epithelium of the vestibular part of the labyrinth, followed by migration into the cupulae and otolithic membranes. The accumulation of labelled material in the lumen of the endolymphatic sac 6 hours after isotope administration, suggests the existence of endolymph flow towards the endolymphatic sac in the early postnatal period.