Secretion and resorption of sulphated glycoproteins by the epithelial lining of the endolymphatic space of the rat were studied autoradiographically with the use of35SO4as a selective marker. This isotope was found to be incorporated into the sensory area of cristae and maculae and a small area of epithelial cells adjacent to the sensory epithelium. Thereafter35S-labelled glycoproteins were secreted into cupulae and otolithic membranes. No such process could be established in the tectorial membrane. From the gradual disappearance of35S-labelled glycoproteins from cupulae and otolithic membrane coupled with an accumulation of this substance in the lumen of the endolymphatic sac, the existence of a longitudinal flow under physiological conditions could be concluded. Resorption of glycoproteins by the saccus epithelium was found to be very slow. Accumulation of35S-labelled glycoproteins in the endolymphatic duct after saccus obstruction indicates that, in addition to the endolymphatic sac, also the duct contributes to the mechanism underlying the longitudinal flow of macromolecules. © 1987.
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