Ultrastructural localization of megalin in the rat cochlear duct

Megalin is an endocytic receptor predominantly expressed in the kidney prox imal tubule cells. In the present study, localization of megalin was examin ed using a post-embedding immunogold method in the rat cochlear duct. Margi nal cells of the stria vascularis were labeled on the apical surface, but n ot on the basolateral surface. This localization pattern resembles kidney p roximal tubule cells. Immunoreactivity was also detected on various other c ells, including epithelial cells of the spiral prominence and epithelial ce lls of Reissner's membrane. In contrast, virtually no gold particles were s een on intermediate cells and basal cells of the stria vascularis, mesothel ial cells of Reissner's membrane or fibrocytes in the lateral wall. Also un labeled were cells in the tympanic wall of the cochlear duct, including sen sory cells and supporting cells of the organ of Corti. The present findings show the involvement of megalin in endocytosis of marginal cells and are s uggestive of different uptake mechanisms for aminoglycosides in the kidney proximal tubule cells and in the cochlear sensory cells. (C) 1999 Elsevier Science B.V. All rights reserved.