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Ultrastructural localization of megalin in the rat cochlear duct
K Mizuta1, A Saito, T Watanabe
1Department of Otolaryngology, Hamamatsu University School of Medicine, Japan. mizuta@hama-med.ac.jp
Abstract:
Megalin is an endocytic receptor predominantly expressed in the kidney proximal tubule cells. In the present study, localization of megalin was examined using a post-embedding immunogold method in the rat cochlear duct. Marginal cells of the stria vascularis were labeled on the apical surface, but not on the basolateral surface. This localization pattern resembles kidney proximal tubule cells. Immunoreactivity was also detected on various other cells, including epithelial cells of the spiral prominence and epithelial cells of Reissner's membrane. In contrast, virtually no gold particles were seen on intermediate cells and basal cells of the stria vascularis, mesothelial cells of Reissner's membrane or fibrocytes in the lateral wall. Also unlabeled were cells in the tympanic wall of the cochlear duct, including sensory cells and supporting cells of the organ of Corti. The present findings show the involvement of megalin in endocytosis of marginal cells and are suggestive of different uptake mechanisms for aminoglycosides in the kidney proximal tubule cells and in the cochlear sensory cells.
Insights
Megalin, an endocytic receptor, is found on the apical surface of rat cochlear marginal cells, similar to kidney cells. This suggests distinct aminoglycoside uptake mechanisms in the cochlea versus the kidney.
Area of Science:
- Oto-nephrology
- Cell Biology
- Molecular Biology
Background:
- Megalin is a key endocytic receptor primarily found in kidney proximal tubule cells.
- Its role and localization in the cochlea, particularly in relation to drug uptake, remain less understood.
Purpose of the Study:
- To investigate the precise localization of the megalin receptor within the rat cochlear duct.
- To compare megalin's distribution in the cochlea with its known pattern in kidney proximal tubule cells.
Main Methods:
- Utilized a post-embedding immunogold method for high-resolution localization studies.
- Examined tissue sections of the rat cochlear duct for megalin immunoreactivity.
Main Results:
- Megalin was primarily localized to the apical surface of marginal cells in the stria vascularis.
- Immunoreactivity was also observed in epithelial cells of the spiral prominence and Reissner's membrane.
- Notably, sensory cells and supporting cells of the organ of Corti, as well as other cochlear cell types, showed no significant megalin labeling.
Conclusions:
- Megalin is involved in the endocytic processes of cochlear marginal cells.
- The distinct localization suggests that uptake mechanisms for substances like aminoglycosides may differ between kidney proximal tubule cells and cochlear sensory cells.