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1 Institut National de la Santé et de la Recherche Médicale U-426 and 2 U-478, Faculté Xavier Bichat, 75870 Paris Cedex 18; and 3 Department of Oto-Rhino-Laryngology, Hôpital Beaujon, AP-HP, 92118 Clichy, France
In the cochlea, endolymph is a K-rich and Na-poor fluid. The
purpose of the present study was to check the presence and to assess
the role of epithelial Na channel (ENaC) in this organ.
-,
-, and
-ENaC subunit mRNA, and proteins were detected in rat cochlea by
RT-PCR and Western blot.
-ENaC subunit mRNA was localized by in situ
hybridization in both epithelial (stria vascularis, spiral prominence,
spiral limbus) and nonepithelial structures (spiral ligament, spiral
ganglion). The
-ENaC-positive tissues were also positive for
-subunit mRNA (except spiral ganglion) or for
-subunit mRNA
(spiral limbus, spiral ligament, and spiral ganglion), but the signals
of
- and
-subunits were weaker than those observed for
-subunit. In vivo, the endocochlear potential was recorded in guinea
pigs under normoxic and hypoxic conditions after endolymphatic
perfusion of ENaC inhibitors (amiloride, benzamil) dissolved either in
K-rich or Na-rich solutions. ENaC inhibitors altered the endocochlear
potential when Na-rich but not when K-rich solutions were perfused. In
conclusion, ENaC subunits are expressed in epithelial and nonepithelial
cochlear structures. One of its functions is probably to maintain the
low concentration of Na in endolymph.
endolymph; stria vascularis; in situ hybridization; endocochlear potential; hypoxia
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