The significance of endothelin for generation of endocochlear potential

The role of intermediate cells (ICs) in the stria vascularis (SV) of the cochlear ducts in the generation of endocochlear potential (EP) is clear because certain mutants cannot generate EP. Recent reports have shown that endothelin (ET) stimulates or inhibits the function of Na+, K(+)-ATPase in various organs. This study was designed to examine the immunocytochemical localization of ET and its receptor in the SV. The cochlear ducts of WBB6F1 (+/+) mice and mutants (W/Wv) devoid of the ICs were used for light and electron microscopic immunocytochemistry using rabbit anti-ET-1, ET-3, and ETA receptor antisera. The location of Na+, K(+)-ATPase using rabbit anti-rat Na+, K(+)-ATPase was also examined. Immunoreactivity to Na+, K(+)-ATPase was seen in the marginal cells (MCs) in both species. Immunoreactivity to ET-1 and ET-3 was preferentially localized in the rough endoplasmic reticulum and cytoplasmic vesicles of the ICs and along the plasma membrane of the ICs and in the MCs apposed to the ICs. Immunoreactive sites for ETA were almost identical to those of ET-1 and ET-3. Because Na+, K(+)-ATPase activities also exist in the MCs of the mutants, it appears likely that ET, synthesized and released by the ICs, may participate in generation of EP by regulating the function of Na+, K(+)-ATPase for production of the endolymph of the MCs.