title: Large Na(+) influx and high Na(+), K (+)-ATPase activity in mitochondria-rich epithelial cells of the inner ear endolymphatic sac.
abstract: Fluid in the mammalian endolymphatic sac (ES) is connected to the endolymph in the cochlea and the vestibule. Since the dominant ion in the ES is Na(+), it has been postulated that Na(+) transport is essential for regulating the endolymph pressure. This study focused on the cellular mechanism of Na(+) transport in ES epithelial cells. To evaluate the Na(+) transport capability of the ES epithelial cells, changes in intracellular Na(+) concentration ([Na(+)](i)) of individual ES cells were measured with sodium-binding benzofurzan isophthalate in a freshly dissected ES sheet and in dissociated ES cells in response to either the K(+)-free or ouabain-containing solution. Analysis of the [Na(+)](i) changes by the Na(+) load and mitochondrial staining with rhodamine 123 showed that the ES cells were classified into two groups; one exhibited an intensive [Na(+)](i) increase, higher Na(+), K(+)-ATPase activity, and intensive mitochondrial staining (mitochondria-rich cells), and the other exhibited a moderate [Na(+)](i) increase, lower Na(+), K(+)-ATPase activity, and moderate mitochondrial staining (filament-rich cells). These results suggest that mitochondria-rich ES epithelial cells (ca. 30% of ES cells) endowed with high Na(+) permeability and Na(+), K(+)-ATPase activity potentially contribute to the transport of Na(+) outside of the endolymphatic sac.
authors.affiliation: Department of Otolaryngology, Kagawa University, Kagawa, Japan. takenori@med.kagawa-u.ac.jp
authors.forename: Takenori
authors.initials: T
authors.lastname: Miyashita
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Tatsumi
authors.forename: Kimihide
authors.initials: K
authors.lastname: Hayakawa
authors.forename: Nozomu
authors.initials: N
authors.lastname: Mori
authors.forename: Masahiro
authors.initials: M
authors.lastname: Sokabe
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004710:Endolymph / Q000378:metabolism; D004712:Endolymphatic Sac / Q000166:cytology* / Q000378:metabolism; D042783:Endothelial Cells / Q000166:cytology / Q000201:enzymology*; D006168:Guinea Pigs; D008928:Mitochondria / Q000378:metabolism*; D009924:Organ Culture Techniques; D012964:Sodium / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*
chemical_list: D012964:Sodium; D000254:Sodium-Potassium-Exchanging ATPase