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.
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Acknowledgements
This work was supported in part by Grants-in-aid for Scientific Research (#13671783 and #16591711 to N.M., #16791003 to T.M. and #16GS0308 to M.S.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan and for General Scientific Research (#13480216 to M.S. and #14580769 to H.T.), Scientific Research on Priority Areas (#15086270 to M.S.) and a grant from Japan Space Forum (to M.S. and H.T.).
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Miyashita, T., Tatsumi, H., Hayakawa, K. et al. Large Na+ influx and high Na+, K+–ATPase activity in mitochondria-rich epithelial cells of the inner ear endolymphatic sac. Pflugers Arch - Eur J Physiol 453, 905–913 (2007). https://doi.org/10.1007/s00424-006-0166-2
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DOI: https://doi.org/10.1007/s00424-006-0166-2