Ultrastructural differentiation of the first Hensen cell in the gerbil cochlea as a distinct cell type.

BACKGROUND: The mammalian cochlea contains beneath and lateral to outer hair cells, several types of supporting cells. The function of these cells has not been explained beyond providing a structural base.
METHODS: The supporting cells of gerbil cochlea were examined by electron microscopy with a view to elucidating their biologic activity on the basis of cytologic structure.
RESULTS: Ultrastructural examination differentiated the laterally located Hensen cells from their medial neighbor connected to the third Deiters cell. The latter cell formed a cover to the outer tunnel between Hensen and Deiters cells, appeared not to reach the basilar membrane, and exhibited a denser cytosol and more mitochondria, compared to Hensen cells. In these respects the cell observed here to cover the outer tunnel, corresponded with the tectal cell described by Henson et al. (1983) in the mustache bat, but not heretofore documented in other animals.
CONCLUSIONS: This distinctive cell in the gerbil differed in displaying unique villus-like structures which projected from the basomedial surface and are referred to as fimbriae. The fimbriae and interspersed filopodia largely filled outer tunnel space and expanded the cell's basal surface. The amplification of basal plasmalemma by fimbriae and their content of mitochondria testify to a role for the tectal cell in ion resorption and an influence on ion content and volume of outer tunnel fluid.