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 oute r hair cells, several types of supporting cells. The function of these cells has not been explained beyond providing a structural base. Meth ods: The supporting cells of gerbil cochlea were examined by electron microscopy with a view to elucidating their biologic activity on the b asis of cytologic structure. Results: Ultrastructural examination diff erentiated the laterally located Hensen cells from their medial neighb or 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 m itochondria, compared to Hensen cells. In these respects the cell obse rved here to cover the outer tunnel, corresponded with the tectal cell described by Henson et al. (1983) in the mustache bat, but not hereto fore documented in other animals. Conclusions: This distinctive cell i n the gerbil differed in displaying unique villus-like structures whic h projected from the basomedial surface and are referred to as fimbria e. The fimbriae and interspersed filopodia largely filled outer tunnel space and expanded the cell's basal surface. The amplification of bas al plasmalemma by fimbriae and their content of mitochondria testify t o a role for the tectal cell in ion resorption and an influence on ion content and volume of outer tunnel fluid. (C) 1994 Wiley-Liss, Inc.