Canalicular reticulum in vestibular hair cells

Abstract

A membrane limited system referred to as canalicular reticulum (CR) has been demonstrated in the apical cytosol of the cochlea’s inner and outer hair cells. Similarities between cochlear and vestibular hair cells prompted investigation of the presence of CR in hair cells of the gerbil vestibular labyrinth. A method of fixation with glutaraldehyde followed by an osmium–ferrocyanide mixture demonstrated abundant CR in the apex of both type I and type II hair cells. The CR was closely associated with numerous Golgi zones in the apex of the vestibular hair cells, indicating its genesis from Golgi cisternae. Also preserved in upper cytosol were discrete complexes of mitochondria with granular reticulum. These complexes offered a possible site for generating the membrane in Golgi zones and CR. Single and parallel cisternae of granular reticulum were observed in the basal half of the hair cells together with numerous synaptic-like vesicles. These cisternae with their terminal blebbing and accompanying canaliculi were interpreted as novel structures mediating synaptic vesicle genesis in vestibular hair cells in a manner comparable to that postulated for cochlear inner hair cells.