Subsurface tubular system in the outer sensory cells of the rat cochlea.

The system of subsurface tubules in the outer sensory cells of the rat cochlea consists of tubules lying immediately beneath the cell membrane. The tubules extend from the region below the cuticular plate, follow without interruption along the contours of the cell membrane, and terminate as a complicated, branched system under the nucleus. Several mitochondria are found on the cytoplasmic side of the tubules. Microtubules are observed in the space between the subsurface tubules and the mitochondria, in contact with the membranes of the subsurface system and, rarely, in contact with small, stalked vesicles. Current theories on the role of the subsurface system are discussed and a new one, considering possible involvement of the system in transport of the synaptic transmitter, is proposed.