The freeze fracture technique in inner ear research.

Freeze-fracture studies on the inner ear have been focused mainly on the normal structure of junctions sealing the endolymphatic compartment, the compartmentalization of the stria vascularis and the junctional stability of the hair cells towards adjacent supporting cells. The hair cells have a very tight type of zonulae occludenetes as compared with other non-sensory epithelia in the inner ear. In contrast to other epithelial cells, the mature hair cells are in most species lacking gap junctions. During embryonic development a loss of gap junctions is an early and significant feature of cells differentiating into future hair cells. The tight junctions in the secretory epithelia (stria vascularis in the cochlea and dark cells around vestibular organs) are morphologically mature before the onset of the ionic maturation of endolymph. Freeze-fracture studies on inner ear pathology are few. The structural alterations of tight junctions in the diseased inner ear are minimal. The functional significance of such small morphological derangements is not known.