Role of amino acids in cochlear degeneration: deprivation of cystine induces death of cochlear hair cells of guinea pigs in vitro.

Redox regulation reportedly plays a role in maintaining cochlear homeostasis. However, little is known about the roles of oxidation-reduction systems in the cochlea. We examined the role of the cystine/cysteine oxidation-reduction system in survival of cochlea hair cells in vitro. The survival of hair cells was evaluated in cochlea specimens following incubation with the medium supplemented with various concentrations of cystine. Dying hair cells were detected by the trypan blue extrusion method. The rates of cell death for both outer and inner hair cells increased significantly with a decrease in the concentration of cystine. In addition, the rate of cell death of IHCs tended to be higher than that of OHCs. These findings suggest that the cystine/cysteine system might be required for maintenance of homeostasis in cochlear hair cells, especially in IHCs.