Effect of gentamycin on vestibular dark cells and melanocytes: an ultrastructural and cytochemical study.

Vestibular dark cells areas in gentamycin (GM)-intoxicated guinea pigs were examined ultrastructurally and cytochemically. After GM treatment the dark cells represented cytoplasmic vacuoles, wide intercellular space, less osmiophilic cytoplasm and irregularly shaped basal portions. Cytochemically, Na+,K(+)-ATPase activity was demonstrated on the basolateral folded plasma membranes of the dark cells similarly in both GM-intoxicated and control guinea pigs. These findings revealed that the dark cells still possessed a function of regulating the ionic composition of the endolymph, although they showed various structural changes. On the other hand, the melanocytes extended their cytoplasmic processes into the basement membrane and the intercellular space of the dark cells. Melanosomes markedly increased in number dose-dependently by GM treatment. The significance and the function of the melanocytes in the dark-cell areas are discussed.