ACUTE MECHANICAL OVERSTIMULATION OF ISOLATED OUTER HAIR-CELLS CAUSES CHANGES IN INTRACELLULAR CALCIUM LEVELS WITHOUT SHAPE CHANGES

Impaired auditory function following acoustic overstimulation, or nois e, is mainly reported to be accompanied by cellular changes such as da mage to the sensory hair bundles, but changes in the cell bodies of th e outer hair cells have also been described. To investigate more close ly the immediate cellular responses to overstimulation, isolated guine a pig outer hair cells were subjected to a 200 Hz oscillating water je t producing intense mechanical stimulation. The water jet was aimed at the cell body of the isolated outer hair cell. Cell shape changes wer e studied using video microscopy, and intracellular calcium concentrat ion changes were monitored by means of the fluorescent calcium indicat or Fluo-3. Cells exposed to a high-intensity stimulus showed surprisin gly small light-microscopical alterations. The cytoplasmic calcium con centration increased in most cells, although some cells appeared very resistant to the mechanical stress. No correlation could be found betw een the calcium concentration changes and the cell length. The changes in calcium concentration reported here are suggested to be involved i n the long-term pathogenesis of noise-induced hair cell damage.