Changes in stereocilia micromechanics following overstimulation in metabolically blocked hair cells

Previous studies have demonstrated that stereocilia micromechanics change during exposure to intense stimulation, and then recover after the stimulus has ended. These changes were associated with a loss of stiffness in the sensory hair bundle. The patterns of growth and recovery in these data suggest that active cellular processes control and limit these phenomena. The present investigation further supports this suggestion. The effects of intense stereocilia stimulation were examined before and after the hair cells were metabolically blocked by cooling or by poisoning with NaCN. In normal cells threshold shift increases with exposure duration, reaching a plateau within 5 to 6 min. Moreover, a post-exposure recovery of the threshold was also noted in the control cells within 15 min. In contrast threshold shift after the first minute in the metabolically blocked cells increased monotonically during the exposure without any indication of a plateau. Similarly, no post-exposure recovery of threshold shift was seen in the stereocilia bundles. These data support the hypothesis that metabolic processes in the region of the sensory hairs are important for limiting the loss of stiffness during exposure, as well as for restoring stiffness during recovery.