INVIVO NOISE EXPOSURE ALTERS THE INVITRO MOTILITY AND VIABILITY OF OUTER HAIR-CELLS

The in vitro motility and viability of outer cells isolated from cochleae of normal control guinea pigs have been compared to that of guinea pigs exposed, just before sacrifice, to low-frequency high-intensity noise inducing acute 30 dB thresholds shifts at all frequencies below 10kHz. The results indicate that the cells' viability is shortened, their contractile response to Ca2+/ATP reduced, while their electrically-induced motility is not modified. These experiments demonstrate that in vivo cochlear dysfunction can correlate with changes in in vitro outer hair cell's properties. Thus the morphological and "functional" investigation of hair cells in vitro can be a valuable approach to the study of cochlea physiopathology. Here the acoustic overstimulation seems to have modified the outer hair cells Ca2+/ATP dependent slow contractile apparatus in a way which could modify in turn their mechanical excitation by the noise.