The Stiffness Change of Conditioning Effect in Inner Hair Cells

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Overexposure to intense sound damages the inner ear cells can lead to permanent threshold shift (PTS). Conditioning effect can protect the ear from acoustic injury. The mechanism of this conditioning effect has been still unknown.In this research project, the mechanism of conditioning effect has been clarified by using 1) stiffness measurement by atomic force microscopy, 2) histological findings of f-actin and prestin by confocal microscope, 3) electrophysiological assay by DPOAE measurement. CBA strain mice were used in this project. The stiffness of outer hair cells has been elevated at 3, 6 hours after heat stress (41.5 degree, 15min). Furthermore, f-actin also has been elevated for 12 hours after heat stress. On the other hand, prestin which is the specific motor protein in outer hair cells, has not been elevated after heat stress. The enhancement of DPOAEs input-output function were observed in the same time, 3 to 6 hours after heat stress. PTS was protected dramatically at 6hours heat stress-trauma interval. These results would show the mechanism of conditioning effect by changing the stiffness with f-actin in inner hair cells.