NOISE EXPOSURE ALTERS THE RESPONSE OF OUTER HAIR-CELLS TO ATP

The outer hair cells (OHCs) are one target of noise-induced effects. T o date there are few studies which examine changes in the function of OHCs induced by noise exposure. There is increasing evidence that ATP may be a neuromodulator acting on OHCs. Therefore, we examined the pos sibility that the response to ATP may be altered by low-level noise ex posure. ATP was tested on cation currents recorded from outer hair cel ls (OHCs) isolated from chronic noise-exposed guinea pigs and compared to currents recorded from normal control animals. The whole-cell vari ant of the patch-clamp technique was used. The incidence of response t o 100 mu M ATP was decreased in OHCs from noise-exposed animals as com pared to controls when normal internal and external solutions were emp loyed. When K+ was substituted by N-methyl-glucamine (NMG(+)) in the p ipette solution, there were significant differences in the magnitudes of ATP-evoked currents between cells from noise-exposed and control an imals. This was observed in both normal and 20 mM Ba2+ external soluti ons. In addition, the response to ATP exhibited a dependency on OHC le ngth. In short OHCs (< 65 mu m) from noise-exposed animals the magnitu de of the response to ATP was significantly reduced. By contrast, the response in long OHCs (> 65 mu m) from noise-exposed animals was incre ased. Results suggest that low-level noise exposure induces changes in OHCs which affect the response of the cell to ATP.