Distribution of ions in cochlear tissues: Effects of noise exposure

Abstract

To assess the role of altered ion distribution in noise‐induced hearing loss, the element content of isolated outer hair cells (OHCs), stria vascularis and spiral ligament was studied utilizing the energy dispersive X‐ray analysis (EDXA) mode of the scanning electron microscope. In the normal chinchilla inner ear, EDXA spectra from non‐nuclear regions of OHCs showed high levels of Cl and K, with relatively low P, S, and Na. OHC nuclei were similar but with high P. In contrast, both non‐nuclear and nuclear regions of stria vascularis were characterized by high P and K, with Cl and Na significantly lower than in OHCs. The element content of the spiral ligament varied in a regular manner with the location sampled. Exposure to a two‐octave (1414–5656 Hz) band of noise for 1 h at intensities from 90‐ to 120‐dB SPL had no effect upon the element content of stria. OHC spectra were also unchanged in intact cells. Degenerating cells showed elevated Cl and K levels. The results suggest that changes in the ionic content of OHCs and stria vascularis are not involved in the temporary effects of noise. However, altered ion distribution does appear to be associated with the degeneration of OHCs after intense sound exposure.