Impact of activities of Na+,K+-atpase and Ca2+-atpase in the cochlear lateral wall on recovery from noise-induced temporary threshold shift

The present study was designed to investigate the relationship between the noise-induced temporary threshold shift (TTS) and the specific activities of sodium potassium adenosine triphosphatase (Na+,K+-ATPase) and calcium adenosine triphosphatase (Ca(2+)ATPase) in the cochlear lateral wall. The specific activities of these enzymes were quantified by microcolorimetric assay. Changes in auditory brain stem response (ABR) thresholds were compared with the quantitative alterations of the specific activities of Na+,K+-ATPase and Ca2+-ATPase in the cochlear lateral wall of guinea pigs with a noise-induced TTS. In the majority of those noise-exposed ears with complete recovery of ABR thresholds, the specific activities of both enzymes returned to at least 70% of the mean specific activity of the control group. Although other factors may be involved, reversible inactivation of Na+,K+-ATPase and Ca2+-ATPase in the cochlear lateral wall may be one component of the TTS. Our present findings could drive further studies on the molecular basis of noise-induced hearing loss.