Recovery of the endocochlear potential and the K + concentrations in the cochlear fluids after acoustic trauma

Abstract

Intense noise stimulation (142 dB, 1/3-octave-band noise centred at 1 kHz for 1 h) causes damage mainly in the second turn of the cochlea. Several hours (3–5) after the noise exposure, the endocochlear potential (EP) was found to be very low (5.7 ± 6.0 mV). Similarly, the K + concentration in the endolymph (K + e) had decreased to low values (18.9 ± 9.5 mM). The return of EP and K + e to normal values took 5–20 days. In contrast to the K + e changes, the perilymph K + concentration (K + p) increased slightly after the noise exposure to 4.5 ± 1.7 mM and returned to normal values one day after the exposure. Differences were found in the time course of the EP, K + e and K + p changes after the arrest of ventilation when animals with acoustic trauma were compared with normal healthy individuals. The anoxic EP in noise-exposed animals never decreased to values more negative than −20 mV. The results imply that the inner ear mechanisms maintaining positive EP, K + e and K + p are severely damaged after acoustic trauma and that their function is restored in 5–20 days. With respect to some parameters (decrease of the EP during anoxia, the value of anoxic negative EP, EP oveshoot after revenilation) the inner ear mechanisms are, however, still abnormal.