Longitudinal distribution of cochlear potentials and the K+ concentration in the endolymph after acoustic trauma

Guinea pigs were exposed to 142 dB third-octave band of noise control at 1 kHz for 1 h. At different times after exposure the endocochlear potential (EP), the anoxic negative endocochlear potential (-EP), the concentration of K+ (K+e) and microphonic potentials were recorded in scala media in four cochlear turns. The remaining hair cells were counted in each animal. Immediately after the exposure, the EP and K+e decreased evenly in all four cochlear turns and gradually returned to normal physiological values in 5-20 days. When measured 20 days after the exposure, essentially normal EP and K+e values were observed, with an apicalwards decline, which was similar to that found along the cochlea in nonexposed animals. Abnormal increased EP was observed in some animals 20 days after the exposure in the first and second turns. In contrast to positive EP and K+e values, the anoxic negative EP attained less negative values in the second turn of exposed animals, i.e., in the turn where the narrow band noise exerted the major destructive effect. An almost normal distribution of hair cells and most negative EP values were found in the fourth turn. The distribution of persistent hair cells correlated positively with the values of the anoxic negative EP and amplitudes of the microphonic potentials. It is assumed that, in addition to the difference in K+ concentration between endolymph and perilymph, the anoxic negative EP is dependent upon the functional state of the organ of Corti.