Decline in the endocochlear potential corresponds to decreased Na,K-ATPase activity in the lateral wall of quiet-aged gerbils

The ion transport-mediating enzyme, Na,K-ATPase, is abundantly present in the cochlear lateral wall. This enzyme is essential for the generation and maintenance of the endocochlear potential. Diminished enzyme activity has been observed previously in the lateral wall of quiet-aged gerbils. The present study was designed to investigate the impact of the age-related decline in Na,K-ATPase specific activity upon auditory function. Measures of the resting endocochlear potential value and the level of Na,K-ATPase specific activity were made in cochleae obtained from gerbils aged in quiet conditions. Analysis revealed a high degree of correspondence between the level of lateral wall Na,K-ATPase specific activity and the value of the endocochlear potential measured in the round window/turn I region of the cochlea. Nonlinear regression models showed a strong relationship between the age-related reductions in enzyme activity and the magnitude of the endocochlear potential. The data suggest that during metabolic presbyacusis a decrease in Na,K-ATPase specific activity can explain most, but not all, of the decline in the endocochlear potential.