Validity of the two-component theory in the production of endocochlear potential

To evaluate the mechanism of endocochlear potential (EP) and the validity of the two-component theory in its production, we perfused the endolymphatic space of normal and kanamycin-deafened guinea pigs with artificial endolymph containing 50 mM K+. The K+ activities and EP were simultaneously measured with a double-barreled K+ electrode during and after perfusion. The relationship between the magnitude of the electrogenic potential and K+ active transport was calculated and compared between the two groups of animals. The results showed that the positive component of the EP (positive EP) was mainly dependent on K+ active transport in the stria vascularis but included other electrogenic components not dependent on K+ active transport. The K+ and Na+ conductances (Gk and Gna) between the endolymph and perilymph were also calculated in the normal and kanamycin-deafened guinea pigs. The Gk was much lower in kanamycin-deafened guinea pigs but the Gna did not differ between the two groups of animals. The theoretical EP value during anoxia (negative EP) was consistent with that observed in each group. The difference in the negative EP was approximately 30 mV, but the steady-state EP did not differ between groups. It is concluded that EP is probably not the simple mathematical sum of the positive and negative potentials but involves more complex mechanisms.