Validity of the Two-Component Theory in the Production of Endocochlear Potential

Abstract

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 mangitude 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.

A model of real time monitoring of the cochlear function during an induced local ischemia

“…Therefore, even small reductions of the EP can modify OHC motility, which in these experiments were be detected as DPOAE changes. EP is maintained by stria vascularis and consists of two components: a positive potential generated by the active transport of potassium ions in the stria vascularis and a pre-existing negative potassium diffusion potential between the endolymph and perilymph, although EP is not the simple sum of these two components (Kuijpers and Bontings, 1970;Bosher, 1979;Komune et al, 1993). As a sensitive parameter of cochlear oxygenation, EP rapidly drops to the negative values following anoxia or ischemia (Konischi et al, 1961;Schmiedt and Adams, 1981;Rebillard and Lavigne-Rebillard, 1992;Mom et al, 1997).…”