Mechanism underlying the formation of the endocochlear potential of the inner ear: its correlation with the K⁺ transport system through the lateral wall

Abstract

　Endolymph, a unique extracellular fluid in the cochlea of the inner ear, exhibits a highly positive potential of +80 mV. This so-called endocochlear potential (EP), which is indispensable for hearing, originates from the lateral cochlear wall. The lateral wall, which comprises the stria vascularis and its neighboring spiral ligament, is likely made up of two epithelial layers. By using electrophysiological and theoretical approaches, we have shown that the EP depends on the K⁺ dynamics in the extra/intracellular compartments of the lateral wall. Of importance, the K⁺ environment seems to be controlled by the unidirectional K⁺ transport throughout the cochlea. Moreover, the results of our recent study suggest that of the several K⁺-transport molecules expressed in the lateral wall, only Na⁺, K⁺-ATPase is likely to be involved in driving the unidirectional K⁺ transport. These findings will contribute not only to elucidation of the mechanism underlying hearing, but also that of the pathophysiological processes involved in deafness caused by impairment of the EP.