The endocochlear potential depends upon two K⁺ diffusion potentials and an electrical barrier in the stria vascularis of the inner ear

Abstract

The endocochlear potential (EP) of +80 mV is essential for audition. Although regulation of the K⁺ concentration in various compartments of the cochlear stria vascularis is crucial for formation of the EP, the mechanism remains uncertain. We have used multi barreled electrodes to measure the potential, K⁺ concentration ([K⁺]), and input resistance in each compartment of the stria vascularis. The stria faces two fluids, perilymph and endolymph, and contains an extracelluar compartment, the intrastrial space (IS), surrounded by two epithelial layers, the marginal cell layer and that composed of intermediate and basal cells. The fluid in the IS exhibits a low [K⁺] and a positive potential, called the intrastrial potential (ISP). We found that the input resistance of the IS was high, indicating that this space is electrically isolated from the neighboring extracellular fluids. This arrangement is crucial for maintaining the positive ISP. Inhibiting the K⁺ transporters of the stria by anoxia, ouabain, or bumetanide caused the [K⁺] of the IS to increase and the intracellular [K⁺] of marginal cells to decrease, reducing of both the ISP and the EP. Calculations indicate that the ISP represents the K⁺ diffusion potential across the apical membranes of intermediate cells through Ba²⁺ sensitive K⁺ channels. The K⁺ diffusion potential across the apical membranes of marginal cells also contributes to the EP. Therefore the EP depends upon two K⁺ diffusion potentials and an electrical barrier in the stria vascularis. [J Physiol Sci. 2008;58 Suppl:S170]