Endocohlear potential is controlled by the extracellular K+-dynamics via K+-transport apparatuses in cochlear stria vascularis of inner ear.

A cochlear extracellular fluid, endolymph, has 150 mM K⁺ and positive potential of ∼+80 mV called "endocochlear potential (EP)". EP is essential for hearing. K⁺-transport via an epithelial tissue "stria vasclularis" in the lateral wall is crucial for maintaining the high K⁺ and EP. Stria vascularis comprises marginal (MCs) and intermediate (ICs) cells. The extracellular space sandwiched by the two is referred as "intrastrial space (IS)" and harbors low K⁺ of ∼2 mM and high potential of ∼+90 mV. This unique property is proposed to be an origin of EP and achieved by cooperation of Na⁺,K⁺,2Cl⁻-cotransporter (NKCC) and Na⁺,K⁺-ATPase at the basolateral membrane of MCs and K⁺ channel at the apical site of ICs. However, the mechanism for its establishment is unknown. We thus measured the potential and K⁺ concentration ([K⁺]) of IS with a double-barreled electrode while applying furosemide, a NKCC-blocker, and anoxia, which dysfunctions Na⁺,K⁺-ATPase. Strial perfusion of furosemide largely declined the potential and increased [K⁺] in IS as well as reduced EP. Anoxia caused the same effect. The amplitude of change in IS-potential and EP paralleled that in K⁺ equilibrium potential toward IS. Hence, low [K⁺] in IS maintained by NKCC and Na⁺,K⁺-ATPase in MCs may promote [K⁺] diffusion via K⁺ channel in ICs, which forms IS potential and EP. [J Physiol Sci. 2007;57 Suppl:S108]