Abstract
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]
