title: The endocochlear potential depends on two K+ diffusion potentials and an electrical barrier in the stria vascularis of the inner ear.
abstract: An endocochlear potential (EP) of +80 mV is essential for audition. Although the regulation of K(+) concentration ([K(+)]) in various compartments of the cochlear stria vascularis seems crucial for the formation of the EP, the mechanism remains uncertain. We have used multibarreled electrodes to measure the potential, [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 (MC) layer and that composed of intermediate and basal cells. 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 this space is electrically isolated from the neighboring extracellular fluids. This arrangement is indispensable for maintaining 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 MCs to decrease, reducing both the ISP and the EP. Calculations indicate that the ISP represents the K(+) diffusion potential across the apical membranes of intermediate cells through Ba(2+)-sensitive K(+) channels. The K(+) diffusion potential across the apical membranes of MCs also contributes to the EP. Because the EP depends on two K(+) diffusion potentials and an electrical barrier in the stria vascularis, interference with any of these elements can interrupt hearing.
authors.affiliation: Division of Molecular and Cellular Pharmacology, Department of Pharmacology, and Department of Otolaryngology, Graduate School of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
authors.forename: Fumiaki
authors.initials: F
authors.lastname: Nin
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hibino
authors.forename: Katsumi
authors.initials: K
authors.lastname: Doi
authors.forename: Toshihiro
authors.initials: T
authors.lastname: Suzuki
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Hisa
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Kurachi
mesh_terms: D000818:Animals; D003051:Cochlea / Q000502:physiology; D007758:Ear, Inner / Q000502:physiology*; D017097:Electric Impedance; D006168:Guinea Pigs; D017136:Ion Transport; D008564:Membrane Potentials; D011188:Potassium / Q000378:metabolism*; D013316:Stria Vascularis / Q000378:metabolism / Q000502:physiology*
chemical_list: D011188:Potassium