title: Potassium secretion by vestibular dark cell epithelium demonstrated by vibrating probe.
abstract: Detection of motion and position by the vestibular labyrinth depends on the accumulation of potassium within a central compartment of the inner ear as a source of energy to drive the transduction process. Much circumstantial evidence points to the vestibular dark cell (VDC) epithelium as being responsible for concentrating K+ within the lumen. We have used the vibrating probe technique to directly observe voltage and ion gradients produced by this tissue to put this assumption on a solid experimental footing. Relative current density (Isc,probe) over the apical membrane of VDC epithelium was measured with the vibrating voltage-sensitive probe, and this technique was validated by performing maneuvers known to either stimulate or inhibit the transepithelial equivalent short circuit current. Basolateral bumetanide (5 x 10(-5) M) and ouabain (1 x 10(-3) M) caused a decrease in Isc,probe by 55 +/- 6% and 39 +/- 3%, respectively while raising the basolateral K+ concentration from 4 to 25 mM caused an increase by 35 +/- 8%. A K+ gradient directed toward the apical membrane was detected with the vibrating K(+)-selective electrode, demonstrating that, indeed, the VDC epithelium secretes K+ under control conditions. This secretion was inhibited by bumetanide (by 94 +/- 7%) and ouabain (by 52 +/- 8%). The results substantiate the supposition that dark cells produce a K+ flux and qualitatively support the correlation between this flux and the transepithelial current.
authors.affiliation: Biophysics Laboratory, Boys Town National Research Hospital, Omaha, NE 68131.
authors.forename: D C
authors.initials: DC
authors.lastname: Marcus
authors.forename: A M
authors.initials: AM
authors.lastname: Shipley
mesh_terms: D000818:Animals; D002034:Bumetanide / Q000494:pharmacology; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004553:Electric Conductivity / Q000187:drug effects; D004558:Electric Stimulation / Q000379:methods; D004848:Epithelium / Q000187:drug effects / Q000502:physiology; D005849:Gerbillinae; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D010042:Ouabain / Q000494:pharmacology; D011188:Potassium / Q000378:metabolism*; D014722:Vestibule, Labyrinth / Q000378:metabolism*
chemical_list: D002034:Bumetanide; D010042:Ouabain; D011188:Potassium