Biophysical Journal 66: 1939-1942 (1994)
© 1994 the Biophysical Society

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Potassium secretion by vestibular dark cell epithelium demonstrated by vibrating probe.

Biophysics Laboratory, Boys Town National Research Hospital, Omaha, NE 68131.

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.

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