DIDS increases K+ secretion through an IsK channel in apical membrane of vestibular dark cell epithelium of gerbil.

Vestibular dark cell epithelium secretes K+ via IsK channels in the apical membrane. The previous observation that disulfonic stilbenes increased the equivalent short circuit current (Isc) suggested that these agents might be useful investigative tools in this tissue. The present experiments were conducted to determine if the increase in Isc was associated with an increase in K+ flux and if the effect was directly on the IsK channel or indirectly via a cytosolic intermediary. Measurements of transepithelial K+ flux with the K(+)-selective vibrating probe and of changes in net cellular solute flux by measurements of epithelial cell height showed that 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) increased K+ flux by a factor of 1.96 +/- 0.71 and caused net solute efflux. The apical membrane was partitioned with a macropatch pipette and DIDS was applied either to the membrane outside the pipette, inside the pipette or to the entire apical membrane. DIDS inside the pipette increased the current across the patch, the membrane conductance, the slowly-inactivating (IsK) component of the membrane current and shifted the reversal voltage toward the equilibrium potential for K+. DIDS outside the patch decreased the patch current and conductance, consistent with shunting of current away from the membrane patch. These findings strongly support the notion that DIDS increases K+ secretion through IsK channels in the apical membrane of vestibular dark cell epithelium by acting directly on the channels or on a tightly colocalized membrane component.