Membrane potential in isolated epithelial cells of the endolymphatic sac in the guinea-pig.

The membrane potential (Em) in epithelial cells isolated from the intermediate portion of the endolymphatic sac (ES) of the guinea-pig was recorded using the whole-cell patch-clamp technique. In the steady state the Em was -53.5+/-1.5 mV (n = 74), which is similar to that in epithelial cells of other tissues. Application of 1 MM ouabain induced a depolarization of Em by approximately 10 mV (n = 6), suggesting that an active ion transport process by Na+-K+-ATPase may be present in the ES epithelial membrane. Increasing extracellular K+ concentrations from 5 to 100 mM induced a significant membrane depolarization that was close to the K+ equilibrium potential calculated by the Nernst equation, indicating that K+ may be a predominant permeable ion in the ES epithelial membrane. Total replacement of extracellular Na+ with NMDG+ led to a significant membrane hyperpolarization of 38.7+/-2.5 mV (n = 18), suggesting that Na+ may be another major permeable ion for the ES epithelial membrane. Reducing extracellular Cl- concentrations from 149.3 to 7 mM had no significant effect on Em, indicating that Cl- may be a negligible permeable ion in the ES epithelial membrane.