Regulation of paracellular ion conductances by NaCl gradients in renal epithelial cells

In the present study, we clarified how the NaCl gradient across the epithelial cells regulates the paracellular ion conductance. Under isotonic conditions, the absorption-directed NaCl gradient elevated the paracellular conductances of Na+ (GNa) and Cl− (GCl), while the secretion-directed NaCl gradient diminished the GNa and GCl. We further investigated the paracellular ionic conductances of NMDG (GNMDG) and gluconate (Ggluconate) by replacing Na+ with NMDG or Cl− with gluconate. The GNMDG was lower than the GNa and the replacement of Na+ with NMDG decreased the GCl. The Ggluconate was lower than the GCl and the replacement of Cl− with gluconate also decreased the GNa. These observations suggest the interaction of cations and anions on paracellular ionic conductances; i.e., cations affect paracellular anion conductances and anions affect paracellular cation conductances.