抄録
The tight junction known as a barrier between apical and basolateral sides has the paracellular conductance (Gp) selective for ions, water and macromolecules. However, the regulatory mechanism of Gp is still unknown. To clarify the mechanism, we studied the effect of water fluxes on the paracellular ion conductance in renal A6 cells, measuring the transepithelial potential and the Gp under the condition that the transcellular ion transport was abolished with applying channel blockers. We estimated the Na+-selective Gp (GNa) and the Cl−-selective Gp (GCl) based on the equilibrium potentials for Na+ and Cl− between apical and basolateral solutions. The basolateral hypotonicity or the apical hypertonicity significantly increased GNa, indicating that the secretion-directed water flux generated by the osmotic gradient between apical and basolateral sides increases GNa. In contrast, the apical hypotonicity increased Gp with no discrimination between GNa and GCl, indicating the absorption-directed water flux increases Gp with no ion selectivity. The secretion-directed water flux without NaCl gradients itself had little effects on Gp, but produced precondition generating Gp elevation observed with NaCl gradients. These results indicate that an inherited system in paracellular pathway regulates the Gp with ion selectivity by sensing the water flux including the direction. Supported by JSPS 18890157, 17590191, 17390057, and 18659056. [J Physiol Sci. 2007;57 Suppl:S224]
