Regulation of paracellular Na⁺ and Cl⁻ conductances by hydrostatic pressure

<jats:title>Abstract</jats:title><jats:p>The effect of hydrostatic pressure on the paracellular ion conductance (Gp) composed of the Na<jats:sup>+</jats:sup> conductance (G<jats:sub>Na</jats:sub>) and the Cl<jats:sup>−</jats:sup> conductance (G<jats:sub>Cl</jats:sub>) has been Investigated. Gp, G<jats:sub>Na</jats:sub> and G<jats:sub>Cl</jats:sub> were time‐dependently increased after applying an osmotic gradient generated by NaCl with basolateral hypotonicity. Hydrostatic pressure (1–4 cm H<jats:sub>2</jats:sub>O) applied from the basolateral side enhanced the osmotic gradient‐induced increase in Gp, G<jats:sub>Na</jats:sub> and G<jats:sub>Cl</jats:sub> in a magnitude‐dependent manner, while the hydrostatic pressure applied from the apical side diminished the osmotic gradient‐induced increase in Gp, G<jats:sub>Na</jats:sub> and G<jats:sub>Cl</jats:sub>. How the hydrostatic pressure influences Gp, G<jats:sub>Na</jats:sub> and G<jats:sub>Cl</jats:sub> under an isosmotic condition was also investigated. Gp, G<jats:sub>Na</jats:sub> and G<jats:sub>Cl</jats:sub> were stably constant under a condition with basolateral application of sucrose canceling the NaCl‐generated osmotic gradient (an isotonic condition). Even under this stable condition, the basolaterally applied hydrostatic pressure drastically elevated Gp, G<jats:sub>Na</jats:sub> and G<jats:sub>Cl</jats:sub>, while apically applied hydrostatic pressure had little effect on Gp, G<jats:sub>Na</jats:sub> or G<jats:sub>Cl</jats:sub>. Taken together, these observations suggest that certain factors controlled by the basolateral osmolality and the basolaterally applied hydrostatic pressure mainly regulate the Gp, G<jats:sub>Na</jats:sub> and G<jats:sub>Cl</jats:sub>.</jats:p>