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

The effect of hydrostatic pressure on the paracellular ion conductance (Gp) composed of the Na + conductance (G Na) and the Cl − conductance (G Cl) has been Investigated. Gp, G Na and G Cl were time-dependently increased after applying an osmotic gradient generated by NaCl with basolateral hypotonicity. Hydrostatic pressure (1–4 cm H 2O) applied from the basolateral side enhanced the osmotic gradient-induced increase in Gp, G Na and G Cl in a magnitude-dependent manner, while the hydrostatic pressure applied from the apical side diminished the osmotic gradient-induced increase in Gp, G Na and G Cl. How the hydrostatic pressure influences Gp, G Na and G Cl under an isosmotic condition was also investigated. Gp, G Na and G Cl 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 Na and G Cl, while apically applied hydrostatic pressure had little effect on Gp, G Na or G Cl. Taken together, these observations suggest that certain factors controlled by the basolateral osmolality and the basolaterally applied hydrostatic pressure mainly regulate the Gp, G Na and G Cl.