Na⁺ and Cl⁻ transepithelial routes in rabbit gallbladder

Summary

The reported experiments demonstrate that in rabbit gallbladder epithelium:

• a) The mucosa-cell Na⁺ and Cl⁻ influxes (45 sec long) are reduced in Cl⁻-free and Na⁺-free bathing solutions respectively; transconcentration effects are observed.

• b) Cell Cl⁻ labelling through the luminal membrane, with³⁶Cl⁻ (1 hr incubation), is nearly abolished if a Na⁺-free bathing solution is used; but cell Na⁺ labelling with²²Na⁺ in the lumen (1 hr incubation) does not change if a Cl⁻-free bathing solution is employed.

• c) Cell Na⁺ and Cl⁻ labelling through the basolateral membrane (1 hr incubation) is negligible; some Cl⁻ labelling is obtained only when the intracellular electrical potential is artificially reduced.

• d) SO ²⁻₄ is found to abolish net water transport, to cross the epithelium, but not to enter the cell.

On the basis of these data a paracellular pathway for net Cl⁻ transport is ruled out, a Na⁺ and Cl⁻ cotransport through the cell luminal barrier and a Na⁺ active extrusion through the basolateral membrane are suggested. No definitive conclusion about Cl⁻ extrusion is possible.