Fig. 1.

Fluid absorptive rate and pH change between the influent (unbuffered saline) and the effluent solution in perfused WT jejunal loops before and after removal of luminal Cl⁻ or luminal Na⁺, or both. a, b Removal of Cl⁻ from the luminal perfusate (substitution by gluconate) reduced fluid absorptive rate by ~50 % (a) and caused a stronger acidification of the effluent (b), suggesting the inhibition of a Cl⁻/HCO₃ ⁻ exchange process. c, d Removal of Na⁺ from the luminal perfusate by substitution with N-methyl-d-glucamine (NMDG) completely abolished absorption (c) and caused a lesser degree of acidification suggesting the inhibition of a Na⁺/H⁺ exchange process. e, f Removal of both Na⁺ and Cl⁻ caused the tissue to secrete more fluid than just with Na⁺ removal (e), but did not further change the pH of the effluent. **p < 0.01, n = 5