Figure 6. Effects of ion substitutions on anion and fluid transport.

A, the response of Calu-3 ‘Alter’ shRNA control cells to 10 μmol l⁻¹ forskolin in control solutions (n= 3). B–D, effect of 10 μmol l⁻¹ forskolin on Calu-3 cells bathed bilaterally with solutions lacking HCO₃⁻/CO₂, Na⁺ or Cl⁻, respectively (n= 6 for each). Forskolin-stimulated HCO₃⁻ secretion was abolished in the nominal absence of HCO₃⁻ or Na⁺, but was increased ∼25% in Cl⁻-free conditions. E, monolayers were bathed with apical Cl⁻-free solution, then stimulated with 10 μmol l⁻¹ forskolin. Panels A–E: •, I_eq; º, HCO₃⁻ secretion. F, forskolin-stimulated fluid transport was abolished in the nominal absence of Na⁺, HCO₃⁻/CO₂ or Cl⁻. ▪, normal medium; ▴, Na⁺-free medium; ▾, Cl⁻-free medium; ♦, HCO₃⁻/CO₂-free medium (n= 6 each condition; means ± SEM).