The effects of bicarbonate and hydroxyl ions on chloride transport by toad bladders.

The association between Cl-, HCO3- and H+ transported by toad bladders was investigated. Net mucosal to serosal Cl- transport by Colombian toad bladders was stimulated by incubation in HCO3- free solutions. In addition, when Colombian or Dominican toad bladders were exposed to low HCO3- concentrations on the mucosal side and 25 mM HCO3- on the serosal side, net mucosal leads to serosal Cl- transport was induced. Neither acetazolamide nor cyanide significantly inhibited Cl- transport under these conditions. The presence of a pH gradient, more acid on the mucosal side, also induced net mucosal leads to serosal Cl- transport. The results suggest that Cl- transport by toad bladders may occur by exchange with HCO3- or OH-; this process may not require carbonic anhydrase or oxidative metabolism. The Cl- transport by toad bladders is qualitatively different from the electrogenic Cl- transport of the thick limb of Henle's loop, but may be similar to a process which occurs in other portions of the nephron.