Functional Role of Basolateral ClC-2 Channels in the Regulation of Duodenal Anion Secretion in Mice.

Background: Although ClC-2 channels are important in colonic Cl ^- secretion, it is unclear about their roles in small intestinal anion secretion. Therefore, we sought to examine whether ClC-2 channels play important roles in anion secretion, particularly duodenal bicarbonate secretion (DBS).
Methods: Duodenal mucosae from mice were stripped of seromuscular layers and mounted in Ussing chambers. Both duodenal short-circuit current (I _sc ) and HCO ₃ ^- secretion in vitro were simultaneously recorded. DBS in vivo was measured by a CO ₂ -sensitive electrode.
Results: Lubiprostone, a selective ClC-2 activator, concentration-dependently increased both duodenal I _sc and DBS only when applied basolaterally, but not when applied apically. Removal of extracellular Cl ^- abolished lubiprostone-induced duodenal I _sc , but did not alter HCO ₃ ^- secretion even in the presence of DIDS, a Cl ^- /HCO ₃ ^- exchanger inhibitor. However, further addition of glibenclamide, a CFTR channel blocker, abolished lubiprostone-evoked HCO ₃ ^- secretion. Moreover, lubiprostone-induced HCO ₃ ^- secretion was impaired in CFTR ^-/- mice compared to wild-type littermates. Luminal perfusion of duodenal lumen with lubiprostone did not alter basal DBS in vivo, but lubiprostone (i.p.) was able to induce DBS, which was also significantly inhibited by Cd ²⁺ , a ClC-2 channel blocker. [Ca ²⁺ ] _cyt level, Ca ²⁺ -activated K ⁺ channel- and cAMP-mediated duodenal I _sc , and HCO ₃ ^- secretion were unchanged by lubiprostone.
Conclusions: We have provided the first evidence for the novel functional role of basolateral ClC-2 channels in the regulation of duodenal anion secretion.