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MUCOSAL BIOLOGY

A novel small molecule CFTR inhibitor attenuates HCO₃^– secretion and duodenal ulcer formation in rats

¹Greater Los Angeles Veterans Affairs Healthcare System and ²Department of Medicine, School of Medicine, and ³Department of Chemistry, University of California; and ⁴Center for Ulcer Research and Education, Digestive Diseases Research Center, and ⁵Brentwood Biomedical Research Institute, Los Angeles, California

Submitted 24 March 2005 ; accepted in final form 13 May 2005

The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) plays a crucial role in mediating duodenal bicarbonate (HCO₃^–) secretion (DBS). Although impaired DBS is observed in CF mutant mice and in CF patients, which would predict increased ulcer susceptibility, duodenal injury is rarely observed in CF patients and is reduced in CF mutant mice. To explain this apparent paradox, we hypothesized that CFTR dysfunction increases cellular [HCO₃^–] and buffering power. To further test this hypothesis, we examined the effect of a novel, potent, and highly selective CFTR inhibitor, CFTR_inh-172, on DBS and duodenal ulceration in rats. DBS was measured in situ using a standard loop perfusion model with a pH stat under isoflurane anesthesia. Duodenal ulcers were induced in rats by cysteamine with or without CFTR_inh-172 pretreatment 1 h before cysteamine. Superfusion of CFTR_inh-172 (0.1–10 µM) over the duodenal mucosa had no effect on basal DBS but at 10 µM inhibited acid-induced DBS, suggesting that its effect was limited to CFTR activation. Acid-induced DBS was abolished at 1 and 3 h and was reduced 24 h after treatment with CFTR_inh-172, although basal DBS was increased at 24 h. CFTR_inh-172 treatment had no effect on gastric acid or HCO₃^– secretion. Duodenal ulcers were observed 24 h after cysteamine treatment but were reduced in CFTR_inh-172-pretreated rats. CFTR_inh-172 acutely produces CFTR dysfunction in rodents for up to 24 h. CFTR inhibition reduces acid-induced DBS but also prevents duodenal ulcer formation, supporting our hypothesis that intracellular HCO₃^– may be an important protective mechanism for duodenal epithelial cells.

CFTR_inh-172; duodenal bicarbonate secretion; duodenal ulcer; cysteamine; luminal acid

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