Adenylyl Cyclase 6 Expression Is Essential for Cholera Toxin–Induced Diarrhea

BackgroundCholera toxin (CT)–induced diarrhea is mediated by cyclic adenosine monophosphate (cAMP)–mediated active Cl– secretion via the cystic fibrosis transmembrane conductance regulator (CFTR). Although the constitutive activation of adenylyl cyclase (AC) in response to CT is due to adenosine diphosphate ribosylation of the small G protein α-subunit activating CFTR with consequent secretory diarrhea, the AC isoform(s) involved remain unknown.MethodsWe generated intestinal epithelial cell–specific adenylyl cyclase 6 (AC6) knockout mice to study its role in CT-induced diarrhea.ResultsAC6 messenger RNA levels were the highest of all 9 membrane-bound AC isoforms in mouse intestinal epithelial cells. Intestinal epithelial-specific AC6 knockout mice (AC6loxloxVillinCre) had undetectable AC6 levels in small intestinal and colonic epithelial cells. No significant differences in fluid and food intake, plasma electrolytes, intestinal/colon anatomy and morphology, or fecal water content were observed between genotypes. Nevertheless, CT-induced fluid accumulation in vivo was completely absent in AC6loxloxVillinCre mice, associated with a lack of forskolin- and CT-induced changes in the short-circuit current (ISC) of the intestinal mucosa, impaired cAMP generation in acutely isolated small intestinal epithelial cells, and significantly impaired apical CFTR levels in response to forskolin.ConclusionsAC6 is a novel target for the treatment of CT-induced diarrhea.