[Chloride secretion in the intestinal epithelium: channels, ions, and intracellular signaling].

Salt and water secretion by epithelial cells is required to hydrate the mucosal surface of both gastrointestinal and respiratory tracts. Intestinal secretion is the result of active transcellular chloride transport by epithelial cells lining the crypts. Defective chloride secretion is responsible for many common disorders such as secretory diarrhea and cystic fibrosis. In this review we deal with the most relevant issues regarding epithelial transcellular chloride secretion. We first consider the principles of membrane transport and transport protein function. Then, we briefly discuss the use of state-of-the-art techniques for electrophysiological studies such as "patch-clamp" and microfluorometry. The epithelial chloride secretion model is described according to observations made in both native tissue and cultured intestinal epithelial cells. Next, we consider the intracellular signaling cascades involved in the regulation of membrane transport systems and transcellular chloride secretion. Finally, the clinical implications of the most recent findings are commented, with emphasis on potential molecular targets for the treatment of cystic fibrosis and secretory diarrhea.