Expression of the chloride channel ClC-2 in the murine small intestine epithelium

The chloride channel ClC-2 has been implicated in neonatal airway chloride secretion. To assess its role in secretion by the small intestine, we asses sed its subcellular expression in ileal segments obtained from mice and stu died the chloride transport properties of this tissue. Chloride secretion a cross the mucosa of murine ileal segments was assessed in Ussing chambers a s negative short-circuit current (I-sc). If ClC-2 contributed to chloride s ecretion, we predicted on the basis of previous studies that negative I-sc would be stimulated by dilution of the mucosal bath and that this response would depend on chloride ion and would be blocked by the chloride channel b locker 5-nitro-2-(3-phenylpropylamino) benzoic acid but not by DIDS. In fac t, mucosal hypotonicity did stimulate a chloride-dependent change in I-sc t hat exhibited pharmacological properties consistent with those of ClC-2. Th is secretory response is unlikely to be mediated by the cystic fibrosis tra nsmembrane conductance regulator (CFTR) channel because it was also observe d in CFTR knockout animals. Assessment of the native expression pattern of ClC-2 protein in the murine intestinal epithelium by confocal and electron microscopy showed that ClC-2 exhibits a novel distribution, a distribution pattern somewhat unexpected for a channel involved in chloride secretion. I mmunolabeled ClC-2 was detected predominantly at the tight junction complex between adjacent intestinal epithelial cells.