ClC-2 contributes to native chloride secretion by a human intestinal cell line, Caco-2

It has been previously determined that ClC-2, a member of the ClC chloride channel superfamily, is expressed in certain epithelial tissues. These find ings fueled speculation that ClC-2 can compensate for impaired chloride tra nsport in epithelial tissues affected by cystic fibrosis and lacking the cy stic fibrosis transmembrane conductance regulator. However, direct evidence linking ClC-2 channel expression to epithelial chloride secretion was lack ing. In the present studies, we show that ClC-2 transcripts and protein are present endogenously in the Caco-2 cell line, a cell line that models the human small intestine. Using an antisense strategy we show that ClC-2 contr ibutes to native chloride currents in Caco-2 cells measured by patch clamp electrophysiology, Antisense ClC-2-transfected monolayers of Caco-2 cells e xhibited less chloride secretion (monitored as iodide efflux) than did mock transfected monolayers, providing the first direct molecular evidence that ClC-2 can contribute to chloride secretion by the human intestinal epithel ium. Further, examination of ClC-2 localization by confocal microscopy reve aled that ClC-2 contributes to secretion from a unique location in this epi thelium, from the apical aspect of the tight junction complex. Hence, these studies provide the necessary rationale for considering ClC-2 as a possibl e therapeutic target for diseases affecting intestinal chloride secretion s uch as cystic fibrosis.