Regulation of ClC-2 chloride channels in T84 cells by TGF-alpha

The almost ubiquitously expressed ClC-2 chloride channel is activated by hy perpolarization and osmotic cell swelling. Osmotic swelling also activates a different class of outwardly rectifying chloride channels, and several re ports point to a link between protein tyrosine phosphorylation and activati on of these channels. This study examines the possibility that transforming growth factor-alpha (TGF-alpha) modulates ClC-2 activity in human colonic epithelial (T84) cells. TGF-alpha (0.17 nM) irreversibly inhibited ClC-2 cu rrent in nystatin-perforated whole cell patch-clamp experiments, whereas a superimposed reversible activation of the current was observed at 8.3 nM TG F-alpha. Both effects required activation of the intrinsic epidermal growth factor receptor (EGFR) tyrosine kinase activity, of phosphoinositide 3-kin ase, and of protein kinase C. With microspectrofluorimetry of the pH-sensit ive fluorescent dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein, TGF- alpha was shown to reversibly alkalinize T84 cells at 8.3 nM but not at 0.1 7 nM, suggesting that 8.3 nM TGF-alpha -induced alkalinization activates Cl C-2 current. This study indicates that ClC-2 channels are targets for EGFR signaling in epithelial cells.