Ht man CIC-2 is a pH-Kegulatfi chloride channel

CIC-2 is a member of the CIC family of voltage-gated chloride channels which is expressed ubiquitously; however, this CI' channel lacks a specific physiological role in mammalian cells. Because pH-modulated CT conductance is a hallmark of many tissues \\iiidi express CIC-2, \ve hypothesized that CIC-2 channels may underlie pH-regulated Cl conductances. Recently, we cloned a human cDNA for CIC-2 from a T84 colon carcinoma cell d)NA library {Cid et al. Human Mol Gen. 4:407, 1995}. To address our hypothesis, this human CIC-2 cDNA was expressed stably with an RSV promoter-driven mammalian expression vector in IB3-1 human airway epithelial cells which contain low levels of endogenous CIC-2 rnRNA. G418-resistanl IB3-! cell clones stably overexpressing CIC-2 inKNA were identified by Northern blot analysis. At physiological pH (pH 7.45) in bath (extracellular) and pipette (iniracellulan solutions, overexpressing clones displayed h\(X'rpolaii/ation-activated (T currents (HACCs) characteristic of CIC-2 currents. These ('1C 2-hki HACCs were inhibited slightly b> an acidic bath pH of 6.2 but were potentiated mjrkudK h> bath pH of 5.0 and of 3 S when compared to pH 7.45. Parental cells or endogenous I y expressing clones had negligable Cl currents at bath pH 7.45 and 6.2; hmu'\er, HACCs were observed at bath pH S.O or 3.8. HACCs had biophysical properties similar to CIC-2 channels including: lime- and hyperpolarization-dependent activation, imvaruK lectifying steady-state 1-V relationship, DIDS and BaCl, insensitivity. partial DPC svnsitujtv and inhibition by CdCl:. ZnCi. and UCI, Acidic pH stimulated CIC-2 HACCs in 1H3-1 cells were inhibited partially by stable expression of an antisense CIC-2 cDNA, suggesting that CIC-2 channels underlie the hyperpolarization-activated and pH-regulated CT currents observed. Taken together, these results suggest that CIC-2 Cl" channels are regulated h\ extracellular pH. are stimulated b> more extreme acidic pH, and may underlie pH-rogulated Cl" conductances measured in stomach, intestine, muscle, kidney and Sung \\heio clinnues m extracellular pH are common and. in some cases, extreme.