Molecular identity and function in transepithelial transport of KATP channels in alveolar epithelial cells

K+ channels play a crucial role in epithelia by repolarizing cells and maintaining electrochemical gradient for Na+ absorption and Cl- secretion. In the airway epithelium, the most frequently studied K+ channels are KvLQT1 and K-Ca. A functional role for K-ATP channels has been also suggested in the lung, where K-ATP channel openers activate alveolar clearance and attenuate ischemia-reperfusion injury. However, the molecular identity of this channel is unknown in airway and alveolar epithelial cells (AEC). We adopted an RT-PCR strategy to identify, in AEC, cDNA transcripts for Kir channels (Kir6.1 or 6.2) and sulfonylurea receptors ( SUR1, 2A, or 2B) forming K-ATP channels. Only Kir6.1 and SUR2B were detected in freshly isolated and cultured alveolar cells. To determine the physiological role of K+ channels in the transepithelial transport of alveolar monolayers, we studied the effect, on total short-circuit currents (I-sc), of basolateral application of glibenclamide, an inhibitor of K-ATP channels, as well as clofilium, charybdotoxin, clotrimazole, and iberiotoxin, inhibitors of KvLQT1 and K-Ca channels, respectively. Interestingly, activity of the three types of K+ channels was detected, since all tested inhibitors decreased I-sc. Furthermore, these K+ channel inhibitors reduced amiloride-sensitive Na+ currents ( mediated by ENaC) and completely abolished stimulation of Cl- currents by forskolin. Conversely, pinacidil, an activator of K-ATP channels, increased Na+ and Cl- transepithelial transport by 33 - 35%. These results suggest the presence, in AEC, of a K-ATP channel, formed from Kir6.1 and SUR2B subunits, which plays a physiological role, with KvLQT1 and K-Ca channels, in Na+ and Cl- transepithelial transport.