A Ba2+-resistant, acid-sensitive K+ conductance in Na+-absorbing H441 human airway epithelial cells

By analysis of whole cell membrane currents in Na+-absorbing H441 human airway epithelial cells, we have identified a K+ conductance (G(K)) resistant to Ba2+ but sensitive to bupivacaine or extracellular acidification. In polarized H441 monolayers, we have demonstrated that bupivacaine, lidocaine, and quinidine inhibit basolateral membrane K+ current (I-B1) whereas Ba2+ has only a weak inhibitory effect. I-B1 was also inhibited by basolateral acidification, and, although subsequent addition of bupivacaine caused a further fall in I-B1, acidification had no effect after bupivacaine, demonstrating that cells grown under these conditions express at least two different bupivacaine-sensitive K+ channels, only one of which is acid sensitive. Basolateral acidification also inhibited short-circuit current (ISC), and basolateral bupivacaine, lidocaine, quinidine, and Ba2+ inhibited ISC at concentrations similar to those needed to inhibit I-B1, suggesting that the K+ channels underlying I-B1 are part of the absorptive mechanism. Analyses using RT-PCR showed that mRNA encoding several two-pore domain K+ (K2P) channels was detected in cells grown under standard conditions (TWIK-1, TREK-1, TASK-2, TWIK-2, KCNK-7, TASK-3, TREK-2, THIK-1, and TALK-2). We therefore suggest that K2P channels underlie GK in unstimulated cells and so maintain the driving force for Na+ absorption. Since this ion transport process is vital to lung function, K2P channels thus play an important but previously undocumented role in pulmonary physiology.