Two-pore-domain potassium channels support anion secretion from human airway Calu-3 epithelial cells

Abstract

Potassium channels are required for the absorption and secretion of fluids and electrolytes in epithelia. Calu-3 cells possess a secretory phenotype, and are a model human airway submucosal gland serous cell. Short-circuit current (I(sc)) recordings from Calu-3 cells indicated that basal anion secretion was reduced by apical application of the K+ channel inhibitors bupivicaine, lidocaine, clofilium, and quinidine. Application of riluzole resulted in a large increase in I(sc), inhibited by apical application of either bupivicane or the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel blocker DPC. These results suggested that one or more members of the two-pore-domain K+ (K(2P)) channel family could influence anion secretion. Using RT-PCR, we found that Calu-3 cells express mRNA transcripts for TASK-2 (KCNK5), TWIK-1 (KCNK1), TWIK-2 (KCNK6) and TREK-1 (KCNK2). TASK-2, TWIK-2 and TREK-1 protein were detected by Western blotting, while immunolocalization of polarized cells confirmed protein expression of TREK-1 and TWIK-2 at the plasma cell membrane. TASK-2 protein staining was localized to intracellular vesicles, located beneath the apical membrane. While the pro-secretory role of basolateral K+ channels is well established, we suggest that apically located K2P channels, not previously described in airway epithelial cells, also play an important role in controlling the rate of transepithelial anion secretion.

In Situ Measurement of Airway Surface Liquid [K+] Using a Ratioable K+-sensitive Fluorescent Dye

“…. The electrochemical gradient favors apical cellular K ϩ efflux through K ϩ channels, which may be facilitated by intrinsic outward rectification as reported for some apical membrane epithelial K ϩ channels (12,13). The ENaC and CFTR inhibition effects are indirect, acting in part by apical membrane hyperpolarization and reduced transepithelial PD.…”

Molecular diversity and function of K+ channels in airway and alveolar epithelial cells

“…Several members of the K 2 P family (Table 2) have been detected in the airway H441 cell line: Twik-1 and -2, Trek-1 and -2, Task-2, -3, and -4, Thik-1, and KCNK7 (25). Their cellular localization has been investigated in Calu-3 cells: Twik-2 and Trek-1 have been detected at the plasma membrane level, mostly at the apical membrane, whereas Task-2 seems to be localized in intracellular vesicles beneath the apical membrane (14). Agents such as bupivicaine, lidocaine, and quinidine have highlighted the presence of functional K 2 P currents through the apical membrane of Calu-3 monolayers.…”

“…The same group also identified K 2 P K ϩ channels at the apical membrane of Calu-3 cells. These channels may participate in K ϩ exit/recycling across the apical membrane and could help transepithelial anion secretion (14). Finally, many Kv channels have also been detected at the apical membrane in ATII cells (42,55).…”

A unique alkaline pH-regulated and fatty acid-activated tandem pore domain potassium channel (K2P) from a marine sponge

“…The presence of a K 2P subunit in choanoflagellates (http://genome.jgipsf.org/Monbr1/Monbr1.home.html; data not shown) suggests that these channels were present before the advent of multicellularity. Given the important role of K 2P channels in epithelia (Davis and Cowley, 2006) and the proposal that epithelial cells were the first specialized cells in the evolution of multicellularity (Adams et al, 2010;Fahey and Degnan, 2010), it is not surprising to find K 2P subunits represented in all animal phyla. Presently, functional expression of K 2P channels from non-mammalian species is lacking but could be useful in providing greater insight into the evolutionary relationships of these important ion channels.…”