Characterization of basolateral K + channels underlying anion secretion in the human airway cell line Calu‐3

Transepithelial anion secretion in many tissues depends upon the activity of basolateral channels. Using monolayers of the Calu‐3 cell line, a human submucosal serous cell model mounted in an Ussing chamber apparatus, we investigated the nature of the K + channels involved in basal, cAMP‐ and Ca 2+ ‐stimulated anion secretion, as reflected by the transepithelial short circuit current ( I sc ). The non‐specific K + channel inhibitor Ba 2+ inhibited the basal I sc by either 77 or 16 % when applied directly to the basolateral or apical membranes, respectively, indicating that a basolateral K + conductance is required for maintenance of basal anion secretion. Using the K + channel blockers clofilium and clotrimazole, we found basal I sc to be sensitive to clofilium, with a small clotrimazole‐sensitive component. By stimulating the cAMP and Ca 2+ pathways, we determined that cAMP‐stimulated anion secretion was almost entirely abolished by clofilium, but insensitive to clotrimazole. In contrast, the Ca 2+ ‐stimulated response was sensitive to both clofilium and clotrimazole. Thus, pharmacologically distinct basolateral K + channels are differentially involved in the control of anion secretion under different conditions. Isolation of the basolateral K + conductance in permeabilized monolayers revealed a small basal and forskolin‐stimulated I sc . Finally, using the reverse transcriptase‐polymerase chain reaction, we found that Calu‐3 cells express the K + channel genes KCNN4 and KCNQ1 and the subunits KCNE2 and KCNE3. We conclude that while KCNN4 contributes to Ca 2+ ‐activated anion secretion by Calu‐3 cells, basal and cAMP‐activated secretion are more critically dependent on other K + channel types, possibly involving one or more class of KCNQ1‐containing channel complexes.