RESUMO
Potassium channels play an important role in providing a driving force for anion secretion from secretory epithelia. To investigate the role of KCNQ K+ channels in mediating rates of basal anion secretion across the human airway submucosal gland serous cell model, the Calu-3 cell, we examined the expression, localization and function of these channels. In addition to our previous knowledge that Calu-3 cells express KCNQ1, using reverse transcriptase polymerase chain reaction we determined expression of KCNQ3, KCNQ4 and KCNQ5 mRNA transcripts. Immunoblotting detected KCNQ1, KCNQ3 and KCNQ5 proteins, while KCNQ4 protein was not found. Immunolocalization using polarized Calu-3 cell monolayers revealed that KCNQ1 and KCNQ3 were located in or toward the apical membrane of the cells, while KCNQ5 was detected in the apical and lateral membranes. Transepithelial transport studies revealed a small chromanol 293B-sensitive current at the apical membrane, likely KCNQ1. Application of XE991, an inhibitor of all members of the KCNQ channel family, inhibited the basal short-circuit current when applied to both sides of the cells to a greater extent than 293B, with the largest inhibition seen upon apical application. This result was confirmed using linopiridine, a less potent analogue of XE991, and suggests that functional KCNQ3 and KCNQ5, in addition to KCNQ1, are present at the apical aspect of these cells. These results demonstrate the role of a number of KCNQ channel members in controlling basal anion secretion across Calu-3 cells, while also demonstrating the importance of apically located K+ channels in mediating anion secretion in the airway epithelium.