Expression of the chloride channel CLC-K in human airway epithelial cells

Airway submucosal gland function is severely disrupted in cystic fibrosis (CF), as a result of genetic mutation
of the cystic fibrosis transmembrane conductance regulator (CFTR), an apical membrane Cl– channel. To identify other
Cl– channel types that could potentially substitute for lost CFTR function in these cells, we investigated the functional and
molecular expression of Cl– channels in Calu-3 cells, a human cell line model of the submucosal gland serous cell. Whole
cell patch clamp recording from these cells identified outwardly rectified, pH- and calcium-sensitive Cl– currents that resemble
those previously ascribed to ClC-K type chloride channels. Using reverse transcription – polymerase chain reaction,
we identified expression of mRNA for ClC-2, ClC-3, ClC-4, ClC-5, ClC-6, ClC-7, ClC-Ka, and ClC-Kb, as well as the
common ClC-K channel b subunit barttin. Western blotting confirmed that Calu-3 cells express both ClC-K and barttin
protein. Thus, Calu-3 cells express multiple members of the ClC family of Cl– channels that, if also expressed in native
submucosal gland serous cells within the CF lung, could perhaps act to partially substitute lost CFTR function. Furthermore,
this work represents the first evidence for functional ClC-K chloride channel expression within the lung.