Mechanisms of anion secretion in Calu-3 human airway epithelial cells by 7,8-benzoquinoline

1 Cultured epithelial monolayers of Calu-3 human airway cells were used to measure anion secretion in response to a number of phenanthrolines and benzoquinolines, using short-circuit current measurements. Calu-3 cells are derived from serous cells of submucosal glands of the airways and are a target for conditions in which muco-ciliary clearance is compromised. 2 Compounds studied were 5,6-benzoquinoline, 5-chloro-1,10-phenanthroline, 7,8-benzoquinoline, 5-nitro-1,10-phenanthroline, benzo[c]cinnoline and 1,10-phenanthroline, which gave EC50 values of 34, 48, 123, 235, 192 and 217 muM, respectively. Of these, 7,8-benzoquinoline was chosen for further detailed study. Concentration-response relationships for all the compounds had Hill slopes greater than 1. 3 Permeabilisation of the apical surface of epithelia with nystatin in the presence of an apical to basolateral potassium ion gradient reduced the EC50 for 7,8-benzoquinoline to 31 muM and altered the Hill slope to close to 1. 4 Using apically permeabilised epithelia it was shown that 7,8-benzoquinoline activates an intermediate-conductance calcium-sensitive potassium channel (KCNN4) and a cAMP-sensitive potassium channel (KCNQ1/KCNE3) in the basolateral epithelial membranes. 5 7.8-Benzoquinoline was shown to increase chloride conductance of apical epithelial membranes, presumed to be by activation of the cystic fibrosis transmembrane conductance regulator. 6 7.8-Benzoquinoline had a minor effect on cAMP accumulation in Calu-3 cells, probably by inhibition of phosphodiesterase, which may contribute to its effect on CFTR- and cAMP-sensitive potassium channels. 7 The usefulness of these novel actions in promoting secretion in airway submucosal glands is discussed.