Evidence that Calu-3 human airway cells secrete bicarbonate

Abstract

The Calu-3 cell line is being investigated as a model for human submucosal gland serous cells. In a previous investigation of basal short- circuit current (I(sc)) in Calu-3 cells, high levels of bumetanide- insensitive basal I(sc) (~60 μA/cm2) were measured in cells grown at an air interface. Basal I(sc) was reduced only 7% by bumetanide, and the largest component of basal I(sc) required both Cl- and HCO3/- in the bathing solutions. Because I(sc) could be partially inhibited by basolateral 4,4'- dinitrostilbene-2,2'-disulfonic acid and because the only known apical exit pathway for anions is the cystic fibrosis transmembrane conductance regulator, which has a relatively poor conductance for HCO3/-, it was concluded that most basal I(sc) is HCO3/- dependent Cl- secretion [M. Singh, M. Krouse, S. Moon, and J. J. Wine. Am. J. Physiol. 272 (Lung Cell. Mol. Physiol. 16): L690-L698, 1997]. We have now measured isotopic fluxes of 36Cl- and 22Na+ across short-circuited Calu-3 cells and found that virtually none of the basal I(sc) is Cl- secretion or Na+ absorption. Thus, in contrast to the earlier report, we conclude that the major component of basal I(sc) is HCO3/- secretion. Stimulation recruits primarily Cl- secretion, as previously proposed.