Evidence that Calu-3 human airway cells secrete bicarbonate.

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[Formula: see text] 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 [Formula: see text], it was concluded that most basal I sc is[Formula: see text]-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 of36Cl-and22Na+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[Formula: see text] secretion. Stimulation recruits primarily Cl- secretion, as previously proposed.