cAMP regulation of Cl(-) and HCO(-)(3) secretion across rat fetal distal lung epithelial cells.

We isolated and cultured fetal distal lung epithelial (FDLE) cells from 17- to 19-day rat fetuses and assayed for anion secretion in Ussing chambers. With symmetrical Ringer solutions, basal short-circuit currents (I(sc)) and transepithelial resistances were 7.9 +/- 0.5 microA/cm(2) and 1,018 +/- 73 Omega.cm(2), respectively (means +/- SE; n = 12). Apical amiloride (10 microM) inhibited basal I(sc) by approximately 50%. Subsequent addition of forskolin (10 microM) increased I(sc) from 3.9 +/- 0.63 microA/cm(2) to 7.51 +/- 0.2 microA/cm(2) (n = 12). Basolateral bumetanide (100 microM) decreased forskolin-stimulated I(sc) from 7.51 +/- 0.2 microA/cm(2) to 5.62 +/- 0.53, whereas basolateral 4,4'-dinitrostilbene-2,2'-disulfonate (5 mM), an inhibitor of HCO secretion, blocked the remaining I(sc). Forskolin addition evoked currents of similar fractional magnitudes in symmetrical Cl(-)- or HCO(-)(3)-free solutions; however, no response was seen using HCO(-)(3)- and Cl(-)-free solutions. The forskolin-stimulated I(sc) was inhibited by glibenclamide but not apical DIDS. Glibenclamide also blocked forskolin-induced I(sc) across monolayers having nystatin-permeablized basolateral membranes. Immunolocalization studies were consistent with the expression of cystic fibrosis transmembrane conductance regulator (CFTR) protein in FDLE cells. In aggregate, these findings indicate the presence of cAMP-activated Cl(-) and HCO(-)(3) secretion across rat FDLE cells mediated via CFTR.