Alveolar Epithelial Ion and Fluid Transport cAMP regulation of Cl and HCO3 secretion across rat fetal distal lung epithelial cells

Lazrak, Ahmed, Ulrich Thome, Carpantanto Myles, Janice Ware, Lan Chen, Charles J. Venglarik, and Sadis Matalon. cAMP regulation of Cl and HCO3 secretion across rat fetal distal lung epithelial cells. Am J Physiol Lung Cell Mol Physiol 282: L650–L658, 2002. First published December 7, 2001; 10.1152/ajplung.00370.2001.—We isolated and cultured fetal distal lung epithelial (FDLE) cells from 17to 19-day rat fetuses and assayed for anion secretion in Ussing chambers. With symmetrical Ringer solutions, basal shortcircuit currents (Isc) and transepithelial resistances were 7.9 0.5 A/cm2 and 1,018 73 cm2, respectively (means SE; n 12). Apical amiloride (10 M) inhibited basal Isc by 50%. Subsequent addition of forskolin (10 M) increased Isc from 3.9 0.63 A/cm2 to 7.51 0.2 A/cm2 (n 12). Basolateral bumetanide (100 M) decreased forskolin-stimulated Isc from 7.51 0.2 A/cm2 to 5.62 0.53, whereas basolateral 4,4 -dinitrostilbene-2,2 -disulfonate (5 mM), an inhibitor of HCO3 secretion, blocked the remaining Isc. Forskolin addition evoked currents of similar fractional magnitudes in symmetrical Cl or HCO3 -free solutions; however, no response was seen using HCO3 and Cl -free solutions. The forskolin-stimulated Isc was inhibited by glibenclamide but not apical DIDS. Glibenclamide also blocked forskolin-induced Isc 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 HCO3 secretion across rat FDLE cells mediated via CFTR.