Pb. Mccray et al., EXPRESSION OF CFTR AND A CAMP-STIMULATED CHLORIDE SECRETORY CURRENT IN CULTURED HUMAN FETAL ALVEOLAR EPITHELIAL-CELLS, American journal of respiratory cell and molecular biology, 9(6), 1993, pp. 578-585
During development the fetal lung secretes fluid that is osmotically l
inked to chloride (Cl-) transport. One possible pathway for Cl- secret
ion across the fetal pulmonary epithelium is through the cystic fibros
is transmembrane conductance regulator (CFTR). CFTR is expressed in ep
ithelia and functions as a Cl- channel regulated by cyclic adenosine m
onophosphate (cAMP)-dependent protein kinase and intracellular ATP. Pr
evious studies have shown that CFTR mRNA is expressed throughout the h
uman fetal pulmonary epithelium and CFTR protein can be immunoprecipit
ated from human fetal lung homogenates. In cultured fetal lung tissue
explants, CFTR mRNA was localized to alveolar epithelial cells. To tes
t the hypothesis that fetal alveolar epithelial cells express function
al CFTR, we immunolocalized CFTR in human fetal lung and looked for ev
idence of Cl- secretion in cultured alveolar epithelial cell monolayer
s. Monoclonal anti-CFTR antibodies localized CFTR in cultured lung exp
lants to the epithelial cells, predominantly at the apical surface. Bi
oelectric properties of cultured monolayers of midgestation fetal alve
olar epithelial cells were measured in modified Ussing chambers. In un
stimulated monolayers, transepithelial electrical potential difference
(Psi(t))= -1.1 +/- 0.1 mV, transepithelial resistance (R(t)) = 768 +/
- 58 Omega.cm(2), and short-circuit current (I-sc) = 1.9 +/- 0.2 mu A/
cm(2) (mean +/- SE, n = 17). Addition of amiloride to the apical surfa
ce significantly decreased basal I-sc. Apical diphenylamine-2-carboxyl
ate (DPC), a Cl- channel inhibitor, caused no significant change in ba
sal I-sc. In the presence of apical amiloride, isoproterenol significa
ntly increased I-sc a response that was inhibited by apical DPC and su
bmucosal bumetanide. The cAMP agonists forskolin and IBMX also stimula
ted I-sc. These results suggest that human fetal alveolar epithelial c
ells express CFTR, which mediates cAMP-stimulated transepithelial Cl-
secretion.