Bioelectric Properties of Cultured Monolayers from Epithelium of Distal Human Fetal Lung

Throughout intrauterine life, Cl(-)-rich liquid is secreted by the pulmonary epithelium. To evaluate the role of the most distal epithelium in liquid secretion, we measured bioelectric properties of monolayers composed of epithelial cells from acinar structures of postmortem human fetal lung (mean gestation, 22.3 wk; range, 18-24 wk). These monolayers formed high-resistance (R) barriers (mean R = 363 Ohm/cm2) when cultured in hormone-supplemented, serum-free medium. The transepithelial electrical potential difference (4.0 mV, lumen negative), was similar to that of whole fetal sheep lung in vivo. Equivalent short-circuit current (Ieq) was inhibited by apical amiloride (-20%), 5-(N-ethyl-N-isopropyl)-amiloride (-33 to -49%), or diphenylamine-2-carboxylate (DPC; -26%), and by basolateral ouabain (-77%), whereas apical 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) had no effect. Bumetanide added to the basolateral bath did not affect resting Ieq, but inhibited Ieq (-19%) in monolayers pretreated with apical amiloride, basolateral terbutaline, and apical ATP, and also inhibited Ieq (-22%) of monolayers pretreated with basolateral amiloride and DIDS. Ieq was stimulated by terbutaline (90-128%), ATP (70-186%), and ionomycin (141%). Stimulation of Ieq by these agents is compatible with induction of Cl- secretion through two pathways: channels that are opened by a rise in adenosine 3',5'-cyclic monophosphate, and channels that are opened by a rise in intracellular Ca2+. Inhibition of Ieq by apical DPC implies that Cl- secretion may contribute to basal Ieq.