Bioelectric properties of cultured epithelial monolayers from distal lung of 18-day fetal rat

In vivo studies of fetal sheep suggest that the liquid present in the lumen of the lung throughout fetal life is derived from Cl- secretion by the pulmonary epithelium. Monolayer preparations of enriched epithelial cells from distal fetal rat (18-day gestation) lung, grown in serum-free media, were histologically similar to acinar (prealveolar) structures of fresh tissue. In Ussing chambers, basal transepithelial potential difference (PD), calculated equivalent short-circuit current (I(eq)), and transepithelial resistance (R) were 4.4 ± 0.3 mV (matrix positive), 35.6 ± 1.6 μA/cm2, and 120.0 ± 4.0 Ωcm2, respectively. Ouabain (10-3 M) eliminated 57% of basal I(eq) within 30 min, amiloride (10-4 M) induced a 13% fall in I(eq), and phlorizin (10-4 M) had no effect on bioelectric properties. Diphenylamine-2-carboxylate (DPC, 3x10-3 M) inhibited I(eq) by 50%. Bumetanide had no effect on baseline bioelectric parameters. The hyperpolarization that accompanied apical or bilateral replacement of Cl- and was enhanced by terbutaline suggested an apical Cl- permselectivity. Effects of Na+ replacement on amiloride-pretreated monolayers were consistent with Na+-dependent Cl- secretion or amiloride-insensitive pathways. Under these growth conditions, this preparation exhibits bioelectric characteristics that are compatible with Cl- secretion and Na+ absorption. The mechanism of Cl- secretion may be similar to that of airways but is uniquely bumetanide insensitive.