Ion transport properties of fetal sheep alveolar epithelial cells in monolayer culture

G. J. Tessier, G. D. Lester, M. R. Langham and S. Cassin Department of Physiology, College of Medicine, University of Florida, Gainesville 32610, USA. Alveolar type II cells were isolated from late-term fetal sheep to investigate ion transport across fetal distal lung epithelium. In Ussing chambers, basal transepithelial potential difference (PD; reference apical side), equivalent short-circuit current (Ieq), and resistance were -0.10 +/- 0.05 mV, 0.10 +/- 0.08 microA/cm2, and 821.5 +/- 38.8 omega .cm2, respectively. Epinephrine (100 nM) increased PD from -0.13 +/- 0.19 to -1.37 +/- 0.20 mV and Ieq from 0.18 +/- 0.26 to 1.47 +/- 0.28 microA/cm2. Propranolol (100 nM) inhibited responses to epinephrine. Forskolin (10 microM) increased PD to -0.81 +/- 0.08 mV and Ieq to 1.02 +/- 0.12 microA/cm2. Mucosal amiloride (200 microM) and serosal bumetanide (10 microM) decreased the forskolin-stimulated PD by 23.42 +/- 4.73 and 25.57 +/- 3.9%, respectively. We conclude that in fetal sheep distal lung epithelium amiloride-inhibitable sodium absorption and bumetanide-sensitive chloride secretion are stimulated by forskolin and that epinephrine effects on ion transport are mediated by beta-adrenergic receptors.