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

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.