Ion transport in cultured fetal and adult rabbit tracheal epithelia
Transepithelial potential difference (Vte), short circuit current (Isc), and transepithelial resistance (Rte) were measured to assess Na+ and Cl- transport in cultured tracheal epithelial cells from fetal and adult rabbits. Cultured fetal and adult cells developed differentiated morphology as determined by electron microscopy. Base-line Vte, Isc, and Rte were equivalent in late gestation (28-30 days) and adult cultures. Amiloride (10(-4) M) (Na+ transport inhibitor) reduced Isc by 7.4 +/- 1.2 microA/cm2 (24%) in adult cultures but only by 1.8 +/- 0.7 microA/cm2 (7%) in fetal cultures (P less than 0.001). Furosemide (10(-4) M) (Cl- transport inhibitor) diminished Isc by 16.5 +/- 3.2 microA/cm2 (53%) in adult cultures and 18.8 +/- 2.8 microA/cm2 (74%) in fetal cultures (P less than 0.01). Epinephrine (10(-6) M) stimulated Isc by 24.2 +/- 5.8 microA/cm2 (72%) in adult cells but only by 7.0 +/- 1.1 microA/cm2 (32%) in fetal cells (P less than 0.05). After epinephrine exposure, furosemide-sensitive Isc increased to 41.5 +/- 7.7 microA/cm2 in adult cells but remained unchanged in fetal cells (P less than 0.001). Our results suggest that fetal cells absorb less Na+ and secrete more Cl- than adult cells and that the Cl- secretory response to epinephrine is greater in adult than in fetal cells.