Ion transport in cultured fetal and adult rabbit tracheal epithelia

Transepithelial potential difference (V(te)), short circuit current (I(sc)), and transepithelial resistance (R(te)) 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 V(te), I(sc), and R(te) were equivalent in late gestation (28-30 days) and adult cultures. Amiloride (10^-4 M) (Na⁺ transport inhibitor) reduced I(sc) by 7.4 ± 1.2 μA/cm² (24%) in adult cultures but only by 1.8 ± 0.7 μA/cm² (7%) in fetal cultures (P < 0.001). Furosemide (10^-4 M) (Cl^- transport inhibitor) diminished I(sc) by 16.5 ± 3.2 μA/cm² (53%) in adult cultures and 18.8 ± 2.8 μA/cm² (74%) in fetal cultures (P < 0.01). Epinephrine (10^-6 M) stimulated I(sc) by 24.2 ± 5.8 μA/cm² (72%) in adult cells but only by 7.0 ± 1.1 μA/cm² (32%) in fetal cells (P < 0.05). After epinephrine exposure, furosemide-sensitive I(sc) increased to 41.5 ± 7.7 μA/cm² in adult cells but remained unchanged in fetal cells (P < 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.