Ion transport properties of pulmonary small airway epithelia are poorly understood. To characterize these properties, airways were excised from anesthetized pigs. Transepithelial potential difference (PD) and conductance were measured in five airway regions: trachea (T, 7.9 +/- 0.2 mm diam), mainstem bronchi (MB, 5.5 +/- 0.2 mm diam), large bronchi (LB, 1.69 +/- 0.12 mm diam), small bronchi (SB, 0.70 +/- 0.06 mm diam), and bronchioles (BR, 0.25 +/- 0.05 mm diam). T and MB were mounted in Ussing-type chambers, and LB, SB, and BR were cannulated with pipettes and perfused. PDs of control tissues were -9.7 +/- 0.8 mV (T), -4.0 +/- 0.5 mV (MB), -4.3 +/- 1.0 mV (LB), -4.5 +/- 0.4 mV (SB), and -1.5 +/- 0.4 mV (BR), lumen negative. Amiloride significantly (P < 0.05) inhibited PDs by 25-70% in all airway regions and decreased conductance 17-33% in all regions except LB where a 10% increase was observed. Bumetanide significantly reduced the amiloride-insensitive PD 54-62% in all regions except BR. Bumetanide had little effect on conductance in T, SB, and BR, but conductance was increased in MB and LB. All airways except the smallest BR significantly hyperpolarized when the solution that bathed the lumen was replaced with Cl--free solution. In bronchioles, hyperpolarization by luminal Cl--free solution was inversely related to fractional inhibition of PD with amiloride but directly related to lumen diameter. These results suggest that 1) porcine tracheas, bronchi, and bronchioles actively absorb Na+, and 2) secretion of Cl- may occur in all airway regions except small bronchioles.
