Ion transport by rabbit nonciliated bronchiolar epithelial cells (Clara cells) in culture

The functions of epithelia that line small airways in mammalian lungs are unknown. To gain insight into the role of small-airway epithelia in lung liquid balance, Clara cells were isolated from excised rabbit lungs by enzymatic digestion, enriched by centrifugal elutriation and density centrifugation, and further purified by differential adherence to collagen matrices. The resulting cell population was composed of 85% Clara cells, 3% ciliated cells, and less than 1% macrophages. The remainder of the cells were not definitively identified. The transepithelial potential difference peaked on day 3 in culture. Preparations studied in Ussing flux chambers exhibited a potential difference of 8 mV (apical bath negative), a resistance of 500 ohm X cm2, and an equivalent short-circuit current (ISCeq) of 16 microA/cm2. Inhibition of the Na+/K+-ATPase by ouabain abolished ISCeq. Exposure of the apical surface to amiloride or replacement of Na+ in the apical bathing solution with an impermeant cation (N-methyl-D-glucamine) decreased ISCeq by 66% and 93%, respectively. Neither amiloride in the basolateral bathing solution, nor bumetanide, nor isoproterenol significantly altered basal ISCeq. These findings indicate that Clara cells in culture form polarized monolayers, Clara cells transport Na+ from the apical to the basolateral bathing solution, and the small airways of the rabbit may function in liquid absorption.