Volume transport across tracheal and bronchial airway epithelia in a tubular culture system

Airway epithelia are thought to play an important role in maintaining the depth (volume) and composition of airway surface liquid (ASL). However, due to the difficulty in measuring airway epithelial volume flow (J(v)) and ASL composition, our knowledge of ASL homeostasis is limited. We have developed a permeable tubular culture system (biofiber) suitable for growing airway epithelia on the biofiber luminal surface, which allows measurements of bioelectric properties and J(v). Canine tracheal and bronchial epithelia readily attach, grow to confluence, and develop an electrical potential difference (-10 to -40 mV) across the biofiber. Using a six-hormone- supplemented medium, we detected a significant basal absorptive J(v) across both the tracheal cells (0.65 ± 0.08 μl · cm-2 · h-1) and bronchial cells (2.21 ± 0.42 μl · cm-2 · h-1), which was significantly reduced by amiloride. Forskolin stimulated a net secretory J(v) in tracheal biofibers (-0.56 ± 0.19 μl · h-1 · cm-2) only. When the culture medium was supplemented with cholera toxin (CT), the basal absorptive J(v) was significantly reduced in the bronchial biofibers and the tracheal biofibers exhibited net secretion. The forskolin-stimulated secretory J(v) in the tracheal biofibers was significantly greater in the presence of CT than in its absence (-1.30 ± 0.29 μl · h-1 · cm-2), whereas bronchial biofibers exhibited no significant J(v) response to forskolin. We conclude that the J(v) measured in tubular culture is highly dependent on the region from which the cells originated as well as the composition of the culture medium. Use of the biofiber culture system to study airway epithelia should give further insight into factors regulating J(v) and composition of ASL.