Native small airways must remain wet enough to be pliable and support ciliary clearance, but dry enough to remain patent for gas flow. The airway epithelial lining must both absorb and secrete ions to maintain a critical level of fluid on its surface.
Despite frequent involvement in lung diseases, the miniscule size has limited studies of the peripheral airway. To meet this challenge, we used a capillary to construct an Ussing chamber (area < 1 mm2) to measure electrolyte transport across small native airways (∼1 mmø) from pig lung. Transepithelial potentials (Vt) were recorded in open circuit conditions while applying constant current pulses across the luminal surface of dissected airways to calculate transepithelial electrical conductance (Gt) and equivalent short circuit current (Isceq) in the presence and absence of selected Na+ and Cl- transport inhibitors (amiloride, GlyH-101, Niflumic acid) and agonists (Forskolin + IBMX, UTP). Considered together the responses suggest an organ composed of both secreting and absorbing epithelia that constitutively and concurrently transport fluids into and out of the airway, i.e., in opposite directions. Since the epithelial lining of the small airways is arranged in long, accordion-like rows of pleats and folds that run axially down the lumen, we surmise that cells within the pleats are mainly secretory while the cells of the folds are principally absorptive.
This structural arrangement could provide local fluid transport from pleats to fold tips that may autonomously regulate the local luminal fluid volume while permitting acute responses to maintain clearance.
