Enhanced Na+ transport in an air-liquid interface culture system

Use of the air-liquid interface culture technique has produced improved morphological differentiation of rodent, canine, and human tracheal epithelia. We have investigated the effect of this culture technique on ion transport activities of cultured canine bronchial epithelia. These cells were isolated from excised airways by enzymatic digestion and plated on permeable collagen membrane substrates. All cultures were maintained utilizing standard culture techniques, by bathing both apical and basolateral sides with hormone supplemented, serum-free media until confluent (days 4-6). Half of the cultures were converted to air-liquid interface cultures (ALIC) by gentle aspiration of the apical medium and half were continued under standard technique culture (STC) conditions. After three additional days, preparations cultured under both conditions were mounted in modified Ussing chambers where bioelectric properties were measured under short-circuit conditions. Mean short-circuit current (Isc) was significantly greater in ALIC (-91.3 +/- 7.84 microA/cm2) than in STC (-54.8 +/- 5.03 microA/cm2). The sodium channel blocker, amiloride, reduced Isc by 68.4 +/- 5.0% in STC and by 84.8 +/- 3.0% in ALIC. 22Na and 36Cl fluxes confirmed the presence of enhanced sodium absorption in ALIC when compared with STC. The depth of the apical fluid, measured by microelectrodes during ALIC, was approximately 15 microns. Studies of cellular metabolism demonstrated a shift in metabolism from an anaerobic to an oxidative pattern in ALIC. This change in the pattern of metabolism suggests that the ALIC technique enhanced sodium transport in canine bronchial epithelia by increasing oxygen delivery to the epithelium.