Development and characterization of rabbit tracheal epithelial cell monolayer models for drug transport studies

The objective of this study was to investigate how culture conditions would affect the morphological, functional, and permeability characteristics of rabbit tracheal epithelial cell layers being considered for drug transport studies.

Rabbit tracheocytes were isolated by protease treatment and plated onto collagen-treated permeable supports at 1.3 x 10(6) cells/cm2. After 24 hr, cell layers were cultured either air-interfaced (AIC) on their apical surface or under conventional liquid covered conditions (LCC).

Scanning electron microscopy revealed mature cilia in AIC cell layers and ciliated cells denuded of cilia in LCC cell layers. Compared with LCC, AIC cell layers (n = 20) achieved a significantly higher peak equivalent short-circuit current (74.1 +/- 6.5 vs. 51.6 +/- 3.4 microA/cm2), a higher potential difference (70.9 +/- 2.8 vs. 60.5 +/- 3.0 mV), and a lower peak transepithelial electrical resistance (1.1 +/- 0.03 vs, 1.5 +/- 0.02 kohms.cm2). About 70% of the short-circuit current in AIC was amiloride-sensitive whereas < 10% was furosemide-sensitive, similar to that found in native tissue. The corresponding values in LCC were 50% and 46%. The permeability of both AIC and LCC to lipophilic solutes (dexamethasone and propranolol) was similar, whereas the permeability of hydrophilic solutes (mannitol, sucrose, and albuterol) in AIC was only half that in LCC.

Given the striking similarity in morphological and functional characteristics of the AIC to those in the in vivo situation, the AIC is favored as an in vitro model for future drug transport studies.