sentence: Isolated tracheal epithelial cells were cultured in the apical chamber of collagen-coated ( rat tail collagen type I , 50 µ g / mL , BD Biosciences ) semi permeable polycarbonate 0.4 - µ m pore membrane supports ( Costar ) in 6 - , 12 - , or 24-well plates with an appropriate volume of mTEC / Plus medium prepared as follows : mTEC / Basic medium ( Dulbecco Modified Eagle Medium ( DMEM ) / Ham ’ s F-12 supplemented with 10 % FBS , 15 mM HEPES , 4 mM glutamine , 3.6 mM NaHCO , penicillin / streptomycin , and 250 ng / mL amphotericin B ) with insulin ( 1 µ g / mL ; Sigma-Aldrich ) , transferrin ( 5 µ g / mL ; Sigma-Aldrich ) , cholera toxin ( 100 ng / mL ; Sigma-Aldrich ) , epidermal growth factor ( 25 ng / mL ; BD Biosciences ) , and bovine pituitary extract ( 30 µ g / mL ; PelFreeze ) .