Absorption experiments were carried out using Transwell inserts
(polycarbonate membrane, 0.4 μm pore size, 12 mm diameter, Corning
Inc., USA). Insertswere placed in 12-well plates. Caco-2 cellswere seeded
at 1 × 105 cells/mL on the membrane insertswith 1.5 mL of medium
in the apical/luminal side and basolateral side, respectively. Cells were
allowed to grow and differentiate to confluent monolayers for
20–26 days post seeding by changing the medium three times a week.
Transepithelial electrical resistance (TEER) of cells grown in the
Transwell was measured using the Millicell-ERS voltmeter (Millipore
Co., USA). Only monolayers with a TEER value higher than 400 Ω cm2
were used for experiments. TEER values were also obtained after completion
of transport experiments.
For experiments, mediumwas decanted, and the cellswere carefully
washed with HBSS (pH 7.4, 37 °C). 1 mL samples containing 37.5 μM
C3G were added to the apical side of the cells. Transepithelial transport
was followed in the CO2 incubator. At 1 h the C3G concentrations at apical
and basolateral sides were sampled, adjusted with HCl (1.0 M) to
make pH ≈ 2, cooled in an ice bath, and measured using HPLC. C3G
transport fromapical side to basolateral side across the apical cell membranewas
the C3G absorption. The adhesion of C3G to apical brushwas
in the serosal solution, which was calculated by deducting absorption
amount from luminal net disappearance.