2.5. Permeability assay
The permeability coefficient of each barrier was measured using FITC-dextran 3-5 kDa (Sigma, USA, FD4). The amount of FITC-dextran transported across the cell barrier was measured for 3 h with 1 h term. The permeability coefficient of each cell barrier was determined using equation (2).
\begin{equation} P_{\text{app}}=\frac{C}{t}\times\frac{V}{A*C_{0}}\ \ \ \ \ \ \ \ \ \ \ (2)\nonumber \\ \end{equation}
Papp is permeability coefficient (cm/s), C is basolateral concentration (mg/ml), V is basolateral volume (ml), t is time (sec), A is cell culture area (cm2), and C0 is initial apical concentration (mg/ml).