2.4. Measurement of TEER
TEER measurement was used to determine barrier integrity. TEER measurement for each module was conducted by a resistance-based method illustrated in Fig. 3A. This method was a four-point probe method like commonly used STX chopstick electrodes.
After co-culturing gut and BBB, the upper and bottom module were detached from each other. Then, resistance of each module was measured using Millicell ERS-2 Volt-Ohm meter (Millipore, USA, MERS00002). TEER of each barrier was determined from the resistance values using equation (1).
\begin{equation} TEER=A*\left(R-R_{\text{blank}}\right)\ \ \ \ \ \ (1)\nonumber \\ \end{equation}
A is cell culture area (cm2), R is resistance of module with cell layer (Ω) and Rblank is resistance of module with no cell (Ω).