  We describe an impedance-based method for cell barrier integrity testing. A
four-electrode electrical impedance spectroscopy (EIS) setup can be realized by
simply connecting a commercial chopstick-like electrode (STX-1) to a
potentiostat allowing monitoring cell barriers cultivated in transwell inserts.
Subsequent electric circuit modeling of the electrical impedance results the
capacitive properties of the barrier next to the well-known transepithelial
electrical resistance (TEER). The versatility of the new method was analyzed by
the EIS analysis of a Caco-2 monolayer in response to (a) different membrane
coating materials, (b) two different permeability enhancers ethylene
glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) and saponin,
and (c) sonoporation. For the different membrane coating materials, the TEERs
of the standard and new protocol coincide and increase during cultivation,
while the capacitance shows a distinct maximum for three different surface
materials (no coating, Matrigel, and collagen I). The permeability enhancers
cause a decline in the TEER value, but only saponin alters the capacitance of
the cell layer by two orders of magnitude. Hence, cell layer capacitance and
TEER represent two independent properties characterizing the monolayer. The use
of commercial chopstick-like electrodes to access the impedance of a barrier
cultivated in transwell inserts enables remarkable insight into the behavior of
the cellular barrier with no extra work for the researcher. This simple method
could evolve into a standard protocol used in cell barrier research.
