Impedance spectroscopy

To investigate the transendothelial electrical resistance, we cultivate an endothelial cell layer over a thin metal electrode. The passive electrical properties of such a cell-covered electrode can be described by a parallel connection of an ohmic resistor (=TER) for the intercellular space and a capacitance for the cell membranes in serial with an ohmic resistor for the culture medium and a capacitor for the metal electrode. Impedance spectroscopy allows the quantification of the properties of these resistors and capacitors with high precision. The technique utilizes the fact that the impedance contribution (the ratio between an applied alternating voltage to the resulting alternating current) of the cell membranes, the medium, the electrode interface and the intercellular space are frequency dependent. Thus, measuring the impedance of the whole measuring chamber at different frequencies between 1 Hz and 1 MHz gives a characteristic spectrum. The quantitative analysis of such a spectrum gives use values for the TER, the ohmic resistance of the medium and the capacitances of the cell membranes and the electrode interface.