Abstract

Reading the impedance of planar gold-film electrodes that are used as growth substrate for adherent cells reveals changes in electrode coverage or cell morphology. Thus, real time impedance data provide insights in various cell phenotypes, such as cell morphology, proliferation, lateral migration or cytotoxicity even over prolonged periods of time. A crucial advantage over standard assays is the continuous cell monitoring. Advanced information content is obtained by using multi-frequency impedance readouts as they allow zooming in on changes in membrane topography, cell-cell or cellmatrix junctions deconvoluting the complex whole cell response, for instance, to G-protein-coupled receptor (GPCRs) activation. Multi-frequency impedance measurements were used to monitor cell adhesion, cell specific structural changes, proliferation and cytotoxicity. The multi-frequency character of the data allows selecting the most sensitive frequency for a particular application, cell type or detail of the cell response after data acquisition is complete. Impedance spectra were calculated for HeLa, HEK293 and CHO cells to demonstrate cell-type specific differences under stationary conditions. Data acquisition was performed using the CardioExcyte96 impedance recording system. Cells covering the electrode impede the applied current due to insulating properties of their membranes and the individual tightness of their cell junctions. Cell responses to experimental challenges will induce corresponding impedance changes. Multifrequency impedance analysis provides a stronger basis for data interpretation as it highlights the changes in specific cell structures. HeLa, HEK293 and CHO cells show different proliferation curves. Frequency-dependent impedance data reveal individual drifts of the most sensitive frequency, i.e. of the maximal responses indicating cell type specific changes in cell junctions and proliferation dynamics. The expected concentration dependent toxicity was observed for DMSO, Escin and Triton-X by multi-frequency impedance recordings showing decreasing impedance values with exposure time and drifting of the maximal responses to lower frequencies. GPCR-mediated signal transduction was investigated by applying the endogenous agonist (dopamine) in dose-response studies or receptor-independent agents that are used for pathway deconvolution (forskolin).
In summary, single and multi-frequency impedance data allow for a non-invasive continuous monitoring of cells with the option to zoom in on certain cell aspects or to tailor the readout to individual cell types for improved data interpretation.