ECIS, xCELLigence and CellZScope are commercially available instruments, able to measure the impedance of cellular monolayers continuously and with high precision. The small currents used allow for label-free, real-time monitoring of the cells in a non-invasive manner. Despite the widespread use of these systems individually, direct comparisons between the systems has not been published.
In this paper, we wanted to compare the temporal sensitivity and resolution of each system. More specifically, we aimed to determine whether the instrument’s impedance measurements could detect the presence of an endothelial monolayer and reliably separate this measurement into basolateral adhesion and paracellular barrier resistances.
The total impedance measurements for all three systems were relatively similar, and very similar for the ECIS and xCELLigence systems. ECIS data can be modelled into Rb (paracellular-barrier) and Ra (basolateral adhesion). This revealed that the xCELLigence measurements were a hybrid of Rb and Ra, as the instrument was unable to discriminate between the two factors.
To compare the sensitivity of the instruments, responses to the inflammatory cytokines TNF and IL1 were measured. All three instruments showed transient decreases followed by prolonged increases in impedance. Although xCELLigence could detect these changes, it was unable to attribute this data to various cellular processes. This reduced both the sensitivity and information value of this instrument. Although both the other instruments are able to reveal processes from the modelled data, ECIS had a higher sensitivity to stimulation than the CellZScope, particularly at the lower seeding densities, which made responses harder to detect. Despite this limitation, the CellZScope is the only instrument that measures transendothelial electrical resistance across Transwells, where both the apical and basolateral compartments can be stimulated or sampled. This work demonstrates that instruments must be carefully selected to ensure they are appropriate for the experiments conducted.
