Non-invasive hERG channel screening based on electrical impedance tomography and extracellular voltage activation (EIT-EVA).

hERG channel screening has been achieved based on electrical impedance tomography and extracellular voltage activation (EIT-EVA) to improve the non-invasive aspect of drug discovery. EIT-EVA screens hERG channels by considering the change in extracellular ion concentration which modifies the extracellular resistance in cell suspension. The rate of ion passing in cell suspension is calculated from the extracellular resistance Rex, which is obtained from the EIT measurement at a frequency of 500 kHz. In the experiment, non-invasive screening is applied by a novel integrated EIT-EVA printed circuit board (PCB) sensor to human embryonic kidney (HEK) 293 cells transfected with the human ether-a-go-go-related gene (hERG) ion channel, while the E-4031 antiarrhythmic drug is used for hERG channel inhibition. The extracellular resistance Rex of the HEK 293 cells suspension is measured by EIT as the hERG channels are activated by EVA over time. The Rex is reconstructed into extracellular conductivity distribution change Δσ to reflect the extracellular K+ ion concentration change Δc resulting from the activated hERG channel. Δc is increased rapidly during the hERG channel non-inhibition state while Δc is increased slower with increasing drug concentration cd. In order to evaluate the EIT-EVA system, the inhibitory ratio index (IR) was calculated based on the rate of Δc over time. Half-maximal inhibitory concentration (IC50) of 2.7 nM is obtained from the cd and IR dose-response relationship. The IR from EIT-EVA is compared with the results from the patch-clamp method, which gives R2 of 0.85. In conclusion, EIT-EVA is successfully applied to non-invasive hERG channel screening.

Non-invasive imaging of ion concentration distribution around cell spheroids by electrical impedance tomographic sensor printed on circuit board under temporal compensation by ion transport impedance model.

A non-invasive imaging called as PCB-EIT imaging has been proposed in order to image spatio-temporal ion concentration distribution around cell spheroids in 0.1 s of temporal resolution by a newly developed electrical impedance tomographic sensor printed on circuit board (PCB-EIT sensor). To realize the high temporal resolution in PCB-EIT imaging, the temporal compensation by the ion transport impedance model interpolating the extracted resistance of extracellular solution Rex obtained from the Cole-Cole equation is employed. To confirm the performance of PCB-EIT imaging, the ion concentration distribution around three cell spheroid types (GFP type (GFPT), Histone type (HT) and wild type (WT)) which are electrically different due to green fluorescent protein expressed in cytoplasm and nucleus of MRC-5. As a result, spatio-temporal ion concentration distributions due to ion transport from cell spheroid are successfully reconstructed by PCB-EIT imaging. The images by PCB-EIT imaging are validated with those by fluorescence ratio imaging within the distribution error εdis of 0.046 ± 0.0038 in maximum. For an evaluation of the ion diffusivity Dm of each cell spheroid type by the mass transfer simulation based on Fick's law, Dm of GFPT shows the highest value among the three cell types in the earlier time range from 4 s, while Dm of HT shows the highest one in the time range from 15 s, which indicates that PCB-EIT imaging is able to evaluate the ion transport characteristics of each cell type.

Study of transmembrane ion transport under tonicity imbalance using a combination of low frequency-electrical impedance spectroscopy (LF-EIS) and improved ion transport model.

Transmembrane ion transport under tonicity imbalance has been investigated using a combination of low frequency-electrical impedance spectroscopy (LF-EIS) and improved ion transport model, by considering the cell diameterd[m] and the initial intracellular ion concentrationcin[mM] as a function of tonicity expressed by sucrose concentrationcs[mM]. The transmembrane ion transport is influenced by extracellular tonicity conditions, leading to a facilitation/inhibition of ion passage through the cell membrane. The transmembrane transport coefficientP[m s-1], which represents the ability of transmembrane ion transport, is calculated by the extracellular ion concentrations obtained by improved ion transport model and LF-EIS measurement.Pis calculated as 4.11 × 10-6and 3.44 × 10-6m s-1atcsof 10 and 30 mM representing hypotonic condition, 2.44 × 10-6m s-1atcsof 50 mM representing isotonic condition, and 3.68 × 10-6, 5.16 × 10-6, 9.51 × 10-6, and 14.89 × 10-6m s-1atcsof 75, 100, 125 and 150 mM representing hypertonic condition. The LF-EIS results indicate that the transmembrane ion transport is promoted under hypertonic and hypotonic conditions compared to isotonic condition. To verify the LF-EIS results, fluorescence intensityF[-] of extracellular potassium ions is observed to obtain the temporal distribution of average potassium ion concentration within the region of 3.6µm from cell membrane interfacecROI[mM]. The slopes of ∆cROI/cROI1to timetare 0.0003, 0.0002, and 0.0006 under hypotonic, isotonic, and hypertonic conditions, wherecROI1denotes initialcROI, which shows the same tendency with LF-EIS result that is verified by the potassium ion fluorescence observation.

Low-Frequency Impedance-Based Cell Discrimination Considering Ion Transport Model in Cell Suspension.

Low-frequency impedance-based (LFI) cell discrimination as a novel non-destructive and non-invasive cell discrimination is proposed. LFI cell discrimination discriminates the cell type by considering an ion transport model in cell suspension. Ion transport model in cell suspension is constructed on the basis of Fick's laws of diffusion in the extracellular region under ion permeability P which represents the characteristics of cell type. P is achieved using the ion transport model equation through an iterative curve fitting to an ion concentration in extracellular region obtained from low-frequency impedance which is assumed to be linearly related to the ion concentration in extracellular region. In experiment, the electrical impedance spectra from the frequency of 200 kHz to 2.0 MHz are measured over time during producing ions from intracellular region to extracellular one in cell suspension using an impedance analyzer and an interdigitated array electrode system. As a target cell type, two different cell types based on Medical Research Council 5 (MRC-5), which are different in intracellular component are used. The curve fitting is performed for the low-frequency impedance at 200 kHz at which impedance reflects the ion concentration in extracellular region in order to obtain P of each cell type. As a result, each cell type has its own P. The proposed LFI cell discrimination successfully discriminates the cell type.