Quantitative Model for Ion Transport and Cytoplasm Conductivity of Chinese Hamster Ovary Cells

Abstract

In mammalian cells cytoplasm ion concentrations and hence cytoplasm conductivity is an important indicator of their physiological state. Changes in the cytoplasm conductivity has been associated with physiological changes such as progression of cancer and apoptosis. In this work, a model that predicts the effects of physiological changes in ion transport on the cytoplasm conductivity of Chinese hamster ovary (CHO) cells is demonstrated. We determined CHO-specific model parameters, Na+/K+ ATPase pumps and ion channels densities, using a flux assay approach. The obtained sodium (PNa), potassium (PK) and chloride (PCl) permeability and Na+/K+ ATPase pump density were estimated to be 5.6 × 10−8 cm/s, 5.6 × 10−8 cm/s, 3.2 × 10−7 cm/s and 2.56 × 10−11 mol/cm2, respectively. The model was tested by comparing the model predictions with the experimentally determined temporal changes in the cytoplasm conductivity of Na+/K+ ATPase pump inhibited CHO cells. Cells’ Na+/K+ ATPase pumps were inhibited using 5 mM Ouabain and the temporal behavior of their cytoplasm conductivity was measured using dielectrophoresis cytometry. The measured results are in close agreement with the model-calculated values. This model will provide insight on the effects of processes such as apoptosis or external media ion concentration on the cytoplasm conductivity of mammalian cells.

Cytoplasmic conductivity as a marker for bioprocess monitoring: Study of Chinese hamster ovary cells under nutrient deprivation and reintroduction

“…(a) Mean force indices for different medium conductivities (0.17–0.45 S/m). Stars and circles indicate the obtained results in our previous work (Fazelkhah et al, , circles; Saboktakin Rizi et al, , stars). (b) Re { K CM } calculated using a double shell model as a function of medium conductivity (Salimi et al, ).…”

“…Previous experimental and numerical analysis of CHO cells has shown that DEP measurement at 6 MHz is primarily sensitive to the cell's cytoplasm conductivity. In a medium with conductivity 0.42 S/m, other parameters such as cell size have a much less significant influence (Fazelkhah et al, ; Saboktakin Rizi et al, ).…”

“…To map the DEP response, measured force indices, of the CHO cells to their cytoplasm conductivity, we used a similar procedure explained in our previous work (Fazelkhah et al, ). By measuring the DEP response of CHO cells at 6 MHz in media with various conductivities, we obtained the plot of FI versus medium conductivity shown in Figure a.…”

“…Numerical models were used to determine if the observed cytoplasm conductivity is what would be expected for CHO cells in a nutrient‐deprived condition. In this work, a quantitative model of ion transport developed for CHO cells (Fazelkhah et al, ) was employed to link the cytoplasm conductivity of cells to their pump activity level during nutrient deprivation and nutrient reintroduction. The model includes passive channels for sodium, potassium, and chloride and an active pathway via Na + /K + ATPase pumps.…”

“…The obtained fluxes through the channels and pumps were used to estimate the dynamics of the CHO cell volume, intracellular ion concentrations, and subsequently cytoplasm conductivity. Details of the model are explained elsewhere (Fazelkhah et al, ). In this paper, the Na + /K + ATPase pump activity level in the model was changed from 0% to 100% in 10 steps.…”