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 diameter d [m] and the initial intracellular ion concentration c(in) [mM] as a function of tonicity expressed by sucrose concentration c(s) [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 coefficient P [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. P is calculated as 4.11 x 10(-6) and 3.44 x 10(-6) m s(-1) at c(s) of 10 and 30 mM representing hypotonic condition, 2.44 x 10(-6) m s(-1) at c(s) of 50 mM representing isotonic condition, and 3.68 x 10(-6), 5.16 x 10(-6), 9.51 x 10(-6), and 14.89 x 10(-6) m s(-1) at c(s) of 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 intensity F [-] of extracellular potassium ions is observed to obtain the temporal distribution of average potassium ion concentration within the region of 3.6 mu m from cell membrane interface c(ROI) [mM]. The slopes of Delta c(ROI)/c(ROI1) to time t are 0.0003, 0.0002, and 0.0006 under hypotonic, isotonic, and hypertonic conditions, where c(ROI1) denotes initial c(ROI), which shows the same tendency with LF-EIS result that is verified by the potassium ion fluorescence observation.