Abstract
Electric cell–substrate impedance sensing (ECIS) is an attractive method for monitoring cell behaviors in tissue culture in real time. The time series impedance fluctuations of the cell-covered electrodes measured by ECIS are the phenomena accompanying cellular micromotion as cells continually rearrange their cell–cell and cell–substrate adhesion sites. Accurate assessment of these fluctuations to extract useful information from raw data is important for both scientific and practical purposes. In this study, we apply discrete wavelet transform (DWT) to analyze the concentration-dependent effect of cytochalasin B on human umbilical vein endothelial cells (HUVECs). The sampling rate of the impedance time series is 1 Hz and each data set consists of 2048 points. Our results demonstrate that, in the Daubechies (db) wavelet family, db1 is the optimal mother wavelet function for DWT-based analysis to assess the effect of cytochalasin B on HUVEC micromotion. By calculating the energy, standard deviation, variance, and signal magnitude area of DWT detail coefficients at level 1, we are able to significantly distinguish cytotoxic concentrations of cytochalasin B as low as 0.1 μM, and in a concentration-dependent manner. Furthermore, DWT-based analysis indicates the possibility to decrease the sampling rate of the micromotion measurement from 1 Hz to 1/16 Hz without decreasing the discerning power. The statistical measures of DWT detail coefficients are effective methods for determining both the sampling rate and the number of individual samples for ECIS-based micromotion assays.
Highlights
Electrical cell–substrate impedance sensing (ECIS) has existed since 1984 and has been used as a versatile cell-based biosensor to monitor subtle changes in cell-cell and cell-substrate interactions under various experimental conditions [1,2,3,4,5,6,7]
A decline in this exponent has been observed for 3T3 cells 20 h after exposure to cytochalasin B from the lowest concentration to the highest [14]. By comparing these measures with the results analyzed by the other analytical tools we proposed in this study, new algorithms to process the fluctuation data measure by ECIS can be established
The frequency-dependent impedance data were continuously recorded for 12 h and the magnitude of the resistance was plotted as a function of frequency and experimental time
Summary
Electrical cell–substrate impedance sensing (ECIS) has existed since 1984 and has been used as a versatile cell-based biosensor to monitor subtle changes in cell-cell and cell-substrate interactions under various experimental conditions [1,2,3,4,5,6,7]. One of the ECIS time course measurements is used to measure the rapid impedance changes in the cell-covered electrodes at a specific frequency with a very high time resolution (sampling rate ≥ 1 Hz). Since electric currents must flow from the electrode surface, underneath the ventral cell surface, and through the paracellular space, these impedance fluctuations are associated with minute morphological changes in cells and have been referred to as micromotion [2,8]. They are observed in small sensing electrodes, approximately. Cellular micromotion has been studied by ECIS, quartz crystal microbalance (QCM), and surface plasmon resonance (SPR).
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