Dielectric properties of isolated adrenal chromaffin cells determined by microfluidic impedance spectroscopy

Modulating Ca2+ influx into adrenal chromaffin cells with short-duration nanosecond electric pulses

Isolated bovine adrenal chromaffin cells exposed to single 2-, 4-, or 5-ns pulses undergo a rapid, transient rise in intracellular Ca2+ mediated by Ca2+ entry via voltage-gated Ca2+ channels (VGCCs), mimicking the activation of these cells in vivo by acetylcholine. However, pulse durations 150 ns or longer elicit larger amplitude and longer-lived Ca2+ responses due to Ca2+ influx via both VGCCs and a yet to be identified plasma membrane pathway(s). To further our understanding of the differential effects of ultrashort versus longer pulse durations on Ca2+ influx, chromaffin cells were loaded with calcium green-1 and exposed to single 3-, 5-, 11-, 25-, or 50-ns pulses applied at their respective Ca2+ activation threshold electric fields. Increasing pulse duration from 3 or 5 ns to only 11 ns was sufficient to elicit increased amplitude and longer-lived Ca2+ responses in the majority of cells, a trend that continued as pulse duration increased to 50 ns. The amplification of Ca2+ responses was not the result of Ca2+ release from intracellular stores and was accompanied by a decreased effectiveness of VGCC inhibitors to block the responses and a reduced reliance on extracellular Na+ and membrane depolarization to evoke the responses. Inhibitors of pannexin channels, P2X receptors, or non-selective cation channels failed to attenuate 50-ns-elicited Ca2+ responses, ruling out these Ca2+-permeable channels as secondary Ca2+ entry pathways. Analytical calculations and numerical modeling suggest that the parameter that best determines the response of chromaffin cells to increasing pulse durations is the time the membrane charges to its peak voltage. These results highlight the pronounced sensitivity of a neuroendocrine cell to pulse durations differing by only tens of nanoseconds, which has important implications for the future development of nanosecond pulse technologies enabling electrostimulation applications for spatially focused and graded in vivo neuromodulation.

Various investigations of ameliorative role of Ashwagandha seeds (Withania somnifera) against amoxicillin toxicity

Several studies showed the adverse effects of amoxicillin on various body organs. So, this research has been designed to evaluate the modulatory role of Ashwagandha seed extract (ASE) against amoxicillin (AM) toxicity. Rats treated with AM (90 mg/kg), protected by ASE doses (100, 200 and 300 mg/kg), and treated by ASE at the same three doses. At the end of the experimental period, DNA comet assay, cytogenetic examinations, sperm-shape analysis, evaluation of the malondialdehyde (MDA) percentages, histopathological examinations, and biophysical tests (modulus, relaxation time, permittivity, entropy, and internal energy change of brain) were documented. The results confirmed that AM treatment induced significant elevation of DNA damage, cytogenetic aberrations, and MDA content in brain, liver, and testis tissues and sperm-shape anomalies. ASE treatment significantly minimized the genetic changes, sperm-shape anomalies, and MDA generation. These enhancements were more pronounced by protective ASE and increased by increasing the dose level. In histopathological examinations, AM treatment caused neurotoxicity in brain tissue. ASE treatment, partially, minimized these damages and the positive effects of therapeutic ASE were more noticeable. Biophysical parameters showed that therapeutic ASE was better for relaxation time, permittivity, and free energy change. Protective and therapeutic ASE were able to recover entropy and internal energy changes in variant degrees.

Amyloid-β Oligomer-Induced Electrophysiological Mechanisms and Electrical Impedance Changes in Neurons

Amyloid plays a critical role in the pathogenesis of Alzheimer's disease (AD) and can aggregate to form oligomers and fibrils in the brain. There is increasing evidence that highly toxic amyloid-β oligomers (AβOs) lead to tau protein aggregation, hyperphosphorylation, neuroinflammation, neuronal loss, synaptic loss, and dysfunction. Although the effects of AβOs on neurons have been investigated using conventional biochemical experiments, there are no established criteria for electrical evaluation. To this end, we explored electrophysiological changes in mouse hippocampal neurons (HT22) following exposure to AβOs and/or naringenin (Nar, a flavonoid compound) using electrical impedance spectroscopy (EIS). AβO-induced HT22 showed a decreased impedance amplitude and increased phase angle, and the addition of Nar reversed these changes. The characteristic frequency was markedly increased with AβO exposure, which was also reversed by Nar. The AβOs decreased intranuclear and cytoplasmic resistance and increased nucleus resistance and extracellular capacitance. Overall, the innovative construction of the eight-element CPE-equivalent circuit model further reflects that the pseudo-capacitance of the cell membrane and cell nucleus was increased in the AβO-induced group. This study conclusively revealed that AβOs induce cytotoxic effects by disrupting the resistance characteristics of unit membranes. The results further support that EIS is an effective technique for evaluating AβO-induced neuronal damage and microscopic electrical distinctions in the sub-microscopic structure of reactive cells.

Potentials induced by applied electrical fields in and around particles comprised of four dielectric layers

Knowledge of the electrical potentials within different compartments of a biological cell induced by applied alternating fields is needed for assessing the effects of electromagnetic radiation on cells, understanding electroporation and other electric field-induced effects, and deriving expressions for the complex permittivity of suspensions of cells. In the work presented in this paper, closed-form analytical expressions have been derived for the electrical potentials within different layers of an inhomogeneous particle consisting of four different dielectric layers and suspended in a homogeneous medium. Those expressions have been used to derive, for the case of a realistic model of a cell containing a large concentric organelle, expressions for the transmembrane potentials (at cell and organelle level) and electric fields within the cell compartments induced by applied fields. The results of the present theoretical model indicate points of departure between the present and previous theoretical models. The present theory also confirms the validity of the equivalence approach introduced by Irimajiri and co-workers for computing the complex permittivity for suspensions of multi-shelled particles. In addition, it shows that the electric field is amplified at the level of the cell and organelle membranes, but not within other cell compartments.

Evaluating Membrane Electrical Properties of SMMC7721 Cells with TiO₂ NPs Applications to Cytotoxicity by Dielectric Spectroscopy

Titanium dioxide nanoparticles (TiO₂ NPs) represent one of the most frequently applied nanomaterials in numerous areas of daily life. Recent studies show that TiO₂ exposure increases the occupational risk of liver injury and inflammation, and even liver cancer to the workers of factories handling these NPs. However, the potential risks and biophysical effects of TiO₂ on hepatic cells need extensive evaluation. To this end, we explored the electrophysiological changes in the human liver cancer cell line SMMC7721 following exposure to TiO₂ NPs. TiO₂ NPs decreased the first (Δε₁) and second dielectric relaxation intensity (Δε₂) of the SMMC7721 cells by 6.62% and 0.86% respectively, and significantly increased the first characteristic frequency (f_c1, 4.82%) and the first Cole-Cole parameter (β₁, 1.24%). The double spherical-shell model showed that TiO₂ NPs significantly lowered the permittivity of unit-membrane and capacitance, as well as the conductivity of extracellular fluid, cytoplasm, and nuclear contents compared to the untreated control. Conclusively, this study revealed that TiO₂ NPs induce cytotoxic effects by disrupting the permeability and electrical conductivity of unit membranes. Further, we report that dielectric spectrum combined with model parameter analysis can evaluate the bioelectrical effects of TiO₂ NPs on human liver cancer cells.

Dielectric Spectroscopy Based Detection of Specific and Nonspecific Cellular Mechanisms

Using radiofrequency dielectric spectroscopy, we have investigated the impact of the interaction between a G protein-coupled receptor (GPCR), the sterile2 α-factor receptor protein (Ste2), and its cognate agonist ligand, the α-factor pheromone, on the dielectric properties of the plasma membrane in living yeast cells (Saccharomyces cerevisiae). The dielectric properties of a cell suspension containing a saturating concentration of α-factor were measured over the frequency range 40Hz–110 MHz and compared to the behavior of a similarly prepared suspension of cells in the absence of α-factor. A spherical three-shell model was used to determine the electrical phase parameters for the yeast cells in both types of suspensions. The relative permittivity of the plasma membrane showed a significant increase after exposure to α-factor (by 0.06 ± 0.05). The equivalent experiment performed on yeast cells lacking the ability to express Ste2 showed no change in plasma membrane permittivity. Interestingly, a large change also occurred to the electrical properties of the cellular interior after the addition of α-factor to the cell suspending medium, whether or not the cells were expressing Ste2. We present a number of different complementary experiments performed on the yeast to support these dielectric data and interpret the results in terms of specific cellular reactions to the presence of α-factor.

Use of an Insulation Layer on the Connection Tracks of a Biosensor with Coplanar Electrodes to Increase the Normalized Impedance Variation

New technologies, such as biosensors and lab-on-a-chip, are reducing time consumption and costs for the detection and characterization of biological cells. One challenge is to detect and characterize cells and bacteria one by one or at a very low concentration. In this case, measurements have very low variations that can be difficult to detect. In this article, the use of an insulation layer on the connection tracks of a biosensor with coplanar electrodes is proposed to improve a biosensor previously developed. The impedance spectroscopy technique was used to analyze the influence of the insulation layer on the cutoff frequencies and on the normalized impedance variation. This solution does not induce changes in the cutoff frequencies, though it permits improving the normalized impedance variations, compared to the same biosensor without the insulation layer.

Influence of Electrode Connection Tracks on Biological Cell Measurements by Impedance Spectroscopy

The limit of detection of a biological sensor is an important parameter because, when it is optimized, it allows the detection of a reduced number of biological cells and the reduction of the detection time. This parameter can be improved upon with a reduction in electrode size, but the rate of detection is similarly reduced as well. To avoid this problem, we propose a sensor matrix composed of 20 × 20 µm² coplanar square electrodes with a standard clean room manufacturing process. However, it was observed that the exposition of electrode connection tracks to the solution reduces the normalized impedance variation. In this pursuit, we propose in this paper an analysis of electrode connection tracks on the normalized impedance variation and cutoff frequencies to biological cell measurements by impedance spectroscopy. The experimental results were obtained using the E4990A Keysight impedance analyser (Keysight Technologies, Santa Rosa, CA, USA) with a frequency band ranging from 100 Hz to 12 MHz, thus allowing for good measurement accuracy. Therefore, it was found that, for the measurements between the electrodes with 9 µm of connection tracks in contact with the solution, the normalized impedance variation was from 3.7% to 4.2% for different measurements, while, for the electrodes with 40 µm of connection tracks in contact with the solution, the normalized impedance variation was from 1.8% to 2.1% for different measurements.