Ion Channel Effects Research Articles

Voltage-Gated Ion Channel Compensatory Effect in DEE: Implications for Future Therapies.

Developmental and Epileptic Encephalopathies (DEEs) represent a clinically and genetically heterogeneous group of rare and severe epilepsies. DEEs commonly begin early in infancy with frequent seizures of various types associated with intellectual disability and leading to a neurodevelopmental delay or regression. Disease-causing genomic variants have been identified in numerous genes and are implicated in over 100 types of DEEs. In this context, genes encoding voltage-gated ion channels (VGCs) play a significant role, and part of the large phenotypic variability observed in DEE patients carrying VGC mutations could be explained by the presence of genetic modifier alleles that can compensate for these mutations. This review will focus on the current knowledge of the compensatory effect of DEE-associated voltage-gated ion channels and their therapeutic implications in DEE. We will enter into detailed considerations regarding the sodium channels SCN1A, SCN2A, and SCN8A; the potassium channels KCNA1, KCNQ2, and KCNT1; and the calcium channels CACNA1A and CACNA1G.

A Bioinspired Membrane with Ultrahigh Li+/Na+ and Li+/K+ Separations Enables Direct Lithium Extraction from Brine.

Membranes with precise Li+/Na+ and Li+/K+ separations are imperative for lithium extraction from brine to address the lithium supply shortage. However, achieving this goal remains a daunting challenge due to the similar valence, chemical properties, and subtle atomic-scale distinctions among these monovalent cations. Herein, inspired by the strict size-sieving effect of biological ion channels, a membrane is presented based on nonporous crystalline materials featuring structurally rigid, dimensionally confined, and long-range ordered ion channels that exclusively permeate naked Li+ but block Na+ and K+. This naked-Li+-sieving behavior not only enables unprecedented Li+/Na+ and Li+/K+ selectivities up to 2707.4 and 5109.8, respectively, even surpassing the state-of-the-art membranes by at least two orders of magnitude, but also demonstrates impressive Li+/Mg2+ and Li+/Ca2+ separation capabilities. Moreover, this bioinspired membranehas to be utilized for creating a one-step lithium extraction strategy from natural brines rich in Na+, K+, and Mg2+ without utilizing chemicals or creating solid waste, and it simultaneously produces hydrogen. This research has proposed a new type of ion-sieving membrane and also provides an envisioning of the design paradigm and development of advanced membranes, ion separation, and lithium extraction.

Protective layer for stable lithium-metal anodes at 60 mA·h/cm2 and 60 mA/cm2 with ion channel and inductive effect

Contradiction between ultrafast nucleation and deposition rates of lithium (Li) crystals at high rate and heterogeneity of Li+ flux resulting from concentration polarization has compromised the performance of Li metal anodes especially at high areal capacity and current density. Here, multifunctional protective layer consisting of MoO3 nanobelt films (MoO3-NF) is introduced on the surface of Li by a simple rolling method. The strong binding energy between Li and MoO3 guides the homogeneous nucleation and deposition of Li, while the nanobelt networks provide effective ion channels for uniform distribution of the Li+ flux. Because of the novel multifunctional protective layer, the MoO3-NF@Li anodes demonstrate a remarkable stability for 800 h with ultralow overpotential of 159 mV at extreme harsh conditions of 60 mA·h/cm2 and 60 mA/cm2. MoO3-NF@Li||LiNi0.6Co0.2Mn0.2O2 full-cells can run 100 cycles with a superior capacity retention of 84.2% under practical test conditions, demonstrating great potential for high output and energy-density metal batteries.

Dynamic Gain Decomposition Reveals Functional Effects of Dendrites, Ion Channels, and Input Statistics in Population Coding.

Modern, high-density neuronal recordings reveal at ever higher precision how information is represented by neural populations. Still, we lack the tools to understand these processes bottom-up, emerging from the biophysical properties of neurons, synapses, and network structure. The concept of the dynamic gain function, a spectrally resolved approximation of a population's coding capability, has the potential to link cell-level properties to network-level performance. However, the concept is not only useful but also very complex because the dynamic gain's shape is co-determined by axonal and somato-dendritic parameters and the population's operating regime. Previously, this complexity precluded an understanding of any individual parameter's impact. Here, we decomposed the dynamic gain function into three components corresponding to separate signal transformations. This allowed attribution of network-level encoding features to specific cell-level parameters. Applying the method to data from real neurons and biophysically plausible models, we found: (1) The encoding bandwidth of real neurons, approximately 400 Hz, is constrained by the voltage dependence of axonal currents during early action potential initiation. (2) State-of-the-art models only achieve encoding bandwidths around 100 Hz and are limited mainly by subthreshold processes instead. (3) Large dendrites and low-threshold potassium currents modulate the bandwidth by shaping the subthreshold stimulus-to-voltage transformation. Our decomposition provides physiological interpretations when the dynamic gain curve changes, for instance during spectrinopathies and neurodegeneration. By pinpointing shortcomings of current models, it also guides inference of neuron models best suited for large-scale network simulations.

Effect of ion channel guiding on the saturation mechanism of single and two-stream free-electron lasers based upon a rectangular hybrid wiggler

The paper studies a simulation of a one-dimensional nonlinear free electron laser that includes a square hybrid wiggler, prebunched electron beam, and ion-channel guiding mechanism. The Lorentz equations of motion and the Maxwell equations were combined to derive a set of non-linear differential equations solved numerically within the framework of slowly varying amplitude and wavenumber. The relativistic electron beam is assumed to be cold, and self-fields of the electron beam and the slippage of the radiation wave are ignored. The appropriate parameters are chosen in such a way that the Raman regime is being considered, where there is high density and low energy. The effect of ion-channel densities on the saturation of the device is studied for both groups Ι and ΙΙ orbits. It is found that as the ion channel density increases, the range of saturation radiation for group Ι circuits increases, too. In contrast, the saturated radiation amplitude for group ΙΙ orbits is decreased with increasing the ion-channel density. Moreover, the results of the numerical calculations show that the saturation length for an FEL with a prebunched beam is considerably shorter than that of a uniform electron beam. A free electron laser (FEL) model called the two-stream FEL, which uses two relativistic electron beams of different energy, is also studied. Comparing the radiation amplitude between FEL and TSFEL shows that TSFEL is more efficient than FEL.

Microelectrode Arrays Measure Blocking of Voltage-Gated Calcium Ion Channels on Supported Lipid Bilayers Derived from Primary Neurons.

Drug studies targeting neuronal ion channels are crucial to understand neuronal function and develop therapies for neurological diseases. The traditional method to study neuronal ion-channel activities heavily relies on the whole-cell patch clamp as the industry standard. However, this technique is both technically challenging and labour-intensive, while involving the complexity of keeping cells alive with low throughput. Therefore, the shortcomings are limiting the efficiency of ion-channel-related neuroscience research and drug testing. Here, this work reports a new system of integrating neuron membranes with organic microelectrode arrays (OMEAs) for ion-channel-related drug studies. This work demonstrates that the supported lipid bilayers (SLBs) derived from both neuron-like (neuroblastoma) cells and primary neurons are integrated with OMEAs for the first time. The increased expression of voltage-gated calcium (CaV) ion channels on differentiated SH-SY5Y SLBs compared to non-differentiated ones is sensed electrically. Also, dose-response of the CaV ion-channel blocking effect on primary cortical neuronal SLBs from rats is monitored. The dose range causing ion channel blocking is comparable to literature. This system overcomes the major challenges from traditional methods (e.g., patch clamp) and showcases an easy-to-test, rapid, ultra-sensitive, cell-free, and high-throughput platform to monitor dose-dependent ion-channel blocking effects on native neuronal membranes.

L-type calcium ion channel-mediated activation of autophagy in vascular smooth muscle cells via thonningianin A (TA) alleviates vascular calcification in type 2 diabetes mellitus

Vascular calcification (VC) is associated with increased morbidity and mortality, especially among people with type 2 diabetes mellitus (T2DM). The pathogenesis of vascular calcification is incompletely understood, and until now, there have been no effective therapeutics for vascular calcification. The L-type calcium ion channel in the cell membrane is vital for Ca2+ influx. The effect of L-type calcium ion channels on autophagy remains to be elucidated. Here, the natural compound thonningianin A (TA) was found to ameliorate vascular calcification in T2DM via the activation of L-type calcium ion channels. The results showed that TA had a concentration-dependent ability to decrease the transcriptional and translational expression of the calcification-related proteins runt-related transcription factor 2 (RUNX2), bone morphogenetic protein 2 (BMP2) and osteopontin (OPN) (P < 0.01) via ATG7-dependent autophagy in β-glycerophosphate (β-GP)- and high glucose (HG)-stimulated primary mouse aortic smooth muscle cells (MASMCs) and alleviate aortic vascular calcification in VitD3-stimulated T2DM mice. However, nifedipine, an inhibitor of L-type calcium ion channels, reversed TA-induced autophagy and Ca2+ influx in MASMCs. Molecular docking analysis revealed that TA was located in the hydrophobic pocket of Cav1.2 α1C and was mainly composed of the residues Ile, Phe, Ala and Met, which confirmed the efficacy of TA in targeting the L-type calcium channel of Cav1.2 on the cell membrane. Moreover, in an in vivo model of vascular calcification in T2DM mice, nifedipine reversed the protective effects of TA on aortic calcification and the expression of the calcification-related proteins RUNX2, BMP2 and OPN (P < 0.01). Collectively, the present results reveal that the activation of cell membrane L-type calcium ion channels can induce autophagy and ameliorate vascular calcification in T2DM. Thonningianin A (TA) can target and act as a potent activator of L-type calcium ion channels. Thus, this research revealed a novel mechanism for autophagy induction via L-type calcium ion channels and provided a potential therapeutic for vascular calcification in T2DM.

Controlling the sub-nano ion channels by crosslinking in PVDF-based anion exchange membrane for enhanced mono/bivalent anion permselectivity and acid reclamation

Tailoring hydrophilicity in poly (vinylidene fluoride) (PVDF) by ozone pre-treatment forms nanophase-separated ion-conducting membranes with the potential to separate mono/bivalent anions and recover acids with high purity. Herein, six PVDF-based anion exchange membranes (AEMs) with three different architectures with varying chemical structures are fabricated to evaluate their effect on Cl−/SO42− separation performance and the H+/Mn + selectivity. The methodologies used to prepare AEMs from the graft copolymer are: (i) pre-quaternization with an alkyl spacer forming a partially quaternized membrane, (ii) crosslinking in the partially quaternized membranes, (iii) insitu quaternization and crosslinking of the graft copolymer. These three different engineering aspects induce different effects of hydrophobicity, free volumes, hydration numbers, and sub-nanometer ion channels with varying diameters in the membrane matrix. The membrane QC-AEM-1 with sub-nano ion channels of a lower diameter, high surface resistance, and low hydration number shows the highest Cl−/SO42− selectivity of 48.7. Q-AEM-2 shows the maximum UH + value of 49 × 10−3 m h−1 whereas QC-AEM-2 shows the highest S value of 69 using HCl/FeCl2 mixture, whereas the crosslinked AEMs without any pre-quaternization show the lowest PSO42−Cl−, UH+, S values. Our results demonstrate that using a perfluorinated membrane backbone such as PVDF is enough to impart a regulated hydrophobicity for optimum selectivity. We believe that controlling the degree of grafting, pre-quaternization, and crosslinking constructs stable sub-nano ion channels with regulated diameters that selectively separate mono/bivalent anions.

Electrophysiological effects of stretch-activated ion channels: a systematic computational characterization.

Cardiac electrophysiology and mechanics are strongly interconnected. Their interaction is, among others, mediated by mechano-electric feedback through stretch-activated ion channels (SACs). The electrophysiological changes induced by SACs may contribute to arrhythmogenesis, but the precise SAC-induced electrophysiological changes remain incompletely understood. Here, we provide a systematic characterization of stretch effects through three distinguished SACs on cardiac electrophysiology using computational modelling. We implemented potassium-selective, calcium-selective and non-selective SACs in the Tomek-Rodriguez-O'Hara-Rudy model of human ventricular electrophysiology. The model was calibrated to experimental data from isolated cardiomyocytes undergoing stretch, considering inter-species differences, and disease-related remodelling of SACs. SAC-mediated effects on the action potential (AP) were analysed by varying stretch amplitude, application timing and/or duration. Afterdepolarizations of different amplitudes were observed with transient 10-ms stretch stimuli of 15-18% applied during phase 4, while stretch ≥18% during phase 4 elicited triggered APs. Longer stimuli shifted the threshold of AP trigger during phase 4 to lower amplitudes, while shorter stimuli increased it. Continuous stretch provoked electrophysiological remodelling. Furthermore, stretch shortened duration or changed morphology of a subsequent electrically evoked AP, and, if applied during a vulnerable time window with sufficient amplitude, prevented its occurrence because of stretch-induced modulation of sodium and L-type calcium channel gating. These effects were more pronounced with disease-related SAC remodelling due to increased stretch sensitivity of diseased hearts. We showed that SACs may induce afterdepolarizations and triggered activities, and prevent subsequent AP generation or change its morphology. These effects depend on cardiomyocyte stretch characteristics and disease-related SACs remodelling and may contribute to cardiac arrhythmogenesis. KEY POINTS: The interplay between cardiac electrophysiology and mechanics is mediated by mechano-electric feedback through stretch-activated ion channels (SACs). These channels may be pro-arrhythmic, but their precise effect on electrophysiology remains unclear. Here we present a systematic in silico characterization of stretch effects through three SACs by implementing inter-species differences as well as disease-related remodelling of SACs in a novel computational model of human ventricular cardiomyocyte electrophysiology. Our simulations showed that, at the cellular level, SACs may provoke electrophysiological remodelling, afterdepolarizations, triggered activities, change the morphology or shorten subsequent electrically evoked action potentials. The model further suggests that a vulnerable window exists in which stretch prevents the following electrically triggered beat occurrence. The pro-arrhythmic effects of stretch strongly depend on disease-related SAC remodelling as well as on stretch characteristics, such as amplitude, time of application and duration. Our study helps in understanding the role of stretch in cardiac arrhythmogenesis and revealing the underlying cellular mechanisms.

Complex dynamics of a non-smooth temperature-sensitive memristive Wilson neuron model

The development of neurodynamics emphasizes more accurate estimation and prediction of neuronal electrical activities in complicated physiological environments, which highlights the importance of reliable multifunctional neuronal modeling. Considering that temperature is a crucial factor in regulating the conductance and memory effect of ion channels, a non-smooth feedback strategy for temperature-dependent sodium and potassium currents is proposed. Accordingly, a Filippov-type Wilson neuron model is established to estimate the firing features of neocortical neurons under the effects of temperature and magnetic induction. The theoretical conditions for the existence and bifurcation of the equilibrium point of subsystems are clarified, further, the comb-shaped fractal structure and bistable firing modes are discovered by multiple numerical methods. The sufficient and necessary conditions of crossing, grazing, and sliding motions are presented qualitatively based on the flow switching theory. Importantly, the mechanism and evolutive rule of the self-excited and hidden sliding firing modes are revealed by employing the fast–slow analysis method. Moreover, a common approach for calculating the largest Lyapunov exponent of non-smooth systems based on Hamilton energy is designed, so that the global bifurcation patterns and multistability of the Filippov system are efficiently identified. The modeling scheme and the obtained results provide significant theoretical support for designing and optimizing intelligent systems.

Quantifying low-energy nitrogen ion channeling in α-titanium by molecular dynamics simulations

Quantification of nitrogen depth distributions resulting from the low-energy ion implantation into titanium nanoparticles allows tunable and controllable modifications of their properties. We have explored the nitrogen ion implantation into α-titanium target at 0.5–4 keV kinetic energies by molecular dynamics simulations, with particular focus on the ion channeling effects for low-index surface orientations ((001), (100), (110), (111)) at different target temperatures (300–1155 K) and different angles of incidence (0–29 °). The results indicate that the channeling significantly alters the depth distributions, being most prominent for (110) orientation, where causes a new distribution maximum to emerge at a significantly deeper position. An increasing target temperature suppresses notably (albeit not fully) the channeling and a tilted ion incident angle from a perpendicular impact allows controllable reduction of the number of channeling ions.

Bifurcation analysis of motoneuronal excitability mechanisms under normal and ALS conditions.

Bifurcation analysis allows the examination of steady-state, non-linear dynamics of neurons and their effects on cell firing, yet its usage in neuroscience is limited to single-compartment models of highly reduced states. This is primarily due to the difficulty in developing high-fidelity neuronal models with 3D anatomy and multiple ion channels in XPPAUT, the primary bifurcation analysis software in neuroscience. To facilitate bifurcation analysis of high-fidelity neuronal models under normal and disease conditions, we developed a multi-compartment model of a spinal motoneuron (MN) in XPPAUT and verified its firing accuracy against its original experimental data and against an anatomically detailed cell model that incorporates known MN non-linear firing mechanisms. We used the new model in XPPAUT to study the effects of somatic and dendritic ion channels on the MN bifurcation diagram under normal conditions and after amyotrophic lateral sclerosis (ALS) cellular changes. Our results show that somatic small-conductance Ca2+-activated K (SK) channels and dendritic L-type Ca2+ channels have the strongest effects on the bifurcation diagram of MNs under normal conditions. Specifically, somatic SK channels extend the limit cycles and generate a subcritical Hopf bifurcation node in the V-I bifurcation diagram of the MN to replace a supercritical node Hopf node, whereas L-type Ca2+ channels shift the limit cycles to negative currents. In ALS, our results show that dendritic enlargement has opposing effects on MN excitability, has a greater overall impact than somatic enlargement, and dendritic overbranching offsets the dendritic enlargement hyperexcitability effects. Together, the new multi-compartment model developed in XPPAUT facilitates studying neuronal excitability in health and disease using bifurcation analysis.

Sophoridine manifests as a leading compound for anti-arrhythmia with multiple ion-channel blocking effects

BackgroundSophoridine (SR) has shown the potential to be an antiarrhythmic agent. However, SR's electrophysiological properties and druggability research are relatively inadequate, which limits the development of SR as an antiarrhythmic candidate. PurposeTo facilitate the development process of SR as an antiarrhythmic candidate, we performed integrated studies on the electrophysiological properties of SR in vitro and ex vivo to gain more comprehensive insights into the multi-ion channel blocking effects of SR, which provided the foundation for the further drugability studies in antiarrhythmic and safety studies. Firstly, SR's electrophysiological properties and antiarrhythmic potentials were recorded and assessed at the cell and tissue levels by comprehensively integrating the patch clamp with the Electrical and Optical Mapping systems. Subsequently, the antiarrhythmic effects of SR were validated by aconitine and ouabain-induced arrhythmia in vivo. Finally, the safety of SR as an antiarrhythmic candidate compound was evaluated based on the guidelines of the Comprehensive in Vitro Proarrhythmia Assay (CiPA). Study designThe antiarrhythmic effect of SR was evaluated at the in vitro, ex vivo, and in vivo levels. MethodsIsolated primary cardiomyocytes and stable cell lines were prepared to explore the electrophysiologic properties of being a multiple ion-channel blocker in vitro by whole-cell patch clamp. Using electrical and optical mapping, the negative chronotropic effect of SR was determined in langendorff-perfused rat or guinea-pig hearts.The antiarrhythmic activity of SR was assessed by the ex vivo tachyarrhythmia models induced by left coronary artery ligation (LCAL) and isoproterenol (ISO). Canonical models of aconitine and ouabain-induced arrhythmia were used to verify the antiarrhythmic effects in vivo. Finally, the pro-arrhythmic risk of SR was detected in Human-Induced Pluripotent Stem Cell-Derived Cardiomyocytes (hSCCMs) using a Microelectrode array (MEA). ResultsSingle-cell patch assay validated the multiple ion-channel blockers of SR in transient outward current potassium currents (Ito), l-type calcium currents (ICa-l), and rapid activation delayed rectifier potassium currents (IKr). SR ex vivo depressed heart rates (HR) and ventricular conduction velocity (CV) and prolonged Q-T intervals in a concentration-dependent manner. Consistent with the changes in HRs, SR extended the active time of hearts and increased the action potential duration measured at 90% repolarization (APD90). SR could also significantly lengthen the onset time and curtail the duration of spontaneous ventricular tachycardia (VT) in the ex vivo arrhythmic model induced by LCAL. Meanwhile, SR could also significantly upregulate the programmed electrical stimulation (PES) frequency after the ISO challenge in forming electrical alternans and re-entrant excitation. Furthermore, SR exerted antiarrhythmic effects in the tachyarrhythmia models induced by aconitine and ouabain in vivo. Notably, the pro-arrhythmic risk of SR was shallow for a moderate inhibition of the human ether-à-go-go-related gene (hERG) channel. Moreover, SR prolonged field potential duration (FPDc) of hSCCMs in a concentration-dependent manner without early after depolarization (EAD) and arrhythmia occurrence. ConclusionOur results indicated that SR manifested as a multiple ion-channel blocker in the electrophysiological properties and exerts antiarrhythmic effects ex vivo and in vivo. Meanwhile, due to the low pro-arrhythmic risk in the hERG inhibition assay and the induction of EAD, SR has great potential as a leading candidate in the treatment of ventricular tachyarrhythmia.

Application of machine learning to improve the efficiency of electrophysiological simulations used for the prediction of drug-induced ventricular arrhythmia

Background and ObjectiveIn silico prediction of drug-induced ventricular arrhythmia often requires computationally intensive simulations, making its application tedious and non-interactive. This inconvenience can be mitigated using matrices of precomputed simulation results, allowing instantaneous computation of biomarkers such as action potential duration at 90% of the repolarisation (APD90). However, preparing such matrices can be computationally intensive for the method developers, limiting the range of simulated conditions. In this work, we aim to optimise the generation of these matrices so that they can be obtained with less effort and for a broader range of input values. MethodsMachine learning methods were applied, building models trained with only a small fraction of the originally simulated results. The predictive performances of the models were assessed by comparing their predicted values with the actual simulation results, using percentual mean absolute error and mean relative error, as well as the percentage of data with a relative error below 5%. ResultsOur method obtained highly accurate estimations of the original values, leading to a nearly one hundred-fold decrease in computation time. This method also allows precomputing more complex matrices, describing the effect of more ion channels on the APD90. The best results were obtained by applying Support Vector Machine models, which yielded errors below 1% in most cases. This approach was further validated by predicting the APD90 of a set of 12 CiPA compounds and exporting the optimal settings for predicting APD90 using a different set of ion channels, always with satisfactory results. ConclusionsThe proposed method effectively reduces the computational effort required to generate matrices of precomputed electrophysiological simulation values. The same approach can be applied in other fields where computationally costly simulations are applied repeatedly using slightly different input values.

The Role οf Ion Channels in the Development and Progression of Prostate Cancer.

Ion channels have major regulatory functions in living cells. Apart from their role in ion transport, they are responsible for cellular electrogenesis and excitability, and may also regulate tissue homeostasis. Although cancer is not officially classified as a channelopathy, it has been increasingly recognized that ion channel aberrations play an important role in virtually all cancer types. Ion channels can exert pro-tumorigenic activities due to genetic or epigenetic alterations, or as a response to molecular signals, such as growth factors, hormones, etc. Increasing evidence suggests that ion channels and pumps play a critical role in the regulation of prostate cancer cell proliferation, apoptosis evasion, migration, epithelial-to-mesenchymal transition, and angiogenesis. There is also evidence suggesting that ion channels might play a role in treatment failure in patients with prostate cancer. Hence, they represent promising targets for diagnosis, staging, and treatment, and their effects may be of particular significance for specific patient populations, including those undergoing anesthesia and surgery. In this article, the role of major types of ion channels involved in the development and progression of prostate cancer are reviewed. Identifying the underlying molecular mechanisms of the pro-tumorigenic effects of ion channels may potentially inform the development of novel therapeutic strategies to counter this malignancy.

Voltage-Dependent Potassium Current Recording on H9c2 Cardiomyocytes via the Whole-Cell Patch-Clamp Technique.

Potassium channels on the myocardial cell membrane play an important role in the regulation of cell electrophysiological activities. Being one of the main ion channels, voltage-gated potassium (Kv) channels are closely associated with some serious heart diseases, such as drug-induced myocardial damage and myocardial infarction. In the present study, the whole-cell patch-clamp technique was employed to determine the effects of 1.5 mM 4-aminopyridine (4-AP, a broad-spectrum potassium channel inhibitor) and aconitine (AC, 25 µM, 50 µM, 100 µM, and 200 µM) on the Kv channel current (IKv) in H9c2 cardiomyocytes. It was found that 4-AP inhibited the IKv by about 54%, while the inhibitory effect of AC on the IKv showed a dose-dependent trend (no effect for 25 µM, 30% inhibitory rate for 50 µM, 46% inhibitory rate for 100 µM and 54% inhibitory rate for 200 µM). Due to the characteristics of higher sensitivity and precision, this technique will promote the exploration of cardiotoxicity and the pharmacological effects of ethnomedicine targeting ion channels.

Voltage-Dependent Potassium Current Recording on H9c2 Cardiomyocytes &lt;em&gt;via&lt;/em&gt; the Whole-Cell Patch-Clamp Technique

Potassium channels on the myocardial cell membrane play an important role in the regulation of cell electrophysiological activities. Being one of the main ion channels, voltage-gated potassium (Kv) channels are closely associated with some serious heart diseases, such as drug-induced myocardial damage and myocardial infarction. In the present study, the whole-cell patch-clamp technique was employed to determine the effects of 1.5 mM 4-aminopyridine (4-AP, a broad-spectrum potassium channel inhibitor) and aconitine (AC, 25 µM, 50 µM, 100 µM, and 200 µM) on the Kv channel current (IKv) in H9c2 cardiomyocytes. It was found that 4-AP inhibited the IKv by about 54%, while the inhibitory effect of AC on the IKv showed a dose-dependent trend (no effect for 25 µM, 30% inhibitory rate for 50 µM, 46% inhibitory rate for 100 µM and 54% inhibitory rate for 200 µM). Due to the characteristics of higher sensitivity and precision, this technique will promote the exploration of cardiotoxicity and the pharmacological effects of ethnomedicine targeting ion channels.

Coupling the Cardiac Voltage-Gated Sodium Channel to Channelrhodopsin-2 Generates Novel Optical Switches for Action Potential Studies.

Voltage-gated sodium (Na+) channels respond to short membrane depolarization with conformational changes leading to pore opening, Na+ influx, and action potential (AP) upstroke. In the present study, we coupled channelrhodopsin-2 (ChR2), the key ion channel in optogenetics, directly to the cardiac voltage-gated Na+ channel (Nav1.5). Fusion constructs were expressed in Xenopus laevis oocytes, and electrophysiological recordings were performed by the two-microelectrode technique. Heteromeric channels retained both typical Nav1.5 kinetics and light-sensitive ChR2 properties. Switching to the current-clamp mode and applying short blue-light pulses resulted either in subthreshold depolarization or in a rapid change of membrane polarity typically seen in APs of excitable cells. To study the effect of individual K+ channels on the AP shape, we co-expressed either Kv1.2 or hERG with one of the Nav1.5-ChR2 fusions. As expected, both delayed rectifier K+ channels shortened AP duration significantly. Kv1.2 currents remarkably accelerated initial repolarization, whereas hERG channel activity efficiently restored the resting membrane potential. Finally, we investigated the effect of the LQT3 deletion mutant ΔKPQ on the AP shape and noticed an extremely prolonged AP duration that was directly correlated to the size of the non-inactivating Na+ current fraction. In conclusion, coupling of ChR2 to a voltage-gated Na+ channel generates optical switches that are useful for studying the effect of individual ion channels on the AP shape. Moreover, our novel optogenetic approach provides the potential for an application in pharmacology and optogenetic tissue-engineering.

Chaotic electron dynamics in a FEL with realizable quadrupole wiggler and Gaussian electron beam

Chaotic motion of electrons causes a considerable decrease in gain and efficiency of free-electron lasers (FELs). In this paper, we study chaotic dynamics of electrons moving with relativistic velocity in a realizable (three-dimensional) quadrupole wiggler when the radial dependency of wiggler magnetic field is fully taken into account using time series, Poincaré surface-of-section maps, and Liapunov exponents. The electron beam is also considered to be realizable with Gaussian density profile and an ion channel is considered as a guiding device for the electron beam. We show that the chaotic behavior of electron motion is due to the nonlinearity of quadrupole wiggler magnetic field and the chaotic electron motion occurs at almost large radial distances in which the wiggler magnetic field is large. Also, we find that one can control the electron chaotic motion by using electron beam with Gaussian density rather than the electron beam with uniform density. Furthermore, we investigate the effect of ion channel and find that when the electrostatic force of ion channel overcomes the nonlinearity effect of quadrupole wiggler magnetic field and self-repulsive force arises from electron beam, the electron motion becomes non-chaotic. We also investigate the electron motion under Budker condition and show that the Budker condition cannot guarantee the electron motion becoming completely non-chaotic.

Validating the Arrhythmogenic Potential of High-, Intermediate-, and Low-Risk Drugs in a Human-Induced Pluripotent Stem Cell-Derived Cardiac Microphysiological System.

Evaluation of arrhythmogenic drugs is required by regulatory agencies before any new compound can obtain market approval. Despite rigorous review, cardiac disorders remain the second most common cause for safety-related market withdrawal. On the other hand, false-positive preclinical findings prohibit potentially beneficial candidates from moving forward in the development pipeline. Complex in vitro models using cardiomyocytes derived from human-induced pluripotent stem cells (hiPSC-CM) have been identified as a useful tool that allows for rapid and cost-efficient screening of proarrhythmic drug risk. Currently available hiPSC-CM models employ simple two-dimensional (2D) culture formats with limited structural and functional relevance to the human heart muscle. Here, we present the use of our 3D cardiac microphysiological system (MPS), composed of a hiPSC-derived heart micromuscle, as a platform for arrhythmia risk assessment. We employed two different hiPSC lines and tested seven drugs with known ion channel effects and known clinical risk: dofetilide and bepridil (high risk); amiodarone and terfenadine (intermediate risk); and nifedipine, mexiletine, and lidocaine (low risk). The cardiac MPS successfully predicted drug cardiotoxicity risks based on changes in action potential duration, beat waveform (i.e., shape), and occurrence of proarrhythmic events of healthy patient hiPSC lines in the absence of risk cofactors. We showcase examples where the cardiac MPS outperformed existing hiPSC-CM 2D models.