Microelectrode Techniques Research Articles

(Invited) Application of Microelectrode Technique to Battery Materials Study

Li-ion batteries use the “composite electrode” which includes active materials, conductive agents, binder, and current collector. In general, the electrode characteristics is affected by not only the active materials property but also the state of “composite”. The state of “composite” has many parameters, for examples, mixing ratio, tap density, thickness, and so on. In order to understand the electrochemical characteristics of an active material, the microelectrode technique is very important. Under microscope observation, the microelectrode is contacted to one active material particle by using micromanipulator. Then, we can evaluate the electrochemical characteristics of one particle. In this presentation, we will introduce the results of “single particle measurement” for Si, LiCoO2, LiNi0.5Mn1.5O4, and so on.In addition, microelectrode technique is also useful for the study of Li metal electrode. Li metal electrode is suffered from dendrite growth during charging, and dead lithium formation during discharging. These phenomenon are mainly induced non-uniformity of the current distribution. In addition to that, SEI (solid electrolyte interphase) should play an important role for the morphological variation of the electrodeposited Li metal. Many researches were conducted based on the surface chemistry in order to reveal the relationship between the nature of SEI layer and the morphology of electrodeposited Li metal. However, the localization of the electrodeposition sites is an obstacle for the quantitative analysis in order to discuss the dendrite initiation and growth. In our study, microelectrode was utilized to observe the morphological variation of the electrodeposited Li metal. Constant current electrodeposition was conducted to observe the electrodeposited Li metal. After the electrodeposition, the microelectrode was transferred to FE-SEM or TEM with transfer vessel without air exposure. Ex-situ SEM and TEM observation was done to discuss the electrolyte effects to the morphology of electrodeposited Li metal. We also would like to introduce the typical results of the morphological variation and SEI nature of the electrodeposited Li metal. Figure 1

New Antiarrhythmic Agent to Stabilize Functional Activity of Rat Heart Sinus Node Cardiomyocytes

Introduction: The aim of this study was to explore the antiarrhythmic activity of the new antiarrhythmic drug, succinic acid ester of 5-hydroxyadamantane-2-one (ADK-1110) and its effect on the functional activity of rat heart sinus node.
 Materials and methods: Experiments were performed on 80 non-linear white awake male rats weighing 200 g, using calcium chloride and aconitine arrhythmia models. The ECG was recorded from all the animals in the II standard lead before the start of the experiment. The effect of ADK-1110 on the electrical activity characteristics of rat heart sinus node pacemakers in vitro was studied on 26 outbred Wistar rats of both sexes with a body weight of 160 to 200 g, using the microelectrode technique.
 Results and discussion: The compound significantly exceeds the known reference drugs in terms of the antiarrhythmic in­dex. The agent also surpasses our previously proposed adamantane derivative ADK-1100 on calcium chloride model and is not inferior to the aconitine one. The electrophysiological analysis of the sinus node pacemaker cardiomyocytes character­istics in vitro under the influence of ADK-1110 revealed that the compound expands the area occupied by true pacemakers.
 Discussion: The obtained data indicate the presence of properties of antiarrhythmics of classes I, III, and IV in ADK-1110. The indicated functional remodeling stabilizes the functional activity of the central part of the sinus node.
 Conclusion: ADK-1110 stabilizes the functional activity of the central part of the sinus node. ADK-1110 also has a cerebrovascular anti-ischemic property.

High fat diet induces change in mitochondria respiration, activation of K-ATP channel and action potential shortening in mice

Obesity is associated with an increased risk of atrial fibrillation (AF). This epidemiologic observation may not be only due to shared co-morbidities but also from direct impacts of metabolic disorders on myocardium. To examine the impact of high fat diet (HFD) induced obesity on electrical properties in mice atria. Eight weeks old C57Bl/6 J mice were subjected to 4 months of HFD (60% fat) or normal diet (ND, 4% fat). Rapid burst atrial pacing were delivered using a trans-esophageal probe to induced AF in anesthetized animals. Action potential (AP) were recorded in left atrium using glass microelectrode technique. Potassium currents were recorded in isolated atrial myocytes using whole cell or perforated patch-clamp configurations. Mitochondrial respiration was studied in saponin-permeabilized atrial muscle fibers using a Clarke electrode. HFD mice showed higher atrial vulnerability to AF as indicated by longer AF episodes. APs were shorter in HFD versus ND mice (AP duration measured at 90% of repolarization: 49.3 ± 1.6 msec in HFD vs. 56.7 ± 2.3 msec in ND, P < 0.01). Glibenclamide, a KATP channel blocker, reversed AP shortening whereas cromakalim, a KATP channel activator, had no effect. Only in perforated patch-clamp configuration, without intracellular dialysis, KATP component of potassium current was enhanced in HFD mice (at +70 mV: 0.41 ± 0.12 pA/pF in HFD vs. 0.13 ± 0.08 pA/pF in ND, P < 0.05). There was no change in mitochondria respiration capacity between ND and HFD, however the ability of palmitoyl-CoA to support mitochondrial respiration was higher in HFD (25.99 ± 4.11% vs. 46.9 ± 3.96% in ND, P = 0.001). In addition, HADHA activity was enhanced in HFD mice. Obesity in mice is associated with atrial AP shortening which appears to result from increased activity of KATP-regulated currents and be associated with a metabolic shift. Shortening of AP duration could contribute to higher vulnerability to AF during obesity.

TASK-1 channel blockade by AVE1231 increases vasocontractile responses and BP in 1- to 2-week-old but not adult rats.

Background and PurposeThe vasomotor role of K2P potassium channels during early postnatal development has never been investigated. We tested the hypothesis that TASK‐1 channel (K2P family member) contribution to arterial vascular tone and BP is higher in the early postnatal period than in adulthood.Experimental ApproachWe studied 10‐ to 15‐day‐old (“young”) and 2‐ to 3‐month‐old (“adult”) male rats performing digital PCR (dPCR) (using endothelium‐intact saphenous arteries), isometric myography, sharp microelectrode technique, quantitative PCR (qPCR) and Western blotting (using endothelium‐denuded saphenous arteries), and arterial pressure measurements under urethane anaesthesia.Key ResultsWe found mRNA of Kcnk1–Kcnk7, Kcnk12, and Kcnk13 genes to be expressed in rat saphenous artery, and Kcnk3 (TASK‐1) and Kcnk6 (TWIK‐2) were most abundant in both age groups. The TASK‐1 channel blocker AVE1231 (1 μmol·L−1) prominently depolarized arterial smooth muscle and increased basal tone level and contractile responses to methoxamine of arteries from young rats but had almost no effect in adult rats. The level of TASK‐1 mRNA and protein expression was higher in arteries from young compared with adult rats. Importantly, intravenous administration of AVE1231 (4 mg·kg−1) had no effect on mean arterial pressure in adult rats but prominently raised it in young rats.Conclusion and ImplicationsWe showed that TASK‐1 channels are important for negative feedback regulation of vasocontraction in young but not adult rats. The influence of TASK‐1 channels most likely contributes to low BP level at perinatal age.

Cardiac electrophysiological effects of ibuprofen in dog and rabbit ventricular preparations: possible implication to enhanced proarrhythmic risk.

Ibuprofen is a widely used nonsteroidal anti-inflammatory drug, which has recently been associated with increased cardiovascular risk, but its electrophysiological effects have not yet been properly studied in isolated cardiac preparations. We studied the effects of ibuprofen on action potential characteristics and several transmembrane ionic currents using the conventional microelectrode technique and the whole-cell configuration of the patch-clamp technique on cardiac preparations and enzymatically isolated ventricular myocytes. In dog (200 µM; n= 6) and rabbit (100 µM; n= 7) papillary muscles, ibuprofen moderately but significantly prolonged repolarization at 1Hz stimulation frequency. In dog Purkinje fibers, repolarization was abbreviated and maximal rate of depolarization was depressed in a frequency-dependent manner. Levofloxacin (40 µM) alone did not alter repolarization, but augmented the ibuprofen-evoked repolarization lengthening in rabbit preparations (n= 7). In dog myocytes, ibuprofen (250 µM) did not significantly influence IK1, but decreased the amplitude of Ito and IKr potassium currents by 28.2% (60mV) and 15.2% (20mV), respectively. Ibuprofen also depressed INaL and ICa currents by 19.9% and 16.4%, respectively. We conclude that ibuprofen seems to be free from effects on action potential parameters at lower concentrations. However, at higher concentrations it may alter repolarization reserve, contributing to the observed proarrhythmic risk in patients.

Complex Arrhythmia Syndrome in a Knock-In Mouse Model Carrier of the N98S Calm1 Mutation.

Calmodulin mutations are associated with arrhythmia syndromes in humans. Exome sequencing previously identified a de novo mutation in CALM1 resulting in a p.N98S substitution in a patient with sinus bradycardia and stress-induced bidirectional ventricular ectopy. The objectives of the present study were to determine if mice carrying the N98S mutation knocked into Calm1 replicate the human arrhythmia phenotype and to examine arrhythmia mechanisms. Mouse lines heterozygous for the Calm1N98S allele (Calm1N98S/+) were generated using CRISPR/Cas9 technology. Adult mutant mice and their wildtype littermates (Calm1+/+) underwent electrocardiographic monitoring. Ventricular de- and repolarization was assessed in isolated hearts using optical voltage mapping. Action potentials and whole-cell currents and [Ca2+]i, as well, were measured in single ventricular myocytes using the patch-clamp technique and fluorescence microscopy, respectively. The microelectrode technique was used for in situ membrane voltage monitoring of ventricular conduction fibers. Two biologically independent knock-in mouse lines heterozygous for the Calm1N98S allele were generated. Calm1N98S/+ mice of either sex and line exhibited sinus bradycardia, QTc interval prolongation, and catecholaminergic bidirectional ventricular tachycardia. Male mutant mice also showed QRS widening. Pharmacological blockade and activation of β-adrenergic receptors rescued and exacerbated, respectively, the long-QT phenotype of Calm1N98S/+ mice. Optical and electric assessment of membrane potential in isolated hearts and single left ventricular myocytes, respectively, revealed β-adrenergically induced delay of repolarization. β-Adrenergic stimulation increased peak density, slowed inactivation, and left-shifted the activation curve of ICa.L significantly more in Calm1N98S/+ versus Calm1+/+ ventricular myocytes, increasing late ICa.L in the former. Rapidly paced Calm1N98S/+ ventricular myocytes showed increased propensity to delayed afterdepolarization-induced triggered activity, whereas in situ His-Purkinje fibers exhibited increased susceptibility for pause-dependent early afterdepolarizations. Epicardial mapping of Calm1N98S/+ hearts showed that both reentry and focal mechanisms contribute to arrhythmogenesis. Heterozygosity for the Calm1N98S mutation is causative of an arrhythmia syndrome characterized by sinus bradycardia, QRS widening, adrenergically mediated QTc interval prolongation, and bidirectional ventricular tachycardia. β-Adrenergically induced ICa.L dysregulation contributes to the long-QT phenotype. Pause-dependent early afterdepolarizations and tachycardia-induced delayed afterdepolarizations originating in the His-Purkinje network and ventricular myocytes, respectively, constitute potential sources of arrhythmia in Calm1N98S/+ hearts.

Class III Antiarrhythmic Effects of Dofetilide in Rabbit Atrial Myocardium.

BACKGROUND: Dofetilide is a new class III antiarrhythmic agent with demonstrated efficacy in ventricular and atrial tachyarrhythmias. We investigated its class III actions and their modulation by stimulation rate in rabbit atrial myocardium. METHODS AND RESULTS: Standard microelectrode techniques were used to record action potentials from rabbit atrial tissue at varying stimulation rates. Dofetilide produced a dose-dependent prolongation of action potential duration at concentrations from 1 nM to 1 µM at an interstimulus interval of 1000 ms. Action potential duration at 90% repolarization (action potential duration) was prolonged from 116 +/- 11.7 ms in control solutions to 13.9 ms at 1 nM dofetilide and 186 +/- 49.3 ms at 1 µM dofetilide (P <.05 for 1 nM vs control; P <.01 for 1 µM vs control). Reduction of interstimulus interval to 500 ms has no significant effect on action potential duration prolongation by dofetilide (P <.05 for 1 nM vs control; P <.01 for 1 µM vs control). Reduction of interstimulus interval to 500 ms had no significant effect on action potential duration prolongation by dofetilide. At faster rates than this, and particularly at an interstimulus interval less than 330 ms, a marked "reverse rate dependence" of the class III effect was observed. Specifically, the high therapeutic concentration of 10 nM showed no effect on action potential duration at interstimulus interval of 250 ms or 200 ms, and even at a concentration of 30 nM, the small class III effect was no longer statistically significant at these rates. CONCLUSIONS: Dofetilide prolongs action potential duration in rabbit atrial myocardium, but this effect is significantly attenuated at stimulation rates above 2 Hz.

Different effects of amiodarone and dofetilide on the dispersion of repolarization between well-coupled ventricular and Purkinje fibers1.

Increased transmural dispersion of repolarization is an established contributing factor to ventricular tachyarrhythmias. In this study, we evaluated the effect of chronic amiodarone treatment and acute administration of dofetilide in canine cardiac preparations containing electrotonically coupled Purkinje fibers (PFs) and ventricular muscle (VM) and compared the effects to those in uncoupled PF and VM preparations using the conventional microelectrode technique. Dispersion between PFs and VM was inferred from the difference in the respective action potential durations (APDs). In coupled preparations, amiodarone decreased the difference in APDs between PFs and VM, thus decreasing dispersion. In the same preparations, dofetilide increased the dispersion by causing a more pronounced prolongation in PFs. This prolongation was even more emphasized in uncoupled PF preparations, while the effect in VM was the same. In uncoupled preparations, amiodarone elicited no change on the difference in APDs. In conclusion, amiodarone decreased the dispersion between PFs and VM, while dofetilide increased it. The measured difference in APD between cardiac regions may be the affected by electrotonic coupling; thus, studying PFs and VM separately may lead to an over- or underestimation of dispersion.

Aqueous Fraction from Hibiscus sabdariffa Relaxes Mesenteric Arteries of Normotensive and Hypertensive Rats through Calcium Current Reduction and Possibly Potassium Channels Modulation.

Background/Objectives: Hibiscus sabdariffa L. (H. sabdariffa (HS)) extract has a vascular relaxant effect on isolated rat thoracic aorta, but data on small resistance arteries, which play an important role on the development of hypertension, are still missing. The purposes of this study were (1) to assess the effect on isolated mesenteric arteries (MA) from normotensive (Wistar and Wistar-Kyoto (WKY)) and spontaneous hypertensive rats (SHR); (2) to elucidate the mechanism(s) of action underling the relaxant effect in light of bioactive components. Methods: Vascular effects of HS aqueous fraction (AF) on isolated MA rings, as well as its mechanisms of action, were assessed using the contractility and intracellular microelectrode technique. The patch clamp technique was used to evaluate the effect of HS AF on the L-type calcium current. Extraction and enrichment of AF were carried out using liquid–liquid extraction, and the yield was analyzed using HPLC. Results: The HS AF induced a concentration-dependent relaxant effect on MA rings of SHR (EC50 = 0.83 ± 0.08 mg/mL), WKY (EC50 = 0.46 ± 0.04 mg/mL), and Wistar rats (EC50 = 0.44 ± 0.08 mg/mL) pre-contracted with phenylephrine (10 µM). In Wistar rats, the HS AF maximum relaxant effect was not modified after endothelium removal or when a guanylate cyclase inhibitor (ODQ, 10 µM) and a selective β2-adrenergic receptor antagonist (ICI-118551, 1 µM) were incubated with the preparation. Otherwise, it was reduced by 34.57 ± 10.66% when vascular rings were pre-contracted with an 80 mM [K+] solution (p < 0.001), which suggests an effect on ionic channels. HS AF 2 mg/mL significantly decreased the peak of the L-type calcium current observed in cardiac myocytes by 24.4%. Moreover, though the vasorelaxant effect of HS, AF was reduced by 27% when the nonselective potassium channels blocker (tetraethylammonium (TEA) 20 mM) was added to the bath (p < 0.01). The extract did not induce a membrane hyperpolarization of smooth muscle cells, which might suggest an absence of a direct effect on background potassium current. Conclusion: These results highlight that the antihypertensive effect of HS probably involves a vasorelaxant effect on small resistance arteries, which is endothelium independent. L-type calcium current reduction contributes to this effect. The results could also provide a link between the vasorelaxant effect and the bioactive compounds, especially anthocyanins.

Ammonia exposure impairs lateral-line hair cells and mechanotransduction in zebrafish embryos

Ammonia (including NH3 and NH4+) is a major pollutant of freshwater environments. However, the toxic effects of ammonia on the early stages of fish are not fully understood, and little is known about the effects on the sensory system. In this study, we hypothesized that ammonia exposure can cause adverse effects on embryonic development and impair the lateral line system of fish. Zebrafish embryos were exposed to high-ammonia water (10, 15, 20, 25, and 30 mM NH4Cl; pH 7.0) for 96 h (0–96 h post-fertilization). The body length, heart rate, and otic vesicle size had significantly decreased with ≥15 mM NH4Cl, while the number and function of lateral-line hair cells had decreased with ≥10 mM NH4Cl. The mechanoelectrical transduction (MET) channel-mediated Ca2+ influx was measured with a scanning ion-selective microelectrode technique to reveal the function of hair cells. We found that NH4+ (≥5 mM NH4Cl) entered hair cells and suppressed the Ca2+ influx of hair cells. Neomycin and La3+ (MET channel blockers) suppressed NH4+ influx, suggesting that NH4+ enters hair cells via MET channels in hair bundles. In conclusion, this study showed that ammonia exposure (≥10 mM NH4Cl) can cause adverse effects in zebrafish embryos, and lateral-line hair cells are sensitive to ammonia exposure.

Quantifying Decay Rates of Electrochemically Active Species Using Microelectrode Voltammetry

The availability, abundance, and energy density of fossil resources have driven progress over the last century leading to dramatic improvements in quality of life worldwide. However, to avert catastrophic climate change, there is an increasingly urgent need to reduce carbon emissions without stifling economic growth. Deep decarbonization necessitates mass deployment of renewable technologies, such as wind and solar photovoltaic, to displace existing carbon-intensive electricity generation. Though increasingly inexpensive, the inherent difficulties in converting the intermittent output of renewable installations into reliable, dispatchable power sources represents an important constraint and motivates research into storage technologies to buffer the intermittency without significantly increasing the cost of electricity.There are several large-scale energy storage technologies available but all suffer some drawbacks. Pumped hydro storage, currently responsible for 99% of the energy storage market in the U.S., has high energy efficiency and is inexpensive with long cycle and calendar life; however, there have been few new installations in the U.S. due largely to the difficulty of permitting new sites, financing large projects, and meeting geographic requirements1,2. Redox flow batteries (RFBs) are an electrochemical technology that holds promise for long duration energy storage due to their location independence, lower capital cost, decoupled energy and power specifications, and inherent safety. The current state of the art RFBs employ vanadium as the active species which is relatively expensive. As system level costs decline, the cost of RFBs will approach materials cost and so finding less expensive materials if critical to reducing RFB price. Some redox active species used to store electricity in RFBs undergo decomposition due to residing outside the thermodynamic solvent stability window, optical sensitivity, or air sensitivity. These decay pathways consume active materials and reduce the lifetime of the RFB. Determining the kinetic parameters of this decomposition and quantifying the impact on system lifetime is the task we address here.Here, we demonstrate the utility of microelectrodes for quantifying rapid decay in electrochemical systems containing soluble redox active components. By holding a sufficiently reducing or oxidizing potential on a microelectrode, as compared to the equilibrium potential of the redox couple of interest, limiting currents can be continuously monitored without significantly altering the state-of-charge of the bulk solution. From this current, a concentration can be extracted and its time-dependent evolution can be fit to a general rate equation. As a model reaction, we evaluate the decay of permanganate, which is under consideration as a positive electrolyte material in alkaline aqueous RFBs3. Preliminary studies have shown permanganate auto reduces to manganate and oxygen, introducing a potential flammability hazard and decreasing the lifetime of RFBs4–6. A better understanding of the factors that influence this decay process will inform mitigation strategies. We find that the decay of permanganate is strongly dependent on supporting electrolyte pH. The decay order was found to approximate a second order with the rate constant near 40 M-1 min-1 in the least stable supporting salt concentrations and approaches zero in the most stable conditions. These numerically fit parameters are in close agreement with observed decomposition times and agree with parameters calculated using UV-vis spectroscopy. The talk will include development of the microelectrode technique, benchmarking with model compounds and UV-vis spectroscopy, and, finally, demonstration on a rapidly decaying model species, permanganate. We anticipate that the technique developed here can be applied to other systems experiencing similarly rapid decay that frustrates conventional methodologies.

Electrical Restitution and Its Modifications by Antiarrhythmic Drugs in Undiseased Human Ventricular Muscle.

IntroductionRe-entry is a basic mechanism of ventricular fibrillation, which can be elicited by extrasystolic activity, but the timing of an extrasystole can be critical. The action potential duration (APD) of an extrasystole depends on the proximity of the preceding beat, and the relation between its timing and its APD is called electrical restitution. The aim of the present work was to study and compare the effect of several antiarrhythmic drugs on restitution in preparations from undiseased human ventricular muscle, and other mammalian species.MethodsAction potentials were recorded in preparations obtained from rat, guinea pig, rabbit, and dog hearts; and from undiseased human donor hearts using the conventional microelectrode technique. Preparations were stimulated with different basic cycle lengths (BCLs) ranging from 300 to 5,000 ms. To study restitution, single test pulses were applied at every 20th beat while the preparation was driven at 1,000 ms BCL.ResultsMarked differences were found between the animal and human preparations regarding restitution and steady-state frequency dependent curves. In human ventricular muscle, restitution kinetics were slower in preparations with large phase 1 repolarization with shorter APDs at 1000 ms BCL compared to preparations with small phase 1. Preparations having APD longer than 300 ms at 1000 ms BCL had slower restitution kinetics than those having APD shorter than 250 ms. The selective IKr inhibitors E-4031 and sotalol increased overall APD and slowed the restitution kinetics, while IKs inhibition did not influence APD and electrical restitution. Mexiletine and nisoldipine shortened APD, but only mexiletine slowed restitution kinetics.DiscussionFrequency dependent APD changes, including electrical restitution, were partly determined by the APD at the BCL. Small phase 1 associated with slower restitution suggests a role of Ito in restitution. APD prolonging drugs slowed restitution, while mexiletine, a known inhibitor of INa, shortened basic APD but also slowed restitution. These results indicate that although basic APD has an important role in restitution, other transmembrane currents, such as INa or Ito, can also affect restitution kinetics. This raises the possibility that ion channel modifier drugs slowing restitution kinetics may have antiarrhythmic properties by altering restitution.

BK channel openers NS1619 and NS11021 reverse hydrogen peroxide-induced membrane potential changes in skeletal muscle

Large conductance calcium-activated potassium (BK) channels play a crucial role in the repolarization and after-hyperpolarization phases of the cell membrane. The channel openers are also used in treatment of some diseases, including hypo/hyperkalemic periodic paralysis. However, little is known about the effects of BK channels and the channel activators on membrane potentials in skeletal muscle. In addition, the effects of reactive oxygen species (ROS) on BK channels in skeletal muscle are also unknown. Therefore, the aim of this study was to determine the effects of BK channel openers and ROS on membrane potentials in skeletal muscle fibers. For this purpose, resting membrane potentials and action potentials (AP) of frog gastrocnemius muscles were recorded in the presence of commonly used BK channel openers NS1619 and NS11021, H2O2 (a type of ROS), and both using intracellular microelectrode technique. The channel activators significantly and dose-dependently decreased amplitude and increased rise time of AP but did not impact repolarization. The presence of H2O2 plus NS1619 or NS11021 resulted in significant change because the channel openers completely reversed the deleterious effects of hydrogen peroxide on the repolarization phase of AP in skeletal muscle fibers. In the present study, the contributions of BK channel activation and the modulatory role of H2O2 on membrane potentials was demonstrated in skeletal muscle fibers, for the first time. Moreover, it should be noted that BK channel openers should be used in the treatment of reactive oxygen species-induced skeletal muscle diseases.

Effect of Carvacrol, TRP Channels Modulator, on Cardiac Electrical Activity.

Despite the wide application of carvacrol (CAR) in medicines, dietary supplements, and foods, there is still insufficient electrophysiological data on the mechanisms of action of CAR, particularly with regard to heart function. Therefore, in this study, we attempted to elucidate whether CAR, whose inhibitory effect on both cardiac and vascular TRPM7 and L-type Ca2+ currents has been demonstrated previously, could modify cardiac electrical activity. We used a combination of optical mapping and microelectrode techniques to track the action potentials (APs) and the spread of electrical activity in a Langendorff-perfused rabbit heart model during atrial/endo/epicardial pacing. Simultaneously, ECG recordings were acquired. Because human trials on CAR are still lacking, we tested the action of CAR on human ventricular preparations obtained from explanted hearts. Activation time (AT), AP duration (APD), and conduction velocity maps were constructed. We demonstrated that at a low concentration (10 μM) of CAR, only marginal changes in the AP parameters were observed. At higher concentrations (≥100 μM), a decrease in AP upstroke velocity (dV/dtmax), suggesting inhibition of Na+ current, and APD (at 50 and 90% repolarization) was detected; also slowing in the spread of electrical signals via the atrioventricular node was observed, suggesting impaired functioning of Ca2+ channels. In addition, a decrease in the T-wave amplitude was seen on the ECG, suggesting an impaired repolarization process. Nevertheless, those changes occurred without a significant impact on the resting membrane potential and were reversible. We suggest that CAR might play a role in modulating cardiac electrical activity at high concentrations.

Method of synaptic transmission hidden parameters evaluation based on inhibition analysis data

Nowadays neuroscience strongly demands application of the mathematical methods for description of many neurophysiological and neurochemical processes among which the synaptic transmission outstands. One of the main problems in synaptic transmission modelling is the lack of the accurate values of dynamic parameters of biomolecules and complexes taking part in this process. The goal of this study is to elaborate the method for evaluation of synaptic transmission parameters that cannot be measured directly (so-called hidden parameters) and apply its results for investigation of the main stages of synaptic transmission in neuronets of hippocampus. The method is based on the parametric identification of the synaptic transmission deterministic model, which includes equations for description of inhibitors action on the main biochemical participants. We used three inhibitors: cilnidipine, 1.2- bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM), 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). The parametric identification was performed by minimization of deviation of modeled field excitatory postsynaptic potential from those measured in rat hippocampus slices with microelectrode technique when inhibitors were applied. The results of the parametric identification of proposed model show that the model can adequately describe the generation of field excitatory postsynaptic potentials and their inhibition. The elaborated method afforded to evaluate the numerical meanings of eleven synaptic transmission hidden parameters. Using these parameters we have modelled the key synaptic transmission stages and got the time courses of the main biochemical participants: calcium ions in presynaptic bouton, SNARE complexes, synaptic vesicles in different states, glutamate in the synaptic cleft and open channels of AMPA receptor on the postsynaptic membrane. Thus, we propose method of hidden parameters evaluation that can be applied for different synaptic contacts in the brain of mammalians.

Competitive cation−π interactions between small cations and polycations with phenyl groups in poly(cation−π) hydrogels

Although cation−π interactions play a critical role in biological systems, experimental studies in aqueous environments are limited due to a lack of suitable systems and methods. The recent success in synthesizing water-soluble poly(cation−π) bearing adjacent cationic/aromatic residues provides excellent systems for studying cation−π interactions in aqueous environments. In this study, we investigated competitive cation−π interactions between small cations and macrocations with phenyl groups in hydrogels consisting of various poly(cation−π)s. By measuring the Donnan potential of the hydrogels equilibrated in NaCl solutions of different ionic strengths using the microelectrode technique, the binding ratios of small cations (Na+) to the phenyl residues of polymer networks were determined. It was found that when NaCl concentration was lower than the macrocation concentration, the activity coefficient of the counterions (Cl–) in the hydrogels was very high (~2), indicating that a large amount of excess Cl– was trapped in the hydrogels due to Na+ adsorption on the phenyl groups of the polymer chains via cation−π interactions. Further calculations showed that each phenyl group can adsorb a maximum of 1.5 Na+ despite the presence of adjacent macrocations. Additionally, we discuss the mechanism by which small cations compete with adjacent macrocations in poly(cation−π) hydrogels.

Comparison between hiPS-CM from RyR2-R420Q CPVT Patients and KI Mice Bearing the Same Mutation

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a genetic arrhythmia that manifests by syncope or sudden death in children and young adults under stress conditions without obvious cardiac structural abnormality. A CPVT mutation located on RyR2 N terminal portion has been identified in two Spanish families (RyR2R420Q). KI mice heterozygous for this mutation presented bradycardia and sino-atrial node dysfunction. Here we generated human induced pluripotent stem cell (hiPSC) from two brothers (one with mutation, the other without mutation as control) of this family and differentiated them into cardiomyocytes (hiPS-CM). In order to verify that the differentiated cells were well cardiomyocytes, we did immunofluorescence labelling for alpha-actinin and RyRs, and compared them with RyR2R420Q KI mice cardiomyocytes with superresolution microscopy. The calcium transient was studied by confocal microscopy as well as the action potential (AP) by micro-electrode technique. The AP duration was longer in RyR2R420Q cells. hiPS-CM are immature cardiomyocytes and contract spontaneously. The beating rate of CPVT hiPS-CM was slower than those of cells derived from the control person. We found all the cells without mutation could follow 1HZ of electrical stimulation while only 55.26% mutation carrying cells could. [Ca2+]i transient was slower both in basal conditions, and after beta-adrenergic stimulation with 100 nM isoproterenol in mutated group. Sarcoplasmic reticulum (SR) Ca2+ load was estimated by rapid caffeine (10mM) application. hiPS-CM from the RyR2R420Q carrier presented smaller SR Ca2+ load than those from the control person. Even if SR Ca2+ load was smaller in RyR2R420Q cells, they often presented proarrythmogenic behavior such as Ca2+ waves. The fact was further enhanced during beta-adrenergic stimulation, pointing to this model as a valuable tool to study the CPVT disease in human cells.

Cycling Performance and Kinetic Mechanism Analysis of a Li Metal Anode in Series-Concentrated Ether Electrolytes.

Li metal batteries are facing unprecedented opportunities because of the urgent demand for high-energy-density rechargeable batteries as well as enormous challenges due to their low Coulombic efficiency and notorious safety issues. Recently, high-concentration electrolytes have attracted much attention owing to their superior properties. However, Li metal plating is an exceedingly complicated process including several elementary steps; it is not comprehensive enough to uncover the mystery of concentrated electrolytes by studying the structure of electrolytes, the existence of anions, cations, and solvent molecules using only conventional means. Here, we first report the apparent cycling performance of Li metal anode in series-concentrated LiTFSI/DOL-DME electrolytes. It shows that the Li metal anode in 4 M LiTFSI/DOL-DME electrolyte can operate 180 cycles stably at 2 mA cm-2 with an average Coulombic efficiency of 98%, in which the Li plating layer is more compact and without dendrites. Subsequently, the kinetic parameters were obtained by the microelectrode technique. We found that appropriate mass transfer, interface, and surface step kinetic parameters (migration number, exchange current density, nucleation rate, and corrosion rate) and their good matching degree are favorable for the cycling of Li metal anodes. This work reveals the relationship between the elementary steps and the apparent cycling performance during the Li plating process under certain operating conditions; it is a major breakthrough in the study of high-concentration electrolytes and can provide a new perspective for future research.

Respiratory Au nucleation and microelectrode techniques reveal key features of bacterial conductive matrix

Key elements of Geobacter's extracellular electron transfer mechanism are characterized combining respiratory formed gold nanoparticles with spectro-electrochemical and microelectrode techniques.

Changes in Electrophysiological Features of Rats’ Working Atrial Myocardium after Its Lipotransfection with MicroRNAs miR-1-3p, miR-153-3p, or miR-133a-3p

MicroRNA is a small, single-stranded nucleotide sequence, which can regulate gene expression at the posttranscriptional level. To date, it is known that some microRNAs play an important role in physiology and pathophysiology of the cardio-vascular system. The effects of lipotransfection with microRNAs, such as miR-1-3p, miR-153-3p, or miR-133-3p, on the electrophysiological indices of the myocardium tissue were studied here for the first time. With the use of the standard microelectrode technique, action potentials (AP) in isolated perfused samples of the rat atrial tissue were recorded after their treatment with a transfection mixture of a liposome forming reagent and miR-1-3p, miR-153-3p, or miR-133-3p. It is demonstrated that the treatment of the myocardial tissue with a transfection agent results in the prolongation of the repolarization phase of AP. It was found that miR-1-3p and miR-153-3p did not affect the pattern of AP within 6 h after the treatment of tissue samples. However, miR133a-3p evoked a statistically significant increase in the AP duration under 90% repolarization. The duration was maximum 4 h after the transfection. Search and analysis of possible targets for miR133a-3p using bioinformatic methods were performed and it was assumed that this microRNA can interact with mRNA of some protein phosphatases. Suppression of protein phosphatases’ expression in cardiomyocytes may underlie the increased AP duration during the application of miR133a-3p found in the present study due to the effect on the proteins of calcium turnover.