Window Current Research Articles

The Effects of Amiodarone and N-Desethylamiodarone on Cardiac Voltage-Gated Sodium Channels

Amiodarone (AMD) is a widely used antiarrhythmic drug with high efficacy for treating atrial fibrillation and tachycardia. The pharmacologic profile of AMD is complex. Although AMD is classified as a class III antiarrhythmic drug, it possesses biophysical characteristics of class I, II, and IV agents. Despite its adverse side-effects, AMD remains the most commonly prescribed antiarrhythmic drug. AMD was described to prolong the QT interval and can lead to torsades de pointes (TdP). The metabolism of AMD takes place using CYP3A4 and CYP2C8. Full metabolism of AMD produces 22 phase I and 11 phase II metabolites, the most prominent of which is produced through an N-deethylation reaction by CYP3A4, giving rise to pharmacologically active N-Desethylamiodarone (DES). We sought to study the effects of AMD on peak and late sodium currents (INaP and INaL, and determine whether these effects change as AMD metabolizes into DES. We hypothesized AMD and DES blocks both INaP and INaL with similar profiles due to their structural similarities. As such, given the inherent small amounts of INa in Nav1.5, we used the Long QT-3-causing mutation, ΔKPQ, to better detect any drug-mediated decrease in INa. We found neither AMD nor DES affects conductance in WT or ΔKPQ channels; however, both drugs hyperpolarize steady-state fast-inactivation, with larger shifts in ΔKPQ than WT-Nav1.5, in a compound- and concentration-specific manner. INaP is significantly blocked by both compounds in ΔKPQ compared to minimal block in WT-Nav1.5. AMD increases window currents and INaL in WT Nav1.5, and decreases these in ΔKPQ, whereas DES increases both window and INaL in both WT and ΔKPQ. We conclude the proarrhythmic effects of AMD may be due to both its effects, and the effects of at least one of its metabolites, on sodium channels.

Mutations in the Voltage Sensors of Domains I and II of Nav1.5 that are Associated with Arrhythmias and Dilated Cardiomyopathy Generate Gating Pore Currents.

Voltage gated sodium channels (Nav) are transmembrane proteins responsible for action potential initiation. Mutations mainly located in the voltage sensor domain (VSD) of Nav1.5, the cardiac sodium channel, have been associated with the development of arrhythmias combined with dilated cardiomyopathy. Gating pore currents have been observed with three unrelated mutations associated with similar clinical phenotypes. However, gating pores have never been associated with mutations outside the first domain of Nav1.5. The aim of this study was to explore the possibility that gating pore currents might be caused by the Nav1.5 R225P and R814W mutations (R3, S4 in DI and DII, respectively), which are associated with rhythm disturbances and dilated cardiomyopathy. Nav1.5 WT and mutant channels were transiently expressed in tsA201 cells. The biophysical properties of the alpha pore currents and the presence of gating pore currents were investigated using the patch-clamp technique. We confirmed the previously reported gain of function of the alpha pores of the mutant channels, which mainly consisted of increased window currents mostly caused by shifts in the voltage dependence of activation. We also observed gating pore currents associated with the R225P and R814W mutations. This novel permeation pathway was open under depolarized conditions and remained temporarily open at hyperpolarized potentials after depolarization periods. Gating pore currents could represent a molecular basis for the development of uncommon electrical abnormalities and changes in cardiac morphology. We propose that this biophysical defect be routinely evaluated in the case of Nav1.5 mutations on the VSD.

Effects of the β1 auxiliary subunit on modification of Rat Nav1.6 sodium channels expressed in HEK293 cells by the pyrethroid insecticides tefluthrin and deltamethrin

We expressed rat Nav1.6 sodium channels with or without the rat β1 subunit in human embryonic kidney (HEK293) cells and evaluated the effects of the pyrethroid insecticides tefluthrin and deltamethrin on whole-cell sodium currents. In assays with the Nav1.6 α subunit alone, both pyrethroids prolonged channel inactivation and deactivation and shifted the voltage dependence of channel activation and steady-state inactivation toward hyperpolarization. Maximal shifts in activation were ~18mV for tefluthrin and ~24mV for deltamethrin. These compounds also caused hyperpolarizing shifts of ~10–14mV in the voltage dependence of steady-state inactivation and increased in the fraction of sodium current that was resistant to inactivation. The effects of pyrethroids on the voltage-dependent gating greatly increased the size of sodium window currents compared to unmodified channels; modified channels exhibited increased probability of spontaneous opening at membrane potentials more negative than the normal threshold for channel activation and incomplete channel inactivation. Coexpression of Nav1.6 with the β1 subunit had no effect on the kinetic behavior of pyrethroid-modified channels but had divergent effects on the voltage-dependent gating of tefluthrin- or deltamethrin-modified channels, increasing the size of tefluthrin-induced window currents but decreasing the size of corresponding deltamethrin-induced currents. Unexpectedly, the β1 subunit did not confer sensitivity to use-dependent channel modification by either tefluthrin or deltamethrin. We conclude from these results that functional reconstitution of channels in vitro requires careful attention to the subunit composition of channel complexes to ensure that channels in vitro are faithful functional and pharmacological models of channels in neurons.

Antiarrhythmic Action of Flecainide in Polymorphic Ventricular Arrhythmias Caused by a Gain-of-Function Mutation in the Nav 1.5 Sodium Channel.

The cardiac sodium channel Nav 1.5, encoded by the gene SCN5A, is associated with a wide spectrum of hereditary arrhythmias. The gain-of-function mutation p.I141V in SCN5A was identified in a large multigenerational family with exercise-induced polymorphic ventricular arrhythmias. The purpose of this study was to evaluate the molecular and clinical effects of flecainide administration on patients with this syndrome. Eleven p.I141V carriers who exhibited frequent multiformic premature ventricular complexes (PVCs) during exercise were subjected to exercise stress tests, both before and after intravenous infusion of 2 mg/kg flecainide. The in vitro effects of flecainide were evaluated using the patch-clamp technique with HEK293 cells expressing the Nav 1.5 channel. The flecainide treatment significantly reduced the frequency of PVCs during and after exercise. Next, the sensitivity of the p.I141V mutant channel to flecainide was compared to that of the wild type channel. Perfusion of flecainide inhibited the peak and window currents in both groups. The clinical investigations of the affected patients, as well as the molecular and pharmacological characterization of the SCN5A p.I141V mutation, provide new evidence supporting the association of this mutation with exercise-induced polymorphic ventricular arrhythmias. These data also demonstrate that flecainide may serve as an effective treatment for the defect in Nav 1.5 that leads to an increased sodium window current.

Temperature-dependence of L-type Ca(2+) current in ventricular cardiomyocytes of the Alaska blackfish (Dallia pectoralis).

To lend insight into the overwintering strategy of the Alaska blackfish (Dallia pectoralis), we acclimated fish to 15 or 5 °C and then utilized whole-cell patch clamp to characterize the effects of thermal acclimation and acute temperature change on the density and kinetics of ventricular L-type Ca(2+) current (I Ca). Peak I Ca density at 5 °C (-1.1 ± 0.1 pA pF(-1)) was 1/8th that at 15 °C (-8.8 ± 0.6 pA pF(-1)). However, alterations of the Ca(2+)- and voltage-dependent inactivation properties of L-type Ca(2+) channels partially compensated against the decrease. The time constant tau (τ) for the kinetics of inactivation of I Ca was ~4.5 times greater at 5 °C than at 15 °C, and the voltage for half-maximal inactivation was shifted from -23.3 ± 1.0 mV at 15 °C to -19.8 ± 1.2 mV at 5 °C. These modifications increase the open probability of the channel and culminate in an approximate doubling of the L-type Ca(2+) window current, which contributes to approximately 15% of the maximal Ca(2+) conductance at 5 °C. Consequently, the charge density of I Ca (Q Ca) and the total Ca(2+) transferred through the L-type Ca(2+) channels (Δ[Ca(2+)]) were not as severely reduced at 5 °C as compared to peak I Ca density. In combination, the results suggest that while the Alaska blackfish substantially down-regulates I Ca with acclimation to low temperature, there is sufficient compensation in the kinetics of the L-type Ca(2+) channel to support the level of cardiac performance required for the fish to remain active throughout the winter.

The Role of Oxygen Vacancies on Switching Characteristics of TiO(x) Resistive Memories.

Using oxygen vacancy rich (VO-rich) TiO(x) dielectric with high work function Ni electrode, large resistance window of > 10x and narrow current distribution were realized in the Ni/VO-rich TiO(x)/TaN resistive random access memory (RRAM) device. It can be ascribed to the formation and rupture of conducting filaments by the percolation of VOs and Ti interstitials. Moreover, the effects of annealing treatment and top electrode on resistive switching properties were investigated. The device with VO-deficient TiO(x) after annealing reduces the defects and exhibits small window and low switching currents. The device with low work function Ti top electrode provides low barrier to increase reset currents and the randomly distributed filamentary paths forms near the Ti causes wide current distribution.

Diamond film deposited on Mo-Re alloy by hot filament chemical vapor deposition with periodic magnetic field

Molybdenum–rhenium (Mo/Re) alloys were investigated as substrates for thin-film, polycrystalline boron-doped diamond electrodes. Boron-doped semimetallic diamond was deposited on Mo-Re (42.5/57.5 wt. %) substrates by hot filament chemical vapor deposition method with a periodic magnetic field (PMF). Cyclic voltammograms showed the wide window and low baseline current of high-quality boron doped diamond electrodes. Overall, the Mo/Re alloys were suitable substrates for diamond growth. PMF may have a great practical application potential in diamond growth by chemical vapor deposition.

0417 : SCN5A+/ΔQKP mice present late sodium current associated with long QT syndrome, dilated cardiomyopathy and ranolazine-sensitive spontaneous ventricular arrhythmias

Deletion of QKP1507-1509 amino-acids in SCN5A gene product, the main cardiac Na+ channel Nav1.5, is associated with a large phenotypic spectrum of long QT syndrome (LQT3), dilated cardiomyopathy (DCM) and high incidence of youth sudden death. This mutation does not affect the peak Na+ current (INa) but rather increases the late/persistent Na+ current (INaL). In order to investigate the mechanisms implicated in the phenotype observed on the mutation carriers, a knock-in mouse model presenting the equivalent QKP1510-1512 mutation has been generated (Scn5a+/ΔQKP). Mouse ECGs were recorded weekly from the age of 3 weeks. Na+ current was recorded with the whole cell patch-clamp technique in ventricular myocytes isolated from 4-week-old mice. Histological analysis was performed in paraffin sections of hearts of 4-week-old mice. At the age of 3 weeks, mice were treated with acute administration of ranolazine (30mg/kg i.p.) or β- blocker propranolol (0.3-1-3mg/kg i.p.) to suppress arrhythmias. Scn5a+/ΔQKP mice in sinus rhythm displayed a prolonged QT interval (QTc = 64±2ms vs. 42±1ms in controls) with a high incidence of spontaneous ventricular extrasystoles and/or non-sustained tachycardia, leading to early mortality. Structural analysis showed right ventricular DCM. Voltage-dependent activation and inactivation properties were significantly altered in Scn5a+/ΔQKP mice, leading to an increase in the arrhythmogenic Na+ window current. INaL was enhanced by more than 2-fold in myocytes from Scn5a+/ΔQKP mice compared to control mice. At 3 weeks, ranolazine significantly decreased QTc and suppressed arrhythmias whereas propranolol alone had no beneficial effects. Scn5a+/ΔQKP mice recapitulate a large part of the diverse clinical phenotype of patients carrying the equivalent mutation. Our results show that the mutation induces a late Na+ current involved in the arrhythmogenic process. Ranolazine, rather than β-blockers, could be a good candidate for pharmacological treatment.

What Currents Underlie Pulmonary Vein Automaticity?

What Currents Underlie Pulmonary Vein Automaticity?

Mutation Specific Drug Response and Cardiac Risk in Long QT Type 3

Long QT type 3 (LQT3) is caused by mutations that cause an increase in the cardiac sodium current during late phases of the cardiac action potential. For a number of LQT3 mutants this is caused by a failure to inactivate fully, and a consequent increase in late sodium current. For several mutations, shifts in voltage dependence of activation and inactivation cause increased sodium channel contribution to more depolarized voltages, an effect referred as increase in window current. The goal of this study was to perform a study in a large number of LQT3 associated mutations and compare the biophysical effect of the mutation to cardiac risk in LQT3 patients and response to treatment. We measured the function of eight common mutations associated with LQT3 with different mechanism underlying channel dysfunction. We compared the functional effects of the channel with the clinical course of these patients and observed that for the two mutations tested with increased sustained current but without increase in current availability (window current), D1784K and D1790G, the patients had significant lower risk of cardiac events, suggesting an increase in current availability may be associated with increased risk for these patients. In addition, we measured mutation specific effects of ranolazine for these mutants. For all mutants tested, ranolazine preferentially blocked late sodium currents. Ranolazine shifts steady-state availability of the inactivation was dependent on the specific mutant tested. Our results suggest that ranolazine may have a mutation dependent effect. Mutations dysfunction may affect drug binding and drug actions in the channel and may alter treatment effectiveness in patients.

A TTX-sensitive resting Na+ permeability contributes to the catecholaminergic automatic activity in rat pulmonary vein.

Ectopic activity arising from pulmonary veins (PV) plays a prominent role in the onset of atrial fibrillation in humans. Rat PV cardiac muscle cells have a lower resting membrane potential (RMP) than the left atria (LA) and presents in the presence of norepinephrine an automatic activity, which occurs in bursts. This study investigated the role of Na channels upon the RMP and the catecholaminergic automatic activity (CAA) in PV cardiac muscle. RMP and CAA experiments were performed in male Wistar rat PV. Whole-cell INa was recorded in isolated PV and LA cardiomyocytes. PV has a higher tetrodotoxin (TTX)-sensitive basal Na(+) permeability than the LA, due to a ∼ 5 mV more negative Na window current in the former tissue. TTX, quinidine, and ranolazine (1 to 10 μM each) decreased CAA incidence and arrhythmias by increasing burst intervals because of a reduction of the slope of slow depolarization between bursts. TTX and ranolazine also reduced burst duration. At 1 Hz, 10 μM quinidine, ranolazine, and TTX inhibited peak INa by 33%, 28%, and 98%, respectively. Each reduced the Na window current. There was no evidence for a TTX- or ranolazine-sensitive late Na current. Na channels confer a TTX-sensitive basal Na(+) permeability to rat PV cardiac muscle cells and contribute to the slope of slow depolarization between bursts of CAA. Na channel blockers act mostly via reduction of the Na window current. Ranolazine also has an anti-α1 adrenergic effect, which contributed to its antiarrhythmic effect.

High frequency stimulation of cardiac myocytes: a theoretical and computational study.

High-frequency stimulation (HFS) has recently been identified as a novel approach for terminating life-threatening cardiac arrhythmias. HFS elevates myocyte membrane potential and blocks electrical conduction for the duration of the stimulus. However, low amplitude HFS can induce rapidly firing action potentials, which may reinitiate an arrhythmia. The cellular level mechanisms underlying HFS-induced electrical activity are not well understood. Using a multiscale method, we show that a minimal myocyte model qualitatively reproduces the influence of HFS on cardiac electrical activity. Theoretical analysis and simulations suggest that persistent activation and de-inactivation of ionic currents, in particular a fast inward window current, underlie HFS-induced action potentials and membrane potential elevation, providing hypotheses for future experiments. We derive analytical expressions to describe how HFS modifies ionic current amplitude and gating dynamics. We show how fast inward current parameters influence the parameter regimes for HFS-induced electrical activity, demonstrating how the efficacy of HFS as a therapy for terminating arrhythmias may depend on the presence of pathological conditions or pharmacological treatments. Finally, we demonstrate that HFS terminates cardiac arrhythmias in a one-dimensional ring of cardiac tissue. In this study, we demonstrate a novel approach to characterize the influence of HFS on ionic current gating dynamics, provide new insight into HFS of the myocardium, and suggest mechanisms underlying HFS-induced electrical activity.

Microfabrication, characterization and in vivo MRI compatibility of diamond microelectrodes array for neural interfacing.

Neural interfacing still requires highly stable and biocompatible materials, in particular for in vivo applications. Indeed, most of the currently used materials are degraded and/or encapsulated by the proximal tissue leading to a loss of efficiency. Here, we considered boron doped diamond microelectrodes to address this issue and we evaluated the performances of a diamond microelectrode array. We described the microfabrication process of the device and discuss its functionalities. We characterized its electrochemical performances by cyclic voltammetry and impedance spectroscopy in saline buffer and observed the typical diamond electrode electrochemical properties, wide potential window and low background current, allowing efficient electrochemical detection. The charge storage capacitance and the modulus of the electrochemical impedance were found to remain in the same range as platinum electrodes used for standard commercial devices. Finally we observed a reduced Magnetic Resonance Imaging artifact when the device was implanted on a rat cortex, suggesting that boron doped-diamond is a very promising electrode material allowing functional imaging.

Novel Timothy syndrome mutation leading to increase in CACNA1C window current

Timothy syndrome (TS) is a rare multisystem genetic disorder characterized by a myriad of abnormalities, including QT prolongation, syndactyly, and neurologic symptoms. The predominant genetic causes are recurrent de novo missense mutations in exon 8/8A of the CACNA1C-encoded L-type calcium channel; however, some cases remain genetically elusive. The purpose of this study was to identify the genetic cause of TS in a patient who did not harbor a CACNA1C mutation in exon 8/A, and was negative for all other plausible genetic substrates. Diagnostic exome sequencing was used to identify the genetic substrate responsible for our case of TS. The identified mutation was characterized using whole-cell patch-clamp technique, and the results of these analyses were modeled using a modified Luo-Rudy dynamic model to determine the effects on the cardiac action potential. Whole exome sequencing revealed a novel CACNA1C mutation, p.Ile1166Thr, in a young male with diagnosed TS. Functional electrophysiologic analysis identified a novel mechanism of TS-mediated disease, with an overall loss of current density and a gain-of-function shift in activation, leading to an increased window current. Modeling studies of this variant predicted prolongation of the action potential as well as the development of spontaneous early afterdepolarizations. Through expanded whole exome sequencing, we identified a novel genetic substrate for TS, p.Ile1166Thr-CACNA1C. Electrophysiologic experiments combined with modeling studies have identified a novel TS mechanism through increased window current. Therefore, expanded genetic testing in cases of TS to the entire CACNA1C coding region, if initial targeted testing is negative, may be warranted.

Gain-of-function mutation of the SCN5A gene causes exercise-induced polymorphic ventricular arrhythmias.

Over the past 15 years, a myriad of mutations in genes encoding cardiac ion channels and ion channel interacting proteins have been linked to a long list of inherited atrial and ventricular arrhythmias. The purpose of this study was to identify the genetic and functional determinants underlying exercise-induced polymorphic ventricular arrhythmia present in a large multigenerational family. A large 4-generation family presenting with exercise-induced polymorphic ventricular arrhythmia, which was followed for 10 years, was clinically characterized. A novel SCN5A mutation was identified via whole exome sequencing and further functionally evaluated by patch-clamp studies using human embryonic kidney 293 cells. Of 37 living family members, a total of 13 individuals demonstrated ≥50 multiformic premature ventricular complexes or ventricular tachycardia upon exercise stress tests when sinus rate exceeded 99±17 beats per minute. Sudden cardiac arrest occurred in 1 individual during follow-up. Exome sequencing identified a novel missense mutation (p.I141V) in a highly conserved region of the SCN5A gene, encoding the Nav1.5 sodium channel protein that cosegregated with the arrhythmia phenotype. The mutation p.I141V shifted the activation curve toward more negative potentials and increased the window current, whereas action potential simulations suggested that it lowered the excitability threshold of cardiac cells. Gain-of-function of Nav1.5 may cause familial forms of exercise-induced polymorphic ventricular arrhythmias.

Mathematical analysis of depolarization block mediated by slow inactivation of fast sodium channels in midbrain dopamine neurons.

Dopamine neurons in freely moving rats often fire behaviorally relevant high-frequency bursts, but depolarization block limits the maximum steady firing rate of dopamine neurons in vitro to ∼10 Hz. Using a reduced model that faithfully reproduces the sodium current measured in these neurons, we show that adding an additional slow component of sodium channel inactivation, recently observed in these neurons, qualitatively changes in two different ways how the model enters into depolarization block. First, the slow time course of inactivation allows multiple spikes to be elicited during a strong depolarization prior to entry into depolarization block. Second, depolarization block occurs near or below the spike threshold, which ranges from -45 to -30 mV in vitro, because the additional slow component of inactivation negates the sodium window current. In the absence of the additional slow component of inactivation, this window current produces an N-shaped steady-state current-voltage (I-V) curve that prevents depolarization block in the experimentally observed voltage range near -40 mV. The time constant of recovery from slow inactivation during the interspike interval limits the maximum steady firing rate observed prior to entry into depolarization block. These qualitative features of the entry into depolarization block can be reversed experimentally by replacing the native sodium conductance with a virtual conductance lacking the slow component of inactivation. We show that the activation of NMDA and AMPA receptors can affect bursting and depolarization block in different ways, depending upon their relative contributions to depolarization versus to the total linear/nonlinear conductance.

NaV1.5 sodium channel window currents contribute to spontaneous firing in olfactory sensory neurons.

Olfactory sensory neurons (OSNs) fire spontaneously as well as in response to odor; both forms of firing are physiologically important. We studied voltage-gated Na(+) channels in OSNs to assess their role in spontaneous activity. Whole cell patch-clamp recordings from OSNs demonstrated both tetrodotoxin-sensitive and tetrodotoxin-resistant components of Na(+) current. RT-PCR showed mRNAs for five of the nine different Na(+) channel α-subunits in olfactory tissue; only one was tetrodotoxin resistant, the so-called cardiac subtype NaV1.5. Immunohistochemical analysis indicated that NaV1.5 is present in the apical knob of OSN dendrites but not in the axon. The NaV1.5 channels in OSNs exhibited two important features: 1) a half-inactivation potential near -100 mV, well below the resting potential, and 2) a window current centered near the resting potential. The negative half-inactivation potential renders most NaV1.5 channels in OSNs inactivated at the resting potential, while the window current indicates that the minor fraction of noninactivated NaV1.5 channels have a small probability of opening spontaneously at the resting potential. When the tetrodotoxin-sensitive Na(+) channels were blocked by nanomolar tetrodotoxin at the resting potential, spontaneous firing was suppressed as expected. Furthermore, selectively blocking NaV1.5 channels with Zn(2+) in the absence of tetrodotoxin also suppressed spontaneous firing, indicating that NaV1.5 channels are required for spontaneous activity despite resting inactivation. We propose that window currents produced by noninactivated NaV1.5 channels are one source of the generator potentials that trigger spontaneous firing, while the upstroke and propagation of action potentials in OSNs are borne by the tetrodotoxin-sensitive Na(+) channel subtypes.

0265: A novel SCN5A mutation associated with exercise-induced polymorphic ventricular arrhythmias resembling CPVT

Cardiac sodium channel is a complex which includes the poreforming alpha subunit and regulatory proteins that allow sodium influx during the depolarization phase of the ventricular action potential. The alpha subunit, Nav1.5, is encoded by SCN5A . Mutations in this gene are responsible for a wide spectrum of hereditary arrhythmias such as cardiac conduction disease and atrial fibrillation. A mutation in SCN5A , leading to a p.I141V substitution, was identified in a large multigenerational family with an arrhythmia syndrome resembling catecholaminergic polymorphic ventricular tachycardia through whole-exome sequencing. The purpose of this study was to identify the molecular mechanisms linking the p.I141V mutation to this arrhythmia. To evaluate the incidence of this substitution on Nav1.5 function, whole-cell patch-clamp experiments were performed on HEK293 cells transfected with the human alpha and beta subunits. The presence of the p.I141V mutation shifted the voltage-dependence of steady state activation towards more negative potentials. Thus, we studied the effect of this mutation on the sodium window current. Compared to the WT, the p.I141V window current exhibited a larger peak and this peak was shifted towards more negative potentials. To investigate the functional consequences of the cardiac hyperexcitability due to the p.I141V mutation, we incorporated biophysical properties of the mutant into atrial, Purkinje and ventricular cell models. The computational analyses imply that the biophysical changes caused by the p.I141V mutation accelerates the spontaneous rate in the Purkinje cell model, and reduce the excitation threshold leading to an increase of the excitability of the cardiac cells. In conclusion, the present study demonstrates that mutations in SCN5A also may result in exercise-induced polymorphic ventricular premature complexes and tachycardia resembling CPVT.

Electrochemical Properties of Boron-Doped Diamond Thin Film Synthesized by MPCVD on Titanium Substrate to Use as an Ozone Generator

Boron doped diamond is an excellent electrode material with a large potential window in aqueous solution and low background current. The wider potential window and lower background currents make the BDD material very attractive for electrochemical analysis experiments.Furthermore, BDD exhibits high chemical and electrochemical stability, which makes the material a suitable electrode material for various applications such as bioelectrochemical applications and water disinfection.In this paper, we had succeeded to generate ozone by using the BDD electrode with high efficiency compared to traditional lead oxide (PbO2) and other BDD electrods.Firstly, a Titanium substrate had been seeded by ultra sonic agitation with diamond powder(30nm ~ 40nm) for an hour, which was used as a nucleation of diamond. After that BDD film was deposited on the substrate by microwave plasma chemical vapor deposition.The morphology of samples was observed by Scanning Electron Microscopy (SEM) and the structural-chemical properties of synthesized diamond layer was investigated by Raman Spectroscopy. Conductivity, carrier concentration and Hall mobility was then determined by a Hall-effect measurement unit, based on the van der Pauw method. The ozone concentration in water, which was measured by Ozone Colorimeter.

T-type Channels Become Highly Permeable to Sodium Ions Using an Alternative Extracellular Turret Region (S5-P) Outside the Selectivity Filter

T-type (Cav3) channels are categorized as calcium channels, but invertebrate ones can be highly sodium-selective channels. We illustrate that the snail LCav3 T-type channel becomes highly sodium-permeable through exon splicing of an extracellular turret and descending helix in domain II of the four-domain Cav3 channel. Highly sodium-permeable T-type channels are generated without altering the invariant ring of charged residues in the selectivity filter that governs calcium selectivity in calcium channels. The highly sodium-permeant T-type channel expresses in the brain and is the only splice isoform expressed in the snail heart. This unique splicing of turret residues offers T-type channels a capacity to serve as a pacemaking sodium current in the primitive heart and brain in lieu of Nav1-type sodium channels and to substitute for voltage-gated sodium channels lacking in many invertebrates. T-type channels would also contribute substantially to sodium leak conductances at rest in invertebrates because of their large window currents.