Rate Of Repolarization Research Articles

Action potential firing and sensory transduction are sustained by membrane potential instabilities in peripheral sensory neurons.

Peripheral sensory neurons are fundamental for stimulus detection, but many of their properties remain poorly understood (Velasco et al., 2022). One of these is the marked instability of the resting membrane potential recorded in such neurons, known as Membrane Potential Instabilities (MPIs). MPIs are enhanced in pain states, but their functional significance and molecular bases remain largely unknown. Here, we addressed this using whole-cell current-clamp recordings in primary cultured mouse trigeminal (TG) neurons. MPI detection and morphological analyses were performed semi-automatically, using custom-made scripts. We found that 82.2% of small diameter neurons recorded displayed MPI activity in the shape of Membrane Potential Transients (MPTs), spontaneously or upon depolarizing current injection. The frequency, amplitude and rates of upstroke and repolarization of MPTs were increased by membrane depolarization. Morphological analyses of the MPTs and of the initial depolarizing phase of action potentials (Aps) revealed that larger and faster MPTs precede AP firing. This was confirmed by a regression analysis showing that the maximal rate of depolarization and amplitude of the MPTs strongly predict subsequent AP firing, following a Boltzmann dependency. MPT activity was enhanced by the application of heat, cold, capsaicin and menthol, via their depolarizing effect on the resting membrane potential. MPT activity was reduced by blocking TTX-resistant, but not TTX-sensitive voltage-gated Na+ channels. Accordingly, MPTs were also reduced in neurons isolated from NaV1.8 and NaV1.9 knockout mice. We hereby identify, for the first time, the molecular determinants of the trigger of MPTs and demonstrate a causal relationship between MPTs and AP firing upon exogenous stimulation of sensory neurons. These findings unveil MPTs as crucial regulators of peripheral sensory processing, with possible implications in pathological conditions featuring altered activities of TTX-resistant NaV channels.

Reduction in Junctophilin 2 Expression in Cardiac Nodal Tissue Results in Intracellular Calcium-Driven Increase in Nodal Cell Automaticity.

Spontaneously depolarizing nodal cells comprise the pacemaker of the heart. Intracellular calcium (Ca2+) plays a critical role in mediating nodal cell automaticity and understanding this so-called Ca2+ clock is critical to understanding nodal arrhythmias. We previously demonstrated a role for Jph2 (junctophilin 2) in regulating Ca2+-signaling through inhibition of RyR2 (ryanodine receptor 2) Ca2+ leak in cardiac myocytes; however, its role in pacemaker function and nodal arrhythmias remains unknown. We sought to determine whether nodal Jph2 expression silencing causes increased sinoatrial and atrioventricular nodal cell automaticity due to aberrant RyR2 Ca2+ leak. A tamoxifen-inducible, nodal tissue-specific, knockdown mouse of Jph2 was achieved using a Cre-recombinase-triggered short RNA hairpin directed against Jph2 (Hcn4:shJph2). In vivo cardiac rhythm was monitored by surface ECG, implantable cardiac telemetry, and intracardiac electrophysiology studies. Intracellular Ca2+ imaging was performed using confocal-based line scans of isolated nodal cells loaded with fluorescent Ca2+ reporter Cal-520. Whole cell patch clamp was conducted on isolated nodal cells to determine action potential kinetics and sodium-calcium exchanger function. Hcn4:shJph2 mice demonstrated a 40% reduction in nodal Jph2 expression, resting sinus tachycardia, and impaired heart rate response to pharmacologic stress. In vivo intracardiac electrophysiology studies and ex vivo optical mapping demonstrated accelerated junctional rhythm originating from the atrioventricular node. Hcn4:shJph2 nodal cells demonstrated increased and irregular Ca2+ transient generation with increased Ca2+ spark frequency and Ca2+ leak from the sarcoplasmic reticulum. This was associated with increased nodal cell AP firing rate, faster diastolic repolarization rate, and reduced sodium-calcium exchanger activity during repolarized states compared to control. Phenome-wide association studies of the JPH2 locus identified an association with sinoatrial nodal disease and atrioventricular nodal block. Nodal-specific Jph2 knockdown causes increased nodal automaticity through increased Ca2+ leak from intracellular stores. Dysregulated intracellular Ca2+ underlies nodal arrhythmogenesis in this mouse model.

Mathematical investigation of the role of re-polarisation of M2 in cancer therapy

<p style='text-indent:20px;'>Tumor-associated macrophages are one of the important immune cells in tumor microenvironment and they have both anti-tumor and pro-tumor roles as determined by their phenotypes. Recent experiments have shown that repolarizing pro-tumor M2 into anti-tumor M1 is a feasible antitumor therapy. Here we propose a mathematical model for the tumor-macrophage interactions with M2 re-polarisation delay to investigate the effect of M2 re-polarisation on tumor growth/decay. By using stability and bifurcation theories of DDE, we study the dynamic of this model analytically and numerically and find that the varies of M2 re-polarisation rate and time delay can cause complex dynamical behaviors such as the changes of stabilities of tumor-free, large and small tumor equilibria, the occurrences of saddle-node, Hopf, homoclinic and B-T bifurcation, etc. Moreover, our study reveals that the increase of M2 re-polarisation rate related to immunotherapeutic agent dose can control the tumor to small tumor dormancy and even eliminate the tumor, but this is not always available when immune escape occurs; Pharmacodynamic delay (M2 re-polarisation delay) also affects tumor progression and may cause persistent oscillatory behavior. In addition, the results also indicate the possibility of pseudo-progression in tumor therapy and efficacy of postoperative M2 re-polarisation therapy to prevent tumor recurrence.</p>

Microwave exposure added characteristics to the wounding-induced variation potential of Aloe arborescens leaves

The influence of radiofrequency electromagnetic radiation on the wounding-induced electric potentials (EPs) in Aloe arborescens plants was investigated. Burn wounding-induced electrical potentials of mature A. arborescens plants were observed under the exposure of 2.45 ​GHz, 3.5 ​GHz and 5.5 ​GHz microwaves at incident power density 1.5 ​± ​0.2 ​W ​m−2. Aloe leaves were subjected to flame wounding at the leaf tips and propagation EPs were recorded by inserting a glass Ag/AgCl microelectrode into the leaf pulp. The propagation of electrical potential and a standard deviation of the fluctuations in electrical potential (SDEF) were investigated. The flame wounding generated propagating characteristic electric potential, and the exposure of microwaves added extra characteristics to the signals by reversing the electrical potential temporally for a shorter duration. The characteristics appeared in the repolarization phase of the signal under 2.45 ​GHz and 3.5 ​GHz exposure; for the 5.5 ​GHz exposure, 3 out of 6 characteristics appeared during the depolarization phase. Averaged polarization rates of the characteristics were increased with the increased microwave frequency. Added characteristics to the electric potential may have resulted from a secondary signal triggered due to microwave exposure, which should be further studied. The repolarization and depolarization rates of the wound signals were not different between control and microwave exposures. SDEFs were also not affected by microwave exposure.

E-cigarettes and their lone constituents induce cardiac arrhythmia and conduction defects in mice

E-cigarette use has surged, but the long-term health effects remain unknown. E-cigarette aerosols containing nicotine and acrolein, a combustion and e-cigarette byproduct, may impair cardiac electrophysiology through autonomic imbalance. Here we show in mouse electrocardiograms that acute inhalation of e-cigarette aerosols disturbs cardiac conduction, in part through parasympathetic modulation. We demonstrate that, similar to acrolein or combustible cigarette smoke, aerosols from e-cigarette solvents (vegetable glycerin and propylene glycol) induce bradycardia, bradyarrhythmias, and elevations in heart rate variability during inhalation exposure, with inverse post-exposure effects. These effects are slighter with tobacco- or menthol-flavored aerosols containing nicotine, and in female mice. Yet, menthol-flavored and PG aerosols also increase ventricular arrhythmias and augment early ventricular repolarization (J amplitude), while menthol uniquely alters atrial and atrioventricular conduction. Exposure to e-cigarette aerosols from vegetable glycerin and its byproduct, acrolein, diminish heart rate and early repolarization. The pro-arrhythmic effects of solvent aerosols on ventricular repolarization and heart rate variability depend partly on parasympathetic modulation, whereas ventricular arrhythmias positively associate with early repolarization dependent on the presence of nicotine. Our study indicates that chemical constituents of e-cigarettes could contribute to cardiac risk by provoking pro-arrhythmic changes and stimulating autonomic reflexes.

Tunable Action Potential Repolarization Governed by Kv3.4 Channels in Dorsal Root Ganglion Neurons.

The Kv3.4 channel regulates action potential (AP) repolarization in nociceptors and excitatory synaptic transmission in the spinal cord. We hypothesize that this is a tunable role governed by protein kinase-C-dependent phosphorylation of the Kv3.4 cytoplasmic N-terminal inactivation domain (NTID) at four nonequivalent sites. However, there is a paucity of causation evidence linking the phosphorylation status of Kv3.4 to the properties of the AP. To establish this link, we used adeno-associated viral vectors to specifically manipulate the expression and the effective phosphorylation status of Kv3.4 in cultured dorsal root ganglion (DRG) neurons from mixed-sex rat embryos at embryonic day 18. These vectors encoded GFP (background control), wild-type (WT) Kv3.4, phosphonull (PN) Kv3.4 mutant (PN = S[8,9,15,21]A), phosphomimic (PM) Kv3.4 mutant (PM = S[8,9,15,21]D), and a Kv3.4 nonconducting dominant-negative (DN) pore mutant (DN = W429F). Following viral infection of the DRG neurons, we evaluated transduction efficiency and Kv3.4 expression and function via fluorescence microscopy and patch clamping. All functional Kv3.4 constructs induced current overexpression with similar voltage dependence of activation. However, whereas Kv3.4-WT and Kv3.4-PN induced fast transient currents, the Kv3.4-PM induced currents exhibiting impaired inactivation. In contrast, the Kv3.4-DN abolished the endogenous Kv3.4 current. Consequently, Kv3.4-DN and Kv3.4-PM produced APs with the longest and shortest durations, respectively, whereas Kv3.4-WT and Kv3.4-PN produced intermediate results. Moreover, the AP widths and maximum rates of AP repolarization from these groups are negatively correlated. We conclude that the expression and effective phosphorylation status of the Kv3.4 NTID confer a tunable mechanism of AP repolarization, which may provide exquisite regulation of pain signaling in DRG neurons.SIGNIFICANCE STATEMENT The AP is an all-or-none millisecond-long electrical impulse that encodes information in the frequency and patterns of repetitive firing. However, signaling may also depend on the plasticity and diversity of the AP waveform. For instance, the shape and duration of the AP may regulate nociceptive synaptic transmission between a primary sensory afferent to a secondary neuron in the spinal cord. Here, we used mutants of the Kv3.4 voltage-gated potassium channel to manipulate its expression and effective phosphorylation status in dorsal root ganglion neurons and directly show how the expression and malleable inactivation properties of Kv3.4 govern the AP duration and repolarization rate. These results elucidate a mechanism of neural AP plasticity that may regulate pain signaling.

Synchronization of repolarization after cardiac resynchronization therapy: A combined clinical and modeling study.

IntroductionThe changes in ventricular repolarization after cardiac resynchronization therapy (CRT) are poorly understood. This knowledge gap is addressed using a multimodality approach including electrocardiographic and echocardiographic measurements in patients and using patient‐specific computational modeling.MethodsIn 33 patients electrocardiographic and echocardiographic measurements were performed before and at various intervals after CRT, both during CRT‐ON and temporary CRT‐OFF. T‐wave area was calculated from vectorcardiograms, and reconstructed from the 12‐lead electrocardiography (ECG). Computer simulations were performed using a patient‐specific eikonal model of cardiac activation with spatially varying action potential duration (APD) and repolarization rate, fit to a patient's ECG.ResultsDuring CRT‐ON T‐wave area diminished within a day and remained stable thereafter, whereas QT‐interval did not change significantly. During CRT‐OFF T‐wave area doubled within 5 days of CRT, while QT‐interval and peak‐to‐end T‐wave interval hardly changed. Left ventricular (LV) ejection fraction only increased significantly increased after 1 month of CRT. Computer simulations indicated that the increase in T‐wave area during CRT‐OFF can be explained by changes in APD following chronic CRT that are opposite to the change in CRT‐induced activation time. These APD changes were associated with a reduction in LV dispersion in repolarization during chronic CRT.ConclusionT‐wave area during CRT‐OFF is a sensitive marker for adaptations in ventricular repolarization during chronic CRT that may include a reduction in LV dispersion of repolarization.

Therapeutic Ultrasound Effects on Human Induced Pluripotent Stem Cell Cardiomyocytes Measured Optically and with Spectral Ultrasound

To the best of our knowledge, therapeutic ultrasound (TUS) is thus far an unexplored means of delivering mechanical stimulation to cardiomyocyte cultures, which is necessary to engineer a more mature cardiomyocyte phenotype in vitro. Spectral ultrasound (SUS) may provide a way to non-invasively, non-disruptively and inexpensively monitor growth and change in cell cultures over long periods. Compared with other measurement methods, SUS as an acoustic measurement tool will not be affected by an acoustic therapy, unlike electrical measurement methods, in which motion caused by acoustic therapy can affect measurements. Further SUS has the potential to provide functional as well as morphological information in cell cultures. Human induced pluripotent stem cell cardiomyocytes (iPS-CMs) were imaged with calcium fluorescence microscopy while TUS was being applied. TUS was applied at 600 kHz and 1, 3.4 and 6 W/cm2 for a continuous 1 s pulse. Measures of the instantaneous beat frequency, repolarization rate and calcium spike amplitude were calculated from the fluorescence data. At 600 kHz, TUS at 1 and 6 W/cm2 had significant effects on the shortening of both the repolarization rate and instantaneous beat rate of the iPS-CMs (p < 0.05), while TUS at 3.4 and 6 W/cm2 had significant effects on the shortening of the calcium spike amplitude (p < 0.05). Three SUS measures and one gray-level measure were captured from the iPS-CM monolayers while they were simultaneously being imaged with calcium-labeled confocal microscopy. The gray-level measure performed the best of all SUS measures; however, it was not reliable enough to produce a consistent determination of the beat rate of the cell. Finally, SUS measures were captured using three different transducers while simultaneously applying TUS. A center-of-mass (COM) measure calculated from the wavelet transform scalogram of the time-averaged radiofrequency data revealed that SUS was able to detect a change in the frequency content of the reflected ultrasound at 1 and 6 W/cm2 before and after ultrasound application (p < 0.05), showing promise for the ability of SUS to measure changes in the beating behavior of iPS-CMs. Overall, SUS is promising as a method for constant monitoring of dynamic cell and tissue culture and growth.

Synchronization of repolarization after cardiac resynchronization therapy: time course and relation to reverse remodeling

Abstract Funding Acknowledgements Type of funding sources: None. Background The changes in ventricular repolarization after cardiac resynchronization therapy (CRT) are poorly understood. Objective Address this knowledge gap using a multimodality approach including electrocardiographic and echocardiographic measurements in patients and patient-specific computational modeling. Methods In a cohort of consecutive CRT patients, electrocardiographic and echocardiographic measurements were performed before and at various intervals after CRT, both during CRT-ON and temporary CRT-OFF. T-wave area was calculated from vectorcardiograms, reconstructed from the 12-lead ECG. Computer simulations were performed using a patient-specific eikonal model of cardiac activation with spatially varying action potential duration (APD) and repolarization rate, based on a patient’s ECG and MRI-based chest and cardiac anatomy. Results In 33 patients T-wave area during CRT-OFF doubled within 5 days of CRT (left figure) while other repolarization markers like QT-interval and peak-to-end T-wave interval hardly changed. Patients with T-wave area increase above the median increase showed a significantly larger increase in left ventricular ejection fraction than those with smaller T-wave area increase (+11±8% vs. +6±6%, respectively; p&amp;lt;0.05, n=76). Computer simulations (figure, right) show the sequence of depolarization and repolarization before CRT, obtained by the patient-specific model (BL LBBB) and following Acute CRT. Repolarization after chronic CRT-OFF was obtained by matching the measured CRT-OFF ECG with that provided by the model. The best match was obtained by changes in APD following chronic CRT that are opposite to the change in CRT-induced activation time. Such APD changes were associated with a reduction in right and left ventricular dispersion in repolarization during chronic CRT-ON compared with acute CRT-ON. Conclusions T-wave area during CRT-OFF is a sensitive marker for adaptations in ventricular repolarization after CRT that are related to CRT-induced reverse remodeling and may involve an inverse relation between activation time and APD, coinciding with lower right and left ventricular dispersion of repolarization and with larger increases in LV ejection fraction during chronic CRT.

Afterhyperpolarization Promotes the Firing of Mitral Cells through a Voltage-Dependent Modification of Action Potential Threshold.

In the olfactory bulb, mitral cells (MCs) display a spontaneous firing that is characterized by bursts of action potentials (APs) intermixed with silent periods. Intraburst firing frequency and duration are heterogeneous among MCs and increase with membrane depolarization. By using patch-clamp recording on rat slices, we dissected out the intrinsic properties responsible for this bursting activity. We showed that the threshold of AP generation dynamically changes as a function of the preceding trajectory of the membrane potential. In fact, the AP threshold became more negative when the membrane was hyperpolarized and had a recovery rate inversely proportional to the membrane repolarization rate. Such variations appeared to be produced by changes in the inactivation state of voltage-dependent Na+ channels. Thus, AP initiation was favored by hyperpolarizing events, such as negative membrane oscillations or inhibitory synaptic input. After the first AP, the following fast afterhyperpolarization (AHP) brought the threshold to more negative values and then promoted the emission of the following AP. This phenomenon was repeated for each AP of the burst making the fast AHP a regenerative mechanism that sustained the firing, AHP with larger amplitudes and faster repolarizations being associated with larger and higher-frequency bursts. Burst termination was found to be because of the development of a slow repolarization component of the AHP (slow AHP). Overall, the AHP characteristics appeared as a major determinant of the bursting properties.

Efekti kadmijuma na transportne procese u proksimalnim tubulskim ćelijama bubrega

Cadmium (Cd) is an extremely toxic metal that is widespread in nature. Due to its favorable properties, it was widely used in the industry for the production of alkaline batteries, accumulators, pigments, and colored alloys. However, it has been shown that exposure to low concentrations of cadmium leads to damage to many organs and organ systems, and the use of this metal in industry is reduced, and it is replaced by other, less harmful materials. Today, fossil fuel combustion and cigarette consumption are important sources of cadmium exposure. Numerous studies have examined the toxic effects of cadmium and they highlight the kidneys, liver, gonads as the organs that suffer the most damage. The kidneys, as the main place of cadmium storage in the body, are mostly exposed to its toxic effects. In the proximal tubular cells of the kidney, exposure to cadmium disrupts transport processes. Although ionized cadmium (Cd 2+) is thought to be largely responsible for the damage that occurs, the role of the cadmium and metallothionein complex (Cd-MT) cannot be ignored. Peritubular exposure to ionized cadmium indirectly leads to a decrease in the activity of the Na + /L-alanine cotransporter and a decrease in the rate of slow repolarization of the luminal membrane, while the Cd-MT complex leads to both direct and indirect inhibition of this transporter. Also, the Cd-MT complex inhibits Na + /Glucosa cotransporter activity. Exposure to cadmium also leads to a decrease in the endocytic uptake of low molecular weight proteins, which is accompanied by microalbuminuria.

Determinination of the Frequency of Altered Cardiac Repolarization by Measuring the Heart rate Corrected QT Interval in COPD Patients

Objectives: To determine the frequency of altered cardiac repolarization by measuring the heart rate corrected QT interval in COPD patients.&#x0D; Setting: Department of Medicine at LUMHS hospital Hyderabad/Jamshoro.&#x0D; Study Design: Descriptive Cross sectional study. &#x0D; Duration of Study: 6 months from 01-03-2019 to 31-08-2019.&#x0D; Methods: A total of 232 patients with severe acute exacerbation of COPD were included in this study. A 12 lead ECG was performed. QT intervals were measured on a resting ECG tracing in lead II. The QT interval was measured manually from the starting point of the QRS complex to the terminal point of the down slope of the T wave.&#x0D; Results: A total of 232 patients with COPD were included in this study. Most of the cases were above 50 years of age. The average age of the patients was 53.74±4.35 years. There were 92.67% (215/232) male and 7.33% (17/232) female. Out of 232 patients, 21.14% were current smoker and 75.86% were ex-smoker. A QTc interval &gt;0.44 seconds was considered abnormally prolonged. Frequency of altered cardiac repolarization by measuring the heart rate corrected QT interval in COPD patients was 31.47% (73/232). Rate of altered cardiac repolarization was not significant among different age groups (p=0.641). Rate of altered cardiac repolarization was significantly high in male as compare to female (33.5% vs. 5.9%; p=0.018). This was not significant between obese and non-obese groups (p=0.100). Rate of altered cardiac repolarization was significantly high in former smoker (p=0.0005) and those patients whose duration of COPD was above 15 years (p=0.0005).&#x0D; Conclusion: Patients with hypoxic chronic obstructive pulmonary disease (COPD) have evidence of a subclinical parasympathetic autonomic neuropathy, with apparent preservation of sympathetic function. Measuring heart rate corrected QT interval (QTc) test is repeatable, easy to perform and a sensitive indicator for autonomic dysfunction in breathlessness individuals with COPD.

Transient ultrasound stimulation has lasting effects on neuronal excitability

BackgroundTranscranial ultrasound stimulation can acutely modulate brain activity, but the lasting effects on neurons are unknown. ObjectiveTo assess the excitability profile of neurons in the hours following transient ultrasound stimulation. MethodsPrimary rat cortical neurons were stimulated with a 40 s, 200 kHz pulsed ultrasound stimulation or sham-stimulation. Intrinsic firing properties were investigated through whole-cell patch-clamp recording by evoking action potentials in response to somatic current injection. Recordings were taken at set timepoints following ultrasound stimulation: 0–2 h, 6–8 h, 12–14 h and 24–26 h. Transmission electron microscopy was used to assess synaptic ultrastructure at the same timepoints. ResultsIn the 0–2 h window, neurons stimulated with ultrasound displayed an increase in the mean frequency of evoked action potentials of 32% above control cell levels (p = 0.023). After 4–6 h this increase was measured as 44% (p = 0.0043). By 12–14 h this effect was eliminated and remained absent 24–26 h post-stimulation. These changes to action potential firing occurred in conjunction with statistically significant differences between control and ultrasound-stimulated neurons in action potential half-width, depolarisation rate, and repolarisation rate, that were similarly eliminated by 24 h following stimulation. These effects occurred in the absence of alterations to intrinsic membrane properties or synaptic ultrastructure. ConclusionWe report that stimulating neurons with 40 s of ultrasound enhances their excitability for up to 8 h in conjunction with modifications to action potential kinetics. This occurs in the absence of major ultrastructural change or modification of intrinsic membrane properties. These results can inform the application of transcranial ultrasound in experimental and therapeutic settings.

Abstract 17074: Methadone Potently Blocks Cardiac IK1 Leading to Membrane Instability

Introduction: Methadone is the second most frequently reported cause of drug-induced cardiac arrest in pharmacovigilance databases, yet the mechanism of its pro-arrhythmia is unclear. Methadone-induced QTU wave prolongation has been repeatedly observed and attributed to inhibition of the delayed rectifier hERG current, but QTU fusion suggests the inwardly rectifying K + current (IK1) might also be affected by methadone. Hypothesis: Methadone pro-arrhythmia is associated with potent block of the IK1 current responsible for rapid terminal repolarization of the cardiac action potential (AP). Methods: Human Kir2.2, encoding the IK1 current, was transiently expressed in COS cells. hERG1a was stably expressed in CHO cells. Cardiac myocytes from swine were obtained by ventricular enzymatic dissociation. Ionic current and APs were measured using patch-clamp methods. Methadone HCl (R+S racemates) was dissolved in Tyrode solution. Results: Methadone suppressed IK1 current with an IC 50 of 1.47 uM (Fig 1A). Methadone also suppressed outward IK1 (-60 mV) measured in swine myocytes (Ba 2+ -sensitive current) with an IC 50 of 1.52 μM. Methadone suppressed hERG currents with an IC 50 of 2.1 μM. APs measured in swine myocytes exhibited significant prolongation (13 ± 4 % increase of APD 90 , p&lt;0.029, n=7) as well as slowing of the rate of terminal repolarization (a specific marker of IK1 blockade) in the presence of 1 μM methadone (Fig. 1B). Fluctuations of diastolic voltage increased by 30 ± 12 and 151 ± 27 % (n=3; p&lt;0.04) in 0.1 and 1 μM methadone, respectively, consistent with a reduction in membrane stability. Conclusions: Methadone is an equipotent blocker of IK1 and hERG. The effect of IK1 block coupled with modest hERG block has a synergistic effect on terminal repolarization that may partially explain the pro-arrhythmic impact of methadone. Moreover, this observation may be generalized to other drugs where unsuspected IK1 blockade may contribute to pro-arrhythmia and torsade de pointes.

Nociceptin/orphanin FQ peptide receptor mediates inhibition of N-type calcium currents in vestibular afferent neurons of the rat.

The vestibular system is modulated by various neuromodulators including opioid peptides. The current study was conducted to determine whether activation of nociceptin/orphanin FQ peptide (NOP) receptors modulates voltage-gated calcium currents and action potential discharge of rat vestibular afferent neurons. We performed whole cell patch-clamp recordings on cultured vestibular afferent neurons from P7-P10 Long-Evans rats. Application of nociceptin/orphanin FQ (N/OFQ), a 17-amino acid neuropeptide that is the endogenous ligand for NOP receptor, inhibits the high-voltage activated (HVA) component of the calcium current in a concentration-dependent manner with a half inhibitory concentration of 26 nM. Said inhibitory action on the calcium current is voltage-dependent, which was made clear by the fact that it was reverted in 80% by a depolarizing prepulse. Furthermore, the effect of N/OFQ was blocked by application of the specific NOP-antagonist UFP101, by preincubation with G-protein blocker pertussis toxin, and by coapplication of the specific N-type calcium-current blocker ω-conotoxin-MVIIA. N/OFQ application causes an increase in the duration and maximum rate of repolarization of action potentials. It also decreases repetitive discharge and discharge elicited by sinusoidal stimulation. These results show that in vestibular afferents, NOP receptor activation inhibits N-type calcium current by activating G proteins, mostly through the Gβγ subunit. This suggests that NOP activation produces a presynaptic modulation of primary vestibular afferent neurons' output into the vestibular nuclei, thus taking part in the integration and gain setting of vestibular information in second-order vestibular nucleus neurons.NEW & NOTEWORTHY Our results show that in primary vestibular afferent neurons, activation of the nociceptin/orphanin FQ peptide receptor inhibits the N-type calcium current by a mechanism mediated by G proteins. We propose that calcium current inhibition modulates neurotransmitter release from vestibular afferents, producing a presynaptic modulation of vestibular input to vestibular nuclei, thus contributing to gain control in the vestibular afferent input.

Potential therapeutic effects of electrogram-guided cardioneuroablation in long QT syndrome: case series

A significant shortening of the corrected QT interval (QTc) in addition to parasympathetic denervation after cardioneuroablation (CNA) was recently demonstrated in patients with vagally mediated bradyarrhythmias and normal QTc range. This study assessed the effects of CNA on ventricular repolarization and heart rate by using QTc measurements in 2 patients with long QT syndrome (LQTS). The case series included 2 consecutive patients with significant sinus bradycardia and refractory paroxysmal atrial fibrillation (AF). All atrial ganglionated plexus (GP) sites in addition to pulmonary vein isolation were successively targeted by using electrogram-guided strategy. QTc was calculated on 12-lead ECG before the procedure (time point 1), at post-ablation 24h (time point 2), and at the last follow-up visit (time point 3), respectively. In the first case, QTc (Bazett) shortened from 612 to 551msec between time points 1 and 2 and was 419msec in time point 3. Similarly, QTc (Bazett) shortened from 480 to 401msec between time points 1 and 3 in the second case. In both cases, minimum and mean heart rates were significantly increased after ablation. The parameters of which are used to estimate both sympathetic and parasympathetic changes in heart rate variability were significantly decreased after ablation. There were no arrhythmia-related symptoms during follow-up. The present case series reports a new ablation strategy systematically targeting autonomic GPs in LQTS patients. CNA shortens QTc (through sympathetic modulation) and increases heart rate. Although promising, these preliminary results need to be confirmed in the larger prospective study.

Functional characterization and physiological roles of the single Shaker outward K+ channel in Medicago truncatula.

The model legume Medicago truncatula possesses a single outward Shaker K+ channel, whereas Arabidopsis thaliana possesses two channels of this type, named AtSKOR and AtGORK, with AtSKOR having been shown to play a major role in K+ secretion into the xylem sap in the root vasculature and with AtGORK being shown to mediate the efflux of K+ across the guard cell membrane, leading to stomatal closure. Here we show that the expression pattern of the single M.truncatula outward Shaker channel, which has been named MtGORK, includes the root vasculature, guard cells and root hairs. As shown by patch-clamp experiments on root hair protoplasts, besides the Shaker-type slowly activating outwardly rectifying K+ conductance encoded by MtGORK, a second K+ -permeable conductance, displaying fast activation and weak rectification, can be expressed by M.truncatula. A knock-out (KO) mutation resulting in an absence of MtGORK activity is shown to weakly reduce K+ translocation to shoots, and only in plants engaged in rhizobial symbiosis, but to strongly affect the control of stomatal aperture and transpirational water loss. In legumes, the early electrical signaling pathway triggered by Nod-factor perception is known to comprise a short transient depolarization of the root hair plasma membrane. In the absence of the functional expression of MtGORK, the rate of the membrane repolarization is found to be decreased by a factor of approximately two. This defect was without any consequence on infection thread development and nodule production in plants grown in vitro, but a decrease in nodule production was observed in plants grown in soil.

Ultrasound Stimulations Induce Prolonged Depolarization and Fast Action Potentials in Leech Neurons.

Objective: Ultrasound (US) stimulation carries the promise of a selective, reversible, and non-invasive modulation of neural activity without the need for genetic manipulation of neural structures. However, the mechanisms of US-induced generation of action potentials (APs) are still unclear. Methods: Here we address this issue by analyzing intracellularly recorded responses of leech nociceptive neurons to controlled delivery of US. Results: US induced a depolarization linearly accumulating in time and outlasting the duration of the stimulation. Spiking activity was reliably induced for an optimal US intensity range. Moreover, we found that APs induced by US differ in smaller amplitude and faster repolarization from those induced by electrical stimulation in the same cell but display the same repolarization rate. Conclusions: These results shed light on the mechanism by which spikes are induced by US and pave the way for designing more efficient US stimulation patterns.

Contribution of potassium channels to action potential repolarization of human embryonic stem cell-derived cardiomyocytes.

The electrophysiological properties of human pluripotent stem cell-derived cardiomyocytes (CMs) have not yet been characterized in a syncytial context. This study systematically characterized the contributions of different repolarizing potassium currents in human embryonic stem cell-derived CMs (hESC-CMs) during long-term culture as cell monolayers. The H9 hESC line was differentiated to CMs and plated to form confluent cell monolayers. Optical mapping was used to record the action potentials (APs) and conduction velocity (CV) during electrophysiological and pharmacological experiments. RT-PCR and Western blot were used to detect the presence and expression levels of ion channel subunits. Long-term culture of hESC-CMs led to shortened AP duration (APD), faster repolarization rate, and increased CV. Selective block of IKr , IKs , IK1 , and IKur significantly affected AP repolarization and APD in a concentration- and culture time-dependent manner. Baseline variations in APD led to either positive or negative APD dependence of drug response. Chromanol 293B produced greater relative AP prolongation in mid- and late-stage cultures, while DPO-1 had more effect in early-stage cultures. CV in cell monolayers in early- and late-stage cultures was most susceptible to slowing by E-4031 and BaCl2 respectively. IKr , IKs , IK1 , and IKur all play an essential role in the regulation of APD and CV in hESC-CMs. During time in culture, increased expression of IKr and IK1 helps to accelerate repolarization, shorten APD, and increase CV. We identified a new pro-arrhythmic parameter, positive APD dependence of ion channel block, which can increase APD and repolarization gradients.

Phase 1 repolarization rate defines Ca2+ dynamics and contractility on intact mouse hearts.

In the heart, Ca2+ influx through L-type Ca2+ channels triggers Ca2+ release from the sarcoplasmic reticulum. In most mammals, this influx occurs during the ventricular action potential (AP) plateau phase 2. However, in murine models, the influx through L-type Ca2+ channels happens in early repolarizing phase 1. The aim of this work is to assess if changes in the open probability of 4-aminopyridine (4-AP)-sensitive Kv channels defining the outward K+ current during phase 1 can modulate Ca2+ currents, Ca2+ transients, and systolic pressure during the cardiac cycle in intact perfused beating hearts. Pulsed local-field fluorescence microscopy and loose-patch photolysis were used to test the hypothesis that a decrease in a transient K+ current (Ito) will enhance Ca2+ influx and promote a larger Ca2+ transient. Simultaneous recordings of Ca2+ transients and APs by pulsed local-field fluorescence microscopy and loose-patch photolysis showed that a reduction in the phase 1 repolarization rate increases the amplitude of Ca2+ transients due to an increase in Ca2+ influx through L-type Ca2+ channels. Moreover, 4-AP induced an increase in the time required for AP to reach 30% repolarization, and the amplitude of Ca2+ transients was larger in epicardium than endocardium. On the other hand, the activation of Ito with NS5806 resulted in a reduction of Ca2+ current amplitude that led to a reduction of the amplitude of Ca2+ transients. Finally, the 4-AP effect on AP phase 1 was significantly smaller when the L-type Ca2+ current was partially blocked with nifedipine, indicating that the phase 1 rate of repolarization is defined by the competition between an outward K+ current and an inward Ca2+ current.