Low-voltage Activity Research Articles

Improved procedural workflow for catheter ablation of paroxysmal AF with high density mapping system and advanced technology: insights from a multicenter, international study

Abstract Background A high incidence of pulmonary vein (PV) reconnection has been reported in patients with clinical recurrences of AF. Low-voltage activity beyond PVs (e.g. antral activity potentials, RAP) likely represent vulnerabilities in antral lesion sets and they may contribute to ablation failures. Purpose The aim of this study is to validate a structured application of an approach that includes the complete abolition of any antral potential achieving electrical quiescence in antral regions. Methods DELETE AF is a prospective, single-arm, international post-market cohort study. Consecutive patients from 10 centers who were undergoing radiofrequency ablation of paroxysmal AF were included. The Lumipoint map-analysis tool was used sequentially on each PV component. Post-ablation, all patients were monitored with ambulatory event monitoring, starting within 30 days post-ablation to proactively detect and manage any recurrences within the 90-day blanking period, as well as Holter monitoring at 3, 6, 9, and 12 months post-ablation. Additional ECG monitoring were performed as indicated by patient symptoms. The ablation endpoint was PV isolation (PVI). Long-term outcome was the recurrence of AF over follow-up. Data are reported as median [IQ range]. Results One-hundred ten cases of AF ablation were analyzed: 28 (25.5%) females, age=63[56-69] years, 24 (21.8%) patients with a history of AT/AFL. The procedure duration was 58[24-76] min (RF delivery time=18[12-28] min, number of ablation spots=77[44-101]) and the fluoroscopy time was 13[9-19] min. Thirty-eight (34.5%) were repeat ablation: in these patients after initial mapping a total of 114 PV gaps (PVGs) in 29 (76.3%) patients and 69 RAPs in 15 patients (39.5%) were found. After ablation, a total of 5 early PVGs in 2 (1.8%) patients (all in de novo procedures) and a total of 10 RAPs in 7 (6.3%) patients (3 out 38 -7.9%- of repeat ablations vs 4 out 72 -5.6%- of de novo cases, p=0.690) were detected after first remapping. Each residual PVG was first targeted and additional focal ablations were performed at any low-voltage propagation suspected within the region of previous antral ablation. Acute procedural success was 100%, with all PVs successfully isolated and RAPs completely abolished in all study patients except for one that still exhibited a residual low-voltage antral signal after adenosine infusion with no PV conduction. Eighty-six (78.2%) patients had complete follow-up information. During the 90-day blanking period, 8 (9.2%) patients experienced an early recurrence. After the blanking period, over a follow-up of 357[190-380] days, 13 patients (15.1%) suffered an AF recurrence (time to recurrence: 207[144-300] days). No major complications or adverse events occurred. Conclusion A structured ablation workflow for catheter ablation, with consistent high-density mapping and improved diagnostic tools to guide the ablation, proved to be safe and effective in paroxysmal AF.

Silencing of the T-type voltage-gated calcium channel α1 subunit by fungus-mediated RNAi altered the structure of F-actin and caused defective behaviors in Ditylenchus destructor.

T-type calcium channels, characterized as low-voltage activated (LVA) calcium channels, play crucial physiological roles across a wide range of tissues, including both the neuronal and nonneuronal systems. Using in situ hybridization and RNA interference (RNAi) techniques in vitro, we previously identified the tissue distribution and physiological function of the T-type calcium channel α1 subunit (DdCα1G) in the plant-parasitic nematode Ditylenchus destructor. To further characterize the functional role of DdCα1G, we employed a combination of immunohistochemistry and fungus-mediated RNAi and found that DdCα1G was clearly distributed in stylet-related tissue, oesophageal gland-related tissue, secretory-excretory duct-related tissue and male spicule-related tissue. Silencing DdCα1G led to impairments in the locomotion, feeding, reproductive ability and protein secretion of nematodes. To confirm the defects in behavior, we used phalloidin staining to examine muscle changes in DdCα1G-RNAi nematodes. Our observations demonstrated that defective behaviors are associated with related muscular atrophy. Our findings provide a deeper understanding of the physiological functions of T-type calcium channels in plant-parasitic nematodes. The T-type calcium channel can be considered a promising target for sustainable nematode management practices.

A nutritional Vitamin B12 deficiency (infantile tremor syndrome) presenting as hemiconvulsion hemiplegia epilepsy syndrome

Hemiplegia Hemiconvulsion Epilepsy syndrome (HHE syndrome) is a condition characterized by the acute onset of unilateral seizures, which progress to cortical atrophy, hemiplegia and later develop epilepsy over weeks to years. Various aetiologies include infectious causes, especially meningitis, encephalitis, trauma, vascular insults, and sometimes idiopathic. Here, we present a 13-month-old female child, first in birth order, born to a non-consanguineous marriage, who presented with mild global developmental delay with acute onset right focal seizures followed by right-sided weakness and drug-resistant epilepsy. The child was found to have clinical and biochemical features of vitamin B12 deficiency with right-sided weakness. MRI of the brain initially showed edema of the left cerebral hemisphere and later atrophy on the left side. The electroencephalogram showed low voltage activity over the left cerebral hemisphere. Post-treatment with cobalamin, improvement in development was noted, with partial improvement in weakness and persistent epilepsy. In the current report, we highlight Hemiplegia Hemiconvulsion Epilepsy (HHE) syndrome on the background of nutritional vitamin B12 deficiency.

Probing the mechanisms of low-voltage activation in T-type CaV3.1 calcium channels

Probing the mechanisms of low-voltage activation in T-type CaV3.1 calcium channels

Robot joint module based on universal joint configuration driven by SMA wires

Modular robots can adapt to different production needs and working conditions. However, the complexity of structures and the choice of driving modes limit the development of modularization. In this paper, a robot joint module with a universal joint configuration driven by shape memory alloy (SMA) wires is proposed, which has 2-DOFs. For lightweight, the main body of the module is made of polylactic acid materials. SMA wires are used as the actuator due to the advantages of large output displacement, high mass-to-energy ratio, and low activation voltage. Adopting antagonistically arranged SMA wires and bias springs combination method increases the recovery speed and driving angles. A locking device is creatively proposed to avoid the influence of self-biasing spring compression. The detailed kinematic model of the module is established. A proportional integral differential controller is used to precisely control module movements, and the attitude angle sensor is used as the monitoring device. Through the maximum rotation angles and trajectory tracking movement experiments, the module is tested comprehensively, and the results show that the module has good movement characteristics and control precision. In addition, analyzing the tracking performance of the module in the time domain shows that the module has a relatively fast tracking speed. This module is beneficial to the research of configurations, actuators, and controls of modular robots.

The natural product argentatin C attenuates postoperative pain via inhibition of voltage-gated sodium and T-type voltage-gated calcium channels.

Postoperative pain occurs in as many as 70% of surgeries performed worldwide. Postoperative pain management still relies on opioids despite their negative consequences, resulting in a public health crisis. Therefore, it is important to develop alternative therapies to treat chronic pain. Natural products derived from medicinal plants are potential sources of novel biologically active compounds for development of safe analgesics. In this study, we screened a library of natural products to identify small molecules that target the activity of voltage-gated sodium and calcium channels that have important roles in nociceptive sensory processing. Fractions derived from the Native American medicinal plant, Parthenium incanum, were assessed using depolarization-evoked calcium influx in rat dorsal root ganglion (DRG) neurons. Further separation of these fractions yielded a cycloartane-type triterpene identified as argentatin C, which was additionally evaluated using whole-cell voltage and current-clamp electrophysiology, and behavioural analysis in a mouse model of postsurgical pain. Argentatin C blocked the activity of both voltage-gated sodium and low-voltage-activated (LVA) calcium channels in calcium imaging assays. Docking analysis predicted that argentatin C may bind to NaV 1.7-1.9 and CaV 3.1-3.3 channels. Furthermore, argentatin C decreased Na+ and T-type Ca2+ currents as well as excitability in rat and macaque DRG neurons, and reversed mechanical allodynia in a mouse model of postsurgical pain. These results suggest that the dual effect of argentatin C on voltage-gated sodium and calcium channels supports its potential as a novel treatment for painful conditions.

Disorder in Ca2+ release unit locations confers robustness but cuts flexibility of heart pacemaking.

Excitation-contraction coupling kinetics is dictated by the action potential rate of sinoatrial-nodal cells. These cells generate local Ca releases (LCRs) that activate Na/Ca exchanger current, which accelerates diastolic depolarization and determines the pace. LCRs are generated by clusters of ryanodine receptors, Ca release units (CRUs), residing in the sarcoplasmic reticulum. While CRU distribution exhibits substantial heterogeneity, its functional importance remains unknown. Using numerical modeling, here we show that with a square lattice distribution of CRUs, Ca-induced-Ca-release propagation during diastolic depolarization is insufficient for pacemaking within a broad range of realistic ICaL densities. Allowing each CRU to deviate randomly from its lattice position allows sparks to propagate, as observed experimentally. As disorder increases, the CRU distribution exhibits larger empty spaces and simultaneously CRU clusters, as in Poisson clumping. Propagating within the clusters, Ca release becomes synchronized, increasing action potential rate and reviving pacemaker function of dormant/nonfiring cells. However, cells with fully disordered CRU positions could not reach low firing rates and their β-adrenergic-receptor stimulation effect was substantially decreased. Inclusion of Cav1.3, a low-voltage activation L-type Ca channel isoform into ICaL, strongly increases recruitment of CRUs to fire during diastolic depolarization, increasing robustness of pacemaking and complementing effects of CRU distribution. Thus, order/disorder in CRU locations along with Cav1.3 expression regulates pacemaker function via synchronization of CRU firing. Excessive CRU disorder and/or overexpression of Cav1.3 boosts pacemaker function in the basal state, but limits the rate range, which may contribute to heart rate range decline with age and disease.

Targeted ablation of residual pulmonary vein potentials in atrial fibrillation ablation through ultra-high-density mapping: Insights from the CHARISMA registry.

Low-voltage activity beyond pulmonary veins (PVs) may contribute to the failure of ablation of atrial fibrillation (AF) in the long term. We aimed to assess the presence of gaps (PVG) and residual potential (residual antral potential [RAP]) within the antral scar by means of an ultra-high-density mapping (UHDM) system. We studied consecutive patients from the CHARISMA registry who were undergoing AF ablation and had complete characterization of residual PV antral activity. The Lumipoint™ (Boston Scientific) map-analysis tool was used sequentially on each PV component. The ablation endpoint was PV isolation (PVI) and electrical quiescence in the antral region. Fifty-eight cases of AF ablation were analyzed. A total of 86 PVGs in 34 (58.6%) patients and 44 RAPs in 34 patients (58.6%) were found. In 16 (27.6%) cases, we found at least one RAP in patients with complete absence of PV conduction. RAPs showed a lower mean voltage than PVG (0.3 ± 0.2 mV vs. 0.7 ± 0.5 mV, p < .0001), whereas the mean number of electrogram peaks was higher (8.4 ± 1.4 vs. 3.2 ± 1.5, p < .0001). The percentage of patients in whom RAPs were detected through Lumipoint™ was higher than through propagation map analysis (58.6% vs. 36.2%, p = .025). Acute procedural success was 100%, with all PVs successfully isolated and RAPs completely abolished in all study patients. During a mean follow-up of 453 ± 133 days, 6 patients (10.3%) suffered an AF/AT recurrence. Local vulnerabilities in antral lesion sets were easily discernible by means of the UHDM system in both de novo and redo patients when no PV conduction was present.

Improved procedural workflow for catheter ablation of paroxysmal AF with high-density mapping system and advanced technology: Rationale and study design of a multicenter international study.

BackgroundThe antral region of pulmonary veins (PV)s seems to play a key role in a strategy aimed at preventing atrial fibrillation (AF) recurrence. Particularly, low‐voltage activity in tissue such as the PV antra and residual potential within the antral scar likely represent vulnerabilities in antral lesion sets, and ablation of these targets seems to improve freedom from AF. The aim of this study is to validate a structured application of an approach that includes the complete abolition of any antral potential achieving electrical quiescence in antral regions.MethodsThe improveD procEdural workfLow for cathETEr ablation of paroxysmal AF with high density mapping system and advanced technology (DELETE AF) study is a prospective, single‐arm, international post‐market cohort study designed to demonstrate a low rate of clinical atrial arrhythmias recurrence with an improved procedural workflow for catheter ablation of paroxysmal AF, using the most advanced point‐by‐point RF ablation technology in a multicenter setting. About 300 consecutive patients with standard indications for AF ablation will be enrolled in this study. Post‐ablation, all patients will be monitored with ambulatory event monitoring, starting within 30 days post‐ablation to proactively detect and manage any recurrences within the 90‐day blanking period, as well as Holter monitoring at 3, 6, 9, and 12 months post‐ablation. Healthcare resource utilization, clinical data, complications, patients' medical complaints related to the ablation procedure and patient's reported outcome measures will be prospectively traced and evaluated.DiscussionThe DELETE AF trial will provide additional knowledge on long‐term outcome following a structured ablation workflow, with high density mapping, advanced algorithms and local impedance technology, in an international multicentric fashion. DELETE AF is registered at ClinicalTrials.gov (NCT05005143).

Low-Voltage Activation Based on Electrohydrodynamics in Positioning Systems for Untethered Robots

In recent years, untethered soft robots, free of the lines that restrict their mobility, have been studied extensively. Our research team has been focusing on the electrohydrodynamic phenomena (EHD) as a driving mechanism for untethered robots. EHD is a phenomenon in which a flow is generated by applying a high voltage to a dielectric liquid. We propose a method to drive a robot in an untethered manner using EHD by vertically stacking two types of liquids: conductive and dielectric. This method is simpler, more energy-efficient, and quieter than conventional systems. Although a lower voltage would prevent the enlargement of the system by limiting the electronic components, the generation of EHD requires a high voltage. Therefore, in this study, to realize the low voltage drive of untethered robots dominated by the electrostatic actuator, we tackled the reduction of the driving voltage by investigating the phenomenon. As a result, we achieved low voltage driving at 15 V and successfully drove with off-the-shelf batteries (18 V). We also investigated the output current flowing through the system to reduce power consumption. Therefore, in addition to improving the energy efficiency of the system, we confirmed that the difference of the generated current depended on the thickness of the dielectric liquid and the concentration of the conductive liquid.

The role of high-density mapping in atrial fibrillation ablation

Aims. To determine the role of the prevalence of low-voltage areas in the occurrence of arrhythmia recurrence after interventional treatment of atrial fibrillation (AF).Methods. The study included 38 patients with paroxysmal (52.6%) and persistent (47.4%) forms of AF who underwent interventional treatment of AF using high-density electroanatomical mapping (at least 10,000 EGM points). Analysis of electroanatomical maps was performed after the completion of the ablation procedure. The area of the low-voltage zones was measured manually. Then, the areas of all regions of low-voltage activity were summed up; the resulting value was expressed as a percentage of the total surface area of the left atrium (LA).Results. The observation period was 12.8±3.2 months. Based on the results of endocardial mapping, all patients were divided into 2 groups according to the prevalence of low-voltage areas in the LA. The first group included patients with an area of low-voltage zones less than 5% of the total surface of the left atrium, and the second with an area of low-voltage areas of more than 5% of the total surface of the left atrium. The patients of the first group had a lower LA volume compared to patients from the second group, with mean values of 119.87±16.35 ml and 154.57±33.23 ml, respectively (p=0.007). In the first group, AF recurrence was recorded in one patient after catheter treatment, in the second group in 5 patients.Conclusion. Common areas of low-voltage activity in the left atrium, detected by high-density mapping before the procedure for catheter treatment of AF, are a predictor of arrhythmia recurrence after interventional treatment.

Low-voltage-activated inward current in murine antral smooth muscle cells is an artifact

Two types of voltage-dependent inward currents were evoked by depolarization in murine antral smooth muscle cells (SMCs) bathed in Ca2+-containing physiological solution: high-voltage-activated (HVA) and low-voltage-activated (LVA) inward currents. We examined whether the LVA current was due to: 1) T-type Ca2+ channels, 2) Ca2+-activated Cl−channels, 3) nonselective cation channels (NSCC), or 4) voltage-dependent K+ channels. Replacement of external Ca2+ (2 mM) with equimolar Ba2+ increased the amplitude of the HVA current but blocked the LVA current. Nicardipine blocked the HVA current, and in the presence of nicardipine, T-type Ca2+ blockers failed to block LVA current. A Cl− channel antagonist had little effect on LVA current. Cation-free external solution completely abolished both HVA and LVA currents. Addition of Ca2+ to the solution restored only HVA currents. Addition of K+ (5 mM) to otherwise cation-free solution induced LVA current that reversed at −20 mV. These data suggest that LVA current is not due to T-type Ca2+ channels, Ca2+-activated Cl− channels, or NSCC. A-type K+ (KA) currents and delayed rectifying K+ (KDR) currents can be resolved in antral SMCs dialyzed with a solution containing 140 mM K+. When cells were exposed to high K+ external solution and dialyzed with Cs+-rich solution in the presence of nicardipine, LVA current was evoked and reversed at positive potentials. LVA currents were blocked by K+ channel blockers, 4-aminopyridine, and tetraethylammonium. In conclusion, LVA inward currents can be generated by K+ influx via KA channels in murine antral SMCs when cells were dialyzed with Cs+-rich solution.

Neurophysiological findings and their prognostic value in critical COVID-19 patients: An observational study

ObjectiveTo describe EEG patterns of critical Coronavirus Disease 2019 (COVID-19) patients with suspicion of encephalopathy and test their association with clinical outcome. MethodsEEG after discontinuation of sedation in all patients, and somesthesic evoked potentials and brainstem auditive evoked potentials when EEG did not show reactivity, were performed. Clinical outcome was assessed at day 7 and 14 after neurophysiological explorations. Results33 patients were included for analysis. We found slowed background activity in 85% of cases, unreactive activity in 42% of cases, low-voltage activity in 21% of cases and rhythmic or periodic delta waves in 61% of cases. EEG epileptic events were never recorded. Clinical outcome at day 14 was associated with unreactive background activity and tended to be associated with rhythmic or periodic delta waves and with low-voltage activity. Results of multimodal evoked potentials were in favor of a preservation of central nervous system somatosensory and auditory functions. ConclusionsAmong critical COVID-19 patients with abnormal arousal at discontinuation of sedation, EEG patterns consistent with encephalopathy are found and are predictive for short term clinical outcome. SignificanceThe abnormal EEG with presence of periodic discharges and lack of reactivity could be related to encephalopathy linked to COVID-19.

Triumeq Increases Excitability of Pyramidal Neurons in the Medial Prefrontal Cortex by Facilitating Voltage-Gated Ca2+ Channel Function.

Combination antiretroviral therapy (cART) suppresses HIV-1 replication, improves immune function, and prolongs the life of people living with HIV (PLWH). However, cART also induces neurotoxicity that could complicate HIV-induced neurodegeneration while reduce its therapeutic efficacy in treating HIV/AIDS. Triumeq is a first-line cART regimen, which is co-formulated by three antiretroviral drugs (ARVs), lamivudine (3TC), abcavir (ABC), and dolutegravir (DTG). Little is known about potential side effects of ARVs on the brain (including those co-formulating Triumeq), and their mechanisms impacting neuronal activity. We assessed acute (in vitro) and chronic (in vivo) effects of Triumeq and co-formulating ARVs on pyramidal neurons in rat brain slices containing the medial prefrontal cortex (mPFC) using patch-clamp recording approaches. We found that acute Triumeq or 3TC in vitro significantly increased firing of mPFC neurons in a concentration- and time-dependent manner. This neuronal hyperactivity was associated with enhanced Ca2+ influx through voltage-gated Ca2+ channels (VGCCs). Additionally, chronic treatment with Triumeq in vivo for 4 weeks (4 wks) also significantly increased firing and Ca2+ influx via VGCCs in mPFC neurons, which was not shown after 2 wks treatment. Such mPFC neuronal hyperexcitability was not found after 4 weeks treatments of individual ARVs. Further, chronic Triumeq exposure in vivo significantly enhanced mRNA expression of low voltage-activated (LVA) L-type Ca2+ channels (Cav1.3 L-channels), while changes in high voltage-activated (HVA) Cav1.2 L-channels were not observed. Collectively, these novel findings demonstrate that chronic cART induces hyperexcitability of mPFC pyramidal neurons by abnormally promoting VGCC overactivation/overexpression of VGCCs (including, but may not limited to, LVA-Cav1.3 L-channels), which could complicate HIV-induced neurotoxicity, and ultimately may contribute to HIV-associated neurocognitive disorders (HAND) in PLWH. Determining additional target(s) of cART in mPFC pyramidal neurons may help to improve the therapeutic strategies by minimizing the side effects of cART for treating HIV/AIDS.

Brain Injury in Critical Illness and a Note on the Virus

Brain Injury in Critical Illness and a Note on the Virus

Astrocyte deletion of \u03b12-Na/K ATPase triggers episodic motor paralysis in mice via a metabolic pathway

Familial hemiplegic migraine is an episodic neurological disorder characterized by transient sensory and motor symptoms and signs. Mutations of the ion pump α2-Na/K ATPase cause familial hemiplegic migraine, but the mechanisms by which α2-Na/K ATPase mutations lead to the migraine phenotype remain incompletely understood. Here, we show that mice in which α2-Na/K ATPase is conditionally deleted in astrocytes display episodic paralysis. Functional neuroimaging reveals that conditional α2-Na/K ATPase knockout triggers spontaneous cortical spreading depression events that are associated with EEG low voltage activity events, which correlate with transient motor impairment in these mice. Transcriptomic and metabolomic analyses show that α2-Na/K ATPase loss alters metabolic gene expression with consequent serine and glycine elevation in the brain. A serine- and glycine-free diet rescues the transient motor impairment in conditional α2-Na/K ATPase knockout mice. Together, our findings define a metabolic mechanism regulated by astrocytic α2-Na/K ATPase that triggers episodic motor paralysis in mice.

Epicardial voltage mapping in patients with postinfarction ventricular tachycardia: a pilot study

Introduction. Radiofrequency ablation (RFA) is an established treatment of post-myocardial infarction ventricular tachycardia (VT). Endocardial VT ablation can be insufficient for VT termination when the scar is intramural/epicardial.Purpose: to assess the extent of epicardial electrophysiological VT substrate in patients with remote myocardial infarction.Materials and methods. Thirteen patients with sustained postinfarction VT, who signed an informed consent, were included into the study. All patients underwent full clinical evaluation. Electroanatomical voltage bi- and unipolar mapping of endocardial and epicardial surfaces was performed. Maps were evaluated for the presence of low-voltage areas and local abnormal ventricular activity (LAVA). RFA was performed at LAVA sites. The end-point of the procedure was scar LAVA abolition and VT noninducibility (procedure success). VT recurrence was detected using an implantable cardioverter-defibrillator and/or ECG monitoring.Results. Epicardial access was successful in 12 patients. Epicardial access was performed at a first procedure in 7 patients, 4 patients had a history of previous endocardial ablation. Epicardial LAVA sites were detected in 9 patients. Endocardial and epicardial arrhythmogenic substrate localization coincided in 8 patients. One patient had only epicardial scar, 1 patient had only septal endocardial scar. In one patient LAVA sites had different localizations on epicardial and endocardial maps. Acute ablation success was noted in 12 patients.Conclusion. In our patient group transmural scar and epicardial electrophysiological arrhythmogenic substrate was detected in 82% of cases. Isolated endocardial ablation may be unsuccessful, in such cases epicardial mapping and ablation might be useful.

Co-existence of a fast tetrodotoxin-sensitive low voltage-activated non selective Na/Ca/K channel and of T-type Ca channels in rat isolated pulmonary vein cardiomyocytes

Ectopic foci in pulmonary veins (PV) are involved in the onset of atrial fibrillation. Norepinephrine (NE) induces an automatic activity occurring in bursts in rat PV cardiomyocytes (CM) which depends on Ca (upstroke) and Na (inter-burst) channels. To characterize low voltage-activated (LVA) Ca currents in rat PVCM susceptible to trigger ectopic foci. Whole-cell ICa (5 mM Ca) was recorded from -100 mV with classical Na- and K-free solutions at room temperature in enzymatically isolated PVCM from male Wistar rats. A fast LVA ICa (FLVA-ICa; −1.5 ± 0.2 pA/pF, n = 45; 26% of peak ICa, max recorded at + 20 mV) was activated between −55 and −20 mV in ∼56% of PVCM and blocked by 10 μM tetrodotoxin (TTX). In that, it was similar to the reported TTX-sensitive Ca current. However, it was markedly increased by addition of NaCl (1 or 3 mM) or KCl (5 or 10 mM). Permeability ratios P’Ca/PNa and P’Ca/PK calculated for bi-ionic conditions were respectively 2.25 ± 0.51 (n = 6) and 1.88 ± 0.25 (n = 14), and not different from a value of 2. NE (10 μM, n = 13) increased FLVA-ICa and negatively shifted its activation threshold, an effect partially reversed by 5 μM Atenolol. It was partially blocked by 5 μM Nifedipine (n = 5) and increased by 300 nM BayK8644 (n = 6), but not blocked by Ranolazine (10 μM, n = 6). NiCl2 (40 μM, n = 9) and TTA-A2 (10 or 100 nM, n = 11) increased FLVA-ICa. Neither Ba nor Sr alone could permeate the FLVA channel or block Ca influx but revealed a large slower activating and inactivating LVA Ca current (SLVA-ICa), present in 10 out of 80 PVCM and absent in LACM. SLVA-ICa was partially blocked by 100 nM TTA-A2. The ionic channel underlying FLVA-ICa is likely a fast voltage-gated non-selective channel permeable to Na/Ca/K with a dihydropyridine binding site. SLVA-ICa might correspond to Ca influx through Cav3.1 channels. The respective role of these channels to triggering ectopic foci in the PV myocardial sleeve remained to be determined.

Contribution of T-Type Calcium Channels to Spinal Cord Injury-Induced Hyperexcitability of Nociceptors.

A hyperexcitable state and spontaneous activity of nociceptors have been suggested to play a critical role in the development of chronic neuropathic pain following spinal cord injury (SCI). In male rats, we employed the action potential-clamp technique to determine the underlying ionic mechanisms responsible for driving SCI-nociceptors to a hyperexcitable state and for triggering their spontaneous activity. We found that the increased activity of low voltage activated T-type calcium channels induced by the injury sustains the bulk (∼60-70%) of the inward current active at subthreshold voltages during the interspike interval in SCI-nociceptors, with a modest contribution (∼10-15%) from tetrodotoxin (TTX)-sensitive and TTX-resistant sodium channels and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels. In current-clamp recordings, inhibition of T-type calcium channels with 1 μm TTA-P2 reduced both the spontaneous and the evoked firing in response to current injections in SCI-nociceptors to a level similar to sham-nociceptors. Electrophysiology in vitro was then combined with the conditioned place preference (CPP) paradigm to determine the relationship between the increased activity of T-type channels in SCI-nociceptors and chronic neuropathic pain following SCI. The size of the interspike T-type calcium current recorded from nociceptors isolated from SCI rats showing TTA-P2-induced CPP (responders) was ∼6 fold greater than the interspike T-type calcium current recorded from nociceptors isolated from SCI rats without TTA-P2-induced CPP (non-responders). Taken together, our data suggest that the increased activity of T-type calcium channels induced by the injury plays a primary role in driving SCI-nociceptors to a hyperexcitable state and contributes to chronic neuropathic pain following SCI.SIGNIFICANCE STATEMENT Chronic neuropathic pain is a major comorbidity of spinal cord injury (SCI), affecting up to 70-80% of patients. Anticonvulsant and tricyclic antidepressant drugs are first line analgesics used to treat SCI-induced neuropathic pain, but their efficacy is very limited. A hyperexcitable state and spontaneous activity of SCI-nociceptors have been proposed as a possible underlying cause for the development of chronic neuropathic pain following SCI. Here, we show that the increased activity of T-type calcium channels induced by the injury plays a major role in driving SCI-nociceptors to a hyperexcitable state and for promoting their spontaneous activity, suggesting that T-type calcium channels may represent a pharmacological target to treat SCI-induced neuropathic pain.

Dopaminergic Modulation of Signal Processing in a Subset of Retinal Bipolar Cells.

The retina and the olfactory bulb are the gateways to the visual and olfactory systems, respectively, similarly using neural networks to initiate sensory signal processing. Sensory receptors receive signals that are transmitted to neural networks before projecting to primary cortices. These networks filter sensory signals based on their unique features and adjust their sensitivities by gain control systems. Interestingly, dopamine modulates sensory signal transduction in both systems. In the retina, dopamine adjusts the retinal network for daylight conditions (“light adaptation”). In the olfactory system, dopamine mediates lateral inhibition between the glomeruli, resulting in odorant signal decorrelation and discrimination. While dopamine is essential for signal discrimination in the olfactory system, it is not understood whether dopamine has similar roles in visual signal processing in the retina. To elucidate dopaminergic effects on visual processing, we conducted patch-clamp recording from second-order retinal bipolar cells, which exhibit multiple types that can convey different temporal features of light. We recorded excitatory postsynaptic potentials (EPSPs) evoked by various frequencies of sinusoidal light in the absence and presence of a dopamine receptor 1 (D1R) agonist or antagonist. Application of a D1R agonist, SKF-38393, shifted the peak temporal responses toward higher frequencies in a subset of bipolar cells. In contrast, a D1R antagonist, SCH-23390, reversed the effects of SKF on these types of bipolar cells. To examine the mechanism of dopaminergic modulation, we recorded voltage-gated currents, hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, and low-voltage activated (LVA) Ca2+ channels. SKF modulated HCN and LVA currents, suggesting that these channels are the target of D1R signaling to modulate visual signaling in these bipolar cells. Taken together, we found that dopamine modulates the temporal tuning of a subset of retinal bipolar cells. Consequently, we determined that dopamine plays a role in visual signal processing, which is similar to its role in signal decorrelation in the olfactory bulb.