Inactivation Of Voltage-gated Sodium Channels Research Articles

The Initial Experience of Eslicarbazepine in Children at Three Canadian Tertiary Pediatric Care Centers.

Eslicarbazepine (ESL) is a once-daily, third-generation antiseizure medication for focal-onset seizures. The primary mechanism of action is enhancing the slow inactivation of voltage-gated sodium channels. The study objective was to review real-world experience regarding retention rate, efficacy, and tolerability of eslicarbazepine, soon after it became available for children in Canada. A retrospective review was performed on all patients prescribed eslicarbazepine from September 2017 to June 2020, with at least 3 years of follow-up data, at 3 Canadian tertiary care pediatric centers. Fifty patients were identified, and the mean age of eslicarbazepine initiation was 12.4 years (range 3-19 years). Most patients had drug-resistant epilepsy, trying a mean of 5.04 (range 0-14) antiseizure medications before the initiation of eslicarbazepine. Twenty-four patients (48.0%) experienced adverse effects, including dizziness (n = 10), drowsiness (n = 6), dizziness and drowsiness (n = 1), nausea and abdominal pain (n = 4), transient unsteadiness and diplopia (n = 1), and negative mood changes (n = 2). None had serious adverse effects, including rash. The retention rate of eslicarbazepine at last follow-up was 70%. Fifteen (30%) had ≥50% seizure reduction, with 2 of these patients becoming seizure free. Ten (20%) had 25% to 50% reduction, 2 (4%) had worsening of seizures, and 17 (34%) had no change in seizure frequency. The study results support the long-term effectiveness and tolerability of eslicarbazepine in a cohort of children with predominantly drug-resistant epilepsy in a real-life setting from 3 Canadian centers with initial use after approval. Adverse effects were nonserious, infrequently leading to eslicarbazepine discontinuation.

Structural basis for the rescue of hyperexcitable cells by the amyotrophic lateral sclerosis drug Riluzole

Neuronal hyperexcitability is a key element of many neurodegenerative disorders including the motor neuron disease Amyotrophic Lateral Sclerosis (ALS), where it occurs associated with elevated late sodium current (INaL). INaL results from incomplete inactivation of voltage-gated sodium channels (VGSCs) after their opening and shapes physiological membrane excitability. However, dysfunctional increases can cause hyperexcitability-associated diseases. Here we reveal the atypical binding mechanism which explains how the neuroprotective ALS-treatment drug riluzole stabilises VGSCs in their inactivated state to cause the suppression of INaL that leads to reversed cellular overexcitability. Riluzole accumulates in the membrane and enters VGSCs through openings to their membrane-accessible fenestrations. Riluzole binds within these fenestrations to stabilise the inactivated channel state, allowing for the selective allosteric inhibition of INaL without the physical block of Na+ conduction associated with traditional channel pore binding VGSC drugs. We further demonstrate that riluzole can reproduce these effects on a disease variant of the non-neuronal VGSC isoform Nav1.4, where pathologically increased INaL is caused directly by mutation. Overall, we identify a model for VGSC inhibition that produces effects consistent with the inhibitory action of riluzole observed in models of ALS. Our findings will aid future drug design and supports research directed towards riluzole repurposing.

δ-Conotoxin Structure Prediction and Analysis through Large-Scale Comparative and Deep Learning Modeling Approaches.

The δ-conotoxins, a class of peptides produced in the venom of cone snails, are of interest due to their ability to inhibit the inactivation of voltage-gated sodium channels causing paralysis and other neurological responses, but difficulties in their isolation and synthesis have made structural characterization challenging. Taking advantage of recent breakthroughs in computational algorithms for structure prediction that have made modeling especially useful when experimental data is sparse, this work uses both the deep-learning-based algorithm AlphaFold and comparative modeling method RosettaCM to model and analyze 18 previously uncharacterized δ-conotoxins derived from piscivorous, vermivorous, and molluscivorous cone snails. The models provide useful insights into the structural aspects of these peptides and suggest features likely to be significant in influencing their binding and different pharmacological activities against their targets, with implications for drug development. Additionally, the described protocol provides a roadmap for the modeling of similar disulfide-rich peptides by these complementary methods.

Delta-Conotoxin Structure Prediction and Analysis through Large-scale Comparative and Deep Learning Modeling Approaches.

The delta-conotoxins, a class of peptide produced in the venom of cone snails, are of interest due to their ability to inhibit the inactivation of voltage-gated sodium channels causing paralysis and other neurological responses, but difficulties in their isolation and synthesis have made structural characterization challenging. Taking advantage of recent breakthroughs in computational algorithms for structure prediction that have made modeling especially useful when experimental data is sparse, this work uses both the deep-learning based algorithm AlphaFold and comparative modeling method RosettaCM to model and analyze 18 previously uncharacterized delta-conotoxins derived from piscivorous, vermivorous, and molluscivorous cone snails. The models provide useful insights into structural aspects of these peptides and suggest features likely to be significant in influencing their binding and different pharmacological activities against their targets, with implications for drug development. Additionally, the described protocol provides a roadmap for the modeling of similar disulfide-rich peptides by these complementary methods.

Conformational photo-trapping in NaV1.5: Inferring local motions at the “inactivation gate”

Rapid and effectual inactivation in voltage-gated sodium channels is required for canonical action-potential firing. This “fast” inactivation arises from swift and reversible protein conformational changes that utilize transmembrane segments and the cytoplasmic linker between channel domains III and IV. Until recently, fast inactivation had been accepted to rely on a “ball-and-chain” mechanism whereby a hydrophobic triplet of DIII-IV amino acids (IFM) impairs conductance by binding to a site in central pore of the channel made available by channel opening. New structures of sodium channels have upended this model. Specifically, cryo-electron microscopic structures of eukaryotic sodium channels depict a peripheral binding site for the IFM motif, outside of the pore, opening the possibility of a yet unidentified allosteric mechanism of fast-inactivation gating. We set out to study fast inactivation by photo-trapping human sodium channels in various functional states under voltage control. This was achieved by genetically encoding the crosslinking unnatural amino acid benzophenone phenylalanine at various sites within the DIII-IV linker in the cardiac sodium channel NaV1.5. These data show dynamic state- and positional-dependent trapping of the transient conformations associated with fast inactivation, each yielding different phenotypes and rates of trapping. These data reveal distinct conformational changes that underlie fast inactivation and point to a dynamic environment around the IFM locus.

Efficacy of Lacosamide and Rufinamide as Adjuncts to Midazolam-Ketamine Treatment Against Cholinergic-Induced Status Epilepticus in Rats.

Benzodiazepine pharmacoresistance develops when treatment of status epilepticus (SE) is delayed. This response may result from gamma-aminobutyric acid A receptors (GABAAR) internalization that follows prolonged SE; this receptor trafficking results in fewer GABAAR in the synapse to restore inhibition. Increase in synaptic N-methyl-D-aspartate receptors (NMDAR) also occurs in rodent models of SE. Lacosamide, a third-generation antiseizure medication (ASM), acts on the slow inactivation of voltage-gated sodium channels. Another ASM, rufinamide, similarly acts on sodium channels by extending the duration of time spent in the inactivation stage. Combination therapy of the benzodiazepine midazolam, NMDAR antagonist ketamine, and ASMs lacosamide (or rufinamide) was investigated for efficacy against soman (GD)-induced SE and neuropathology. Adult male rats implanted with telemetry transmitters for monitoring electroencephalographic (EEG) activity were exposed to a seizure-inducing dose of GD and treated with an admix of atropine sulfate and HI-6 1 minute later and with midazolam monotherapy or combination therapy 40 minutes after EEG seizure onset. Rats were monitored continuously for seizure activity for two weeks, after which brains were processed for assessment of neurodegeneration, neuronal loss, and neuroinflammatory responses. Simultaneous administration of midazolam, ketamine, and lacosamide (or rufinamide) was more protective against GD-induced SE compared with midazolam monotherapy. In general, lacosamide triple therapy had more positive outcomes on measures of epileptogenesis, EEG power integral, and the number of brain regions protected from neuropathology compared with rats treated with rufinamide triple therapy. Overall, both drugs were well tolerated in these combination models. SIGNIFICANCE STATEMENT: We currently report on improved efficacy of antiseizure medications lacosamide and rufinamide, each administered in combination with ketamine (NMDAR antagonist) and midazolam (benzodiazepine), in combatting soman (GD)-induced seizure, epileptogenesis, and brain pathology over that provided by midazolam monotherapy, or dual therapy of midazolam and lacosamide (or rufinamide) in rats. Administration of lacosamide as adjunct to midazolam and ketamine was particularly effective against GD-induced toxicity. However, protection was incomplete, suggesting the need for further study.

Unblock the Block! Preventing Inhibitory Failure to Maintain Inhibitory Restraint.

Disrupting Epileptiform Activity by Preventing Parvalbumin Interneuron Depolarization Block Călin A, Ilie AS, Akerman CJ. J Neurosci. 2021;41(45):9452-9465. doi:10.1523/JNEUROSCI.1002-20.2021. Epub 2021 Oct 5.Inhibitory synaptic mechanisms oppose epileptic network activity in the brain. The breakdown in this inhibitory restraint and propagation of seizure activity has been linked to the overwhelming of feedforward inhibition, which is provided in large part by parvalbumin-expressing (PV) interneurons in the cortex. The underlying cellular processes therefore represent potential targets for understanding and preventing the propagation of seizure activity. Here we use an optogenetic strategy to test the hypothesis that depolarization block in PV interneurons is a significant factor during the loss of inhibitory restraint. Depolarization block results from the inactivation of voltage-gated sodium channels and leads to impaired action potential firing. We used focal NMDA stimulation to elicit reproducible epileptiform discharges in hippocampal organotypic brain slices from male and female mice and combined this with targeted recordings from defined neuronal populations. Simultaneous patch-clamp recordings from PV interneurons and pyramidal neurons revealed epileptiform activity that was associated with an overwhelming of inhibitory synaptic mechanisms and the emergence of a partial, and then complete, depolarization block in PV interneurons. To counteract this depolarization block, we developed protocols for eliciting pulsed membrane hyperpolarization via the inhibitory opsin, archaerhodopsin. This optical approach was effective in counteracting cumulative inactivation of voltage-gated channels, maintaining PV interneuron action potential firing properties during the inhibitory restraint period, and reducing the probability of initiating epileptiform activity. These experiments support the idea that depolarization block is a point of weakness in feedforward inhibitory synaptic mechanisms and represents a target for preventing the initiation and spread of seizure activity.

The effect of chronic treatment with sodium channel blocker lacosamide on early development of absence seizures in genetic absence epilepsy rats

ObjectiveLacosamide (LCM) is a new generation antiepileptic drug that affects the slow inactivation of voltage-gated sodium channels. We studied whether chronic LCM treatment prior to onset of absence seizures was able to prevent/reduce the development of absence seizures in GAERS rats, a well-validated animal model of absence epilepsy and epileptogenesis. Drug effects on the duration, mean duration, number and spectral characteristics of spike-wave discharges (SWDs) were measured both 1 and 2 months after treatment withdrawal and compared with the ethosuximide (ETX) that has anti-epileptogenic activity in GAERS. Furthermore, the acute effects of LCM on SWDs in adult GAERS were evaluated. MethodsGAERS rats were administered either with LCM (10 mg/kg/day or 30 mg/kg/day, i.p) or ETX (25 mg/kg/day, i.p) or saline (%0.9 NaCl) until PN60 for 40 consecutive days starting from PN20. Animals were stereotaxically implanted with cortical screw electrodes under ketamine/xylazine anesthesia at PN53. Following recovery period, EEG were recorded at PN60 (last day of drug administration)− 61–62, PN90–91–92 and PN120–121–122 time periods for 3 consecutive days. ResultsThe chronic treatment with both LCM and ETX led to an ∼50% reduction in the development of spontaneous absence seizures in GAERS at PN90 and PN120 after the treatment withdrawal at PN60. The spectral analysis of EEG data revealed significant slowing of the peak frequency of SWDs in LCM treated animals at PN62. ConclusionThese results confirm that chronic LCM treatment modifies the development of absence seizures in GAERS and suggest that LCM exerts beneficial effects on absence seizure epileptogenesis.

Lacosamide-Related Arrhythmias: A Systematic Analysis and Review of the Literature.

Lacosamide (LCM) is a new antiepileptic drug used as an adjunctive treatment for partial seizures with and without secondary generalization. One of the modes of action is the enhancement of slow inactivation of voltage-gated sodium channels. Experimental studies and clinical trials suggest that LCM acts upon both neurons and the heart and may increase the risk of cardiac arrhythmias. A systematic review was conducted to investigate characteristics of arrhythmias related to the use of LCM for the treatment of seizures. The search terms “lacosamide”, “arrhythmias”, “AV block”, “atrial fibrillations/flutter”, “cardiac conductions defects”, “ventricular tachycardia”, “ventricular fibrillation were used. Case reports and retrospective studies were gathered by searching Medline/PubMed, Google Scholar, CINAHL (Cumulative Index to Nursing and Allied Health Literature), Cochrane CENTRAL (Cochrane Central Register of Controlled Trials), and Web of Science databases. Seventeen articles were selected for review. Ventricular tachycardia was the most reported LCM related arrhythmia (29.4%), followed by new-onset atrial fibrillation (17.6%), complete heart block (17.6%), Mobitz type 1 Atrio-ventricular block (11.8%), sinus pauses (11.8%), pulseless electrical activity (5.9%) and widening QRS complex (5.9%). Further research and clinical trials are needed to explore the etiopathogenesis and causative relationship between the use of LCM and arrhythmias.

Disrupting Epileptiform Activity by Preventing Parvalbumin Interneuron Depolarization Block

Inhibitory synaptic mechanisms oppose epileptic network activity in the brain. The breakdown in this inhibitory restraint and propagation of seizure activity has been linked to the overwhelming of feedforward inhibition, which is provided in large part by parvalbumin-expressing (PV) interneurons in the cortex. The underlying cellular processes therefore represent potential targets for understanding and preventing the propagation of seizure activity. Here we use an optogenetic strategy to test the hypothesis that depolarization block in PV interneurons is a significant factor during the loss of inhibitory restraint. Depolarization block results from the inactivation of voltage-gated sodium channels and leads to impaired action potential firing. We used focal NMDA stimulation to elicit reproducible epileptiform discharges in hippocampal organotypic brain slices from male and female mice and combined this with targeted recordings from defined neuronal populations. Simultaneous patch-clamp recordings from PV interneurons and pyramidal neurons revealed epileptiform activity that was associated with an overwhelming of inhibitory synaptic mechanisms and the emergence of a partial, and then complete, depolarization block in PV interneurons. To counteract this depolarization block, we developed protocols for eliciting pulsed membrane hyperpolarization via the inhibitory opsin, archaerhodopsin. This optical approach was effective in counteracting cumulative inactivation of voltage-gated channels, maintaining PV interneuron action potential firing properties during the inhibitory restraint period, and reducing the probability of initiating epileptiform activity. These experiments support the idea that depolarization block is a point of weakness in feedforward inhibitory synaptic mechanisms and represents a target for preventing the initiation and spread of seizure activity.SIGNIFICANCE STATEMENT GABAA receptor-mediated synaptic transmission opposes seizure activity by establishing an inhibitory restraint against spreading excitation. Parvalbumin-expressing (PV) interneurons contribute significantly to this inhibitory restraint, but it has been suggested that these cells are overwhelmed as they enter a state of "depolarization block." Here we test the importance of this process by devising an optogenetic strategy to selectively relieve depolarization block in PV interneurons. By inducing brief membrane hyperpolarization, we show that it is possible to reduce depolarization block in PV interneurons, maintain their action potential firing in the face of strong excitation, and disrupt epileptiform activity in an in vitro model. This represents a proof of principle that targeting rate-limiting processes can strengthen the inhibitory restraint of epileptiform activity.

The insecticide deltamethrin enhances sodium channel slow inactivation of human Nav1.9, Nav1.8 and Nav1.7

The insecticide deltamethrin of the pyrethroid class mainly targets voltage-gated sodium channels (Navs). Deltamethrin prolongs the opening of Navs by slowing down fast inactivation and deactivation. Pyrethroids are supposedly safe for humans, however, they have also been linked to the gulf-war syndrome, a neuropathic pain condition that can develop following exposure to certain chemicals. Inherited neuropathic pain conditions have been linked to mutations in the Nav subtypes Nav1.7, Nav1.8, and Nav1.9. Here, we examined the effect of deltamethrin on the human isoforms Nav1.7, Nav1.8, and Nav1.9_C4 (chimera containing the C-terminus of rat Nav1.4) heterologously expressed in HEK293T and ND7/23 cells using whole-cell patch-clamp electrophysiology. For all three Nav subtypes, we observed increased persistent and tail currents that are typical for Nav channels modified by deltamethrin. The most surprising finding was an enhanced slow inactivation induced by deltamethrin in all three Nav subtypes. An enhanced slow inactivation is contrary to the prolonged opening caused by pyrethroids and has not been described for deltamethrin or any other pyrethroid before. Furthermore, we found that the fraction of deltamethrin-modified channels increased use-dependently. However, for Nav1.8, the use-dependent potentiation occurred only when the holding potential was increased to −90 mV, a potential at which the tail currents decay more slowly. This indicates that use-dependent modification is due to an accumulation of tail currents. In summary, our findings support a novel mechanism whereby deltamethrin enhances slow inactivation of voltage-gated sodium channels, which may, depending on the cellular resting membrane potential, reduce neuronal excitability and counteract the well-described pyrethroid effects of prolonging channel opening.

Sodium channel activation underlies transfluthrin repellency in Aedes aegypti

BackgroundVolatile pyrethroid insecticides, such as transfluthrin, have received increasing attention for their potent repellent activities in recent years for controlling human disease vectors. It has been long understood that pyrethroids kill insects by promoting activation and inhibiting inactivation of voltage-gated sodium channels. However, the mechanism of pyrethroid repellency remains poorly understood and controversial.Methodology/Principal findingsHere, we show that transfluthrin repels Aedes aegypti in a hand-in-cage assay at nonlethal concentrations as low as 1 ppm. Contrary to a previous report, transfluthrin does not elicit any electroantennogram (EAG) responses, indicating that it does not activate olfactory receptor neurons (ORNs). The 1S-cis isomer of transfluthrin, which does not activate sodium channels, does not elicit repellency. Mutations in the sodium channel gene that reduce the potency of transfluthrin on sodium channels decrease transfluthrin repellency but do not affect repellency by DEET. Furthermore, transfluthrin enhances DEET repellency.Conclusions/SignificanceThese results provide a surprising example that sodium channel activation alone is sufficient to potently repel mosquitoes. Our findings of sodium channel activation as the principal mechanism of transfluthrin repellency and potentiation of DEET repellency have broad implications in future development of a new generation of dual-target repellent formulations to more effectively repel a variety of human disease vectors.

Derivative of Scorpion Neurotoxin BeM9 Is Selective for Insect Voltage-Gated Sodium Channels

Scorpion α-toxins are small proteins inhibiting the inactivation of voltage-gated sodium channels. They can selectively act on either mammalian (mammal toxins) or insect channels (insect toxins), or affect both types of channels (α-like toxins). Currently no model has been proposed that fully explains the dependence of selectivity upon amino acid sequence, but some patterns have already been established. Thus, most mammal toxins have an aspartic acid residue in position 8, which is involved in the formation of the nest motif, but it is still not clear whether this residue interacts directly with channels. The objective of our study was to obtain a derivative of the α-like toxin BeM9 with the replacement of lysine in position 8 by glutamate (K8E), changing the charge, but excluding the formation of the nest motif. In addition, we replaced the tyrosine in position 17 with glycine (Y17G), which is characteristic of mammal toxins. Surprisingly, the double-mutant derivative BeM9EG lost its activity on mammalian channels, becoming an insect toxin. To explain these changes, we constructed models of BeM9 and BeM9EG complexes with channels, and also performed molecular dynamics of isolated toxins. Analysis of intermolecular contacts in the complexes did not explain the reason for the selectivity change. Nevertheless, the structure of intramolecular contacts and data on molecular mobility indicate an important role of residues K8 and Y17 in stabilizing a certain conformation of BeM9 loops. We assume that the replacement of these residues allosterically affects the efficiency of toxin binding to channels.

Structure of MeuNaTxα-1 toxin from scorpion venom highlights the importance of the nest motif.

Old world scorpions produce an abundance of toxins called α-NaTx, which interfere with the fast inactivation of voltage-gated sodium channels. Their selectivity to channels of mammals or insects depends on a part of toxin named the specificity module. We report here the spatial structure of a major and broadly active toxin MeuNaTxα-1 from the venom of Mesobuthus eupeus. Notably, its specificity module is markedly different from other α-NaTx with known 3D structure. Close inspection shows that its conformation is a result of an interplay between protein motifs such as the nest and niche, which eventually shape α-NaTx structural diversity.

Efficacy and Tolerability of Lacosamide for Focal Epileptic Patients: Study from Epilepsy Clinic in Makkah.

Lacosamide is characterized by its novel dual mode of action on account of its structural components; its molecule contains a functional amino acid that selectively and slowly promotes the inactivation of voltage-gated sodium channels. This study aims to assess the effectiveness and tolerability of Lacosamide with respect to its use in the treatment of focal epileptic patients. This retrospective cohort study used data collected from the clinical notes or diaries of all epileptic patients who were treated in King Abdullah Medical City during the time period from 2014 to 2019. The multivariate Generalized Estimating Equation (GEE) repeated measure logistic regression analysis was used to assess the odds of having an improvised seizure rate. Majority of the focal epileptic patients (57.9%) were diagnosed with temporal epilepsy, while 26.3% patients had frontal epileptic lesion/diagnoses. Majority of the patients (54.4%) had received a combination of old and new treatment. Out of the seven patients who reported side effects, 57.14% experienced dizziness and headache, tremors (n = 1), loss of balance (n = 1) and increased seizure with abnormal vision acuity and psychosis (n = 1). 84.2% patients experienced reduced median seizure frequency in 12-month period. However, on the basis of clinical characteristics, no significant difference was observed in the seizure control rate. No statistically significant differences were observed between male and female patients with respect to their average improvement rate across the four time points. Lacosamide is an effective and well tolerable drug for patients with focal epilepsy.

Autonomic functions in focal epilepsy: A comparison between lacosamide and carbamazepine monotherapy

ObjectiveSome antiepileptic drugs (AEDs), like sodium channel blockers are significantly associated with autonomic dysfunction in patients with epilepsy. Unlike other sodium-blockers AEDs, lacosamide (LCM) is a third generation AEDs which enhances the slow inactivation of voltage-gated sodium channels. So far, data about LCM on autonomic nervous system are still unknown. This study was designed to investigate cardiovascular autonomic and sudomotor function in patients affected by focal epilepsy on LCM monotherapy, compared to patients treated with carbamazepine (CBZ) monotherapy and healthy subjects. MethodsPatients on LCM underwent autonomic function tests including head up tilt test (HUTT), Valsalva maneuver, deep breathing, hand grip, and cold face. Heart rate variability (HRV) analysis was performed in rest condition and during HUTT. Sudomotor function was assessed through Sudoscan. All results were compared with patients on carbamazepine (CBZ) monotherapy and with healthy subjects. ResultsFourteen patients on LCM monotherapy, 12 patients on CBZ monotherapy and 16 healthy controls were studied. At cardiovascular function tests, delta systolic blood pressure (∆SBP) at 3 min of HUTT and ∆SBP early phase II-late phase II at Valsalva maneuver were significantly lower in CBZ group compared to LCM patients. Spectral analysis of HRV showed no significant differences among LCM, CBZ and control groups. No difference in sudomotor function was found in all three groups. ConclusionsIn conclusion, our findings suggest that LCM and CBZ on monotherapy do not affect autonomic cardiovascular and sudomotor functions compared to controls. Nevertheless, patients on CBZ showed a lower sympathetic reactivity with respect to LCM.

Role of Lacosamide in Preventing Pentylenetetrazole Kindling-Induced Alterations in the Expression of the Gamma-2 Subunit of the GABAA Receptor in Rats.

Epilepsy remains challenging to treat still no etiologic treatment has been identified, however, some antiepileptic drugs (AEDs) are able to modify the pathogenesis of the disease. Lacosamide (LCM) has been shown to possess complex anticonvulsant and neuroprotective actions, being an enhancer of the slow inactivation of voltage-gated sodium channels, and it has the potential to prevent epileptogenesis. Recent evidence has shown that LCM indirectly improves the function of GABAA receptors. Receptors at most GABAergic synapses involve the gamma-2 subunit, which contributes to both phasic and tonic inhibition, and its presence assures benzodiazepine sensitivity. Moreover, mutant gamma-2 subunits were associated with generalized epilepsy syndromes. In animal models, the expression of the gamma-2 subunit of the gamma-aminobutyric acid A receptor (GABAAg2) was shown to be increased in pentylenetetrazole (PTZ)-induced chemical kindling in Wistar rats. This study hypothesized that LCM might affect the kindling process by influencing the expression of GABAA receptors in the hippocampus. The gene and protein expression levels of the GABAAg2 were studied using RT-qPCR and immunofluorescent staining. It was found that LCM treatment (10 mg/kg i.p. daily for 57 days) reduced the maximal intensity of the PTZ-induced seizures but did not prevent kindling. On the other hand, LCM treatment reverted the increase of mRNA expression of GABAAg2 in the hippocampus and prevented the decrease of GABAAg2 protein in the hippocampal CA1 region. LCM could exhibit modulatory effects on the GABAergic system of the hippocampus that may be independent of the anticonvulsant action.

Type II toxins from sea anemone Heteractis crispa with various effects on activation and inactivation of voltage-gated sodium channels

Type II toxins from sea anemone Heteractis crispa with various effects on activation and inactivation of voltage-gated sodium channels

Refined structure of BeM9 reveals arginine hand, an overlooked structural motif in scorpion toxins affecting sodium channels.

Sodium channel alpha-toxins from scorpion venom (α-NaTx) inhibit the inactivation of voltage-gated sodium channels. We used solution NMR to investigate the structure of BeM9 toxin from Mesobuthus eupeus scorpion, a prototype α-NaTx classified as an "α-like" toxin due to its wide spectrum of activity on insect and mammalian channels. We identified a new motif that we named "arginine hand," whereby arginine side chain forms several hydrogen bonds with main chain atoms. The arginine hand was found in the "specificity module," a part of the molecule that dictates toxin selectivity; and just single arginine-to-lysine point mutation drastically changed BeM9 selectivity profile.

Electroencephalographic and Electrocardiographic Effect of Intravenous Lacosamide in Refractory Focal Epilepsy.

Lacosamide selectively enhances slow inactivation of voltage-gated sodium channels to achieve seizure reduction. We studied the effect of intravenous lacosamide given as one of three single doses on EEG and electrocardiogram, as well as its tolerability in patients with drug-resistant epilepsy. This Canadian, investigator-initiated, multicenter, double-blind study recruited patients with refractory focal epilepsy admitted to a seizure monitoring unit. Participants received a loading dose of 100, 200, or 400 mg lacosamide over 30 minutes during continuous monitoring by video-EEG and 12-lead electrocardiogram. The number of interictal spikes, frequency and quantity of background EEG rhythms, corrected QT interval (QTc), PR interval, heart rate (HR), blood pressure, and respiration rate during 60 minutes before the administration were compared with 60 minutes after the infusion. We documented any adverse event during and after the infusion. Seventy-one patients completed the study. There was a significant decrease in interictal spikes (P = 0.039) and decreased frequency of the alpha rhythm (P = 0.003). No significant difference in beta, theta, and delta frequency or amount was noted. There were significant increases in PR interval (153.4-155.8 ms, P = 0.031) and HR (73.4-75.5 bpm, P = 0.022), but QTc, blood pressure, and respiration rate were not affected. Twelve patients (16.9%) experienced transient and mild adverse events, mainly dizziness and leg tingling. More adverse events occurred with 400 mg lacosamide than with the lower doses (P = 0.048). Intravenous lacosamide is effective in decreasing interictal spikes. Despite a small effect on EEG and electrocardiogram rhythms, it is well tolerated with no serious adverse events.