Voltage-gated Sodium Ion Channels Research Articles

Safinamide, an inhibitor of monoamine oxidase, modulates the magnitude, gating, and hysteresis of sodium ion current

BackgroundSafinamide (SAF), an α-aminoamide derivative and a selective, reversible monoamine oxidase (MAO)-B inhibitor, has both dopaminergic and nondopaminergic (glutamatergic) properties. Several studies have explored the potential of SAF against various neurological disorders; however, to what extent SAF modulates the magnitude, gating, and voltage-dependent hysteresis [Hys(V)] of ionic currents remains unknown.MethodsWith the aid of patch-clamp technology, we investigated the effects of SAF on voltage-gated sodium ion (NaV) channels in pituitary GH3 cells.ResultsSAF concentration-dependently stimulated the transient (peak) and late (sustained) components of voltage-gated sodium ion current (INa) in pituitary GH3 cells. The conductance–voltage relationship of transient INa [INa(T)] was shifted to more negative potentials with the SAF presence; however, the steady-state inactivation curve of INa(T) was shifted in a rightward direction in its existence. SAF increased the decaying time constant of INa(T) induced by a train of depolarizing stimuli. Notably, subsequent addition of ranolazine or mirogabalin reversed the SAF-induced increase in the decaying time constant. SAF also increased the magnitude of window INa induced by an ascending ramp voltage Vramp. Furthermore, SAF enhanced the Hys(V) behavior of persistent INa induced by an upright isosceles-triangular Vramp. Single-channel cell-attached recordings indicated SAF effectively increased the open-state probability of NaV channels. Molecular docking revealed SAF interacts with both MAO and NaV channels.ConclusionSAF may interact directly with NaV channels in pituitary neuroendocrine cells, modulating membrane excitability.

Trifunctional Saxitoxin Conjugates for Covalent Labeling of Voltage-Gated Sodium Channels.

Voltage-gated sodium ion channels (NaV s) are integral membrane protein complexes responsible for electrical signal conduction in excitable cells. Methods that enable selective labeling of NaV s hold potential value for understanding how channel regulation and post-translational modification are influenced during development and in response to diseases and disorders of the nervous system. We have developed chemical reagents patterned after (+)-saxitoxin (STX) - a potent and reversible inhibitor of multiple NaV isoforms - and affixed with a reactive electrophile and either a biotin cofactor, fluorophore, or 'click' functional group for labeling wild-type channels. Our studies reveal enigmatic structural effects of the probes on the potency and efficiency of covalent protein modification. Among the compounds analyzed, a STX-maleimide-coumarin derivative is most effective at irreversibly blocking Na+ conductance when applied to recombinant NaV s and endogenous channels expressed in hippocampal neurons. Mechanistic analysis supports the conclusion that high-affinity toxin binding is a prerequisite for covalent protein modification. Results from these studies are guiding the development of next-generation tool compounds for selective modification of NaV s expressed in the plasma membranes of cells.

1524-P: Selective Deletion of Nav1.7 in Cerebellar Purkinje Neurons Prevents Diet-Induced Obesity by Promoting Voluntary Locomotion

The pacemaker activity of cerebellum Purkinje neurons is well-known to be essential in multiple physiological functions, including voluntary locomotion, balance, aggressive behavior, and cognitive behavior. However, the specific ionic mechanism of Purkinje neurons in regulating voluntary locomotion is still unclear. To this end, we ex vivo electrophysiologically recorded the activity changes of Purkinje neurons after wheel running by using Pcp2-Cre/Rosa26-LTL-tdTOMATO reporter mice with tdTOMATO selectively expressed in Purkinje neurons. We found that the Purkinje neural activity was reduced by wheel running, associated with decreases in voltage-gated sodium current and expression of the voltage-gated sodium ion channel Nav1.7 (Scn9a), suggesting a potential role of Nav1.7-mediated sodium current. To test whether Nav1.7 is required for the activity dynamics of Purkinje neurons induced by voluntary wheel running and subsequent beneficial metabolic effects, we crossed Scn9a flox/flox mice with Pcp2-Cre mice to generate a mouse model with Nav1.7 selectively deleted from Purkinje neurons (Pcp2-Cre/Scn9a flox/flox, Nav1.7-KOPcp2). Nav1.7-KOPcp2 significantly decreased Purkinje neural dynamics, mimicking wheel running-induced neural activity reduction. Nav1.7-KOPcp2 mice also significantly increased voluntary locomotion compared to the control littermates. Further, Nav1.7-KOPcp2 mice showed decreased body weight gain, reduced blood glucose, and improved insulin sensitivity when fed a high-fat diet (HFD). These beneficial metabolic effects were associated with increased running activity but not food intake. In summary, these findings provide evidence to support the vital role of the Nav1.7 ion channel expressed by Purkinje neurons in the beneficial metabolic effects of voluntary locomotion activity. Disclosure B. Feng: None. P. Gao: None. J. Harms: None. P. Luo: None. P. Xu: None. Y. He: None. Funding National Institutes of Health (R01DK123098, R01DK129548)

The Therapeutic Value of Tetrodotoxin

Tetrodotoxin is a very important toxin to study because there are many cases of intoxication of tetrodotoxin. In this review, we will illustrate the therapeutic value of tetrodotoxin by explaining the mechanism of tetrodotoxin, the importance of tetrodotoxin as a pain treatment, and some clinical evidence. Tetrodotoxin can prevent the neurons from traveling through the voltage-gated sodium ion channel and stop the transmission of the neurons and stimuli, which makes tetrodotoxin able to treat several types of pain such as visceral pain and cancer pain. By blocking the neurons and stimuli in the body, the feeling of pain will not occur in the body. The two clinical examples show that Tetrodotoxin is effective in treating pain but not as effective as morphine. Therefore, the use of tetrodotoxin to treat pain may reduce the use of morphine.

Inhibition of voltage-gated sodium ion channel by corannulene and computational inversion blockage underlying mechanisms

Corannulene (Cor), a special carbon material, evidenced strong protein binding capacity which regulating lysozyme crystallization and controlling reactive oxygen species (ROS) generation. Ion channel protein play role in regulating ion channel functions to affect physiological functions. However, the interaction between Cor and ion channel protein have not been studied. In this study, PEG/Cor nanoparticles (PEG/Cor Nps) were prepared by mPEG-DSPE. The PEG/Cor Nps localized in cytoplasm and produced cytotoxicity at high concentration. Whole cell patch clamp examined ion channel functions after incubate PEG/Cor Nps with PC-12 cell. we found that PEG/Cor Nps inhibited voltage-gated Na+ ion channels in a dose- and time-dependent manner but not act on voltage-gated K+ ion channels. The potential mechanisms were revealed by all-atom molecular dynamic (MD) simulations. The results showed that PEG/Cor Nps block the pore of sodium ion channel protein due to dose- and time-dependent accumulation. Besides, the orientation angle (θ) configuration of PEG/Cor Nps will be inverted with the accumulation to generate two blocking mechanisms. Different from other carbon nanomaterials, the blockage mechanism of PEG/Cor Nps provides novel insights into the mechanisms of interaction between carbon nanomaterials and protein.

Gut touch: Molecules, cells, circuits, and purpose.

Most animals conduct the entire digestive process within the GI tract while keeping the luminal contents entirely outside the body, separated by the tightly sealed GI epithelium. Therefore, like the skin and oral cavity, the GI tract must sense the chemical and physical properties of luminal contents at this interface to perfect function. Specialized sensory enteroendocrine cells (EECs) in the GI epithelium interact intimately with luminal contents. Recently, we discovered an EEC subpopulation that expresses mechanically gated ion channel Piezo2 and is developmentally and functionally like the population of skin's touch sensors - the Merkel cells. Given these similarities, we hypothesized that the gut has intrinsic tactile sensitivity, which we call gut touch. The Piezo2+ EEC mechanotransduction mechanism involves voltage-gated calcium and sodium ion channels and intracellular calcium stores to amplify and prolong the cytoplasmic calcium elevation, which drives the release of signaling molecules such as serotonin. The released EEC signaling molecules activate multiple downstream intrinsic sensory endings that drive intrinsic reflex motility and secretion circuits. I will end by exploring the physiologic purpose of gut touch and how gut touch disruptions lead to human disease.

Protein reconstitution into giant unilamellar vesicles from native nanodiscs.

The reconstitution of purified membrane proteins into lipid bilayers represents a tedious challenge as it relies mainly on empirically optimized purification protocols tailored to the target protein, including laborious detergent selection. The situation is even more complex when the protein's function or structural stability depends on its lipid environment. Using nanodisc-forming amphiphilic polymers helps circumnavigate these problems by allowing the extracted protein to stay in its native lipid environment. Yet, thus far, nanodiscs are of limited use for transport studies due to the problematic protein transfer to vesicles or planar bilayers. Here we exploited the recently introduced glycopolymer Glyco-DIBMA to purify integral membrane proteins such as the voltage-gated potassium ion channel KvAP, the voltage-gated sodium ion channel NavMs, the bacterial translocon complex SecYEG, the eukaryotic serotonin-gated cation channel 5Ht3A, as well as the phospholipid translocating scramblase TMEM16. We used fluorescence correlation spectroscopy to quantify the abundance of the labeled proteins in nanodiscs and optimize protein transfer into giant unilamellar vesicles (GUVs). We thus could achieve protein densities of roughly one copy per diffraction-limited focal area or ∼5400 copies in a GUV with a diameter of ∼20 µm. Such protein density is sufficient for visualizing the reconstituted proteins in vesicular membranes by conventional fluorescence microscopy. The proteins retain functionality, as our GUV influx and efflux studies demonstrated. This project was supported by a grant from the FWF (Austrian Science Fund): P34826.

Attenuation of Seizures, Cognitive Deficits, and Brain Histopathology by Phytochemicals of Imperata cylindrica (L.) P. Beauv (Poaceae) in Acute and Chronic Mutant Drosophila melanogaster Epilepsy Models.

Imperata cylindrica is a globally distributed plant known for its antiepileptic attributes, but there is a scarcity of robust evidence for its efficacy. The study investigated neuroprotective attributes of Imperata cylindrica root extract on neuropathological features of epilepsy in a Drosophila melanogaster mutant model of epilepsy. It was conducted on 10-day-old (at the initiation of study) male post-eclosion bang-senseless paralytic Drosophila (parabss1) involved acute (1-3 h) and chronic (6-18 days) experiments; n = 50 flies per group (convulsions tests); n = 100 flies per group (learning/memory tests and histological examination). Administrations were done in 1 g standard fly food, per os. The mutant flies of study (parabss1) showed marked age-dependent progressive brain neurodegeneration and axonal degeneration, significant (P < 0.05) bang sensitivity and convulsions, and cognitive deficits due to up-regulation of the paralytic gene in our mutants. The neuropathological findings were significantly (P < 0.05) alleviated in dose and duration-dependent fashions to near normal/normal after acute and chronic treatment with extract similar to sodium valproate. Therefore, para is expressed in neurons of brain tissues in our mutant flies to bring about epilepsy phenotypes and behaviors of the current juvenile and old-adult mutant D. melanogaster models of epilepsy. The herb exerts neuroprotection by anticonvulsant and antiepileptogenic mechanisms in mutant D. melanogaster due to plant flavonoids, polyphenols, and chromones (1 and 2) which exert antioxidative and receptor or voltage-gated sodium ion channels' inhibitory properties, and thus causing reduced inflammation and apoptosis, increased tissue repair, and improved cell biology in the brain of mutant flies. The methanol root extract provides anticonvulsant and antiepileptogenic medicinal values which protect epileptic D. melanogaster. Therefore, the herb should be advanced for more experimental and clinical studies to confirm its efficacy in treating epilepsy.

SCN5A promotes the growth and lung metastasis of triple-negative breast cancer through EF2-kinase signaling

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer often associated with early metastasis, poor prognosis, and shortened survival. The main causes of its high mortality level are attributed to significant genetic heterogenity, rapid development of chemoresistance, and a limited number of targeted therapeutics. Therefore, as described herein, we investigated the role of the SCN5A gene encoding the voltage-gated sodium ion channel NaV1.5 in vitro and in vivo in TNBC models. Cell proliferation, colony formation, invasion, western blot and in vivo analyzes were performed. We found that SCN5A gene/NaV1.5 and its neonatal spliced isoform nNaV1.5 were markedly upregulated in TNBC cells and that they promoted cell proliferation, colony formation, motility/migration, and invasion. Therapeutic targeting of NaV1.5/nNaV1.5 via systemic injection of specific siRNAs incorporated in single-lipid nanoparticles suppressed tumor growth and lung metastasis in orthotopic TNBC models. We further demonstrated that targeting of NaV1.5/nNaV1.5 expression associated with eukaryotic elongation factor-2 kinase (EF2K) expression. This approach led to the inhibition EF2K's oncogenic signaling and its clinically significant downstream targets, including integrin β1/Src/focal adhesion kinase, c-myc, cyclin D1, phosphoinositide 3-kinase/Akt, p-ERK, p-IF2α and p-PI3K. Targeting of NaV1.5/nNaV1.5 also induced robust apoptosis in TNBCs in vivo. Inhibition of both isoforms of SCN5A in TNBC cells enhanced the effect of first-line chemotherapeutics such as paclitaxel. In conclusion, our results provide the first evidence that expression of SCN5A has an important role in the growth of primary and lung-metastatic TNBCs and that targeting of NaV1.5/nNaV1.5 by systemically administered therapeutics is a potential molecularly targeted strategy to control TNBC progression and may enhance the efficacy of currently used chemotherapeutics.

In Silico Analysis of Tetrodotoxin Binding in Voltage-Gated Sodium Ion Channels from Toxin-Resistant Animal Lineages.

Multiple animal species have evolved resistance to the neurotoxin tetrodotoxin (TTX) through changes in voltage-gated sodium ion channels (VGSCs). Amino acid substitutions in TTX-resistant lineages appear to be positionally convergent with changes in homologous residues associated with reductions in TTX block. We used homology modeling coupled with docking simulations to test whether positionally convergent substitutions generate functional convergence at the level of TTX-channel interactions. We found little evidence that amino acids at convergent positions generated similar patterns among TTX-resistant animal lineages across several metrics, including number of polar contacts, polar contact position, and estimates of binding energy. Though binding energy values calculated for TTX docking were reduced for some TTX-resistant channels, not all TTX-resistant channels and not all of our analyses returned reduced binding energy values for TTX-resistant channels. Our results do not support a simple model of toxin resistance where a reduced number of bonds between TTX and the channel protein prevents blocking. Rather models that incorporate flexibility and movement of the protein overall may better describe how homologous substitutions in the channel cause changes in TTX block.

Peripheral Ion Channel Genes Screening in Painful Small Fiber Neuropathy.

Neuropathic pain is a characteristic feature of small fiber neuropathy (SFN), which in 18% of the cases is caused by genetic variants in voltage-gated sodium ion channels. In this study, we assessed the role of fifteen other ion channels in neuropathic pain. Patients with SFN (n = 414) were analyzed for ANO1, ANO3, HCN1, KCNA2, KCNA4, KCNK18, KCNN1, KCNQ3, KCNQ5, KCNS1, TRPA1, TRPM8, TRPV1, TRPV3 and TRPV4 variants by single-molecule molecular inversion probes-next-generation sequencing. These patients did not have genetic variants in SCN3A, SCN7A-SCN11A and SCN1B-SCN4B. In twenty patients (20/414, 4.8%), a potentially pathogenic heterozygous variant was identified in an ion-channel gene (ICG). Variants were present in seven genes, for two patients (0.5%) in ANO3, one (0.2%) in KCNK18, two (0.5%) in KCNQ3, seven (1.7%) in TRPA1, three (0.7%) in TRPM8, three (0.7%) in TRPV1 and two (0.5%) in TRPV3. Variants in the TRP genes were the most frequent (n = 15, 3.6%), partly in patients with high mean maximal pain scores VAS = 9.65 ± 0.7 (n = 4). Patients with ICG variants reported more severe pain compared to patients without such variants (VAS = 9.36 ± 0.72 vs. VAS = 7.47 ± 2.37). This cohort study identified ICG variants in neuropathic pain in SFN, complementing previous findings of ICG variants in diabetic neuropathy. These data show that ICG variants are central in neuropathic pain of different etiologies and provides promising gene candidates for future research.

Homeostatic and adaptive energetics: Nonequilibrium fluctuations beyond detailed balance in voltage-gated ion channels.

Stochastic thermodynamics has largely succeeded in characterizing both equilibrium and far-from-equilibrium phenomena. Yet many opportunities remain for application to mesoscopic complex systems-especially biological ones-whose effective dynamics often violate detailed balance and whose microscopic degrees of freedom are often unknown or intractable. After reviewing excess and housekeeping energetics-the adaptive and homeostatic components of a system's dissipation-we extend stochastic thermodynamics with a trajectory class fluctuation theorem for nonequilibrium steady-state, nondetailed-balanced complex systems. We then take up the neurobiological examples of voltage-gated sodium and potassium ion channels to apply and illustrate the theory, elucidating their nonequilibrium behavior under a biophysically plausible action potential drive. These results uncover challenges for future experiments and highlight the progress possible understanding the thermodynamics of complex systems-without exhaustive knowledge of every underlying degree of freedom.

Nav1.8 in keratinocytes contributes to ROS-mediated inflammation in inflammatory skin diseases

Reactive oxygen species (ROS)-activated proinflammatory signals in keratinocytes play a crucial role in the immunoregulation of inflammatory skin diseases, including rosacea and psoriasis. Nav1.8 is a voltage-gated sodium ion channel, and its abnormal expression in the epidermal layer contributes to pain hypersensitivity in the skin. However, whether and how epidermal Nav1.8 is involved in skin immunoregulation remains unclear. This study was performed to identify the therapeutic role of Nav1.8 in inflammatory skin disorders. We found that Nav1.8 expression was significantly upregulated in the epidermis of rosacea and psoriasis skin lesions. Nav1.8 knockdown ameliorated skin inflammation in LL37-and imiquimod-induced inflammation mouse models. Transcriptome sequencing results indicated that Nav1.8 regulated the expression of pro-inflammatory mediators (IL1β and IL6) in keratinocytes, thereby contributing to immune infiltration in inflammatory skin disorders. In vitro, tumor necrosis factor alpha (TNFα), a cytokine that drives the development of various inflammatory skin disorders, increased Nav1.8 expression in keratinocytes. Knockdown of Nav1.8 eliminated excess ROS production, thereby attenuating the TNFα-induced production of inflammatory mediators; however, a Nav1.8 blocker did not have the same effect. Mechanistically, Nav1.8 reduced superoxide dismutase 2 (SOD2) activity by directly binding to SOD2 to prevent its deacetylation and mitochondrial localization, subsequently inducing ROS accumulation. Collectively, our study describes a central role for Nav1.8 in regulating pro-inflammatory responses in the skin and indicates a novel therapeutic strategy for rosacea and psoriasis.

Preventing Axonal Sodium Overload or Mitochondrial Calcium Uptake Protects Axonal Mitochondria from Oxidative Stress-Induced Alterations.

In neuroinflammatory and neurodegenerative disorders such as multiple sclerosis, mitochondrial damage caused by oxidative stress is believed to contribute to neuroaxonal damage. Previously, we demonstrated that exposure to hydrogen peroxide (H2O2) alters mitochondrial morphology and motility in myelinated axons and that these changes initiate at the nodes of Ranvier, where numerous sodium channels are located. Therefore, we suggested that mitochondrial damage may lead to ATP deficit, thereby affecting the efficiency of the sodium-potassium ATPase and eventually leading to sodium overload in axons. The increased intra-axonal sodium may revert the axonal sodium-calcium exchangers and thus may lead to a pathological calcium overload in the axoplasm and mitochondria. Here, we used the explanted murine ventral spinal roots to investigate whether modulation of sodium or calcium influx may prevent mitochondrial alterations in myelinated axons during exogenous application of H2O2 inducing oxidative stress. For that, tetrodotoxin, an inhibitor of voltage-gated sodium ion channels, and ruthenium 360, an inhibitor of the mitochondrial calcium uniporter, were applied simultaneously with hydrogen peroxide to axons. Mitochondrial shape and motility were analyzed. We showed that inhibition of axonal sodium influx prevented oxidative stress-induced morphological changes (i.e., increase in circularity and area and decrease in length) and preserved mitochondrial membrane potential, which is crucial for ATP production. Blocking mitochondrial calcium uptake prevented decrease in mitochondrial motility and also preserved membrane potential. Our findings indicate that alterations of both mitochondrial morphology and motility in the contexts of oxidative stress can be counterbalanced by modulating intramitochondrial ion concentrations pharmacologically. Moreover, motile mitochondria show preserved membrane potentials, pointing to a close association between mitochondrial motility and functionality.

Markov-type kinetic models for sodium and potassium ion channels for generation of action potential in synthetic neurons

Synthetic biology is an exciting area of research that hopes to understand the building blocks of life. With the goal of constructing a predictive model to ultimately guide the bottom-up construction of a synthetic neuron that can qualitatively recapitulate the electrophysiology of biological neurons, we construct and investigate Markov-type models of voltage-gated sodium (Nav) and potassium (Kv3.1) ion channels that capture their complex kinetics. We also mapped a Hodgkin-Huxley model of an inward rectifying potassium channel (Kir2.1) to a Markov-type model.

Structure-function of DHEA binding proteins.

Dehydroepiandrosterone (3β-hydroxy-5-androsten-17-one, DHEA) and its sulfated metabolite DHEA-S are the most abundant circulating steroids and are precursors for active sex steroid hormones, estradiol and testosterone. DHEA has a broad range of reported effects in the central nervous system (CNS), cardiovascular system, adipose tissue, kidney, liver, and in the reproductive system. The mechanisms by which DHEA and DHEA-S initiate their biological effects are diverse. DHEA and DHEA-S may directly bind to plasma membrane (PM) receptors, including a DHEA-specific, G-protein coupled receptor (GPCR) in endothelial cells; various neuroreceptors, e.g., aminobutyric-acid-type A (GABA(A)), N-methyl-d-aspartate (NMDA) and sigma-1 (S1R) receptors (NMDAR and SIG-1R). DHEA and DHEA-S directly bind the nuclear androgen and estrogen receptors (AR, ERα, or ERβ) although with significantly lower binding affinities compared to the steroid hormones, e.g., testosterone, dihydrotestosterone, and estradiol, which are the cognate ligands for AR and ERs. Thus, extra-gonadal metabolism of DHEA to the sex hormones must be considered for many of the biological benefits of DHEA. DHEA also actives GPER1 (G protein coupled estrogen receptor 1). DHEA activates constitutive androstane receptor CAR (CAR) and proliferator activated receptor (PPARα) by indirect dephosphorylation. DHEA affects voltage-gated sodium and calcium ion channels and DHEA-2 activates TRPM3 (Transient Receptor Potential Cation Channel Subfamily M Member 3). This chapter updates our previous 2018 review pertaining to the physiological, biochemical, and molecular mechanisms of DHEA and DHEA-S activity.

Recombinant expression and antigenicity of two peptide families of neurotoxins from Androctonus sp.

Scorpion neurotoxins such as those that modify the mammalian voltage-gated sodium ion channels (Nav) are the main responsible for scorpion envenomation. Their neutralization is crucial in the production of antivenoms against scorpion stings. In the present study, two in silico designed genes - one that codes for a native neurotoxin from the venom of the Anatolian scorpion Androctonus crassicauda, named Acra 4 - and another non-native toxin - named consensus scorpion toxin (SccTx) obtained from the alignment of the primary structures of the most toxic neurotoxins from the Middle Eastern and North African scorpions - were recombinantly expressed in E. coli Origami. Following bacterial expression, the two expressed neurotoxins, hereafter named HisrAcra4 and HisrSccTx, were obtained from inclusion bodies. Both recombinant neurotoxins were obtained in multiple Cys-Cys isoforms. After refolding, the active protein fractions were identified with molecular masses of 8,947.6 and 9,989.1 Da for HisrAcra4 and HisrSccTx, respectively, which agreed with their expected theoretical masses. HisrAcra4 and HisrSccTx were used as antigens to immunize two groups of rabbits, to produce either anti-HisrAcra4 or anti-HisrSccTx serum antibodies, which in turn could recognize and neutralize neurotoxins from venoms of scorpion species from the Middle East and North Africa. The antibodies obtained from rabbits neutralized the 3LD50 of Androctonus australis, Leiurus quinquestriatus hebraeus and Buthus occitanus venoms, but they did not neutralize A. crassicauda and A. mauritanicus venoms. In addition, the anti-HisrAcra4 antibodies did not neutralize any of the five scorpion venoms tested. However, an antibody blend of anti-HisrAcra4 and anti-HisrSccTx was able to neutralize A. crassicauda and A. mauritanicus venoms. Two recombinant Nav neurotoxins, from different peptide families, were used as antigens to generate IgGs for neutralizing scorpion venoms of species from the Middle East and North Africa.

General mechanism of spider toxin family I acting on sodium channel Nav1.7.

Various peptide toxins in animal venom inhibit voltage-gated sodium ion channel Nav1.7, including Nav-targeting spider toxin (NaSpTx) Family I. Toxins in NaSpTx Family I share a similar structure, i.e., N-terminal, loops 1–4, and C-terminal. Here, we used Mu-theraphotoxin-Ca2a (Ca2a), a peptide isolated from Cyriopagopus albostriatus, as a template to investigate the general properties of toxins in NaSpTx Family I. The toxins interacted with the cell membrane prior to binding to Nav1.7 via similar hydrophobic residues. Residues in loop 1, loop 4, and the C-terminal primarily interacted with the S3–S4 linker of domain II, especially basic amino acids binding to E818. We also identified the critical role of loop 2 in Ca2a regarding its affinity to Nav1.7. Our results provide further evidence that NaSpTx Family I toxins share similar structures and mechanisms of binding to Nav1.7.

Nerve excitability study – a method to assess the pathophysiology of peripheral nervous system disorders

Nerve excitability study is an interesting extension of classical neurography. The principle of the test is to stimulate the nerve with a long-term depolarising or hyperpolarising stimulus, followed by a test stimulus that induces a complex motor or sensory potential of a given amplitude. The analysis of the intensity of the test stimulus used in chronic depolarisation or hyperpolarisation of the nerve fibre allows for the assessment of changes in nerve excitability. The median nerve is stimulated, and it is possible to assess the excitability of sensory or motor fibres. Nerve excitability study is the only method to evaluate the function of neuronal membrane ion channels in vivo. Test results are impacted by the following membrane-related factors: voltage-gated sodium and potassium ion channels, sodium and potassium ATPase, as well as the degree of fibre myelination and the levels of extracellular and intracellular electrolytes. Nerve excitability study yields a result in the form of a series of complex peripheral nerve excitability parameters, such as the relationship between the stimulus and the excitation threshold, rheobase, fibre chronaxie, threshold electrotonus, and reactivation after action potential. Nerve excitability study helps assess the pathophysiology of nerve fibre damage in various disorders of the peripheral nervous system, such as hereditary polyneuropathies, neurodegenerative or metabolic diseases. The test is highly sensitive, e.g. it shows pre-symptomatic excitability changes. It can also be used to monitor treatment outcomes in metabolic and drug-induced polyneuropathies and to search for peripheral markers of central nervous system channelopathies.

The Expression of Sodium Channel Alpha Subunit (Nav1.7) Receptors in Intracranial Meningioma and Its Comparison to Urothelial, Prostate and Ovarian Cancers

Nav1.7/SCN9A is a voltage gated sodium ion channel (VGSC), expressed by nociceptive neurons. Its role in pain mechanism was well- established but its involvement in the carcinogenic pathways is still under investigation. We aimed to explore the expression of Nav1.7/ SCN9A receptors in intracranial meningiomas and compare it with urothelial, prostate, and ovarian cancers. Methods: Ten paraffin embedded tissue samples of brain meningioma and 5 cases each of bladder, prostate and ovarian carcinomas were utilized. Immunohistochemistry (IHC) was performed using anti-SCN9A antibody. Cases were scored based on the intensity of expression and number of positive tumour cells. A score of (+3) indicated highest intensity, (+2) as moderate and (+1) as weak intensity. Similarly, 50-100% expression in cells was labelled as (+3), moderate, 30-50% as (+2) and 10-20% as weak or (+1) expression, and (0) as negative. Results: Nine cases of meningioma were in grade I and single case was grade III. The nine grade I meningioma were negative for SCN9/Nav1.7 expression while the single grade III case was positive. Tumour cells in urothelial, prostate, and ovarian carcinomas were all strongly positive for SCN9/Nav1.7, having intensity expression as (+3). Conclusions: This study suggests an emerging role of Nav1.7/SCN9A receptor expression in urothelial, prostate, and ovarian cancers as well as grade III meningiomas compared to grade I meningioma. This clarifies that Nav1.7/SCN9A has a possible role in carcinogenesis of most body tumours. Key Words: Nav1.7, sodium channels, Ion channels, Channelopathy, meningioma, carcinoma