Structure and Pharmacology of Voltage-Gated Sodium and Calcium Channels

Neurotoxin-Derived Optical Probes for Biological and Medical Imaging

The superb specificity and potency of biological toxins targeting various ion channels and receptors are of major interest for the delivery of therapeutics to distinct cell types and subcellular compartments. Fused with reporter proteins or labelled with fluorophores and nanocomposites, animal toxins and their detoxified variants also offer expanding opportunities for visualisation of a range of molecular processes and functions in preclinical models, as well as clinical studies. This article presents state-of-the-art optical probes derived from neurotoxins targeting ion channels, with discussions of their applications in basic and translational biomedical research. It describes the design and production of probes and reviews their applications with advantages and limitations, with prospects for future improvements. Given the advances in imaging tools and expanding research areas benefiting from the use of optical probes, described here resources should assist the discovery process and facilitate high-precision interrogation and therapeutic interventions.

Molnupiravir, a ribonucleoside antiviral prodrug against SARS-CoV-2, alters the voltage-gated sodium current and causes adverse events

Molnupiravir (MOL) is a ribonucleoside prodrug for oral treatment of COVID-19. Common adverse effects of MOL are headache, diarrhea, and nausea, which may be associated with altered sodium channel function. Here, we investigated the effect of MOL on voltage-gated Na+ current (INa) in pituitary GH3 cells. We show that MOL had distinct effects on transient and late INa, in combination with decreased time constant in the slow component of INa inactivation. The 50% inhibitory concentration (IC50) values of MOL for suppressing transient and late INa were 26.1 and 6.3 μM, respectively. The overall steady-state current-voltage relationship of INa remained unchanged upon MOL exposure. MOL-induced alteration of INa may lead to changes in physiological function through sodium channels. Apart from its effect on inhibiting RNA virus replication, MOL exerts inhibitory effects on plasmalemma INa, which might constitute an additional yet crucial underlying mechanism of its pharmacological activity or adverse events.

Case report: A novel CACNA1S mutation associated with hypokalemic periodic paralysis

Background

Hypokalemic periodic paralysis (HypoKPP) is a rare neuromuscular genetic disorder causing recurrent episodes of flaccid paralysis. Most cases are associated with CACNA1S mutation, causing defect of calcium channel and subsequent impairment of muscle functions. Due to defined management approaches early diagnosis is crucial for promptly treatment and prevention new attacks.

Materials and methods

We report a case of HypoKPP associated with previously unreported mutation in CACNA1S gene (p.R900M). Molecular modeling of CaV1.1 was applied to evaluate its pathogenicity.

Results

As a patient referred between attacks neurological status, laboratory and neurophysiological examination were unremarkable. Molecular modeling predicted that the p.R900M mutation affects the process of calcium channels activation.

Conclusion

Novel CACNA1S mutation, associated with HypoKPP was identified. Monte-Carlo energy minimization of the CaV1.1 model supported the association of this mutation with this disease.

Lewis acid-driven self-assembly of diiridium macrocyclic catalysts imparts substrate selectivity and glutathione tolerance

Molecular inorganic catalysts (MICs) tend to have solvent-exposed metal centers that lack substrate specificity and are easily inhibited by biological nucleophiles. Unfortunately, these limitations exclude many MICs from being considered for in vivo applications. To overcome this challenge, a strategy to spatially confine MICs using Lewis acid-driven self-assembly is presented. It was shown that in the presence of external cations (e.g., Li+, Na+, K+, or Cs+) or phosphate buffered saline, diiridium macrocycles spontaneously formed supramolecular iridium-cation species, which were characterized by X-ray crystallography and dynamic light scattering. These nanoassemblies selectively reduced sterically unhindered C[double bond, length as m-dash]O groups via transfer hydrogenation and tolerated up to 1 mM of glutathione. In contrast, when non-coordinating tetraalkylammonium cations were used, the diiridium catalysts were unable to form higher-ordered structures and discriminate between different aldehyde substrates. This work suggests that in situ coordination self-assembly could be a versatile approach to enable or enhance the integration of MICs with biological hosts.

A Genetically Encoded Actuator Selectively Boosts L-type Calcium Channels in Diverse Physiological Settings

L-type Ca 2+ channels (Ca V 1.2/1.3) convey influx of calcium ions (Ca 2+ ) that orchestrate a bevy of biological responses including muscle contraction and gene transcription. Deficits in Ca V 1 function play a vital role in cardiac and neurodevelopmental disorders. Yet conventional pharmacological approaches to upregulate Ca V 1 are limited, as excessive Ca 2+ influx leads to cytotoxicity. Here, we develop a genetically encoded enhancer of Ca V 1.2/1.3 channels (GeeC) to manipulate Ca 2+ entry in distinct physiological settings. Specifically, we functionalized a nanobody that targets the Ca V macromolecular complex by attaching a minimal effector domain from a Ca V enhancer-leucine rich repeat containing protein 10 (Lrrc10). In cardiomyocytes, GeeC evoked a 3-fold increase in L-type current amplitude. In neurons, GeeC augmented excitation-transcription (E-T) coupling. In all, GeeC represents a powerful strategy to boost Ca V 1.2/1.3 function in distinct physiological settings and, in so doing, lays the groundwork to illuminate new insights on neuronal and cardiac physiology and disease.

Voltage-Mediated Water Dynamics Enables On-Demand Transport of Sugar Molecules in Two-Dimensional Channels

The constructing of artificial channels with gating functions is an important undertaking for gaining insight into biological process and achieving efficient bionic functions. Typically, controllable transport within such channels relies on either electrostatic or specific interactions between the transporting species and the channel. However, for molecules with weak interactions with the channel, achieving precise gating of the transport remains a significant challenge. In this regard, this study proposes a voltage gating membrane of two-dimensional channels that selectively transport of neutral molecules glucose with a dimension of 0.60 nm. The permeation of glucose is switched on/off by electrochemically manipulating the water dynamics in the nanochannel. Voltage driven-intercalation of ion into the two-dimensional channel causes water to stratify and move closer to the channel walls, thereby resulting in the channel center being emptier for glucose diffusion. Due to the sub-nanometer size dimension of the channel, selective permeation of glucose over sucrose is also achieved in this approach.

Treating Epilepsy with Natural Products: Nonsense or Possibility?

Epilepsy is a neurological disease characterized by recurrent seizures that can lead to uncontrollable muscle twitching, changes in sensitivity to sensory perceptions, and disorders of consciousness. Although modern medicine has effective antiepileptic drugs, the need for accessible and cost-effective medication is urgent, and products derived from plants could offer a solution. For this review, we have focused on natural compounds that have shown anticonvulsant activity in in vivo models of epilepsy at relevant doses. In some cases, the effects have been confirmed by clinical data. The results of our search are summarized in tables according to their molecular targets. We have critically evaluated the data we present, identified the most promising therapeutic candidates, and discussed these in the text. Their perspectives are supported by both pharmacokinetic properties and potential interactions. This review is intended to serve as a basis for future research into epilepsy and related disorders.

Profiling Chemobiological Connection between Natural Product and Target Space Based on Systematic Analysis

Natural products provide valuable starting points for new drugs with unique chemical structures. Here, we retrieve and join the LOTUS natural product database and ChEMBL interaction database to explore the relations and rhythm between chemical features of natural products and biotarget spaces. Our analysis revealed relations between the biogenic pathways of natural products and species taxonomy. Nitrogen-containing natural products were more likely to achieve high activity and have a higher potential to become candidate compounds. An apparent trend existed in the target space of natural products originating from different biological sources. Highly active alkaloids were more related to targets of neurodegenerative or neural diseases. Oligopeptides and polyketides were mainly associated with protein phosphorylation and HDAC receptors. Fatty acids readily intervened in various physiological processes involving prostanoids and leukotrienes. We also used FusionDTA, a deep learning model, to predict the affinity between all LOTUS natural products and 622 therapeutic drug targets, exploring the potential target space for natural products. Our data exploration provided a global perspective on the gaps in the chemobiological space of natural compounds through systematic analysis and prediction of their target space, which can be used for new drug design or natural drug repurposing.

Voltage-gated sodium channels: from roles and mechanisms in the metastatic cell behavior to clinical potential as therapeutic targets

During the second half of the last century, the prevalent knowledge recognized the voltage-gated sodium channels (VGSCs) as the proteins responsible for the generation and propagation of action potentials in excitable cells. However, over the last 25 years, new non-canonical roles of VGSCs in cancer hallmarks have been uncovered. Their dysregulated expression and activity have been associated with aggressive features and cancer progression towards metastatic stages, suggesting the potential use of VGSCs as cancer markers and prognostic factors. Recent work has elicited essential information about the signalling pathways modulated by these channels: coupling membrane activity to transcriptional regulation pathways, intracellular and extracellular pH regulation, invadopodia maturation, and proteolytic activity. In a promising scenario, the inhibition of VGSCs with FDA-approved drugs as well as with new synthetic compounds, reduces cancer cell invasion in vitro and cancer progression in vivo. The purpose of this review is to present an update regarding recent advances and ongoing efforts to have a better understanding of molecular and cellular mechanisms on the involvement of both pore-forming α and auxiliary β subunits of VGSCs in the metastatic processes, with the aim at proposing VGSCs as new oncological markers and targets for anticancer treatments.

Scanning mutagenesis of the voltage-gated sodium channel NaV1.2 using base editing

It is challenging to apply traditional mutational scanning to voltage-gated sodium channels (NaVs) and functionally annotate the large number of coding variants in these genes. Using a cytosine base editor and a pooled viability assay, we screen a library of 368 guide RNAs (gRNAs) tiling NaV1.2 to identify more than 100 gRNAs that change NaV1.2 function. We sequence base edits made by a subset of these gRNAs to confirm specific variants that drive changes in channel function. Electrophysiological characterization of these channel variants validates the screen results and provides functional mechanisms of channel perturbation. Most of the changes caused by these gRNAs are classifiable as loss of function along with two missense mutations that lead to gain of function in NaV1.2 channels. This two-tiered strategy to functionally characterize ion channel protein variants at scale identifies a large set of loss-of-function mutations in NaV1.2.

PI(4,5)P2 regulates the gating of NaV1.4 channels

Voltage-gated sodium (NaV) channels are densely expressed in most excitable cells and activate in response to depolarization, causing a rapid influx of Na+ ions that initiates the action potential. The voltage-dependent activation of NaV channels is followed almost instantaneously by fast inactivation, setting the refractory period of excitable tissues. The gating cycle of NaV channels is subject to tight regulation, with perturbations leading to a range of pathophysiological states. The gating properties of most ion channels are regulated by the membrane phospholipid, phosphatidylinositol (4,5) bisphosphate (PI(4,5)P2). However, it is not known whether PI(4,5)P2 modulates the activity of NaV channels. Here, we utilize optogenetics to activate specific, membrane-associated phosphoinositide (PI)-phosphatases that dephosphorylate PI(4,5)P2 while simultaneously recording NaV1.4 channel currents. We show that dephosphorylating PI(4,5)P2 left-shifts the voltage-dependent gating of NaV1.4 to more hyperpolarized membrane potentials, augments the late current that persists after fast inactivation, and speeds the rate at which channels recover from fast inactivation. These effects are opposed by exogenous diC8PI(4,5)P2. We provide evidence that PI(4,5)P2 is a negative regulator that tunes the gating behavior of NaV1.4 channels.

Missense mutations in the membrane domain of PRRT2 affect its interaction with Nav1.2 voltage-gated sodium channels

PRRT2 is a neuronal protein that controls neuronal excitability and network stability by modulating voltage-gated Na⁺ channel (Nav). PRRT2 pathogenic variants cause pleiotropic syndromes including epilepsy, paroxysmal kinesigenic dyskinesia and episodic ataxia attributable to loss-of-function pathogenetic mechanism. Based on the evidence that the transmembrane domain of PRRT2 interacts with Nav1.2/1.6, we focused on eight missense mutations located within the domain that show expression and membrane localization similar to the wild-type protein. Molecular dynamics simulations showed that the mutants do not alter the structural stability of the PRRT2 membrane domain and preserve its conformation. Using affinity assays, we found that the A320V and V286M mutants displayed respectively decreased and increased binding to Nav1.2. Accordingly, surface biotinylation showed an increased Nav1.2 surface exposure induced by the A320V mutant. Electrophysiological analysis confirmed the lack of modulation of Nav1.2 biophysical properties by the A320V mutant with a loss-of-function phenotype, while the V286M mutant displayed a gain-of-function with respect to wild-type PRRT2 with a more pronounced left-shift of the inactivation kinetics and delayed recovery from inactivation. The data confirm the key role played by the PRRT2-Nav interaction in the pathogenesis of the PRRT2-linked disorders and suggest an involvement of the A320 and V286 residues in the interaction site. Given the similar clinical phenotype caused by the two mutations, we speculate that circuit instability and paroxysmal manifestations may arise when PRRT2 function is outside the physiological range.

Heterogeneity of voltage gated sodium current density between neurons decorrelates spiking and suppresses network synchronization in Scn1b null mouse models

Voltage gated sodium channels (VGSCs) are required for action potential initiation and propagation in mammalian neurons. As with other ion channel families, VGSC density varies between neurons. Importantly, sodium current (INa) density variability is reduced in pyramidal neurons of Scn1b null mice. Scn1b encodes the VGSC β1/ β1B subunits, which regulate channel expression, trafficking, and voltage dependent properties. Here, we investigate how variable INa density in cortical layer 6 and subicular pyramidal neurons affects spike patterning and network synchronization. Constitutive or inducible Scn1b deletion enhances spike timing correlations between pyramidal neurons in response to fluctuating stimuli and impairs spike-triggered average current pattern diversity while preserving spike reliability. Inhibiting INa with a low concentration of tetrodotoxin similarly alters patterning without impairing reliability, with modest effects on firing rate. Computational modeling shows that broad INa density ranges confer a similarly broad spectrum of spike patterning in response to fluctuating synaptic conductances. Network coupling of neurons with high INa density variability displaces the coupling requirements for synchronization and broadens the dynamic range of activity when varying synaptic strength and network topology. Our results show that INa heterogeneity between neurons potently regulates spike pattern diversity and network synchronization, expanding VGSC roles in the nervous system.

Concerted suppressive effects of carisbamate, an anti-epileptic alkyl-carbamate drug, on voltage-gated Na+ and hyperpolarization-activated cation currents

Carisbamate (CRS, RWJ-333369) is a new anti-seizure medication. It remains unclear whether and how CRS can perturb the magnitude and/or gating kinetics of membrane ionic currents, despite a few reports demonstrating its ability to suppress voltage-gated Na+ currents. In this study, we observed a set of whole-cell current recordings and found that CRS effectively suppressed the voltage-gated Na+ (INa) and hyperpolarization-activated cation currents (Ih) intrinsically in electrically excitable cells (GH3 cells). The effective IC50 values of CRS for the differential suppression of transient (INa(T)) and late INa (INa(L)) were 56.4 and 11.4 μM, respectively. However, CRS strongly decreased the strength (i.e., Δarea) of the nonlinear window component of INa (INa(W)), which was activated by a short ascending ramp voltage (Vramp); the subsequent addition of deltamethrin (DLT, 10 μM) counteracted the ability of CRS (100 μM, continuous exposure) to suppress INa(W). CRS strikingly decreased the decay time constant of INa(T) evoked during pulse train stimulation; however, the addition of telmisartan (10 μM) effectively attenuated the CRS (30 μM, continuous exposure)-mediated decrease in the decay time constant of the current. During continued exposure to deltamethrin (10 μM), known to be a pyrethroid insecticide, the addition of CRS resulted in differential suppression of the amplitudes of INa(T) and INa(L). The amplitude of Ih activated by a 2-s membrane hyperpolarization was diminished by CRS in a concentration-dependent manner, with an IC50 value of 38 μM. For Ih, CRS altered the steady-state I-V relationship and attenuated the strength of voltage-dependent hysteresis (Hys(V)) activated by an inverted isosceles-triangular Vramp. Moreover, the addition of oxaliplatin effectively reversed the CRS-mediated suppression of Hys(V). The predicted docking interaction between CRS and with a model of the hyperpolarization-activated cyclic nucleotide-gated (HCN) channel or between CRS and the hNaV1.7 channel reflects the ability of CRS to bind to amino acid residues in HCN or hNaV1.7 channel via hydrogen bonds and hydrophobic interactions. These findings reveal the propensity of CRS to modify INa(T) and INa(L) differentially and to effectively suppress the magnitude of Ih. INa and Ih are thus potential targets of the actions of CRS in terms of modulating cellular excitability.

Cav 1.3-selective inhibitors of voltage-gated L-type Ca2+ channels: Fact or (still) fiction?

Voltage-gated L-type Ca2+ -channels (LTCCs) are the target of Ca2+ -channel blockers (CCBs), which are in clinical use for the evidence-based treatment of hypertension and angina. Their cardiovascular effects are largely mediated by the Cav 1.2-subtype. However, based on our current understanding of their physiological and pathophysiological roles, Cav 1.3 LTCCs also appear as attractive drug targets for the therapy of various diseases, including treatment-resistant hypertension, spasticity after spinal cord injury and neuroprotection in Parkinson's disease. Since CCBs inhibit both Cav 1.2 and Cav 1.3, Cav 1.3-selective inhibitors would be valuable tools to validate the therapeutic potential of Cav 1.3 channel inhibition in preclinical models. Despite a number of publications reporting the discovery of Cav 1.3-selective blockers, their selectivity remains controversial. We conclude that at present no pharmacological tools exist that are suitable to confirm or refute a role of Cav 1.3 channels in cellular responses. We also suggest essential criteria for a small molecule to be considered Cav 1.3-selective.

NaV1.7 channels are expressed in the lower airways of the human respiratory tract

Na_V channels expression have been reported in upper airways and tracheal smooth muscle cells controlling the generation and propagation of action potentials in the respiratory tract sensory neurons, but information about the presence of these proteins in the bronchioalveolar structures in human lungs was missing. The main objective covered in this work was to determine whether the Na_V1.7 channels are expressed in lower airways, and to identify the cellular identities expressing these proteins. We detected high levels of the mRNA coding for Na_V1.7 channels in isolated lung fibroblasts obtained from both normal lungs, and fibrotic lungs of patients with respiratory diseases. The protein was detected with two different antibodies in the bronchioalveolar tissue, alveolar endothelium, and capillary endothelium, in normal and pathologic lungs. These evidences are useful in the dissection of molecular mechanisms of pulmonary pathologies, and lead to consider the Na_V1.7 channels as potential therapeutic targets for the treatment of pulmonary diseases.

Pain-causing stinging nettle toxins target TMEM233 to modulate NaV1.7 function

Voltage-gated sodium (NaV) channels are critical regulators of neuronal excitability and are targeted by many toxins that directly interact with the pore-forming α subunit, typically via extracellular loops of the voltage-sensing domains, or residues forming part of the pore domain. Excelsatoxin A (ExTxA), a pain-causing knottin peptide from the Australian stinging tree Dendrocnide excelsa, is the first reported plant-derived NaV channel modulating peptide toxin. Here we show that TMEM233, a member of the dispanin family of transmembrane proteins expressed in sensory neurons, is essential for pharmacological activity of ExTxA at NaV channels, and that co-expression of TMEM233 modulates the gating properties of NaV1.7. These findings identify TMEM233 as a previously unknown NaV1.7-interacting protein, position TMEM233 and the dispanins as accessory proteins that are indispensable for toxin-mediated effects on NaV channel gating, and provide important insights into the function of NaV channels in sensory neurons.

The Acute Effects and Mechanism of Ketamine on Nicotine-Induced Neurogenic Relaxation of the Corpus Cavernosum in Mice

The present study aimed to investigate the acute effects and the mechanism of ketamine on nicotine-induced relaxation of the corpus cavernosum (CC) in mice. This study measured the intra-cavernosal pressure (ICP) of male C57BL/6 mice and the CC muscle activities using an organ bath wire myograph. Various drugs were used to investigate the mechanism of ketamine on nicotine-induced relaxation. Direct ketamine injection into the major pelvic ganglion (MPG) inhibited MPG-induced increases in ICP. D-serine/L-glutamate-induced relaxation of the CC was inhibited by MK-801 (N-methyl-D-aspartate (NMDA) receptor inhibitor), and nicotine-induced relaxation was enhanced by D-serine/L-glutamate. NMDA had no effect on CC relaxation. Nicotine-induced relaxation of the CC was suppressed by mecamylamine (a non-selective nicotinic acetylcholine receptor antagonist), lidocaine, guanethidine (an adrenergic neuronal blocker), N^w-nitro-L-arginine (a non-selective nitric oxide synthase inhibitor), MK-801, and ketamine. This relaxation was almost completely inhibited in CC strips pretreated with 6-hydroxydopamine (a neurotoxic synthetic organic compound). Ketamine inhibited cavernosal nerve neurotransmission via direct action on the ganglion and impaired nicotine-induced CC relaxation. The relaxation of the CC was dependent on the interaction of the sympathetic and parasympathetic nerves, which may be mediated by the NMDA receptor.

The intramembrane COOH-terminal domain of PRRT2 regulates voltage-dependent Na+ channels

Proline-rich transmembrane protein 2 (PRRT2) is the single causative gene for pleiotropic paroxysmal syndromes including epilepsy, kinesigenic dyskinesia, episodic ataxia and migraine. PRRT2 is a neuron-specific type-2 membrane protein with a COOH-terminal intramembrane domain and a long proline-rich NH₂-terminal cytoplasmic region. A large array of experimental data indicates that PRRT2 is a neuron stability gene that negatively controls intrinsic excitability by regulating surface membrane localization and biophysical properties of voltage-dependent Na⁺ channels Nav1.2 and Nav1.6, but not Nav1.1. To further investigate the regulatory role of PRRT2, we studied the structural features of this membrane protein with molecular dynamics simulations, and its structure-function relationships with Nav1.2 channels by biochemical and electrophysiological techniques. We found that the intramembrane COOH-terminal region maintains a stable conformation over time, with the first transmembrane domain forming a helix-loop-helix motif within the bilayer. The unstructured NH₂-terminal cytoplasmic region bound to the Nav1.2 better than the isolated COOH-terminal intramembrane domain, mimicking full-length PRRT2, while the COOH-terminal intramembrane domain was able to modulate Na⁺ current and channel biophysical properties, still maintaining the striking specificity for Nav1.2 vs Nav1.1. channels. The results identify PRRT2 as a dual-domain protein in which the NH₂-terminal cytoplasmic region acts as a binding antenna for Na⁺ channels, while the COOH-terminal membrane domain regulates channel exposure on the membrane and its biophysical properties.

Somatic and terminal CB1 receptors are differentially coupled to voltage-gated sodium channels in neocortical neurons

Endogenous cannabinoid signaling is vital for important brain functions, and the same pathways can be modified pharmacologically to treat pain, epilepsy, and posttraumatic stress disorder. Endocannabinoid-mediated changes to excitability are predominantly attributed to 2-arachidonoylglycerol (2-AG) acting presynaptically via the canonical cannabinoid receptor, CB1. Here, we identify a mechanism in the neocortex by which anandamide (AEA), another major endocannabinoid, but not 2-AG, powerfully inhibits somatically recorded voltage-gated sodium channel (VGSC) currents in the majority of neurons. This pathway involves intracellular CB1 that, when activated by anandamide, decreases the likelihood of recurrent action potential generation. WIN 55,212-2 similarly activates CB1 and inhibits VGSC currents, indicating that this pathway is also positioned to mediate the actions of exogenous cannabinoids on neuronal excitability. The coupling between CB1 and VGSCs is absent at nerve terminals, and 2-AG does not block somatic VGSC currents, indicating functional compartmentalization of the actions of two endocannabinoids.

Modulation of Slow Desensitization (Tachyphylaxis) of Acid-Sensing Ion Channel (ASIC)1a

Among the proton-activated channels of the ASIC family, ASIC1a exhibits a specific tachyphylaxis phenomenon in the form of a progressive decrease in the response amplitude during a series of activations. This process is well known, but its mechanism is poorly understood. Here, we demonstrated a partial reversibility of this effect using long-term whole-cell recording of CHO cells transfected with rASIC1a cDNA. Thus, tachyphylaxis represents a slow desensitization of ASIC1a. Prolonged acidifications provided the same recovery from slow desensitization as short acidifications of the same frequency. Slow desensitization and steady-state desensitization are independent processes although the latter attenuates the development of the former. We found that drugs which facilitate ASIC1a activation (e.g., amitriptyline) cause an enhancement of slow desensitization, while inhibition of ASIC1a by 9-aminoacridine attenuates this process. Overall, for a broad variety of exposures, including increased calcium concentration, different pH conditions, and modulating drugs, we found a correlation between their effects on ASIC1a response amplitude and the development of slow desensitization. Thus, our results demonstrate that slow desensitization occurs only when ASIC1a is in the open state.

Germline de novo variant F747S extends the phenotypic spectrum of CACNA1D Ca2+ channelopathies

Germline gain-of-function missense variants in the pore-forming Cav1.3 α1-subunit (CACNA1D gene) confer high risk for a severe neurodevelopmental disorder with or without endocrine symptoms. Here, we report a 4-week-old new-born with the novel de novo missense variant F747S with a so far not described prominent jittering phenotype in addition to symptoms previously reported for CACNA1D mutations including developmental delay, elevated aldosterone level and transient hypoglycemia. We confirmed the pathogenicity of this variant in whole-cell patch-clamp experiments with wild-type and F747S mutant channels heterologously expressed together with α2δ1 and cytosolic β3 or membrane-bound β2a subunits. Mutation F747S caused the quantitatively largest shift in the voltage dependence of activation (-28 mV) reported so far for CACNA1D germline mutations. It also shifted inactivation to more negative voltages, slowed the time course of current inactivation and slowed current deactivation upon repolarization with both co-expressed β-subunits. In silico modelling and molecular docking, simulations revealed that this gain-of-function phenotype can be explained by formation of a novel inter-domain hydrogen bond between mutant residues S747 (IIS6) with N1145 (IIIS6) stabilizing selectively the activated open channel state. F747S displayed 2-6-fold increased sensitivity for the L-type Ca2+ channel blocker isradipine compared to wild type. Our data confirm the pathogenicity of the F747S variant with very strong gain-of-function gating changes, which may contribute to the novel jittering phenotype. Increased sensitivity for isradipine suggests this drug for potential symptomatic off-label treatment for carriers of this mutation.

Mechanisms controlling the trafficking, localization, and abundance of presynaptic Ca2+ channels

Voltage-gated Ca2+ channels (VGCCs) mediate Ca2+ influx to trigger neurotransmitter release at specialized presynaptic sites termed active zones (AZs). The abundance of VGCCs at AZs regulates neurotransmitter release probability (Pr ), a key presynaptic determinant of synaptic strength. Given this functional significance, defining the processes that cooperate to establish AZ VGCC abundance is critical for understanding how these mechanisms set synaptic strength and how they might be regulated to control presynaptic plasticity. VGCC abundance at AZs involves multiple steps, including channel biosynthesis (transcription, translation, and trafficking through the endomembrane system), forward axonal trafficking and delivery to synaptic terminals, incorporation and retention at presynaptic sites, and protein recycling. Here we discuss mechanisms that control VGCC abundance at synapses, highlighting findings from invertebrate and vertebrate models.

Blockers of Skeletal Muscle Nav1.4 Channels: From Therapy of Myotonic Syndrome to Molecular Determinants of Pharmacological Action and Back

The voltage-gated sodium channels represent an important target for drug discovery since a large number of physiological processes are regulated by these channels. In several excitability disorders, including epilepsy, cardiac arrhythmias, chronic pain, and non-dystrophic myotonia, blockers of voltage-gated sodium channels are clinically used. Myotonia is a skeletal muscle condition characterized by the over-excitability of the sarcolemma, resulting in delayed relaxation after contraction and muscle stiffness. The therapeutic management of this disorder relies on mexiletine and other sodium channel blockers, which are not selective for the Na_v1.4 skeletal muscle sodium channel isoform. Hence, the importance of deepening the knowledge of molecular requirements for developing more potent and use-dependent drugs acting on Na_v1.4. Here, we review the available treatment options for non-dystrophic myotonia and the structure-activity relationship studies performed in our laboratory with a focus on new compounds with potential antimyotonic activity.

CACNA1C-Related Channelopathies

The CACNA1C gene encodes the pore-forming subunit of the CaV1.2 L-type Ca2+ channel, a critical component of membrane physiology in multiple tissues, including the heart, brain, and immune system. As such, mutations altering the function of these channels have the potential to impact a wide array of cellular functions. The first mutations identified within CACNA1C were shown to cause a severe, multisystem disorder known as Timothy syndrome (TS), which is characterized by neurodevelopmental deficits, long-QT syndrome, life-threatening cardiac arrhythmias, craniofacial abnormalities, and immune deficits. Since this initial description, the number and variety of disease-associated mutations identified in CACNA1C have grown tremendously, expanding the range of phenotypes observed in affected patients. CACNA1C channelopathies are now known to encompass multisystem phenotypes as described in TS, as well as more selective phenotypes where patients may exhibit predominantly cardiac or neurological symptoms. Here, we review the impact of genetic mutations on CaV1.2 function and the resultant physiological consequences.

Pathophysiology of Cav1.3 L-type calcium channels in the heart

Ca²⁺ plays a crucial role in excitation-contraction coupling in cardiac myocytes. Dysfunctional Ca²⁺ regulation alters the force of contraction and causes cardiac arrhythmias. Ca²⁺ entry into cardiomyocytes is mediated mainly through L-type Ca²⁺ channels, leading to the subsequent Ca²⁺ release from the sarcoplasmic reticulum. L-type Ca²⁺ channels are composed of the conventional Ca_v1.2, ubiquitously expressed in all heart chambers, and the developmentally regulated Ca_v1.3, exclusively expressed in the atria, sinoatrial node, and atrioventricular node in the adult heart. As such, Ca_v1.3 is implicated in the pathogenesis of sinoatrial and atrioventricular node dysfunction as well as atrial fibrillation. More recently, Ca_v1.3 de novo expression was suggested in heart failure. Here, we review the functional role, expression levels, and regulation of Ca_v1.3 in the heart, including in the context of cardiac diseases. We believe that the elucidation of the functional and molecular pathways regulating Ca_v1.3 in the heart will assist in developing novel targeted therapeutic interventions for the aforementioned arrhythmias.

Voltage-Gated Sodium Channel NaV1.5 Controls NHE-1-Dependent Invasive Properties in Colon Cancer Cells

Colorectal cancer (CRC) is the second leading cause of death worldwide, with 0.9 million deaths per year. The metastatic stage of the disease is identified in about 20% of cases at the first diagnosis and is associated with low patient-survival rates. Voltage-gated sodium channels (Na_V) are abnormally overexpressed in several carcinomas including CRC and are strongly associated with the metastatic behavior of cancer cells. Acidification of the extracellular space by Na⁺/H⁺ exchangers (NHE) contributes to extracellular matrix degradation and cell invasiveness. In this study, we assessed the expression levels of pore-forming α-subunits of Na_V channels and NHE exchangers in tumor and adjacent non-malignant tissues from colorectal cancer patients, CRC cell lines and primary tumor cells. In all cases, SCN5A (gene encoding for Na_V1.5) was overexpressed and positively correlated with cancer stage and poor survival prognosis for patients. In addition, we identified an anatomical differential expression of SCN5A and SLC9A1 (gene encoding for NHE-1) being particularly relevant for tumors that originated on the sigmoid colon epithelium. The functional activity of Na_V1.5 channels was characterized in CRC cell lines and the primary cells of colon tumors obtained using tumor explant methodologies. Furthermore, we assessed the performance of two new small-molecule Na_V1.5 inhibitors on the reduction of sodium currents, as well as showed that silencing SCN5A and SLC9A1 substantially reduced the 2D invasive capabilities of cancer cells. Thus, our findings show that both Na_V1.5 and NHE-1 represent two promising targetable membrane proteins against the metastatic progression of CRC.

Calcium-permeable channelrhodopsins for the photocontrol of calcium signalling

Channelrhodopsins are light-gated ion channels used to control excitability of designated cells in large networks with high spatiotemporal resolution. While ChRs selective for H+, Na+, K+ and anions have been discovered or engineered, Ca2+-selective ChRs have not been reported to date. Here, we analyse ChRs and mutant derivatives with regard to their Ca2+ permeability and improve their Ca2+ affinity by targeted mutagenesis at the central selectivity filter. The engineered channels, termed CapChR1 and CapChR2 for calcium-permeable channelrhodopsins, exhibit reduced sodium and proton conductance in connection with strongly improved Ca2+ permeation at negative voltage and low extracellular Ca2+ concentrations. In cultured cells and neurons, CapChR2 reliably increases intracellular Ca2+ concentrations. Moreover, CapChR2 can robustly trigger Ca2+ signalling in hippocampal neurons. When expressed together with genetically encoded Ca2+ indicators in Drosophila melanogaster mushroom body output neurons, CapChRs mediate light-evoked Ca2+ entry in brain explants.

Structural basis for NaV1.7 inhibition by pore blockers

Voltage-gated sodium channel Na_V1.7 plays essential roles in pain and odor perception. Na_V1.7 variants cause pain disorders. Accordingly, Na_V1.7 has elicited extensive attention in developing new analgesics. Here we present cryo-EM structures of human Na_V1.7/β1/β2 complexed with inhibitors XEN907, TC-N1752 and Na_V1.7-IN2, explaining specific binding sites and modulation mechanism for the pore blockers. These inhibitors bind in the central cavity blocking ion permeation, but engage different parts of the cavity wall. XEN907 directly causes α- to π-helix transition of DIV-S6 helix, which tightens the fast inactivation gate. TC-N1752 induces π-helix transition of DII-S6 helix mediated by a conserved asparagine on DIII-S6, which closes the activation gate. Na_V1.7-IN2 serves as a pore blocker without causing conformational change. Electrophysiological results demonstrate that XEN907 and TC-N1752 stabilize Na_V1.7 in inactivated state and delay the recovery from inactivation. Our results provide structural framework for Na_V1.7 modulation by pore blockers, and important implications for developing subtype-selective analgesics.

Plant and fungi derived analgesic natural products targeting voltage-gated sodium and calcium channels

Voltage-gated sodium and calcium channels (VGSCs and VGCCs) play an important role in the modulation of physiologically relevant processes in excitable cells that range from action potential generation to neurotransmission. Once their expression and/or function is altered in disease, specific pharmacological approaches become necessary to mitigate the negative consequences of such dysregulation. Several classes of small molecules have been developed with demonstrated effectiveness on VGSCs and VGCCs; however, off-target effects have also been described, limiting their use and spurring efforts to find more specific and safer molecules to target these channels. There are a great number of plants and herbal preparations that have been empirically used for the treatment of diseases in which VGSCs and VGCCs are involved. Some of these natural products have progressed to clinical trials, while others are under investigation for their action mechanisms on signaling pathways, including channels. In this review, we synthesize information from ~30 compounds derived from natural sources like plants and fungi and delineate their effects on VGSCs and VGCCs in human disease, particularly pain. [Figure: see text].

Autism associated mutations in β2 subunit of voltage-gated calcium channels constitutively activate gene expression

Membrane depolarization triggers gene expression through voltage-gated calcium channels (VGCC) in a process called Excitation-transcription (ET) coupling. Mutations in the channel subunits α₁1.2, or β_2d, are associated with neurodevelopmental disorders such as ASD. Here, we found that two mutations S143F and G113S within the rat Cavβ_2a corresponding to autistic related mutations Cavβ_2d^S197F and Cavβ_2d^G167S in the human Cavβ_2d, activate ET-coupling via the RAS/ERK/CREB pathway. Membrane depolarization of HEK293 cells co-expressing α₁1.2 and α_2δ with Cavβ_2a^S143F or Cavβ_2a^G113S triggers constitutive transcriptional activation, which is correlated with facilitated channel activity. Similar to the Timothy-associated autistic mutation α₁1.2^G406R, constitutive gene activation is attributed to a hyperpolarizing shift in the activation kinetics of Cav1.2. Pulldown of RasGRF2 and RhoGEF by wt and the Cavβ_2a autistic mutants is consistent with Cavβ₂/Ras activation in ET coupling and implicates Rho signaling as yet another molecular pathway activated by Cavα₁1.2/Cavβ2 . Facilitated spontaneous channel activity preceding enhanced gene activation via the Ras/ERK/CREB pathway, appears a general molecular mechanism for Ca²⁺ channel mediated ASD and other neurodevelopmental disorders.

Role of ion channels in the mechanism of proteinuria (Review)

Proteinuria is a common clinical manifestation of kidney diseases, such as glomerulonephritis, nephrotic syndrome, immunoglobulin A nephropathy and diabetic nephropathy. Therefore, proteinuria is considered to be a risk factor for renal dysfunction. Furthermore, proteinuria is also significantly associated with the progression of kidney diseases and increased mortality. Its occurrence is closely associated with damage to the structure of the glomerular filtration membrane. An impaired glomerular filtration membrane can affect the selective filtration function of the kidneys; therefore, several macromolecular substances, such as proteins, may pass through the filtration membrane and promote the manifestation of proteinuria. It has been reported that ion channels play a significant role in the mechanisms underlying proteinuria. Ion channel mutations or other dysfunctions have been implicated in several diseases, therefore ion channels could be used as major therapeutic targets. The mechanisms underlying the action of ion channels and ion transporters in proteinuria have been overlooked in the literature, despite their importance in identifying novel targets for treating proteinuria and delaying the progression of kidney diseases. The current review article focused on the four key ion channel groups, namely Na⁺, Ca²⁺, Cl^- and K⁺ ion channels and the associated ion transporters.

When the Gates Swing Open Only: Arrhythmia Mutations That Target the Fast Inactivation Gate of Nav1.5

Na_v1.5 is the main voltage-gated sodium channel found in cardiac muscle, where it facilitates the fast influx of Na⁺ ions across the cell membrane, resulting in the fast depolarization phase-phase 0 of the cardiac action potential. As a result, it plays a major role in determining the amplitude and the upstroke velocity of the cardiac impulse. Quantitively, cardiac sodium channel activates in less than a millisecond to trigger the cardiac action potential and inactivates within 2-3 ms to facilitate repolarization and return to the resting state in preparation for firing the next action potential. Missense mutations in the gene that encodes Na_v1.5 (SCN5A), change these time constants which leads to a wide spectrum of cardiac diseases ranging from long QT syndrome type 3 (LQT3) to sudden cardiac death. In this mini-review I will focus on the missense mutations in the inactivation gate of Na_v1.5 that results in arrhythmia, attempting to correlate the location of the missense mutation to their specific phenotype.

A lysine residue from an extracellular turret switches the ion preference in a Cav3 T-Type channel from calcium to sodium ions

Cav3 T-type calcium channels from great pond snail Lymnaea stagnalis have a selectivity-filter ring of five acidic residues, EE(D)DD. Splice variants with exons 12b or 12a spanning the extracellular loop between the outer helix IIS5 and membrane-descending pore helix IIP1 (IIS5-P1) in Domain II of the pore module possess calcium selectivity or dominant sodium permeability, respectively. Here, we use AlphaFold2 neural network software to predict that a lysine residue in exon 12a is salt-bridged to the aspartate residue immediately C terminal to the second-domain glutamate in the selectivity filter. Exon 12b has a similar folding but with an alanine residue in place of lysine in exon 12a. We express LCav3 channels with mutated exons Ala-12b-Lys and Lys-12a-Ala and demonstrate that they switch the ion preference to high sodium permeability and calcium selectivity, respectively. We propose that in the calcium-selective variants, a calcium ion chelated between Domain II selectivity-filter glutamate and aspartate is knocked-out by the incoming calcium ion in the process of calcium permeation, whereas sodium ions are repelled. The aspartate is neutralized by the lysine residue in the sodium-permeant variants, allowing for sodium permeation through the selectivity-filter ring of four negatively charged residues akin to the prokaryotic sodium channels with four glutamates in the selectivity filter. The evolutionary adaptation in invertebrate LCav3 channels highlight the involvement of a key, ubiquitous aspartate, "a calcium beacon" of sorts in the outer pore of Domain II, as determinative for the calcium ion preference over sodium ions through eukaryotic Cav1, Cav2, and Cav3 channels.

Effective Modulation by Lacosamide on Cumulative Inhibition of INa during High-Frequency Stimulation and Recovery of INa Block during Conditioning Pulse Train

The effects of lacosamide (LCS, Vimpat®), an anti-convulsant and analgesic, on voltage-gated Na+ current (INa) were investigated. LCS suppressed both the peak (transient, INa(T)) and sustained (late, INa(L)) components of INa with the IC50 values of 78 and 34 μM found in GH3 cells and of 112 and 26 μM in Neuro-2a cells, respectively. In GH3 cells, the voltage-dependent hysteresis of persistent INa (INa(P)) during the triangular ramp pulse was strikingly attenuated, and the decaying time constant (τ) of INa(T) or INa(L) during a train of depolarizing pulses was further shortened by LCS. The recovery time course from the INa block elicited by the preceding conditioning train can be fitted by two exponential processes, while the single exponential increase in current recovery without a conditioning train was adequately fitted. The fast and slow τ's of recovery from the INa block by the same conditioning protocol arose in the presence of LCS. In Neuro-2a cells, the strength of the instantaneous window INa (INa(W)) during the rapid ramp pulse was reduced by LCS. This reduction could be reversed by tefluthrin. Moreover, LCS accelerated the inactivation time course of INa activated by pulse train stimulation, and veratridine reversed its decrease in the decaying τ value in current inactivation. The docking results predicted the capability of LCS binding to some amino-acid residues in sodium channels owing to the occurrence of hydrophobic contact. Overall, our findings unveiled that LCS can interact with the sodium channels to alter the magnitude, gating, voltage-dependent hysteresis behavior, and use dependence of INa in excitable cells.

From HDAC to Voltage-Gated Ion Channels: What's Next? The Long Road of Antiepileptic Drugs Repositioning in Cancer

Simple Summary

Although in the last decades the clinical outcome of cancer patients considerably improved, the major drawbacks still associated with chemotherapy are the unwanted side effects and the development of drug resistance. Therefore, a continuous effort in trying to discover new tumor markers, possibly of diagnostic, prognostic and therapeutic value, is being made. This review is aimed at highlighting the anti-tumor activity that several antiepileptic drugs (AEDs) exert in breast, prostate and other types of cancers, mainly focusing on their ability to block the voltage-gated Na⁺ and Ca⁺⁺ channels, as well as to inhibit the activity of histone deacetylases (HDACs), all well-documented tumor markers and/or molecular targets. The existence of additional AEDs molecular targets is highly suspected. Therefore, the repurposing of already available drugs as adjuvants in cancer treatment would have several advantages, such as reductions in dose-related toxicity CVs will be sent in a separate mail to the indicated address of combined treatments, lower production costs, and faster approval for clinical use.

Abstract

Cancer is a major health burden worldwide. Although the plethora of molecular targets identified in the last decades and the deriving developed treatments, which significantly improved patients’ outcome, the occurrence of resistance to therapies remains the major cause of relapse and mortality. Thus, efforts in identifying new markers to be exploited as molecular targets in cancer therapy are needed. This review will first give a glance on the diagnostic and therapeutic significance of histone deacetylase (HDAC) and voltage gated ion channels (VGICs) in cancer. Nevertheless, HDAC and VGICs have also been reported as molecular targets through which antiepileptic drugs (AEDs) seem to exert their anticancer activity. This should be claimed as a great advantage. Indeed, due to the slowness of drug approval procedures, the attempt to turn to off-label use of already approved medicines would be highly preferable. Therefore, an updated and accurate overview of both preclinical and clinical data of commonly prescribed AEDs (mainly valproic acid, lamotrigine, carbamazepine, phenytoin and gabapentin) in breast, prostate, brain and other cancers will follow. Finally, a glance at the emerging attempt to administer AEDs by means of opportunely designed drug delivery systems (DDSs), so to limit toxicity and improve bioavailability, is also given.

Biallelic CACNA2D1 loss-of-function variants cause early-onset developmental epileptic encephalopathy

Voltage-gated calcium (CaV) channels form three subfamilies (CaV1-3). The CaV1 and CaV2 channels are heteromeric, consisting of an α1 pore-forming subunit, associated with auxiliary CaVβ and α2δ subunits. The α2δ subunits are encoded in mammals by four genes, CACNA2D1-4. They play important roles in trafficking and function of the CaV channel complexes. Here we report biallelic variants in CACNA2D1, encoding the α2δ-1 protein, in two unrelated individuals showing a developmental and epileptic encephalopathy. Patient 1 has a homozygous frameshift variant c.818_821dup/p.(Ser275Asnfs*13) resulting in nonsense-mediated mRNA decay of the CACNA2D1 transcripts, and absence of α2δ-1 protein detected in patient-derived fibroblasts. Patient 2 is compound heterozygous for an early frameshift variant c.13_23dup/p.(Leu9Alafs*5), highly probably representing a null allele and a missense variant c.626G>A/p.(Gly209Asp). Our functional studies show that this amino-acid change severely impairs the function of α2δ-1 as a calcium channel subunit, with strongly reduced trafficking of α2δ-1G209D to the cell surface and a complete inability of α2δ-1G209D to increase the trafficking and function of CaV2 channels. Thus, biallelic loss-of-function variants in CACNA2D1 underlie the severe neurodevelopmental disorder in these two patients. Our results demonstrate the critical importance and non-interchangeability of α2δ-1 and other α2δ proteins for normal human neuronal development.

The Single Residue K12 Governs the Exceptional Voltage Sensitivity of Mitochondrial Voltage-Dependent Anion Channel Gating

The voltage-dependent anion channel (VDAC) is a β-barrel channel of the mitochondrial outer membrane (MOM) that passively transports ions, metabolites, polypeptides, and single-stranded DNA. VDAC responds to a transmembrane potential by "gating," i.e. transitioning to one of a variety of low-conducting states of unknown structure. The gated state results in nearly complete suppression of multivalent mitochondrial metabolite (such as ATP and ADP) transport, while enhancing calcium transport. Voltage gating is a universal property of β-barrel channels, but VDAC gating is anomalously sensitive to transmembrane potential. Here, we show that a single residue in the pore interior, K12, is responsible for most of VDAC's voltage sensitivity. Using the analysis of over 40 μs of atomistic molecular dynamics (MD) simulations, we explore correlations between motions of charged residues inside the VDAC pore and geometric deformations of the β-barrel. Residue K12 is bistable; its motions between two widely separated positions along the pore axis enhance the fluctuations of the β-barrel and augment the likelihood of gating. Single channel electrophysiology of various K12 mutants reveals a dramatic reduction of the voltage-induced gating transitions. The crystal structure of the K12E mutant at a resolution of 2.6 Å indicates a similar architecture of the K12E mutant to the wild type; however, 60 μs of atomistic MD simulations using the K12E mutant show restricted motion of residue 12, due to enhanced connectivity with neighboring residues, and diminished amplitude of barrel motions. We conclude that β-barrel fluctuations, governed particularly by residue K12, drive VDAC gating transitions.

Evaluation of Cardiovascular Concerns of Intravenous Lacosamide Therapy in Epilepsy Patients

Objective

Voltage-gated sodium channels (VGSCs) play an important role in neuronal excitability and epilepsies. In addition to the brain, VGSCs are also abundant enriched in cardiac tissues and are responsible for normal cardiac rhythm. Theoretically, sodium channel blocking antiseizure medications (SCB-ASMs) may have unwanted cardiac side effects. Lacosamide (LCM) is increasingly used in patients with status epilepticus (SE) due to the availability of intravenous formula. The concerns about the proarrhythmic effect are even higher due to the need for rapid administration of LCM. There were limited data on the cardiac safety of intravenous LCM. Hereby, we performed a study to observe the effect of intravenous loading of LCM in patients with seizures in our Neurological Intensive Care Unit (NICU).

Methods

We retrospectively reviewed the patients using parenteral LCM for seizures in NICU. A routine infusion time of 30 min was performed. The electrocardiogram (ECG) and blood pressure were recorded before and after LCM injection.

Results

We retrospectively reviewed the clinical data of 38 patients using LCM for treating seizures. Two patients had cardiac side effects after LCM loading, one (3.0%) with new-onset first-degree AV block and the other (3.0%) with atrial premature complex. For the quantitative changes of ECG parameter analysis, there was no change in QRS complex, corrected QT intervals, and heart rate except that the PR interval was mildly increased. A mild decrease in the diastolic blood pressure and mean arterial pressure were also observed. None of the above-mentioned parameter alterations required clinical intervention.

Conclusion

We evaluated the cardiac safety concern in real-world epilepsy patients requiring intravenous LCM. Near half of this cohort responded to LCM therapy and there was no life-threatening cardiac adverse effect. Intravenous LCM does have some effects on the ECG parameters and blood pressure but without clinical relevance. Despite the theoretical concern of cardiac adverse effects of LCM, the benefit of seizure control outweighed the risk in patients with status epilepticus or seizure clusters, such as hyperthermia, pulmonary edema, cardiac arrhythmias, or cardiovascular collapse.

From α1s splicing to γ1 function: A new twist in subunit modulation of the skeletal muscle L-type Ca2+ channel

Melzer discusses a recent JGP study showing that alternative splicing of the skeletal muscle L-type calcium channel impacts on a modulatory effect of its γ subunit.

Structural Advances in Voltage-Gated Sodium Channels

Voltage-gated sodium (Na_V) channels are responsible for the rapid rising-phase of action potentials in excitable cells. Over 1,000 mutations in Na_V channels are associated with human diseases including epilepsy, periodic paralysis, arrhythmias and pain disorders. Natural toxins and clinically-used small-molecule drugs bind to Na_V channels and modulate their functions. Recent advances from cryo-electron microscopy (cryo-EM) structures of Na_V channels reveal invaluable insights into the architecture, activation, fast inactivation, electromechanical coupling, ligand modulation and pharmacology of eukaryotic Na_V channels. These structural analyses not only demonstrate molecular mechanisms for Na_V channel structure and function, but also provide atomic level templates for rational development of potential subtype-selective therapeutics. In this review, we summarize recent structural advances of eukaryotic Na_V channels, highlighting the structural features of eukaryotic Na_V channels as well as distinct modulation mechanisms by a wide range of modulators from natural toxins to synthetic small-molecules.

N-type fast inactivation of a eukaryotic voltage-gated sodium channel

Voltage-gated sodium (Na_V) channels initiate action potentials. Fast inactivation of Na_V channels, mediated by an Ile-Phe-Met motif, is crucial for preventing hyperexcitability and regulating firing frequency. Here we present cryo-electron microscopy structure of Na_VEh from the coccolithophore Emiliania huxleyi, which reveals an unexpected molecular gating mechanism for Na_V channel fast inactivation independent of the Ile-Phe-Met motif. An N-terminal helix of Na_VEh plugs into the open activation gate and blocks it. The binding pose of the helix is stabilized by multiple electrostatic interactions. Deletion of the helix or mutations blocking the electrostatic interactions completely abolished the fast inactivation. These strong interactions enable rapid inactivation, but also delay recovery from fast inactivation, which is ~160-fold slower than human Na_V channels. Together, our results provide mechanistic insights into fast inactivation of Na_VEh that fundamentally differs from the conventional local allosteric inhibition, revealing both surprising structural diversity and functional conservation of ion channel inactivation.

CaVβ-subunit dependence of forward and reverse trafficking of CaV1.2 calcium channels

Auxiliary CaVβ subunits interact with the pore forming CaVα1 subunit to promote the plasma membrane expression of high voltage-activated calcium channels and to modulate the biophysical properties of Ca2+ currents. However, the effect of CaVβ subunits on channel trafficking to and from the plasma membrane is still controversial. Here, we have investigated the impact of CaVβ1b and CaVβ2a subunits on plasma membrane trafficking of CaV1.2 using a live-labeling strategy. We show that the CaVβ1b subunit is more potent in increasing CaV1.2 expression at the plasma membrane than the CaVβ2a subunit and that this effect is not related to modification of intracellular trafficking of the channel (i.e. neither forward trafficking, nor recycling, nor endocytosis). We conclude that the differential effect of CaVβ subunit subtypes on CaV1.2 surface expression is likely due to their differential ability to protect CaV1.2 from degradation.

Retinitis Pigmentosa: Progress in Molecular Pathology and Biotherapeutical Strategies

Retinitis pigmentosa (RP) is genetically heterogeneous retinopathy caused by photoreceptor cell death and retinal pigment epithelial atrophy that eventually results in blindness in bilateral eyes. Various photoreceptor cell death types and pathological phenotypic changes that have been disclosed in RP demand in-depth research of its pathogenic mechanism that may account for inter-patient heterogeneous responses to mainstream drug treatment. As the primary method for studying the genetic characteristics of RP, molecular biology has been widely used in disease diagnosis and clinical trials. Current technology iterations, such as gene therapy, stem cell therapy, and optogenetics, are advancing towards precise diagnosis and clinical applications. Specifically, technologies, such as effective delivery vectors, CRISPR/Cas9 technology, and iPSC-based cell transplantation, hasten the pace of personalized precision medicine in RP. The combination of conventional therapy and state-of-the-art medication is promising in revolutionizing RP treatment strategies. This article provides an overview of the latest research on the pathogenesis, diagnosis, and treatment of retinitis pigmentosa, aiming for a convenient reference of what has been achieved so far.

Pathophysiological Responses to Conotoxin Modulation of Voltage-Gated Ion Currents

Voltage-gated ion channels are plasma membrane proteins that generate electrical signals following a change in the membrane voltage. Since they are involved in several physiological processes, their dysfunction may be responsible for a series of diseases and pain states particularly related to neuronal and muscular systems. It is well established for decades that bioactive peptides isolated from venoms of marine mollusks belonging to the Conus genus, collectively known as conotoxins, can target different types and isoforms of these channels exerting therapeutic effects and pain relief. For this reason, conotoxins are widely used for either therapeutic purposes or studies on ion channel mechanisms of action disclosure. In addition their positive property, however, conotoxins may generate pathological states through similar ion channel modulation. In this narrative review, we provide pieces of evidence on the pathophysiological impacts that different members of conotoxin families exert by targeting the three most important voltage-gated channels, such as sodium, calcium, and potassium, involved in cellular processes.

Druggability of Voltage-Gated Sodium Channels-Exploring Old and New Drug Receptor Sites

Voltage-gated ion channels are important drug targets because they play crucial physiological roles in both excitable and non-excitable cells. About 15% of clinical drugs used for treating human diseases target ion channels. However, most of these drugs do not provide sufficient specificity to a single subtype of the channels and their off-target side effects can be serious and sometimes fatal. Recent advancements in imaging techniques have enabled us for the first time to visualize unique and hidden parts of voltage-gated sodium channels in different structural conformations, and to develop drugs that further target a selected functional state in each channel subtype with the potential for high precision and low toxicity. In this review we describe the druggability of voltage-gated sodium channels in distinct functional states, which could potentially be used to selectively target the channels. We review classical drug receptors in the channels that have recently been structurally characterized by cryo-electron microscopy with natural neurotoxins and clinical drugs. We further examine recent drug discoveries for voltage-gated sodium channels and discuss opportunities to use distinct, state-dependent receptor sites in the voltage sensors as unique drug targets. Finally, we explore potential new receptor sites that are currently unknown for sodium channels but may be valuable for future drug discovery. The advancement presented here will help pave the way for drug development that selectively targets voltage-gated sodium channels.

Cav3 T-Type Voltage-Gated Ca2+ Channels and the Amyloidogenic Environment: Pathophysiology and Implications on Pharmacotherapy and Pharmacovigilance

Voltage-gated Ca2+ channels (VGCCs) were reported to play a crucial role in neurotransmitter release, dendritic resonance phenomena and integration, and the regulation of gene expression. In the septohippocampal system, high- and low-voltage-activated (HVA, LVA) Ca2+ channels were shown to be involved in theta genesis, learning, and memory processes. In particular, HVA Cav2.3 R-type and LVA Cav3 T-type Ca2+ channels are expressed in the medial septum-diagonal band of Broca (MS-DBB), hippocampal interneurons, and pyramidal cells, and ablation of both channels was proven to severely modulate theta activity. Importantly, Cav3 Ca2+ channels contribute to rebound burst firing in septal interneurons. Consequently, functional impairment of T-type Ca2+ channels, e.g., in null mutant mouse models, caused tonic disinhibition of the septohippocampal pathway and subsequent enhancement of hippocampal theta activity. In addition, impairment of GABA A/B receptor transcription, trafficking, and membrane translocation was observed within the septohippocampal system. Given the recent findings that amyloid precursor protein (APP) forms complexes with GABA B receptors (GBRs), it is hypothesized that T-type Ca2+ current reduction, decrease in GABA receptors, and APP destabilization generate complex functional interdependence that can constitute a sophisticated proamyloidogenic environment, which could be of potential relevance in the etiopathogenesis of Alzheimer's disease (AD). The age-related downregulation of T-type Ca2+ channels in humans goes together with increased Aβ levels that could further inhibit T-type channels and aggravate the proamyloidogenic environment. The mechanistic model presented here sheds new light on recent reports about the potential risks of T-type Ca2+ channel blockers (CCBs) in dementia, as observed upon antiepileptic drug application in the elderly.