CoroNa Na+ Indicators

Semantic Scholar extracted view of "Target technology - bring the insect to the insecticide not the insecticide to the insect" by O. Jones et al.

How the occurrence of multiple sodium channel paralogs has influenced the evolutionary history of three groups of fishes is reviewed: pufferfish, gymnotiform and mormyriform electric fish. Voltage-dependent sodium channels are critical for electrical excitability. Invertebrates possess a single sodium channel gene; two rounds of genome duplication early in vertebrates increased the number to four. Since the teleost-tetrapod split, independent gene duplications in each lineage have further increased the number of sodium channel genes to 10 in tetrapods and 8 in teleosts. Here we review how the occurrence of multiple sodium channel paralogs has influenced the evolutionary history of three groups of fishes: pufferfish, gymnotiform and mormyriform electric fish. Pufferfish (tetraodontidae) produce a neurotoxin, tetrodotoxin, that binds to and blocks the pore of sodium channels. Pufferfish evolved resistance to their own toxins by amino acid substitutions in the pore of their sodium channels. These substitutions had to occur in parallel across multiple paralogs for organismal resistance to evolve. Gymnotiform and mormyriform fishes independently evolved electric organs to generate electricity for communication and object localization. Two sodium channel genes are expressed in muscle in most fishes. In both groups of weakly electric fishes, one gene lost its expression in muscle and became compartmentalized in the evolutionary novel electric organ, which is a muscle derivative. This gene then evolved at elevated rates, whereas the gene that is still expressed in muscle does not show elevated rates of evolution. In the electric organ-expressing gene, amino acid substitutions occur in parts of the channel involved in determining how long the channel will be open or closed. The enhanced rate of sequence evolution of this gene likely underlies the species-level variations in the electric signal.

Semantic Scholar extracted view of "Molecular characterization of a sodium channel gene from the Silkworm Bombyx mori." by Ya-Ming Shao et al.

Semantic Scholar extracted view of "Human and rat Nav1.3 voltage-gated sodium channels differ in inactivation properties and sensitivity to the pyrethroid insecticide tefluthrin." by Jianguo Tan et al.

A comparative study of multiple variants of the sodium channel transcripts in the mosquito Culex quinquefasciatus is presented, providing a functional basis for further characterizing how alternative splicing of a voltage-gated sodium channel contributes to diversity in neuronal signaling in mosquitoes in response to pyrethroids. Voltage-gated sodium channels are the target sites of both DDT and pyrethroid insecticides. The importance of alternative splicing as a key mechanism governing the structural and functional diversity of sodium channels and the resulting development of insecticide and acaricide resistance is widely recognized, as shown by the extensive research on characterizing alternative splicing and variants of sodium channels in medically and agriculturally important insect species. Here we present the first comparative study of multiple variants of the sodium channel transcripts in the mosquito Culex quinquefasciatus. The variants were classified into two categories, CxNa-L and CxNa-S based on their distinguishing sequence sizes of ~6.5 kb and ~4.0 kb, respectively, and generated via major extensive alternative splicing with minor small deletions/ insertions in susceptible S-Lab, low resistant HAmCqG0, and highly resistant HAmCqG8 Culex strains. Four alternative Cx-Na-L splice variants were identified, including three full length variants with three optional exons (2, 5, and 21i) and one with in-frame-stop codons. Large, multi-exon-alternative splices were identified in the CxNa-S category. All CxNa-S splicing variants in the S-Lab and HAmCqG0 strains contained in-frame stop codons, suggesting that any resulting proteins would be truncated. The ~1000 to ~3000-fold lower expression of these splice variants with stop codons compared with the CxNa-L splicing variants may support the lower importance of these variants in S-Lab and HAmCqG0. Interestingly, two alternative splicing variants of CxNa-S in HAmCqG8 included entire ORFs but lacked exons 5 to18 and these two variants had much higher expression levels in HAmCqG8 than in S-Lab and HAmCqG0. These results provide a functional basis for further characterizing how alternative splicing of a voltage-gated sodium channel contributes to diversity in neuronal signaling in mosquitoes in response to pyrethroids, and possibly indicates the role of these variants in the development of pyrethroid resistance.

Comparisons of the effects of TEH1 and TipE on the function of three Drosophila sodium channel splice variants in Xenopus oocytes suggest that TEH 1 may play a broader role than TipE in regulating sodium channel function and neuronal excitability in vivo. β subunits of mammalian sodium channels play important roles in modulating the expression and gating of mammalian sodium channels. However, there are no orthologs of β subunits in insects. Instead, an unrelated protein, TipE in Drosophila melanogaster and its orthologs in other insects, is thought to be a sodium channel auxiliary subunit. In addition, there are four TipE-homologous genes (TEH1-4) in D. melanogaster and three to four orthologs in other insect species. TipE and TEH1-3 have been shown to enhance the peak current of various insect sodium channels expressed in Xenopus oocytes. However, limited information is available on how these proteins modulate the gating of sodium channels, particularly sodium channel variants generated by alternative splicing and RNA editing. In this study, we compared the effects of TEH1 and TipE on the function of three Drosophila sodium channel splice variants, DmNav9-1, DmNav22, and DmNav26, in Xenopus oocytes. Both TipE and TEH1 enhanced the amplitude of sodium current and accelerated current decay of all three sodium channels tested. Strikingly, TEH1 caused hyperpolarizing shifts in the voltage-dependence of activation, fast inactivation and slow inactivation of all three variants. In contrast, TipE did not alter these gating properties except for a hyperpolarizing shift in the voltage-dependence of fast inactivation of DmNav26. Further analysis of the gating kinetics of DmNav9-1 revealed that TEH1 accelerated the entry of sodium channels into the fast inactivated state and slowed the recovery from both fast- and slow-inactivated states, thereby, enhancing both fast and slow inactivation. These results highlight the differential effects of TipE and TEH1 on the gating of insect sodium channels and suggest that TEH1 may play a broader role than TipE in regulating sodium channel function and neuronal excitability in vivo.

Upon analysis of the obtained sequence, functional regions of the putative sodium channel responsible for the selectivity filter, inactivation gate, voltage sensor, and phosphorylation have been predicted. Voltage-gated sodium channel genes and associated proteins have been cloned and studied in many mammalian and invertebrate species. However, there is no data available about the sodium channel gene(s) in the crayfish, although the animal has frequently been used as a model to investigate various aspects of neural cellular and circuit function. In the present work, by using RNA extracts from crayfish abdominal ganglia samples, the complete open reading frame of a putative sodium channel gene has firstly been cloned and molecular properties of the associated peptide have been analyzed. The open reading frame of the gene has a length of 5793 bp that encodes for the synthesis of a peptide, with 1930 amino acids, that is 82 % similar to the α-peptide of a sodium channel in a neighboring species, Cancer borealis. The transmembrane topology analysis of the crayfish peptide indicated a pattern of four folding domains with several transmembrane segments, as observed in other known voltage-gated sodium channels. Upon analysis of the obtained sequence, functional regions of the putative sodium channel responsible for the selectivity filter, inactivation gate, voltage sensor, and phosphorylation have been predicted. The expression level of the putative sodium channel gene, as defined by a qPCR method, was measured and found to be the highest in nervous tissue.

Semantic Scholar extracted view of "Indoxacarb, Metaflumizone, and Other Sodium Channel Inhibitor Insecticides: Mechanism and Site of Action on Mammalian Voltage-Gated Sodium Channels." by Richard T. von Stein et al.

The atomic structure of a eukaryotic Nav channel is required to reveal the molecular basis for ion selectivity, voltage-dependent activation and inactivation, and recognition of toxins, agonists, and antagonists. Navigating regulated cell excitation Voltage-gated sodium (Nav) channels respond to a change in voltage potential by allowing sodium ions to move into cells, thus initiating electrical signaling. Mutations in Nav channels cause neurological and cardiovascular disorders, making the channels important therapeutic targets. Shen et al. determined a high-resolution structure of a Nav channel from the American cockroach by electron microscopy. The structure affords insight into voltage sensing and ion permeability and provides a foundation for understanding function and disease mechanism of Nav and the related Cav ion channels. Science, this issue p. eaal4326 The cryo–electron microscopy structure of a cockroach sodium channel provides a foundation for understanding the channel’s function and disease mechanism. INTRODUCTION Voltage-gated sodium (Nav) channels are responsible for the generation and propagation of action potentials in excitable cells. They undergo voltage-dependent activation to initiate electrical signaling at millisecond scale and inactivate by both fast and slow mechanisms. The eukaryotic Nav channels comprise a pore-forming α subunit and auxiliary β subunits that facilitate membrane localization and modulate channel properties. The α subunit is a single polypeptide chain that folds to four homologous repeats (domains I to IV), each containing six transmembrane segments, S1 to S6. The S5 and S6 segments enclose the central pore domain, and their intervening sequences constitute the selectivity filter (SF). One residue at the corresponding SF locus in each repeat, Asp/Glu/Lys/Ala (DEKA), determines Na+ selectivity. The S1 to S4 segments in each repeat form a voltage-sensing domain (VSD), wherein S4 carries repetitively occurring positive residues essential for voltage sensing. More than 1000 mutations have been identified in human Nav channels associated with various neurological and cardiovascular disorders. Nav channels represent important targets for multiple pharmaceutical drugs and natural toxins. The atomic structure of a eukaryotic Nav channel is required to reveal the molecular basis for ion selectivity, voltage-dependent activation and inactivation, and recognition of toxins, agonists, and antagonists. RATIONALE The technological breakthrough of electron microscopy (EM) has offered unprecedented opportunity for structure elucidation of eukaryotic Nav channels, but the bottleneck exists in the generation of sufficient amounts of high-quality proteins. After extensive screening, we succeeded in obtaining homogeneous proteins of PaFPC1, a putative Nav channel from the American cockroach. Despite the lack of electrophysiological characterizations, PaFPC1 contains all the hallmarks of a Nav channel except for the fast inactivation motif. We designated the protein NavPaS. RESULTS The cryogenic EM (cryo-EM) structure of NavPaS was determined with an overall resolution of 3.8 Å, allowing side-chain assignment for the complete transmembrane fold, extracellular loops of the pore domain, the intact III-IV linker, and the carboxy-terminal domain (CTD). A poly-Ala backbone was modeled for an amino-terminal domain that is located below VSDI. In addition, 20 sugar moieties were built into seven glycosylation sites on the extracellular loops. Conserved disulfide bonds are observed within the extracellular loops and between P2II and S6II segments. The asymmetric selectivity filter vestibule is constituted by the side chains of the signature DEKA residues and the carbonyl oxygens of the two preceding residues in each repeat. The closed pore domain has only one small fenestration constituted by the S6III and S6IV segments. The four VSDs exhibit distinct conformations, with the corresponding gating charges located at different heights relative to their respective charge transfer center. Extensive interactions are observed between the III-IV linker, CTD, VSDIV, S4-S5IV, S6IV, and S6III segments of NavPaS. Despite the sequence variations of the III-IV linker and the lack of Ile/Met/Phe/Thr motif, the structure provides an important clue to understanding the fast inactivation mechanism of Nav channels. CONCLUSION The structure of a single-chain eukaryotic Nav channel serves as the framework for elucidating function and disease mechanisms of Nav channels. It provides the molecular template for interpretation of a wealth of experimental observations accumulated over the past six decades. Structural comparison between the related NavPaS and Cav1.1 reveals conformational shifts that may shed light on the understanding of the electromechanical coupling mechanism of voltage-gated channels. Structure-guided protein engineering will facilitate future mechanistic investigations of Nav and Cav channels. The cryo-EM structure of a eukaryotic Nav channel at 3.8-Å resolution. (Left) The overall structure of NavPaS/PaFPC1, a putative Nav channel identified from American cockroach. The glycosyl moieties and disulfide bonds are shown as sticks and spheres, respectively. The structure is domain colored. (Right) The pore domain of NavPaS. The permeation path is illustrated by brown dots in the pore domain, and the corresponding pore radii along the conducting passage are tabulated on the right. The functional entities along the permeation path—including the selectivity filter, the central cavity, and the intracellular activation gate—are annotated. Voltage-gated sodium (Nav) channels are responsible for the initiation and propagation of action potentials. They are associated with a variety of channelopathies and are targeted by multiple pharmaceutical drugs and natural toxins. Here, we report the cryogenic electron microscopy structure of a putative Nav channel from American cockroach (designated NavPaS) at 3.8 angstrom resolution. The voltage-sensing domains (VSDs) of the four repeats exhibit distinct conformations. The entrance to the asymmetric selectivity filter vestibule is guarded by heavily glycosylated and disulfide bond–stabilized extracellular loops. On the cytoplasmic side, a conserved amino-terminal domain is placed below VSDI, and a carboxy-terminal domain binds to the III-IV linker. The structure of NavPaS establishes an important foundation for understanding function and disease mechanism of Nav and related voltage-gated calcium channels.

Semantic Scholar extracted view of "A residue in the transmembrane segment 6 of domain I in insect and mammalian sodium channels regulate differential sensitivities to pyrethroid insecticides." by Eugenio E Oliveira et al.

This review focuses on insect-selective peptide toxins and their utility for the study of insect NaV and CaV channels and it might be possible to exploit the phyletic specificity of these toxins as the basis for rational development of novel classes of ion channel insecticides. Numerous metazoans express venoms for the purpose of defense, competitor deterrence, or prey capture. Peptide neurotoxins are particularly well represented in the venoms of arachnids, cnidarians and mollusks and these toxins often possess high affinity and specificity for particular classes of ion channels. Some of these toxins have become the defining pharmacology for certain vertebrate ion channel subtypes. Unfortunately, due to differences in the structure, pharmacology, and ion selectivity of insect voltage-gated sodium (NaV) and calcium (CaV) channels compared with their vertebrate counterparts, these peptide toxins have proven less useful for the characterization of insect ion channels. Despite these disparities in channel structure and function, the armament of peptide toxins that specifically modulate the activity of insect ion channels is slowly expanding. This review focuses on insect-selective peptide toxins and their utility for the study of insect NaV and CaV channels. The high affinity and selectivity of some of these neurotoxins means that they have the potential to become the defining pharmacology for specific subtypes of insect ion channels. In addition, it might be possible to exploit the phyletic specificity of these toxins as the basis for rational development of novel classes of ion channel insecticides.

Semantic Scholar extracted view of "13.09 – Ion Channels*" by V. Suppiramaniam et al.

The increase of frequency and distribution of kdr mutations clearly shows the importance of this mechanism in the process of pyrethroid resistance, and several species-specific and highly sensitive methods have been designed in order to genotype individual mosquitoes for kdr in large scale, which may serve as important tolls for monitoring the dynamics of pyreysroid resistance in natural populations. Constant and extensive use of chemical insecticides has created a selection pressure and favored resistance development in many insect species worldwide. One of the most important pyrethroid resistance mechanisms is classified as target site insensitivity, due to conformational changes in the target site that impair a proper binding of the insecticide molecule. The voltage-gated sodium channel (NaV) is the target of pyrethroids and DDT insecticides, used to control insects of medical, agricultural and veterinary importance, such as anophelines. It has been reported that the presence of a few non-silent point mutations in the NaV gene are associated with pyrethroid resistance, termed as ‘kdr’ (knockdown resistance) for preventing the knockdown effect of these insecticides. The presence of these mutations, as well as their effects, has been thoroughly studied in Anopheles mosquitoes. So far, kdr mutations have already been detected in at least 13 species (Anopheles gambiae, Anopheles arabiensis, Anopheles sinensis, Anopheles stephensi, Anopheles subpictus, Anopheles sacharovi, Anopheles culicifacies, Anopheles sundaicus, Anopheles aconitus, Anopheles vagus, Anopheles paraliae, Anopheles peditaeniatus and Anopheles albimanus) from populations of African, Asian and, more recently, American continents. Seven mutational variants (L1014F, L1014S, L1014C, L1014W, N1013S, N1575Y and V1010L) were described, with the highest prevalence of L1014F, which occurs at the 1014 site in NaV IIS6 domain. The increase of frequency and distribution of kdr mutations clearly shows the importance of this mechanism in the process of pyrethroid resistance. In this sense, several species-specific and highly sensitive methods have been designed in order to genotype individual mosquitoes for kdr in large scale, which may serve as important tolls for monitoring the dynamics of pyrethroid resistance in natural populations. We also briefly discuss investigations concerning the course of Plasmodium infection in kdr individuals. Considering the limitation of insecticides available for employment in public health campaigns and the absence of a vaccine able to brake the life cycle of the malaria parasites, the use of pyrethroids is likely to remain as the main strategy against mosquitoes by either indoor residual spraying (IR) and insecticide treated nets (ITN). Therefore, monitoring insecticide resistance programs is a crucial need in malaria endemic countries.

The successful expression of a sodium channel, AaNav1–1, from Aedes aegypti in Xenopus oocytes, and the functional examination of nine sodium channel mutations that are associated with pyrethroid resistance in various Ae. Pyrethroid insecticides are widely used as one of the most effective control measures in the global fight against agricultural arthropod pests and mosquito-borne diseases, including malaria and dengue. They exert toxic effects by altering the function of voltage-gated sodium channels, which are essential for proper electrical signaling in the nervous system. A major threat to the sustained use of pyrethroids for vector control is the emergence of mosquito resistance to pyrethroids worldwide. Here, we report the successful expression of a sodium channel, AaNav1–1, from Aedes aegypti in Xenopus oocytes, and the functional examination of nine sodium channel mutations that are associated with pyrethroid resistance in various Ae. aegypti and Anopheles gambiae populations around the world. Our analysis shows that five of the nine mutations reduce AaNav1–1 sensitivity to pyrethroids. Computer modeling and further mutational analysis revealed a surprising finding: Although two of the five confirmed mutations map to a previously proposed pyrethroid-receptor site in the house fly sodium channel, the other three mutations are mapped to a second receptor site. Discovery of this second putative receptor site provides a dual-receptor paradigm that could explain much of the molecular mechanisms of pyrethroid action and resistance as well as the high selectivity of pyrethroids on insect vs. mammalian sodium channels. Results from this study could impact future prediction and monitoring of pyrethroid resistance in mosquitoes and other arthropod pests and disease vectors.

A better understanding of regulation of membrane excitability through RNA alternative splicing and translational repression of Navs should provide new leads to treat epilepsy. The voltage-gated sodium channel (Nav) plays a key role in regulation of neuronal excitability. Aberrant regulation of Nav expression and/or function can result in an imbalance in neuronal activity which can progress to epilepsy. Regulation of Nav activity is achieved by coordination of a multitude of mechanisms including RNA alternative splicing and translational repression. Understanding of these regulatory mechanisms is complicated by extensive genetic redundancy: the mammalian genome encodes ten Navs. By contrast, the genome of the fruitfly, Drosophila melanogaster, contains just one Nav homologue, encoded by paralytic (DmNav). Analysis of splicing in DmNav shows variants exhibit distinct gating properties including varying magnitudes of persistent sodium current (INaP). Splicing by Pasilla, an identified RNA splicing factor, alters INaP magnitude as part of an activity-dependent mechanism. Enhanced INaP promotes membrane hyperexcitability that is associated with seizure-like behaviour in Drosophila. Nova-2, a mammalian Pasilla homologue, has also been linked to splicing of Navs and, moreover, mouse gene knockouts display seizure-like behaviour.Expression level of Navs is also regulated through a mechanism of translational repression in both flies and mammals. The translational repressor Pumilio (Pum) can bind to Nav transcripts and repress the normal process of translation, thus regulating sodium current (INa) density in neurons. Pum2-deficient mice exhibit spontaneous EEG abnormalities. Taken together, aberrant regulation of Nav function and/or expression is often epileptogenic. As such, a better understanding of regulation of membrane excitability through RNA alternative splicing and translational repression of Navs should provide new leads to treat epilepsy.

Semantic Scholar extracted view of "The effects of knock-down resistance mutations and alternative splicing on voltage-gated sodium channels in Musca domestica and Drosophila melanogaster." by A. J. Thompson et al.