Primary structure of the receptor for calcium channel blockers from skeletal muscle

Structural biology of voltage-gated calcium channels

Voltage-gated calcium (Cav) channels mediate Ca2+ influx in response to membrane depolarization, playing critical roles in diverse physiological processes. Dysfunction or aberrant regulation of Cav channels can lead to life-threatening consequences. Cav-targeting drugs have been clinically used to treat cardiovascular and neuronal disorders for several decades. This review aims to provide an account of recent developments in the structural dissection of Cav channels. High-resolution structures have significantly advanced our understanding of the working and disease mechanisms of Cav channels, shed light on the molecular basis for their modulation, and elucidated the modes of actions (MOAs) of representative drugs and toxins. The progress in structural studies of Cav channels lays the foundation for future drug discovery efforts targeting Cav channelopathies.

Channels of Evolution: Unveiling Evolutionary Patterns in Diatom Ca2+ Signalling

Diatoms are important primary producers in marine and freshwater environments, but little is known about the signalling mechanisms they use to detect changes in their environment. All eukaryotic organisms use Ca2+ signalling to perceive and respond to environmental stimuli, employing a range of Ca2+-permeable ion channels to facilitate the movement of Ca2+ across cellular membranes. We investigated the distribution of different families of Ca2+ channels in diatom genomes, with comparison to other members of the stramenopile lineage. The four-domain voltage-gated Ca2+ channels (Cav) are present in some centric diatoms but almost completely absent in pennate diatoms, whereas single-domain voltage-gated EukCatA channels were found in all diatoms. Glutamate receptors (GLRs) and pentameric ligand-gated ion channels (pLGICs) also appear to have been lost in several pennate species. Transient receptor potential (TRP) channels are present in all diatoms, but have not undergone the significant expansion seen in brown algae. All diatom species analysed lacked the mitochondrial uniporter (MCU), a highly conserved channel type found in many eukaryotes, including several stramenopile lineages. These results highlight the unique Ca2+-signalling toolkit of diatoms and indicate that evolutionary gains or losses of different Ca2+ channels may contribute to differences in cellular-signalling mechanisms between species.

The importance of cache domains in α2δ proteins and the basis for their gabapentinoid selectivity

In this hybrid review, we have first collected and reviewed available information on the structure and function of the enigmatic cache domains in α₂δ proteins. These are organized into two double cache (dCache_1) domains, and they are present in all α₂δ proteins. We have also included new data on the key function of these domains with respect to amino acid and gabapentinoid binding to the universal amino acid-binding pocket, which is present in α₂δ-1 and α₂δ-2. We have now identified the reason why α₂δ-3 and α₂δ-4 do not bind gabapentinoid drugs or amino acids with bulky side chains. In relation to this, we have determined that the bulky amino acids Tryptophan and Phenylalanine prevent gabapentin from inhibiting cell surface trafficking of α₂δ-1. Together, these novel data shed further light on the importance of the cache domains in α₂δ proteins.

Voltage gated sodium and calcium channels: Discovery, structure, function, and Pharmacology

Voltage-gated sodium channels initiate action potentials in nerve and muscle, and voltage-gated calcium channels couple depolarization of the plasma membrane to intracellular events such as secretion, contraction, synaptic transmission, and gene expression. In this Review and Perspective article, I summarize early work that led to identification, purification, functional reconstitution, and determination of the amino acid sequence of the protein subunits of sodium and calcium channels and showed that their pore-forming subunits are closely related. Decades of study by antibody mapping, site-directed mutagenesis, and electrophysiological recording led to detailed two-dimensional structure-function maps of the amino acid residues involved in voltage-dependent activation and inactivation, ion permeation and selectivity, and pharmacological modulation. Most recently, high-resolution three-dimensional structure determination by X-ray crystallography and cryogenic electron microscopy has revealed the structural basis for sodium and calcium channel function and pharmacological modulation at the atomic level. These studies now define the chemical basis for electrical signaling and provide templates for future development of new therapeutic agents for a range of neurological and cardiovascular diseases.

A governance of ion selectivity based on the occupancy of the "beacon" in one- and four-domain calcium and sodium channels

One of nature's exceptions was discovered when a Cav3 T-type channel was observed to switch phenotype from a calcium channel into a sodium channel by neutralizing an aspartate residue in the high field strength (HFS) +1 position within the ion selectivity filter. The HFS+1 site is dubbed a "beacon" for its location at the entryway just above the constricted, minimum radius of the HFS site's electronegative ring. A classification is proposed based on the occupancy of the HFS+1 "beacon" which correlates with the calcium- or sodium-selectivity phenotype. If the beacon is a glycine, or neutral, non-glycine residue, then the cation channel is calcium-selective or sodium-permeable, respectively (Class I). Occupancy of a beacon aspartate are calcium-selective channels (Class II) or possessing a strong calcium block (Class III). A residue lacking in position of the sequence alignment for the beacon are sodium channels (Class IV). The extent to which animal channels are sodium-selective is dictated in the occupancy of the HFS site with a lysine residue (Class III/IV). Governance involving the beacon solves the quandary the HFS site as a basis for ion selectivity, where an electronegative ring of glutamates at the HFS site generates a sodium-selective channel in one-domain channels but generates a calcium-selective channel in four-domain channels. Discovery of a splice variant in an exceptional channel revealed nature's exploits, highlighting the "beacon" as a principal determinant for calcium and sodium selectivity, encompassing known ion channels composed of one and four domains, from bacteria to animals.

Advances in CaV1.1 gating: New insights into permeation and voltage-sensing mechanisms

The CaV1.1 voltage-gated Ca2+ channel carries L-type Ca2+ current and is the voltage-sensor for excitation-contraction (EC) coupling in skeletal muscle. Significant breakthroughs in the EC coupling field have often been close on the heels of technological advancement. In particular, CaV1.1 was the first voltage-gated Ca2+ channel to be cloned, the first ion channel to have its gating current measured and the first ion channel to have an effectively null animal model. Though these innovations have provided invaluable information regarding how CaV1.1 detects changes in membrane potential and transmits intra- and inter-molecular signals which cause opening of the channel pore and support Ca2+ release from the sarcoplasmic reticulum remain elusive. Here, we review current perspectives on this topic including the recent application of functional site-directed fluorometry.

A CUG-initiated CATSPERθ functions in the CatSper channel assembly and serves as a checkpoint for flagellar trafficking

Calcium signaling is critical for successful fertilization. In spermatozoa, calcium influx into the sperm flagella mediated by the sperm-specific CatSper calcium channel is necessary for hyperactivated motility and male fertility. CatSper is a macromolecular complex and is repeatedly arranged in zigzag rows within four linear nanodomains along the sperm flagella. Here, we report that the Tmem249-encoded transmembrane (TM) domain-containing protein, CATSPERθ is essential for the CatSper channel assembly during sperm tail formation. CATSPERθ facilitates the channel assembly by serving as a scaffold for a pore-forming subunit CATSPER4. CATSPERθ is specifically localized at the interface of a CatSper dimer and can self-interact, suggesting its potential role in CatSper dimer formation. Male mice lacking CATSPERθ are infertile because the sperm lack the entire CatSper channel from sperm flagella, rendering sperm unable to hyperactivate, regardless of their normal expression in the testis. In contrast, genetic abrogation of any of the other CatSper TM subunits results in loss of CATSPERθ protein in the spermatid cells during spermatogenesis. CATSPERθ might act as a checkpoint for the properly assembled CatSper channel complex to traffic to sperm flagella. This study provides insights into the CatSper channel assembly and elucidates the physiological role of CATSPERθ in sperm motility and male fertility.

Fifty years of gating currents and channel gating

We celebrate this year the 50th anniversary of the first electrophysiological recordings of the gating currents from voltage-dependent ion channels done in 1973. This retrospective tries to illustrate the context knowledge on channel gating and the impact gating-current recording had then, and how it continued to clarify concepts, elaborate new ideas, and steer the scientific debate in these 50 years. The notion of gating particles and gating currents was first put forward by Hodgkin and Huxley in 1952 as a necessary assumption for interpreting the voltage dependence of the Na and K conductances of the action potential. 20 years later, gating currents were actually recorded, and over the following decades have represented the most direct means of tracing the movement of the gating charges and gaining insights into the mechanisms of channel gating. Most work in the early years was focused on the gating currents from the Na and K channels as found in the squid giant axon. With channel cloning and expression on heterologous systems, other channels as well as voltage-dependent enzymes were investigated. Other approaches were also introduced (cysteine mutagenesis and labeling, site-directed fluorometry, cryo-EM crystallography, and molecular dynamics [MD] modeling) to provide an integrated and coherent view of voltage-dependent gating in biological macromolecules. The layout of this retrospective reflects the past 50 years of investigations on gating currents, first addressing studies done on Na and K channels and then on other voltage-gated channels and non-channel structures. The review closes with a brief overview of how the gating-charge/voltage-sensor movements are translated into pore opening and the pathologies associated with mutations targeting the structures involved with the gating currents.

A CUG-initiated CATSPERθ functions in the CatSper channel assembly and serves as a checkpoint for flagellar trafficking

Calcium signaling is critical for successful fertilization. In spermatozoa, calcium influx into the sperm flagella mediated by the sperm specific CatSper calcium channel is necessary for hyperactivated motility and male fertility. CatSper is a macromolecular complex and is repeatedly arranged in zigzag rows within four linear nanodomains along the sperm flagella. Here, we report that the Tmem249 -encoded transmembrane domain containing protein, CATSPERθ, is essential for the CatSper channel assembly during sperm tail formation. CATSPERθ facilitates the channel assembly by serving as a scaffold for a pore forming subunit CATSPER4. CATSPERθ is specifically localized at the interface of a CatSper dimer and can self-interact, suggesting its potential role in CatSper dimer formation. Male mice lacking CATSPERθ are infertile because the sperm lack the entire CatSper channel from sperm flagella, rendering sperm unable to hyperactivate, regardless of their normal expression in the testis. In contrast, genetic abrogation of any of the other CatSper transmembrane subunits results in loss of CATSPERθ protein in the spermatid cells during spermatogenesis. CATSPERθ might acts as a checkpoint for the properly assembled CatSper channel complex to traffic to sperm flagella. This study provides insights into the CatSper channel assembly and elucidates the physiological role of CATSPERθ in sperm motility and male fertility.

Regulation of Presynaptic Calcium Channels

Voltage-gated calcium channels (VGCCs), especially Cav2.1 and Cav2.2, are the major mediators of Ca2+ influx at the presynaptic membrane in response to neuron excitation, thereby exerting a predominant control on synaptic transmission. To guarantee the timely and precise release of neurotransmitters at synapses, the activity of presynaptic VGCCs is tightly regulated by a variety of factors, including auxiliary subunits, membrane potential, G protein-coupled receptors (GPCRs), calmodulin (CaM), Ca2+-binding proteins (CaBP), protein kinases, various interacting proteins, alternative splicing events, and genetic variations.

CaV1.1 Calcium Channel Signaling Complexes in Excitation-Contraction Coupling: Insights from Channelopathies

In skeletal muscle, excitation-contraction (EC) coupling relies on the mechanical coupling between two ion channels: the L-type voltage-gated calcium channel (CaV1.1), located in the sarcolemma and functioning as the voltage sensor of EC coupling, and the ryanodine receptor 1 (RyR1), located on the sarcoplasmic reticulum serving as the calcium release channel. To this day, the molecular mechanism by which these two ion channels are linked remains elusive. However, recently, skeletal muscle EC coupling could be reconstituted in heterologous cells, revealing that only four proteins are essential for this process: CaV1.1, RyR1, and the cytosolic proteins CaVβ1a and STAC3. Due to the crucial role of these proteins in skeletal muscle EC coupling, any mutation that affects any one of these proteins can have devastating consequences, resulting in congenital myopathies and other pathologies.Here, we summarize the current knowledge concerning these four essential proteins and discuss the pathophysiology of the CaV1.1, RyR1, and STAC3-related skeletal muscle diseases with an emphasis on the molecular mechanisms. Being part of the same signalosome, mutations in different proteins often result in congenital myopathies with similar symptoms or even in the same disease.

Targeting N-type calcium channels in young-onset of some neurological diseases

Calcium (Ca ²⁺) is an important second messenger in charge of many critical processes in the central nervous system (CNS), including membrane excitability, neurotransmission, learning, memory, cell proliferation, and apoptosis. In this way, the voltage-gated calcium channels (VGCCs) act as a key supply for Ca²⁺ entry into the cytoplasm and organelles. Importantly, the dysregulation of these channels has been reported in many neurological diseases of young-onset, with associated genetic factors, such as migraine, multiple sclerosis, and Huntington's disease. Notably, the literature has pointed to the role of N-type Ca²⁺ channels (NTCCs) in controlling a variety of processes, including pain, inflammation, and excitotoxicity. Moreover, several Ca²⁺ channel blockers that are used for therapeutic purposes have been shown to act on the N-type channels. Therefore, this review provides an overview of the NTCCs in neurological disorders focusing mainly on Huntington's disease, multiple sclerosis, and migraine. It will discuss possible strategies to generate novel therapeutic strategies.

Structural basis for the severe adverse interaction of sofosbuvir and amiodarone on L-type Cav channels

Drug-drug interaction of the antiviral sofosbuvir and the antiarrhythmics amiodarone has been reported to cause fatal heartbeat slowing. Sofosbuvir and its analog, MNI-1, were reported to potentiate the inhibition of cardiomyocyte calcium handling by amiodarone, which functions as a multi-channel antagonist, and implicate its inhibitory effect on L-type Ca_v channels, but the molecular mechanism has remained unclear. Here we present systematic cryo-EM structural analysis of Ca_v1.1 and Ca_v1.3 treated with amiodarone or sofosbuvir alone, or sofosbuvir/MNI-1 combined with amiodarone. Whereas amiodarone alone occupies the dihydropyridine binding site, sofosbuvir is not found in the channel when applied on its own. In the presence of amiodarone, sofosbuvir/MNI-1 is anchored in the central cavity of the pore domain through specific interaction with amiodarone and directly obstructs the ion permeation path. Our study reveals the molecular basis for the physical, pharmacodynamic interaction of two drugs on the scaffold of Ca_v channels.

Modulation of L-type calcium channels in Alzheimer's disease: A potential therapeutic target

Calcium plays a fundamental role in various signaling pathways and cellular processes in the human organism. In the nervous system, voltage-gated calcium channels such as L-type calcium channels (LTCCs) are critical elements in mediating neurotransmitter release, synaptic integration and plasticity. Dysfunction of LTCCs has been implicated in both aging and Alzheimer's Disease (AD), constituting a key component of calcium hypothesis of AD. As such, LTCCs are a promising drug target in AD. However, due to their structural and functional complexity, the mechanisms by which LTCCs contribute to AD are still unclear. In this review, we briefly summarize the structure, function, and modulation of LTCCs that are the backbone for understanding pathological processes involving LTCCs. We suggest targeting molecular pathways up-regulating LTCCs in AD may be a more promising approach, given the diverse physiological functions of LTCCs and the ineffectiveness of LTCC blockers in clinical studies.

Targeted transcript analysis in muscles from patients with genetically diverse congenital myopathies

Congenital myopathies are a group of early onset muscle diseases of variable severity often with characteristic muscle biopsy findings and involvement of specific muscle types. The clinical diagnosis of patients typically relies on histopathological findings and is confirmed by genetic analysis. The most commonly mutated genes encode proteins involved in skeletal muscle excitation–contraction coupling, calcium regulation, sarcomeric proteins and thin–thick filament interaction. However, mutations in genes encoding proteins involved in other physiological functions (for example mutations in SELENON and MTM1, which encode for ubiquitously expressed proteins of low tissue specificity) have also been identified. This intriguing observation indicates that the presence of a genetic mutation impacts the expression of other genes whose product is important for skeletal muscle function. The aim of the present investigation was to verify if there are common changes in transcript and microRNA expression in muscles from patients with genetically heterogeneous congenital myopathies, focusing on genes encoding proteins involved in excitation–contraction coupling and calcium homeostasis, sarcomeric proteins, transcription factors and epigenetic enzymes. Our results identify RYR1, ATPB2B and miRNA-22 as common transcripts whose expression is decreased in muscles from congenital myopathy patients. The resulting protein deficiency may contribute to the muscle weakness observed in these patients. This study also provides information regarding potential biomarkers for monitoring disease progression and response to pharmacological treatments in patients with congenital myopathies.

Two novel CACNA1F gene mutations cause two different phenotypes: Aland Eye Disease and incomplete Congenital Stationary Night Blindness

Congenital Stationary Night Blindness type 2 (CSNB2) and Aland island Eye Disease (AIED) associated with CACNA1F mutation demonstrate a significant phenotype overlapping. We report two cases with different clinical presentation carrying two novel mutations in CACNA1F gene. Subjects underwent a complete neurophtahlmological examination associated with structural and electrofunctional insight. Next Generation Sequencing (NGS) analysis of 31 genes previously associated with retinal dystrophy (RD) was performed. Messenger RNAs derived from probands 'peripheral blood samples were analyzed by RT-PCR and cDNA sequencing. The neuro-ophthalmological examinations revealed different clinical, structural and morphological presentations, more severe in patient 1 compared with patient 2. Molecular analysis revealed, that both patients had the hemizygous form of two novel mutations in CACNA1F gene. Patient 1 presented a duplication (c.425dupC) in exon 4, resulting in shifting of the reading frame with the insertion of a premature Stop codon. In Patient 2 variant c.5156G > C localized in the donor's splicing site of exon 43 was identified. Complementary DNA sequencing demonstrated skipping of exon 43 with a deletion of 55 amino acids that causes a frame shift with insertion of a Stop codon. These findings suggest that the effect and the localization of the mutations in the CACNA1F gene can explain different clinical phenotypes. Clinical spectrum is more severe and resembles the AIED phenotype when the mutation affects the first part of the protein, while it is more similar to CSNB2 if the mutation is localized at the end of the protein. Genetic testing results to be an essential tool to provide more accurate diagnosis and prognosis in patients with inherited retinal degenerative disorders and could help, in the future, to develop more specific therapeutic strategies.

The 70-year search for the voltage sensing mechanism of ion channels

This retrospective on the voltage‐sensing mechanisms and gating models of ion channels begins in 1952 with the charged gating particles postulated by Hodgkin and Huxley, viewed as charges moving across the membrane and controlling its permeability to Na⁺ and K⁺ ions. Hodgkin and Huxley postulated that their movement should generate small and fast capacitive currents, which were recorded 20 years later as gating currents. In the early 1980s, several voltage‐dependent channels were cloned and found to share a common architecture: four homologous domains or subunits, each displaying six transmembrane α‐helical segments, with the fourth segment (S4) displaying four to seven positive charges invariably separated by two non‐charged residues. This immediately suggested that this segment was serving as the voltage sensor of the channel (the molecular counterpart of the charged gating particle postulated by Hodgkin and Huxley) and led to the development of the sliding helix model. Twenty years later, the X‐ray crystallographic structures of many voltage‐dependent channels allowed investigation of their gating by molecular dynamics. Further understanding of how channels gate will benefit greatly from the acquisition of high‐resolution structures of each of their relevant functional or structural states. This will allow the application of molecular dynamics and other approaches. It will also be key to investigate the energetics of channel gating, permitting an understanding of the physical and molecular determinants of gating. The use of multiscale hierarchical approaches might finally prove to be a rewarding strategy to overcome the limits of the various single approaches to the study of channel gating.

Nanosecond Pulsed Electric Field (nsPEF): Opening the Biotechnological Pandora’s Box

Nanosecond Pulsed Electric Field (nsPEF) is an electrostimulation technique first developed in 1995; nsPEF requires the delivery of a series of pulses of high electric fields in the order of nanoseconds into biological tissues or cells. They primary effects in cells is the formation of membrane nanopores and the activation of ionic channels, leading to an incremental increase in cytoplasmic Ca2+ concentration, which triggers a signaling cascade producing a variety of effects: from apoptosis up to cell differentiation and proliferation. Further, nsPEF may affect organelles, making nsPEF a unique tool to manipulate and study cells. This technique is exploited in a broad spectrum of applications, such as: sterilization in the food industry, seed germination, anti-parasitic effects, wound healing, increased immune response, activation of neurons and myocites, cell proliferation, cellular phenotype manipulation, modulation of gene expression, and as a novel cancer treatment. This review thoroughly explores both nsPEF’s history and applications, with emphasis on the cellular effects from a biophysics perspective, highlighting the role of ionic channels as a mechanistic driver of the increase in cytoplasmic Ca2+ concentration.

New Insights in CaVβ Subunits: Role in the Regulation of Gene Expression and Cellular Homeostasis

The voltage-gated calcium channels (CaVs or VGCCs) are fundamental regulators of intracellular calcium homeostasis. When electrical activity induces their activation, the influx of calcium that they mediate or their interaction with intracellular players leads to changes in intracellular Ca²⁺ levels which regulate many processes such as contraction, secretion and gene expression, depending on the cell type. The essential component of the pore channel is the CaVα₁ subunit. However, the fine-tuning of Ca²⁺-dependent signals is guaranteed by the modulatory role of the auxiliary subunits β, α₂δ, and γ of the CaVs. In particular, four different CaVβ proteins (CaVβ1, CaVβ2, CaVβ3, and CaVβ4) are encoded by four different genes in mammalians, each of them displaying several splice variants. Some of these isoforms have been described in regulating CaVα₁ docking and stability at the membrane and controlling the channel complex’s conformational changes. In addition, emerging evidences have highlighted other properties of the CaVβ subunits, independently of α₁ and non-correlated to its channel or voltage sensing functions. This review summarizes the recent findings reporting novel roles of the auxiliary CaVβ subunits and in particular their direct or indirect implication in regulating gene expression in different cellular contexts.

Naview: A d3.js Based JavaScript Library for Drawing and Annotating Voltage-Gated Sodium Channels Membrane Diagrams

Voltage-gated sodium channels (Nav) are membrane proteins essential to initiating and propagating action potential in neurons and other excitable cells. For a given organism there are often multiple, specialized sodium channels found in different tissues, whose mutations can cause deleterious effects observed in numerous diseases. Consequently, there is high medical and pharmacological interest in these proteins. Scientific literature often uses membrane diagrams to depict important patterns in these channels including the six transmembrane segments (S1–S6) present in four different homologous domains (D1–D4), the S4 voltage sensors, the pore-lining residue segments and the ion selectivity filter residues, glycosylation and phosphorylation residues, toxin binding sites and the inactivation loop, among others. Most of these diagrams are illustrated either digitally or by hand and programs specifically dedicated to the interactive and data-friendly generation of such visualizations are scarce or non-existing. This paper describes Naview, an open-source javascript visualization compatible with modern web browsers for the dynamic drawing and annotation of voltage-gated sodium channels membrane diagrams based on the D3.js library. By using a graphical user interface and combining user-defined annotations with optional UniProt code as inputs, Naview allows the creation and customization of membrane diagrams. In this interface, a user can also map and display important sodium channel properties, residues, regions and their relationships through symbols, colors, and edge connections. Such features can facilitate data exploration and provide fast, high-quality publication-ready graphics for this highly active area of research.

Contribution of CACNA1H Variants in Autism Spectrum Disorder Susceptibility

Autism Spectrum Disorder (ASD) is a highly heterogeneous neuropsychiatric disorder with a strong genetic component. The genetic architecture is complex, consisting of a combination of common low-risk and more penetrant rare variants. Voltage-gated calcium channels (VGCCs or Ca_v) genes have been implicated as high-confidence susceptibility genes for ASD, in accordance with the relevant role of calcium signaling in neuronal function. In order to further investigate the involvement of VGCCs rare variants in ASD susceptibility, we performed whole genome sequencing analysis in a cohort of 105 families, composed of 124 ASD individuals, 210 parents and 58 unaffected siblings. We identified 53 rare inherited damaging variants in Ca_v genes, including genes coding for the principal subunit and genes coding for the auxiliary subunits, in 40 ASD families. Interestingly, biallelic rare damaging missense variants were detected in the CACNA1H gene, coding for the T-type Ca_v3.2 channel, in ASD probands from two different families. Thus, to clarify the role of these CACNA1H variants on calcium channel activity we performed electrophysiological analysis using whole-cell patch clamp technology. Three out of four tested variants were shown to mildly affect Ca_v3.2 channel current density and activation properties, possibly leading to a dysregulation of intracellular Ca²⁺ ions homeostasis, thus altering calcium-dependent neuronal processes and contributing to ASD etiology in these families. Our results provide further support for the role of CACNA1H in neurodevelopmental disorders and suggest that rare CACNA1H variants may be involved in ASD development, providing a high-risk genetic background.

Ionic channels in nerve membranes, 50 years on

This retrospective traces the hypothesis of ion channels from an early statement in a 1970 essay in this journal (Hille, B., 1970, Prog. Biophys. Mol. Biol. 21, 1-32) to its realization today in biophysical, molecular, biochemical, and structural terms. The Na⁺ and K⁺ channels of the action potential have been isolated, reconstituted, cloned, mutated, and expressed. They are conformationally flexible, multi-pass glycosylated membrane proteins. Refined atomic structures of several conformational states are known. The discoveries over this half century history illustrate the growth of a field from initial ideas to a mature discipline of biology, physiology, and biomedical science.

Mechanisms and Physiological Implications of Cooperative Gating of Ion Channels Clusters

Ion channels play a central role in the regulation of nearly every cellular process. Dating back to the classic 1952 Hodgkin-Huxley model of the generation of the action potential, ion channels have always been thought of as independent agents. A myriad of recent experimental findings exploiting advances in electrophysiology, structural biology, and imaging techniques, however, have posed a serious challenge to this long-held axiom as several classes of ion channels appear to open and close in a coordinated, cooperative manner. Ion channel cooperativity ranges from variable-sized oligomeric cooperative gating in voltage-gated, dihydropyridine-sensitive Ca_v1.2 and Ca_v1.3 channels to obligatory dimeric assembly and gating of voltage-gated Na_v1.5 channels. Potassium channels, transient receptor potential channels, hyperpolarization cyclic nucleotide-activated channels, ryanodine receptors (RyRs), and inositol trisphosphate receptors (IP₃Rs) have also been shown to gate cooperatively. The implications of cooperative gating of these ion channels range from fine tuning excitation-contraction coupling in muscle cells to regulating cardiac function and vascular tone, to modulation of action potential and conduction velocity in neurons and cardiac cells, and to control of pace-making activity in the heart. In this review, we discuss the mechanisms leading to cooperative gating of ion channels, their physiological consequences and how alterations in cooperative gating of ion channels may induce a range of clinically significant pathologies.

Alterations in Excitatory and Inhibitory Synaptic Development Within the Mesolimbic Dopamine Pathway in a Mouse Model of Prenatal Drug Exposure

The rise in rates of opioid abuse in recent years in the United States has led to a dramatic increase in the incidence of neonatal abstinence syndrome (NAS). Despite improved understanding of NAS and its acute symptoms, there remains a paucity of information regarding the long-term effects of prenatal exposure to drugs of abuse on neurological development. The primary goal of this study was to investigate the effects of prenatal drug exposure on synaptic connectivity within brain regions associated with the mesolimbic dopamine pathway, the primary reward pathway associated with drug abuse and addiction, in a mouse model. Our secondary goal was to examine the role of the Ca+2 channel subunit α2δ-1, known to be involved in key developmental synaptogenic pathways, in mediating these effects. Pregnant mouse dams were treated orally with either the opioid drug buprenorphine (commonly used in medication-assisted treatment for substance use patients), gabapentin (neuropathic pain drug that binds to α2δ-1 and has been increasingly co-abused with opioids), a combination of both drugs, or vehicle daily from gestational day 6 until postnatal day 11. Confocal fluorescence immunohistochemistry (IHC) imaging of the brains of the resulting wild-type (WT) pups at postnatal day 21 revealed a number of significant alterations in excitatory and inhibitory synaptic populations within the anterior cingulate cortex (ACC), nucleus accumbens (NAC), and medial prefrontal cortex (PFC), particularly in the buprenorphine or combinatorial buprenorphine/gabapentin groups. Furthermore, we observed several drug- and region-specific differences in synaptic connectivity between WT and α2δ-1 haploinsufficient mice, indicating that critical α2δ-1-associated synaptogenic pathways are disrupted with early life drug exposure.

Linking Diabetes Mellitus with Alzheimer's Disease: Bioinformatics Analysis for the Potential Pathways and Characteristic Genes

As the surging epidemics with significant disability, Alzheimer's disease (AD) and type II diabetes mellitus (T2DM) with microvascular complications are widely prevalent, sharing considerable similarities in putative pathomechanism. Despite a spurt of researches on the biology, knowledge about their interactive mechanisms is still rudimentary. Applying bioinformatics ways to explore the differentially co-expressed genes contributes to achieve our objectives to find new therapeutic targets. In this study, we firstly integrated gene expression omnibus datasets (GSE28146 and GSE43950) to identify differentially expressed genes. The enrichment analysis of pivotal genes, like gene ontology and pathway signaling proceeded subsequently. Besides, the related protein-protein interaction (PPI) network was then constructed. To further explain the inner connections, we ended up unearthing the biological significance of valuable targets. As a result, a set of 712, 630, 487, and 997 genes were differentially identified in T2DM with microvascular complications and AD at incipient, moderate, and severe, respectively. The enrichment analysis involving both diseases implicated the dominance of immune system, especially the noteworthy chemokine signaling. Multiple comparisons confirmed that CACNA2D3, NUMB, and IER3 were simultaneously participate in these two conditions, whose respective associations with neurological and endocrine diseases, and regulators including interacting chemicals, transcription factors, and miRNAs were analyzed. Bioinformatics analysis eventually concluded that immune-related biological functions and pathways closely link AD and T2DM with microvascular complications. Further exploration of the regulatory factors about CACNA2D3, NUMB, and IER3 in neuroendocrine field may provide us a promising direction to discover potential strategies for the comorbidity status.

De novo variants in CACNA1E found in patients with intellectual disability, developmental regression and social cognition deficit but no seizures

BACKGROUND

De novo variants in the voltage-gated calcium channel subunit α1 E gene (CACNA1E) have been described as causative of epileptic encephalopathy with contractures, macrocephaly and dyskinesias.

METHODS

Following the observation of an index patient with developmental delay and autism spectrum disorder (ASD) without seizures who had a de novo deleterious CACNA1E variant, we screened GeneMatcher for other individuals with CACNA1E variants and neurodevelopmental phenotypes without epilepsy. The spectrum of pathogenic CACNA1E variants was compared to the mutational landscape of variants in the gnomAD control population database.

RESULTS

We identified seven unrelated individuals with intellectual disability, developmental regression and ASD-like behavioral profile, and notably without epilepsy, who had de novo heterozygous putatively pathogenic variants in CACNA1E. Age of onset of clinical manifestation, presence or absence of regression and degree of severity were variable, and no clear-cut genotype-phenotype association could be recognized. The analysis of disease-associated variants and their comparison to benign variants from the control population allowed for the identification of regions in the CACNA1E protein that seem to be intolerant to substitutions and thus more likely to harbor pathogenic variants. As in a few reported cases with CACNA1E variants and epilepsy, one patient showed a positive clinical behavioral response to topiramate, a specific calcium channel modulator.

LIMITATIONS

The significance of our study is limited by the absence of functional experiments of the effect of identified variants, the small sample size and the lack of systematic ASD assessment in all participants. Moreover, topiramate was given to one patient only and for a short period of time.

CONCLUSIONS

Our results indicate that CACNA1E variants may result in neurodevelopmental disorders without epilepsy and expand the mutational and phenotypic spectrum of this gene. CACNA1E deserves to be included in gene panels for non-specific developmental disorders, including ASD, and not limited to patients with seizures, to improve diagnostic recognition and explore the possible efficacy of topiramate.

Voltage sensor movements of CaV1.1 during an action potential in skeletal muscle fibers

The skeletal muscle L-type Ca²⁺ channel (Ca_V1.1) works primarily as a voltage sensor for skeletal muscle action potential (AP)-evoked Ca²⁺ release. Ca_V1.1 contains four distinct voltage-sensing domains (VSDs), yet the contribution of each VSD to AP-evoked Ca²⁺ release remains unknown. To investigate the role of VSDs in excitation-contraction coupling (ECC), we encoded cysteine substitutions on each S4 voltage-sensing segment of Ca_V1.1, expressed each construct via in vivo gene transfer electroporation, and used in cellulo AP fluorometry to track the movement of each Ca_V1.1 VSD in skeletal muscle fibers. We first provide electrical measurements of Ca_V1.1 voltage sensor charge movement in response to an AP waveform. Then we characterize the fluorescently labeled channels' VSD fluorescence signal responses to an AP and compare them with the waveforms of the electrically measured charge movement, the optically measured free myoplasmic Ca²⁺, and the calculated rate of Ca²⁺ release from the sarcoplasmic reticulum for an AP, the physiological signal for skeletal muscle fiber activation. A considerable fraction of the fluorescence signal for each VSD occurred after the time of peak Ca²⁺ release, and even more occurred after the earlier peak of electrically measured charge movement during an AP, and thus could not directly reflect activation of Ca²⁺ release or charge movement, respectively. However, a sizable fraction of the fluorometric signals for VSDs I, II, and IV, but not VSDIII, overlap the rising phase of charge moved, and even more for Ca²⁺ release, and thus could be involved in voltage sensor rearrangements or Ca²⁺ release activation.

Transcriptional profiles of genes related to electrophysiological function in Scn5a+/- murine hearts

The Scn5a gene encodes the major pore-forming Nav 1.5 (α) subunit, of the voltage-gated Na+ channel in cardiomyocytes. The key role of Nav 1.5 in action potential initiation and propagation in both atria and ventricles predisposes organisms lacking Scn5a or carrying Scn5a mutations to cardiac arrhythmogenesis. Loss-of-function Nav 1.5 genetic abnormalities account for many cases of the human arrhythmic disorder Brugada syndrome (BrS) and related conduction disorders. A murine model with a heterozygous Scn5a deletion recapitulates many electrophysiological phenotypes of BrS. This study examines the relationships between its Scn5a+/- genotype, resulting transcriptional changes, and the consequent phenotypic presentations of BrS. Of 62 selected protein-coding genes related to cardiomyocyte electrophysiological or homeostatic function, concentrations of mRNA transcribed from 15 differed significantly from wild type (WT). Despite halving apparent ventricular Scn5a transcription heterozygous deletion did not significantly downregulate its atrial expression, raising possibilities of atria-specific feedback mechanisms. Most of the remaining 14 genes whose expression differed significantly between WT and Scn5a+/- animals involved Ca2+ homeostasis specifically in atrial tissue, with no overlap with any ventricular changes. All statistically significant changes in expression were upregulations in the atria and downregulations in the ventricles. This investigation demonstrates the value of future experiments exploring for and clarifying links between transcriptional control of Scn5a and of genes whose protein products coordinate Ca2+ regulation and examining their possible roles in BrS.

Improper Remodeling of Organelles Deputed to Ca2+ Handling and Aerobic ATP Production Underlies Muscle Dysfunction in Ageing

Proper skeletal muscle function is controlled by intracellular Ca2+ concentration and by efficient production of energy (ATP), which, in turn, depend on: (a) the release and re-uptake of Ca2+ from sarcoplasmic-reticulum (SR) during excitation-contraction (EC) coupling, which controls the contraction and relaxation of sarcomeres; (b) the uptake of Ca2+ into the mitochondrial matrix, which stimulates aerobic ATP production; and finally (c) the entry of Ca2+ from the extracellular space via store-operated Ca2+ entry (SOCE), a mechanism that is important to limit/delay muscle fatigue. Abnormalities in Ca2+ handling underlie many physio-pathological conditions, including dysfunction in ageing. The specific focus of this review is to discuss the importance of the proper architecture of organelles and membrane systems involved in the mechanisms introduced above for the correct skeletal muscle function. We reviewed the existing literature about EC coupling, mitochondrial Ca2+ uptake, SOCE and about the structural membranes and organelles deputed to those functions and finally, we summarized the data collected in different, but complementary, projects studying changes caused by denervation and ageing to the structure and positioning of those organelles: a. denervation of muscle fibers-an event that contributes, to some degree, to muscle loss in ageing (known as sarcopenia)-causes misplacement and damage: (i) of membrane structures involved in EC coupling (calcium release units, CRUs) and (ii) of the mitochondrial network; b. sedentary ageing causes partial disarray/damage of CRUs and of calcium entry units (CEUs, structures involved in SOCE) and loss/misplacement of mitochondria; c. functional electrical stimulation (FES) and regular exercise promote the rescue/maintenance of the proper architecture of CRUs, CEUs, and of mitochondria in both denervation and ageing. All these structural changes were accompanied by related functional changes, i.e., loss/decay in function caused by denervation and ageing, and improved function following FES or exercise. These data suggest that the integrity and proper disposition of intracellular organelles deputed to Ca2+ handling and aerobic generation of ATP is challenged by inactivity (or reduced activity); modifications in the architecture of these intracellular membrane systems may contribute to muscle dysfunction in ageing and sarcopenia.

How Postdoctoral Research in Paul Greengard's Laboratory Shaped My Scientific Career, Although I Never Did Another Phosphorylation Assay

In this short review, I describe from personal experience how every step in the career of any scientist, no matter how disjointed and pragmatic each might seem at the time, will almost inevitably meld together, to help us all tackle novel projects. My postdoctoral research in Paul Greengard's laboratory, where I investigated neurotransmitter-mediated phosphorylation of Synapsin I, was instrumental in my career progression, and Paul's support was instrumental in my ability to make a leap into independent research.

Conflicting Nongenomic Effects of Progesterone in the Myometrium of Pregnant Rats

Recently, it has been suggested that progesterone affects the contractile activity of pregnant myometrium via nongenomic pathways; therefore, we aimed to clarify whether progesterone causes and/or inhibits pregnant myometrial contractions via nongenomic pathways. Our in vitro experiments using myometrial strips obtained from rats at 20 days of gestation revealed that progesterone caused myometrial contractions in a concentration- and time-dependent manner at concentrations up to 5 × 10-7 M; however, this effect decreased at concentrations higher than 5 × 10-5 M. Similarly, progesterone enhanced oxytocin-induced contractions up to 5 × 10-7 M and inhibited contractions at concentrations higher than 5 × 10-5 M. Conversely, progesterone did not enhance high-KCl-induced contractions but inhibited contractions in a concentration- and time-dependent manner at concentrations higher than 5 × 10-7 M. We also found that RU486 did not affect progesterone-induced contractions or the progesterone-induced inhibition of high-KCl-induced contractions; however, progesterone-induced contractions were blocked by calcium-free phosphate saline solution, verapamil, and nifedipine. In addition, FPL64176, an activator of L-type voltage-dependent calcium channels, enhanced high-KCl-induced contractions and rescued the decrease in high-KCl-induced contractions caused by progesterone. Together, these results suggest that progesterone exerts conflicting nongenomic effects on the contractions of pregnant myometrium via putative L-type voltage-dependent calcium channels.

Functions of Presynaptic Voltage-gated Calcium Channels

Voltage-gated calcium channels are the principal conduits for depolarization-mediated Ca²⁺ entry into excitable cells. In this review, the biophysical properties of the relevant members of this family of channels, those that are present in presynaptic terminals, will be discussed in relation to their function in mediating neurotransmitter release. Voltage-gated calcium channels have properties that ensure they are specialized for particular roles, for example, differences in their activation voltage threshold, their various kinetic properties, and their voltage-dependence of inactivation. All these attributes play into the ability of the various voltage-gated calcium channels to participate in different patterns of presynaptic vesicular release. These include synaptic transmission resulting from single action potentials, and longer-term changes mediated by bursts or trains of action potentials, as well as release resulting from graded changes in membrane potential in specialized sensory synapses.

Dstac Regulates Excitation-Contraction Coupling in Drosophila Body Wall Muscles

Stac3 regulates excitation-contraction coupling (EC coupling) in vertebrate skeletal muscles by regulating the L-type voltage-gated calcium channel (Ca_v channel). Recently a stac-like gene, Dstac, was identified in Drosophila and found to be expressed by both a subset of neurons and muscles. Here, we show that Dstac and Dmca1D, the Drosophila L-type Ca_v channel, are necessary for normal locomotion by larvae. Immunolabeling with specific antibodies against Dstac and Dmca1D found that Dstac and Dmca1D are expressed by larval body-wall muscles. Furthermore, Ca²⁺ imaging of muscles of Dstac and Dmca1D deficient larvae found that Dstac and Dmca1D are required for excitation-contraction coupling. Finally, Dstac appears to be required for normal expression levels of Dmca1D in body-wall muscles. These results suggest that Dstac regulates Dmca1D during EC coupling and thus muscle contraction.

Disruption of the Key Ca2+ Binding Site in the Selectivity Filter of Neuronal Voltage-Gated Calcium Channels Inhibits Channel Trafficking

Voltage-gated calcium channels are exquisitely Ca²⁺ selective, conferred primarily by four conserved pore-loop glutamate residues contributing to the selectivity filter. There has been little previous work directly measuring whether the trafficking of calcium channels requires their ability to bind Ca²⁺ in the selectivity filter or to conduct Ca²⁺. Here, we examine trafficking of neuronal Ca_V2.1 and 2.2 channels with mutations in their selectivity filter and find reduced trafficking to the cell surface in cell lines. Furthermore, in hippocampal neurons, there is reduced trafficking to the somatic plasma membrane, into neurites, and to presynaptic terminals. However, the Ca_V2.2 selectivity filter mutants are still influenced by auxiliary α₂δ subunits and, albeit to a reduced extent, by β subunits, indicating the channels are not grossly misfolded. Our results indicate that Ca²⁺ binding in the pore of Ca_V2 channels may promote their correct trafficking, in combination with auxiliary subunits. Furthermore, physiological studies utilizing selectivity filter mutant Ca_V channels should be interpreted with caution.

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Selectivity filter mutations in Ca_V2 channels block inward Ba²⁺ currents

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Surprisingly, these mutations severely reduce trafficking of the Ca_V2 channels

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Pore mutant N-type channels show reduced expression in presynaptic terminals

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Pore mutant channels still require β and α₂δ and thus are not grossly misfolded

Presynaptic calcium channels: specialized control of synaptic neurotransmitter release

Chemical synapses are heterogeneous junctions formed between neurons that are specialized for the conversion of electrical impulses into the exocytotic release of neurotransmitters. Voltage-gated Ca2+ channels play a pivotal role in this process as they are the major conduits for the Ca2+ ions that trigger the fusion of neurotransmitter-containing vesicles with the presynaptic membrane. Alterations in the intrinsic function of these channels and their positioning within the active zone can profoundly alter the timing and strength of synaptic output. Advances in optical and electron microscopic imaging, structural biology and molecular techniques have facilitated recent breakthroughs in our understanding of the properties of voltage-gated Ca2+ channels that support their presynaptic functions. Here we examine the nature of these channels, how they are trafficked to and anchored within presynaptic boutons, and the mechanisms that allow them to function optimally in shaping the flow of information through neural circuits.

Skeletal muscle CaV1.1 channelopathies

Ca_V1.1 is specifically expressed in skeletal muscle where it functions as voltage sensor of skeletal muscle excitation-contraction (EC) coupling independently of its functions as L-type calcium channel. Consequently, all known Ca_V1.1-related diseases are muscle diseases and the molecular and cellular disease mechanisms relate to the dual functions of Ca_V1.1 in this tissue. To date, four types of muscle diseases are known that can be linked to mutations in the CACNA1S gene or to splicing defects. These are hypo- and normokalemic periodic paralysis, malignant hyperthermia susceptibility, Ca_V1.1-related myopathies, and myotonic dystrophy type 1. In addition, the Ca_V1.1 function in EC coupling is perturbed in Native American myopathy, arising from mutations in the Ca_V1.1-associated protein STAC3. Here, we first address general considerations concerning the possible roles of Ca_V1.1 in disease and then discuss the state of the art regarding the pathophysiology of the Ca_V1.1-related skeletal muscle diseases with an emphasis on molecular disease mechanisms.

Structure and Pharmacology of Voltage-Gated Sodium and Calcium Channels

Voltage-gated sodium and calcium channels are evolutionarily related transmembrane signaling proteins that initiate action potentials, neurotransmission, excitation-contraction coupling, and other physiological processes. Genetic or acquired dysfunction of these proteins causes numerous diseases, termed channelopathies, and sodium and calcium channels are the molecular targets for several major classes of drugs. Recent advances in the structural biology of these proteins using X-ray crystallography and cryo-electron microscopy have given new insights into the molecular basis for their function and pharmacology. Here we review this recent literature and integrate findings on sodium and calcium channels to reveal the structural basis for their voltage-dependent activation, fast and slow inactivation, ion conductance and selectivity, and complex pharmacology at the atomic level. We conclude with the theme that new understanding of the diseases and therapeutics of these channels will be derived from application of the emerging structural principles from these recent structural analyses.

Ca2+ Channels Mediate Bidirectional Signaling between Sarcolemma and Sarcoplasmic Reticulum in Muscle Cells

The skeletal muscle and myocardial cells present highly specialized structures; for example, the close interaction between the sarcoplasmic reticulum (SR) and mitochondria—responsible for excitation-metabolism coupling—and the junction that connects the SR with T-tubules, critical for excitation-contraction (EC) coupling. The mechanisms that underlie EC coupling in these two cell types, however, are fundamentally distinct. They involve the differential expression of Ca²⁺ channel subtypes: Ca_V1.1 and RyR1 (skeletal), vs. Ca_V1.2 and RyR2 (cardiac). The Ca_V channels transform action potentials into elevations of cytosolic Ca²⁺, by activating RyRs and thus promoting SR Ca²⁺ release. The high levels of Ca²⁺, in turn, stimulate not only the contractile machinery but also the generation of mitochondrial reactive oxygen species (ROS). This forward signaling is reciprocally regulated by the following feedback mechanisms: Ca²⁺-dependent inactivation (of Ca²⁺ channels), the recruitment of Na⁺/Ca²⁺ exchanger activity, and oxidative changes in ion channels and transporters. Here, we summarize both well-established concepts and recent advances that have contributed to a better understanding of the molecular mechanisms involved in this bidirectional signaling.

All-Optical Detection of Neuronal Membrane Depolarization in Live Cells Using Colloidal Quantum Dots

Luminescent semiconductor quantum dots (QDs) have recently been suggested as novel probes for imaging and sensing cell membrane voltages. However, a key bottleneck for their development is a lack of techniques to assess QD responses to voltages generated in the aqueous electrolytic environments typical of biological systems. Even more generally, there have been relatively few efforts to assess the response of QDs to voltage changes in live cells. Here, we develop a platform for monitoring the photoluminescence (PL) response of QDs under AC and DC voltage changes within aqueous ionic environments. We evaluate both traditional CdSe/CdS and more biologically compatible InP/ZnS QDs at a range of ion concentrations to establish their PL/voltage characteristics on chip. Wide-field, few-particle PL measurements with neuronal cells show the QDs can be used to track local voltage changes with greater sensitivity (ΔPL up to twice as large) than state-of-the-art calcium imaging dyes, making them particularly appealing for tracking subthreshold events. Additional physiological observation studies showed that while CdSe/CdS dots have greater PL responses on membrane depolarization, their lower cytotoxicity makes InP/ZnS far more suitable for voltage sensing in living systems. Our results provide a methodology for the rational development of QD voltage sensors and highlight their potential for imaging changes in cell membrane voltage.

Cryo-EM structures of apo and antagonist-bound human Cav3.1

Among the ten subtypes of mammalian voltage-gated calcium (Cav) channels, Cav3.1-Cav3.3 constitute the T-type, or the low-voltage-activated, subfamily, the abnormal activities of which are associated with epilepsy, psychiatric disorders and pain1-5. Here we report the cryo-electron microscopy structures of human Cav3.1 alone and in complex with a highly Cav3-selective blocker, Z9446,7, at resolutions of 3.3 Å and 3.1 Å, respectively. The arch-shaped Z944 molecule reclines in the central cavity of the pore domain, with the wide end inserting into the fenestration on the interface between repeats II and III, and the narrow end hanging above the intracellular gate like a plug. The structures provide the framework for comparative investigation of the distinct channel properties of different Cav subfamilies.

Correcting the R165K substitution in the first voltage-sensor of CaV1.1 right-shifts the voltage-dependence of skeletal muscle calcium channel activation

The voltage-gated calcium channel CaV1.1a primarily functions as voltage-sensor in skeletal muscle excitation-contraction (EC) coupling. In embryonic muscle the splice variant CaV1.1e, which lacks exon 29, additionally function as a genuine L-type calcium channel. Because previous work in most laboratories used a CaV1.1 expression plasmid containing a single amino acid substitution (R165K) of a critical gating charge in the first voltage-sensing domain (VSD), we corrected this substitution and analyzed its effects on the gating properties of the L-type calcium currents in dysgenic myotubes. Reverting K165 to R right-shifted the voltage-dependence of activation by ~12 mV in both CaV1.1 splice variants without changing their current amplitudes or kinetics. This demonstrates the exquisite sensitivity of the voltage-sensor function to changes in the specific amino acid side chains independent of their charge. Our results further indicate the cooperativity of VSDs I and IV in determining the voltage-sensitivity of CaV1.1 channel gating.

Voltage Sensor Movements during Hyperpolarization in the HCN Channel

The hyperpolarization-activated cyclic nucleotide-gated (HCN) channel is a voltage-gated cation channel that mediates neuronal and cardiac pacemaker activity. The HCN channel exhibits reversed voltage dependence, meaning it closes with depolarization and opens with hyperpolarization. Different from Na⁺, Ca²⁺, and Kv1-Kv7 channels, the HCN channel does not have domain-swapped voltage sensors. We introduced a reversible, metal-mediated cross bridge into the voltage sensors to create the chemical equivalent of a hyperpolarized conformation and determined the structure using cryoelectron microscopy (cryo-EM). Unlike the depolarized HCN channel, the S4 helix is displaced toward the cytoplasm by two helical turns. Near the cytoplasm, the S4 helix breaks into two helices, one running parallel to the membrane surface, analogous to the S4-S5 linker of domain-swapped voltage-gated channels. These findings suggest a basis for allosteric communication between voltage sensors and the gate in this kind of channel. They also imply that voltage sensor movements are not the same in all voltage-gated channels.

Cryo-EM structure of the KvAP channel reveals a non-domain-swapped voltage sensor topology

Conductance in voltage-gated ion channels is regulated by membrane voltage through structural domains known as voltage sensors. A single structural class of voltage sensor domain exists, but two different modes of voltage sensor attachment to the pore occur in nature: domain-swapped and non-domain-swapped. Since the more thoroughly studied Kv1-7, Nav and Cav channels have domain-swapped voltage sensors, much less is known about non-domain-swapped voltage-gated ion channels. In this paper, using cryo-EM, we show that KvAP from Aeropyrum pernix has non-domain-swapped voltage sensors as well as other unusual features. The new structure, together with previous functional data, suggests that KvAP and the Shaker channel, to which KvAP is most often compared, probably undergo rather different voltage-dependent conformational changes when they open.

Involvement of N-type Ca2+ channel in microglial activation and its implications to aging-induced exaggerated cytokine response

Voltage-dependent calcium channel (VDCC) is generally believed to be active only in excitable cells. However, we have reported recently that N-type VDCC (Cav2.2) could become functional in non-excitable cells under pathological conditions. In the present study, we show that Cav2.2 channels are also functional in physiological microglial activation process. By using a mouse microglial cell line (MG6), we examined the effects of a Cav2.2 blocker on the activation of MG6 cells, when treated with lipopolysaccharide (LPS) / interferon γ (IFNγ) or with interleukin-4 (IL-4). As a result, blocking the activation of Cav2.2 enhanced so-called alternative activation process of microglia (transition to neuroprotective M2 microglia) without changing the efficacy of the transition to neuroinflammatory M1 microglia. This enhanced M2 transition involved the activation of a transcription factor hypoxia inducible factor 2 (HIF-2), since a specific blocker of HIF-2 completely abolished this enhancement. We then examined whether Cav2.2 activation was involved in aging-related neuroinflammation. Using primary culture of microglia, we found that the efficacy of microglial M1 transition was enhanced but that M2 transition was reduced by aging, in agreement with a general notion that aging induces enhanced neuroinflammation. Finally, we show here that the moderate blockade of Cav2.2 expression in microglia restores this age-dependent reduction of microglial M2 transition and reduces the aging-induced exaggerated cytokine response, as revealed by a fast recovery from depressive-like behaviors in microglia-specific Cav2.2 deficient mice. These results suggest a critical role for microglial Cav2.2 channel in the aging-related neuroinflammation.

Blockade of microglial Cav1.2 Ca2+ channel exacerbates the symptoms in a Parkinson's disease model

Cav1.2 channels are an L-type voltage-dependent Ca²⁺ channel, which is specifically blocked by calcium antagonists. Voltage-dependent Ca²⁺ channels are generally considered to be functional only in excitable cells like neurons and muscle cells, but recently they have been reported to also be functional in non-excitable cells like microglia, which are key players in the innate immune system and have been shown to be involved in the pathophysiology of Parkinson’s disease. Here, we show that Cav1.2 channels are expressed in microglia, and that calcium antagonists enhanced the neuroinflammatory M1 transition and inhibited neuroprotective M2 transition of microglia in vitro. Moreover, intensive degeneration of dopaminergic neurons and accompanying behavioural deficits were observed in microglia-specific Cav1.2 knockdown mice intoxicated with MPTP, a neurotoxin that induces Parkinson’s disease-like symptoms, suggesting detrimental effects of microglial Cav1.2 blockade on Parkinson’s disease. Therefore, microglial Cav1.2 channel may have neuroprotective roles under physiological conditions and may also contribute to recovery from disease conditions.

Calcium Channelopathies: Structural Insights into Disorders of the Muscle Excitation–Contraction Complex

Ion channels are membrane proteins responsible for the passage of ions down their electrochemical gradients and across biological membranes. In this, they generate and shape action potentials and provide secondary messengers for various signaling pathways. They are often part of larger complexes containing auxiliary subunits and regulatory proteins. Channelopathies arise from mutations in the genes encoding ion channels or their associated proteins. Recent advances in cryo-electron microscopy have resulted in an explosion of ion channel structures in multiple states, generating a wealth of new information on channelopathies. Disease-associated mutations fall into different categories, interfering with ion permeation, protein folding, voltage sensing, ligand and protein binding, and allosteric modulation of channel gating. Prime examples of these are Ca2+-selective channels expressed in myocytes, for which multiple structures in distinct conformational states have recently been uncovered. We discuss the latest insights into these calcium channelopathies from a structural viewpoint.