Molecular diversity of voltage-dependent Ca2+ channels

Separate mechanisms regulating accumbal taurine levels during baseline conditions and following ethanol exposure in the rat

Ethanol-induced dopamine release in the nucleus accumbens (nAc) is associated with reward and reinforcement, and for ethanol to elevate nAc dopamine levels, a simultaneous increase in endogenous taurine is required within the same brain region. By employing in vivo microdialysis in male Wistar rats combined with pharmacological, chemogenetic and metabolic approaches, our aim with this study was to identify mechanisms underlying ethanol-induced taurine release. Our results demonstrate that the taurine elevation, elicited by either systemic or local ethanol administration, occurs both in presence and absence of action potential firing or NMDA receptor blockade. Inhibition of volume regulated anion channels did not alter the ethanol-induced taurine levels, while inhibition of the taurine transporter occluded the ethanol-induced taurine increase, putatively due to a ceiling effect. Selective manipulation of nAc astrocytes using Gq-coupled designer receptors exclusively activated by designer drugs (DREADDs) did not affect ethanol-induced taurine release. However, activation of Gi-coupled DREADDs, or metabolic inhibition using fluorocitrate, rather enhanced than depressed taurine elevation. Finally, ethanol-induced taurine increase was fully blocked in rats pre-treated with the L-type Ca2+-channel blocker nicardipine, suggesting that the release is Ca2+ dependent. In conclusion, while astrocytes appear to be important regulators of basal taurine levels in the nAc, they do not appear to be the main cells underlying ethanol-induced taurine release.

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.

Structural basis for human Cav1.2 inhibition by multiple drugs and the neurotoxin calciseptine

Cav1.2 channels play crucial roles in various neuronal and physiological processes. Here, we present cryo-EM structures of human Cav1.2, both in its apo form and in complex with several drugs, as well as the peptide neurotoxin calciseptine. Most structures, apo or bound to calciseptine, amlodipine, or a combination of amiodarone and sofosbuvir, exhibit a consistent inactivated conformation with a sealed gate, three up voltage-sensing domains (VSDs), and a down VSDII. Calciseptine sits on the shoulder of the pore domain, away from the permeation path. In contrast, when pinaverium bromide, an antispasmodic drug, is inserted into a cavity reminiscent of the IFM-binding site in Nav channels, a series of structural changes occur, including upward movement of VSDII coupled with dilation of the selectivity filter and its surrounding segments in repeat III. Meanwhile, S4-5III merges with S5III to become a single helix, resulting in a widened but still non-conductive intracellular gate.

Excitation-transcription coupling, neuronal gene expression and synaptic plasticity

Excitation-transcription coupling (E-TC) links synaptic and cellular activity to nuclear gene transcription. It is generally accepted that E-TC makes a crucial contribution to learning and memory through its role in underpinning long-lasting synaptic enhancement in late-phase long-term potentiation and has more recently been linked to late-phase long-term depression: both processes require de novo gene transcription, mRNA translation and protein synthesis. E-TC begins with the activation of glutamate-gated N-methyl-D-aspartate-type receptors and voltage-gated L-type Ca2+ channels at the membrane and culminates in the activation of transcription factors in the nucleus. These receptors and ion channels mediate E-TC through mechanisms that include long-range signalling from the synapse to the nucleus and local interactions within dendritic spines, among other possibilities. Growing experimental evidence links these E-TC mechanisms to late-phase long-term potentiation and learning and memory. These advances in our understanding of the molecular mechanisms of E-TC mean that future efforts can focus on understanding its mesoscale functions and how it regulates neuronal network activity and behaviour in physiological and pathological conditions.

Transcriptomic profile of cationic channels in human pulmonary arterial hypertension

The dysregulation of K⁺ channels is a hallmark of pulmonary arterial hypertension (PAH). Herein, the channelome was analyzed in lungs of patients with PAH in a public transcriptomic database. Sixty six (46%) mRNA encoding cationic channels were dysregulated in PAH with most of them downregulated (83%). The principal component analysis indicated that dysregulated cationic channel expression is a signature of the disease. Changes were very similar in idiopathic, connective tissue disease and congenital heart disease associated PAH. This analysis 1) is in agreement with the widely recognized pathophysiological role of TASK1 and K_V1.5, 2) supports previous preliminary reports pointing to the dysregulation of several K⁺ channels including the downregulation of K_V1.1, K_V1.4, K_V1.6, K_V7.1, K_V7.4, K_V9.3 and TWIK2 and the upregulation of K_Ca1.1 and 3) points to other cationic channels dysregulated such as Kv7.3, TALK2, Ca_V1 and TRPV4 which might play a pathophysiological role in PAH. The significance of other changes found in Na⁺ and TRP channels remains to be investigated.

Neurotransmitter Release Site Replenishment and Presynaptic Plasticity

An action potential (AP) triggers neurotransmitter release from synaptic vesicles (SVs) docking to a specialized release site of presynaptic plasma membrane, the active zone (AZ). The AP simultaneously controls the release site replenishment with SV for sustainable synaptic transmission in response to incoming neuronal signals. Although many studies have suggested that the replenishment time is relatively slow, recent studies exploring high speed resolution have revealed SV dynamics with milliseconds timescale after an AP. Accurate regulation is conferred by proteins sensing Ca²⁺ entering through voltage-gated Ca²⁺ channels opened by an AP. This review summarizes how millisecond Ca²⁺ dynamics activate multiple protein cascades for control of the release site replenishment with release-ready SVs that underlie presynaptic short-term plasticity.

The Effects of General Anesthetics on Synaptic Transmission

General anesthetics are a class of drugs that target the central nervous system and are widely used for various medical procedures. General anesthetics produce many behavioral changes required for clinical intervention, including amnesia, hypnosis, analgesia, and immobility; while they may also induce side effects like respiration and cardiovascular depressions. Understanding the mechanism of general anesthesia is essential for the development of selective general anesthetics which can preserve wanted pharmacological actions and exclude the side effects and underlying neural toxicities. However, the exact mechanism of how general anesthetics work is still elusive. Various molecular targets have been identified as specific targets for general anesthetics. Among these molecular targets, ion channels are the most principal category, including ligand-gated ionotropic receptors like γ-aminobutyric acid, glutamate and acetylcholine receptors, voltage-gated ion channels like voltage-gated sodium channel, calcium channel and potassium channels, and some second massager coupled channels. For neural functions of the central nervous system, synaptic transmission is the main procedure for which information is transmitted between neurons through brain regions, and intact synaptic function is fundamentally important for almost all the nervous functions, including consciousness, memory, and cognition. Therefore, it is important to understand the effects of general anesthetics on synaptic transmission via modulations of specific ion channels and relevant molecular targets, which can lead to the development of safer general anesthetics with selective actions. The present review will summarize the effects of various general anesthetics on synaptic transmissions and plasticity.

Disrupted Calcium Signaling in Animal Models of Human Spinocerebellar Ataxia (SCA)

Spinocerebellar ataxias (SCAs) constitute a heterogeneous group of more than 40 autosomal-dominant genetic and neurodegenerative diseases characterized by loss of balance and motor coordination due to dysfunction of the cerebellum and its efferent connections. Despite a well-described clinical and pathological phenotype, the molecular and cellular events that underlie neurodegeneration are still poorly undaerstood. Emerging research suggests that mutations in SCA genes cause disruptions in multiple cellular pathways but the characteristic SCA pathogenesis does not begin until calcium signaling pathways are disrupted in cerebellar Purkinje cells. Ca²⁺ signaling in Purkinje cells is important for normal cellular function as these neurons express a variety of Ca²⁺ channels, Ca²⁺-dependent kinases and phosphatases, and Ca²⁺-binding proteins to tightly maintain Ca²⁺ homeostasis and regulate physiological Ca²⁺-dependent processes. Abnormal Ca²⁺ levels can activate toxic cascades leading to characteristic death of Purkinje cells, cerebellar atrophy, and ataxia that occur in many SCAs. The output of the cerebellar cortex is conveyed to the deep cerebellar nuclei (DCN) by Purkinje cells via inhibitory signals; thus, Purkinje cell dysfunction or degeneration would partially or completely impair the cerebellar output in SCAs. In the absence of the inhibitory signal emanating from Purkinje cells, DCN will become more excitable, thereby affecting the motor areas receiving DCN input and resulting in uncoordinated movements. An outstanding advantage in studying the pathogenesis of SCAs is represented by the availability of a large number of animal models which mimic the phenotype observed in humans. By mainly focusing on mouse models displaying mutations or deletions in genes which encode for Ca²⁺ signaling-related proteins, in this review we will discuss the several pathogenic mechanisms related to deranged Ca²⁺ homeostasis that leads to significant Purkinje cell degeneration and dysfunction.

Calcium Signaling and Tissue Calcification

Calcification is a regulated physiological process occurring in bones and teeth. However, calcification is commonly found in soft tissues in association with aging and in a variety of diseases. Over the last two decades, it has emerged that calcification occurring in diseased arteries is not simply an inevitable build-up of insoluble precipitates of calcium phosphate. In some cases, it is an active process in which transcription factors drive conversion of vascular cells to an osteoblast or chondrocyte-like phenotype, with the subsequent production of mineralizing "matrix vesicles." Early studies of bone and cartilage calcification suggested roles for cellular calcium signaling in several of the processes involved in the regulation of bone calcification. Similarly, calcium signaling has recently been highlighted as an important component in the mechanisms regulating pathological calcification. The emerging hypothesis is that ectopic/pathological calcification occurs in tissues in which there is an imbalance in the regulatory mechanisms that actively prevent calcification. This review highlights the various ways that calcium signaling regulates tissue calcification, with a particular focus on pathological vascular calcification.

Presynaptic Calcium Channels

Presynaptic Ca²⁺ entry occurs through voltage-gated Ca²⁺ (Ca_V) channels which are activated by membrane depolarization. Depolarization accompanies neuronal firing and elevation of Ca²⁺ triggers neurotransmitter release from synaptic vesicles. For synchronization of efficient neurotransmitter release, synaptic vesicles are targeted by presynaptic Ca²⁺ channels forming a large signaling complex in the active zone. The presynaptic Ca_V2 channel gene family (comprising Ca_V2.1, Ca_V2.2, and Ca_V2.3 isoforms) encode the pore-forming α1 subunit. The cytoplasmic regions are responsible for channel modulation by interacting with regulatory proteins. This article overviews modulation of the activity of Ca_V2.1 and Ca_V2.2 channels in the control of synaptic strength and presynaptic plasticity.

A New Generation of Dihydropyridine Calcium Channel Blockers: Photostabilization of Liquid Formulations Using Nonionic Surfactants

The stability profile of a new 1,4-dihydropyridine derivative (DHP), representative of a series with a hexahydroquinoline ring, was studied to design light-stable liquid formulations. This molecule, named M3, has been shown among the analogs to have a high capacity to block both L- and T-type calcium channels. The ethanol solution of the drug was subjected to a photodegradation test, in accordance with standard rules. The concentrations of the drug and its byproducts were estimated using multivariate curve resolution, applied to the spectral data collected during the test. The improvement of both the photostability and water solubility of M3 was investigated by adding the surfactant polysorbate 20 in a 1:5 ratio to aqueous solutions of the drug. These formulations were exposed to stressing light in containers of bleu polyethylene terephthalate (PET), amber PET, and covered amber PET. The best results were obtained when using the covered amber PET container, reaching a degradation percentage of the drug less than 5% after 12 h under an irradiance power of 450 W/m². The stability of the compound was compared to that of nimodipine (NIM) under the same conditions.

Therapeutic Effect of Agmatine on Neurological Disease: Focus on Ion Channels and Receptors

The central nervous system (CNS) is the most injury-prone part of the mammalian body. Any acute or chronic, central or peripheral neurological disorder is related to abnormal biochemical and electrical signals in the brain cells. As a result, ion channels and receptors that are abundant in the nervous system and control the electrical and biochemical environment of the CNS play a vital role in neurological disease. The N-methyl-D-aspartate receptor, 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl) propanoic acid receptor, kainate receptor, acetylcholine receptor, serotonin receptor, α2-adrenoreceptor, and acid-sensing ion channels are among the major channels and receptors known to be key components of pathophysiological events in the CNS. The primary amine agmatine, a neuromodulator synthesized in the brain by decarboxylation of L-arginine, can regulate ion channel cascades and receptors that are related to the major CNS disorders. In our previous studies, we established that agmatine was related to the regulation of cell differentiation, nitric oxide synthesis, and murine brain endothelial cell migration, relief of chronic pain, cerebral edema, and apoptotic cell death in experimental CNS disorders. In this review, we will focus on the pathophysiological aspects of the neurological disorders regulated by these ion channels and receptors, and their interaction with agmatine in CNS injury.

Ion Channels in Pulmonary Hypertension: A Therapeutic Interest?

Pulmonary arterial hypertension (PAH) is a multifactorial and severe disease without curative therapies. PAH pathobiology involves altered pulmonary arterial tone, endothelial dysfunction, distal pulmonary vessel remodeling, and inflammation, which could all depend on ion channel activities (K⁺, Ca²⁺, Na⁺ and Cl^-). This review focuses on ion channels in the pulmonary vasculature and discusses their pathophysiological contribution to PAH as well as their therapeutic potential in PAH.

Cancer astrocytes have a more conserved molecular status in long recurrence free survival (RFS) IDH1 wild-type glioblastoma patients: new emerging cancer players

Glioblastoma is a devastating disease that despite all the information gathered so far, its optimal management remains elusive due to the absence of validated targets from clinical studies. A better clarification of the molecular mechanisms is needed. In this study, having access to IDH1 wild-type glioblastoma of patients with exceptionally long recurrence free survival (RFS), we decided to compare their mutational and gene expression profile to groups of IDH1 wild-type glioblastoma of patients with shorter RFS, by using NGS technology. The exome analysis revealed that Long-RFS tumors have a lower mutational rate compared to the other groups. A total of 158 genes were found differentially expressed among the groups, 112 of which distinguished the two RFS extreme groups. Overall, the exome data suggests that shorter RFS tumors could be, chronologically, in a more advanced state in the muli-step tumor process of sequential accumulation of mutations. New players in this kind of cancer emerge from the analysis, confirmed at the RNA/DNA level, identifying, therefore, possible oncodrivers or tumor suppressor genes.

Bilirubin augments Ca2+ load of developing bushy neurons by targeting specific subtype of voltage-gated calcium channels

Neonatal brain is particularly vulnerable to pathological levels of bilirubin which elevates and overloads intracellular Ca²⁺, leading to neurotoxicity. However, how voltage-gated calcium channels (VGCCs) are functionally involved in excess calcium influx remains unknown. By performing voltage-clamp recordings from bushy cells in the ventral cochlear nucleus (VCN) in postnatal rat pups (P4-17), we found the total calcium current density was more than doubled over P4-17, but the relative weight of VGCC subtypes changed dramatically, being relatively equal among T, L, N, P/Q and R-type at P4-6 to predominantly L, N, R over T and P/Q at P15-17. Surprisingly, acute administration of bilirubin augmented the VGCC currents specifically mediated by high voltage-activated (HVA) P/Q-type calcium currents. This augment was attenuated by intracellular loading of Ca²⁺ buffer EGTA or calmodulin inhibitory peptide. Our findings indicate that acute exposure to bilirubin increases VGCC currents, primarily by targeting P/Q-type calcium channels via Ca²⁺ and calmodulin dependent mechanisms to overwhelm neurons with excessive Ca²⁺. Since P/Q-subtype calcium channels are more prominent in neonatal neurons (e.g. P4-6) than later stages, we suggest this subtype-specific enhancement of P/Q-type Ca²⁺ currents likely contributes to the early neuronal vulnerability to hyperbilirubinemia in auditory and other brain regions.

Inhibitory effects of a standardized extract of Justicia pectoralis in an experimental rat model of airway hyper-responsiveness

OBJECTIVE

Justicia pectoralis is a plant useful for the treatment of respiratory diseases. Here, we studied the antiasthmatic properties of a standardized extract of J. pectoralis (Jp).

METHODS

Ovalbumin (OVA)-sensitized rats were actively challenged with saline or OVA to study airway hyper-responsiveness after oral treatment with saline or Jp. The ability of Jp to inhibit hyper-reactivity was evaluated in isolated trachea mounted in isolated organ bath chamber.

KEY FINDINGS

Using KCl or carbachol as contractile agents, tracheal rings of OVA-challenged rats contracted with higher magnitude than trachea of rats challenged with saline. Such hyper-responsive phenotype of OVA-challenged tissues decreased with Jp administration. In Ca⁺ -free medium, Jp or its major constituent coumarin inhibited preferentially the contractions induced by Ca²⁺ addition in tissues of OVA-challenged rats stimulated with KCl or acetylcholine. In tissues depleted of their internal Ca⁺ stores in the presence of thapsigargin, Jp inhibited the contraction induced by capacitative Ca²⁺ entry. By gavage, Jp abolished the increase caused by challenge with OVA on the levels of IL-1β and TNF-α in the bronchoalveolar fluid and also impaired the changes in gene expression of canonical transient receptor proteins.

CONCLUSIONS

Jp has antiasthmatic properties in an experimental model that reproduces tracheal hyper-reactivity.

Antispasmodic, bronchodilator, vasorelaxant and cardiosuppressant effects of Buxus papillosa

Background

The present research was carried out to investigate pharmacological properties of Buxus papillosa C.K. Schneid. (Buxaceae).

Methods

Buxus papillosa extracts of leaves (BpL), stem (BpS), roots (BpR) and BpL fractions: hexane (BpL-H), aqueous (BpL-A) also plant constituent, cyclomicrobuxine effect were studied in jejunum, atria, aorta and tracheal preparations from rabbit and guine-peg.

Results

Ca⁺⁺ antagonistic effect of BpS, BpR, BpL-H, BpL-A and cyclomicrobuxine were conclusively suggested, when spontaneous contractions of rabbit jejunal preparation was relaxed along with subsequent relaxation of potassium chloride (80 mM) induced contractions. Ca⁺⁺ antagonistic effect was further confirmed, when a prominent right shift like that of verapamil was observed in Ca⁺⁺ concentration-response curves, drawn in a tissue pretreated with BpL (0.3–1.0 mg/mL). In rabbit tracheal tissues BpL, BpS, BpR, BpL-H and BpL-A produced a prominent relaxation in contractions induced by potassium chloride (80 mM) and carbachol (1 μm). When tested in rabbit aortic rings, BpL, BpS, BpR, BpL-H and BpL-A showed concentration-dependent (0.1–3.0 mg/mL) vasorelaxant effect against phenylephrine (1 μM) and high K⁺-induced contractions. In isolated guinea-pig right atria, BpL, BpS, BpR, BpL-H and BpL-A suppressed atrial force of spontaneous contractions, with BpL-A being most potent.

Conclusions

Our results reveal that Buxus papillosa possesses gut, airways and cardiovascular inhibitory actions.

Hypoxic Rise in Cytosolic Calcium and Renal Proximal Tubule Injury Mediated by a Nickel-Sensitive Pathway

In the kidney, cell injury resulting from ischemia and hypoxia is thought to be due, in part, to increased cytosolic Ca2+ levels, [Ca2+]i, leading to activation of lytic enzymes, cell dysfunction, and necrosis. We report evidence of a progressive and exponential increase in [Ca2+]i (from 245 ± 10 to 975 ± 100 nM at 45 mins), cell permeabilization and propidium iodide (PI) staining of the nucleus, and partial loss of cell transport functions such as Na+-gradient–dependent uptakes of 14C-alpha-methyiglucopyranoside and inorganic phosphate (32Pi) in proximal convoluted tubules of adult rabbits subjected to hypoxia. The rise in [Ca2+]i depended on the presence of extracellular [Ca2+] and could be blocked by 50 μM Ni2+ but not by verapamil (100 μM). Presence of 50 μM Ni2+ also reduced the hypoxia-induced morphological and functional injuries. We also used HEK 293 cells, a kidney cell line, incubated in media without glucose and exposed for 3.5 hrs to 1% O2–5% CO2 and then returned to glucose-containing media for another 3.5 hrs in an air–5% CO2 atmosphere and finally exposed for 1 min to media containing 1 μM Pl. NiCl2 (50 μM) or pentobarbital (300 μM) more than phenobarbital (1.5 mM), when present in the incubation medium during both the hypoxic and the reoxygenation periods, induced significant (P < 0.001) reductions in the number of cell nuclei stained with Pl, similar to their relative potency as inhibitors of T channels. Our findings indicate that hypoxia-induced alterations in calcium level and subsequent cell injury in the proximal convoluted tubule and in HEK cells involve a nickel-sensitive and dihydropyridine insensitive pathway or channel.

Upregulation of L-type calcium channels in colonic inhibitory motoneurons of P/Q-type calcium channel-deficient mice

Enteric inhibitory motoneurons use nitric oxide and a purine neurotransmitter to relax gastrointestinal smooth muscle. Enteric P/Q-type Ca2+ channels contribute to excitatory neuromuscular transmission; their contribution to inhibitory transmission is less clear. We used the colon from tottering mice (tg/tg, loss of function mutation in the α1A pore-forming subunit of P/Q-type Ca2+ channels) to test the hypothesis that P/Q-type Ca2+ channels contribute to inhibitory neuromuscular transmission and colonic propulsive motility. Fecal pellet output in vivo and the colonic migrating motor complex (ex vivo) were measured. Neurogenic circular muscle relaxations and inhibitory junction potentials (IJPs) were also measured ex vivo. Colonic propulsive motility in vivo and ex vivo was impaired in tg/tg mice. IJPs were either unchanged or somewhat larger in tissues from tg/tg compared with wild-type (WT) mice. Nifedipine (L-type Ca2+ channel antagonist) inhibited IJPs by 35 and 14% in tissues from tg/tg and WT mice, respectively. The contribution of N- and R-type channels to neuromuscular transmission was larger in tissues from tg/tg compared with WT mice. The resting membrane potential of circular muscle cells was similar in tissues from tg/tg and WT mice. Neurogenic relaxations of circular muscle from tg/tg and WT mice were similar. These results demonstrate that a functional deficit in P/Q-type channels does not alter propulsive colonic motility. Myenteric neuron L-type Ca2+ channel function increases to compensate for loss of functional P/Q-type Ca2+ channels. This compensation maintains inhibitory neuromuscular transmission and normal colonic motility.

Genetic Candidate Variants in Two Multigenerational Families with Childhood Apraxia of Speech

Childhood apraxia of speech (CAS) is a severe and socially debilitating form of speech sound disorder with suspected genetic involvement, but the genetic etiology is not yet well understood. Very few known or putative causal genes have been identified to date, e.g., FOXP2 and BCL11A. Building a knowledge base of the genetic etiology of CAS will make it possible to identify infants at genetic risk and motivate the development of effective very early intervention programs. We investigated the genetic etiology of CAS in two large multigenerational families with familial CAS. Complementary genomic methods included Markov chain Monte Carlo linkage analysis, copy-number analysis, identity-by-descent sharing, and exome sequencing with variant filtering. No overlaps in regions with positive evidence of linkage between the two families were found. In one family, linkage analysis detected two chromosomal regions of interest, 5p15.1-p14.1, and 17p13.1-q11.1, inherited separately from the two founders. Single-point linkage analysis of selected variants identified CDH18 as a primary gene of interest and additionally, MYO10, NIPBL, GLP2R, NCOR1, FLCN, SMCR8, NEK8, and ANKRD12, possibly with additive effects. Linkage analysis in the second family detected five regions with LOD scores approaching the highest values possible in the family. A gene of interest was C4orf21 (ZGRF1) on 4q25-q28.2. Evidence for previously described causal copy-number variations and validated or suspected genes was not found. Results are consistent with a heterogeneous CAS etiology, as is expected in many neurogenic disorders. Future studies will investigate genome variants in these and other families with CAS.

Next-generation sequencing identifies novel CACNA1A gene mutations in episodic ataxia type 2

Episodic Ataxia type 2 (EA2) is a rare autosomal dominantly inherited neurological disorder characterized by recurrent disabling imbalance, vertigo, and episodes of ataxia lasting minutes to hours. EA2 is caused most often by loss of function mutations of the calcium channel gene CACNA1A. In addition to EA2, mutations in CACNA1A are responsible for two other allelic disorders: familial hemiplegic migraine type 1 (FHM1) and spinocerebellar ataxia type 6 (SCA6). Herein, we have utilized next-generation sequencing (NGS) to screen the coding sequence, exon-intron boundaries, and Untranslated Regions (UTRs) of five genes where mutation is known to produce symptoms related to EA2, including CACNA1A. We performed this screening in a group of 31 unrelated patients with EA2 symptoms. Both novel and known mutations were detected through NGS technology, and confirmed through Sanger sequencing. Genetic testing showed in total 15 mutation bearing patients (48%), of which nine were novel mutations (6 missense and 3 small frameshift deletion mutations) and six known mutations (4 missense and 2 nonsense).These results demonstrate the efficiency of our NGS-panel for detecting known and novel mutations for EA2 in the CACNA1A gene, also identifying a novel missense mutation in ATP1A2 which is not a normal target for EA2 screening.

Apamin Boosting of Synaptic Potentials in CaV2.3 R-Type Ca2+ Channel Null Mice

SK2- and KV4.2-containing K+ channels modulate evoked synaptic potentials in CA1 pyramidal neurons. Each is coupled to a distinct Ca2+ source that provides Ca2+-dependent feedback regulation to limit AMPA receptor (AMPAR)- and NMDA receptor (NMDAR)-mediated postsynaptic depolarization. SK2-containing channels are activated by Ca2+ entry through NMDARs, whereas KV4.2-containing channel availability is increased by Ca2+ entry through SNX-482 (SNX) sensitive CaV2.3 R-type Ca2+ channels. Recent studies have challenged the functional coupling between NMDARs and SK2-containing channels, suggesting that synaptic SK2-containing channels are instead activated by Ca2+ entry through R-type Ca2+ channels. Furthermore, SNX has been implicated to have off target affects, which would challenge the proposed coupling between R-type Ca2+ channels and KV4.2-containing K+ channels. To reconcile these conflicting results, we evaluated the effect of SK channel blocker apamin and R-type Ca2+ channel blocker SNX on evoked excitatory postsynaptic potentials (EPSPs) in CA1 pyramidal neurons from CaV2.3 null mice. The results show that in the absence of CaV2.3 channels, apamin application still boosted EPSPs. The boosting effect of CaV2.3 channel blockers on EPSPs observed in neurons from wild type mice was not observed in neurons from CaV2.3 null mice. These data are consistent with a model in which SK2-containing channels are functionally coupled to NMDARs and KV4.2-containing channels to CaV2.3 channels to provide negative feedback regulation of EPSPs in the spines of CA1 pyramidal neurons.

Rab3 interacting molecule 3 mutations associated with autism alter regulation of voltage-dependent Ca²⁺ channels

Autism is a neurodevelopmental psychiatric disorder characterized by impaired reciprocal social interaction, disrupted communication, and restricted and stereotyped patterns of interests. Autism is known to have a strong genetic component. Although mutations in several genes account for only a small proportion of individuals with autism, they provide insight into potential biological mechanisms that underlie autism, such as dysfunction in Ca(2+) signaling, synaptic dysfunction, and abnormal brain connectivity. In autism patients, two mutations have been reported in the Rab3 interacting molecule 3 (RIM3) gene. We have previously demonstrated that RIM3 physically and functionally interacts with voltage-dependent Ca(2+) channels (VDCCs) expressed in neurons via the β subunits, and increases neurotransmitter release. Here, by introducing corresponding autism-associated mutations that replace glutamic acid residue 176 with alanine (E176A) and methionine residue 259 with valine (M259V) into the C2B domain of mouse RIM3, we demonstrate that both mutations partly cancel the suppressive RIM3 effect on voltage-dependent inactivation of Ba(2+) currents through P/Q-type CaV2.1 recombinantly expressed in HEK293 cells. In recombinant N-type CaV2.2 VDCCs, the attenuation of the suppressive RIM3 effect on voltage-dependent inactivation is conserved for M259V but not E176A. Slowing of activation speed of P/Q-type CaV2.1 currents by RIM3 is abolished in E176A, while the physical interaction between RIM3 and β subunits is significantly attenuated in M259V. Moreover, increases by RIM3 in depolarization-induced Ca(2+) influx and acetylcholine release are significantly attenuated by E176A in rat pheochromocytoma PC12 cells. Thus, our data raise the interesting possibility that autism phenotypes are elicited by synaptic dysfunction via altered regulation of presynaptic VDCC function and neurotransmitter release.

Age-dependent contribution of P/Q- and R-type Ca2+ channels to neuromuscular transmission in lethargic mice

β-Subunits of voltage-gated calcium channels (VGCCs) regulate assembly and membrane localization of the pore-forming α1-subunit and strongly influence channel function. β4-Subunits normally coassociate with α1A-subunits which comprise P/Q-type (Cav2.1) VGCCs. These control acetylcholine (ACh) release at adult mammalian neuromuscular junctions (NMJs). The naturally occurring lethargic (lh) mutation of the β4-subunit in mice causes loss of the α1-binding site, possibly affecting P/Q-type channel expression or function, and thereby ACh release. End-plate potentials and miniature end-plate potentials were recorded at hemidiaphragm NMJs of 5-7-week and 3-5-month-old lh and wild-type (wt) mice. Sensitivity to antagonists of P/Q- [ω-agatoxin IVA (ω-Aga-IVA)], L- (nimodipine), N- (ω-conotoxin GVIA), and R-type [C192H274N52O60S7 (SNX-482)] VGCCs was compared in juvenile and adult lh and wt mice. Quantal content (m) of adult, but not juvenile, lh mice was reduced compared to wt. ω-Aga-IVA (~60%) and SNX-482 (~ 45%) significantly reduced m in adult lh mice. Only Aga-IVA affected wt adults. In juvenile lh mice, ω-Aga-IVA and SNX-482 decreased m by >75% and ~20%, respectively. Neither ω-conotoxin GVIA nor nimodipine affected ACh release in any group. Immunolabeling revealed α1E and α1A, β1, and β3 staining at adult lh, but not wt NMJs. Therefore, in lh mice, when the β-subunit that normally coassociates with α1A to form P/Q channels is missing, P/Q-type channels partner with other β-subunits. However, overall participation of P/Q-type channels is reduced and compensated for by R-type channels. R-type VGCC participation is age-dependent, but is less effective than P/Q-type at sustaining NMJ function.

Pharmacological basis for medicinal use of Lens culinaris in gastrointestinal and respiratory disorders

Crude extract of Lens culinaris (Lc.Cr), which tested positive for presence of anthraquinones, flavonoids, saponins, sterol, tannins, and terpenes exhibited protective effect against castor oil-induced diarrhea in mice at 100-1000 mg/kg. In rabbit jejunum preparations, Lc.Cr caused relaxation of spontaneous contractions at 0.03-5.0 mg/mL. Lc.Cr inhibited carbachol (CCh, 1 μM) and K(+) (80 mM)-induced contractions in a pattern similar to dicyclomine, but different from verapamil and atropine. Lc.Cr shifted the Ca(++) concentration-response curves to the right, like dicyclomine and verapamil. Pretreatment of tissues with Lc.Cr (0.03-0.1 mg/mL) caused leftward shift of isoprenaline-induced inhibitory CRCs, similar to papaverine. In guinea-pig ileum, Lc.Cr produced rightward parallel shift of CCh curves, followed by non-parallel shift at higher concentration with suppression of maximum response, similar to dicyclomine, but different from verapamil and atropine. Lc.Cr (3.0-30 mg/kg) caused suppression of carbachol (CCh, 100 µg/kg)-induced increase in inspiratory pressure of anesthetized rats. In guinea-pig trachea, Lc.Cr relaxed CCh and high K(+) -induced contractions, shifted CCh curves to right and potentiated isoprenaline response. These results suggest that L. culinaris possesses antidiarrheal, antispasmodic, and bronchodilator activities mediated possibly through a combination of Ca(++) antagonist, anticholinergic, and phosphodiesterase inhibitory effects, and this study provides sound mechanistic background to its medicinal use in disorders of gut and airways hyperactivity, like diarrhea and asthma.

Successful reduction of off-target hERG toxicity by structural modification of a T-type calcium channel blocker

To obtain an optimized T-type calcium channel blocker with reduced off-target hERG toxicity, we modified the structure of the original compound by introducing a zwitterion and reducing the basicity of the nitrogen. Among the structurally modified compounds we designed, compounds 5 and 6, which incorporate amides in place of the original compound's amines, most appreciably alleviated hERG toxicity while maintaining T-type calcium channel blocking activity. Notably, the benzimidazole amide 5 selectively blocked T-type calcium channels without inhibiting hERG (hERG/T-type⩾220) and L-type channels (L-type/T-type=96), and exhibited an excellent pharmacokinetic profile in rats.

L-type calcium channels play a critical role in maintaining lens transparency by regulating phosphorylation of aquaporin-0 and myosin light chain and expression of connexins

Homeostasis of intracellular calcium is crucial for lens cytoarchitecture and transparency, however, the identity of specific channel proteins regulating calcium influx within the lens is not completely understood. Here we examined the expression and distribution profiles of L-type calcium channels (LTCCs) and explored their role in morphological integrity and transparency of the mouse lens, using cDNA microarray, RT-PCR, immunoblot, pharmacological inhibitors and immunofluorescence analyses. The results revealed that Ca (V) 1.2 and 1.3 channels are expressed and distributed in both the epithelium and cortical fiber cells in mouse lens. Inhibition of LTCCs with felodipine or nifedipine induces progressive cortical cataract formation with time, in association with decreased lens weight in ex-vivo mouse lenses. Histological analyses of felodipine treated lenses revealed extensive disorganization and swelling of cortical fiber cells resembling the phenotype reported for altered aquaporin-0 activity without detectable cytotoxic effects. Analysis of both soluble and membrane rich fractions from felodipine treated lenses by SDS-PAGE in conjunction with mass spectrometry and immunoblot analyses revealed decreases in β-B1-crystallin, Hsp-90, spectrin and filensin. Significantly, loss of transparency in the felodipine treated lenses was preceded by an increase in aquaporin-0 serine-235 phosphorylation and levels of connexin-50, together with decreases in myosin light chain phosphorylation and the levels of 14-3-3ε, a phosphoprotein-binding regulatory protein. Felodipine treatment led to a significant increase in gene expression of connexin-50 and 46 in the mouse lens. Additionally, felodipine inhibition of LTCCs in primary cultures of mouse lens epithelial cells resulted in decreased intracellular calcium, and decreased actin stress fibers and myosin light chain phosphorylation, without detectable cytotoxic response. Taken together, these observations reveal a crucial role for LTCCs in regulation of expression, activity and stability of aquaporin-0, connexins, cytoskeletal proteins, and the mechanical properties of lens, all of which have a vital role in maintaining lens function and cytoarchitecture.

A macromolecular trafficking complex composed of β₂-adrenergic receptors, A-Kinase Anchoring Proteins and L-type calcium channels

Abstract Sympathetic modulation of cardiac L-type calcium channels is an important mechanism for regulating heart rate and cardiac contractility. At the molecular level, activation of β-adrenergic receptors (βAR) increases calcium influx into cardiac myocytes by activating protein kinase A (PKA), leading to subsequent phosphorylation of L-type calcium channels. In the case of the β2AR, this process is facilitated by the presence of A-Kinase Anchoring Proteins (AKAPs) that serve as scaffolding proteins for the L-type calcium channel and the β2AR complex. Our work has shown that, in addition to facilitating PKA phosphorylation of the channel, AKAPs also promote an increase in the Cav1.2 channel surface expression. Here we review the molecular mechanisms of β2AR/AKAP/L-type channel interactions and trafficking.

Omega-conotoxins as experimental tools and therapeutics in pain management

Neuropathic pain afflicts a large percentage of the global population. This form of chronic, intractable pain arises when the peripheral or central nervous systems are damaged, either directly by lesion or indirectly through disease. The comorbidity of neuropathic pain with other diseases, including diabetes, cancer, and AIDS, contributes to a complex pathogenesis and symptom profile. Because most patients present with neuropathic pain refractory to current first-line therapeutics, pharmaceuticals with greater efficacy in pain management are highly desired. In this review we discuss the growing application of ω-conotoxins, small peptides isolated from Conus species, in the management of neuropathic pain. These toxins are synthesized by predatory cone snails as a component of paralytic venoms. The potency and selectivity with which ω-conotoxins inhibit their molecular targets, voltage-gated Ca²⁺ channels, is advantageous in the treatment of neuropathic pain states, in which Ca²⁺ channel activity is characteristically aberrant. Although ω-conotoxins demonstrate analgesic efficacy in animal models of neuropathic pain and in human clinical trials, there remains a critical need to improve the convenience of peptide drug delivery methods, and reduce the number and severity of adverse effects associated with ω-conotoxin-based therapies.

Exploring the dominant role of Cav1 channels in signalling to the nucleus

Calcium is important in controlling nuclear gene expression through the activation of multiple signal-transduction pathways in neurons. Compared with other voltage-gated calcium channels, Ca_V1 channels demonstrate a considerable advantage in signalling to the nucleus. In this review, we summarize the recent progress in elucidating the mechanisms involved. Ca_V1 channels, already advantaged in their responsiveness to depolarization, trigger communication with the nucleus by attracting colocalized clusters of activated CaMKII (Ca²⁺/calmodulin-dependent protein kinase II). Ca_V2 channels lack this ability, but must work at a distance of >1 μm from the Ca_V1-CaMKII co-clusters, which hampers their relative efficiency for a given rise in bulk [Ca²⁺]_i (intracellular [Ca²⁺]). Moreover, Ca²⁺ influx from Ca_V2 channels is preferentially buffered by the ER (endoplasmic reticulum) and mitochondria, further attenuating their effectiveness in signalling to the nucleus.

Calcium homeostasis in aging neurons

The nervous system becomes increasingly vulnerable to insults and prone to dysfunction during aging. Age-related decline of neuronal function is manifested by the late onset of many neurodegenerative disorders, as well as by reduced signaling and processing capacity of individual neuron populations. Recent findings indicate that impairment of Ca(2+) homeostasis underlies the increased susceptibility of neurons to damage, associated with the aging process. However, the impact of aging on Ca(2+) homeostasis in neurons remains largely unknown. Here, we survey the molecular mechanisms that mediate neuronal Ca(2+) homeostasis and discuss the impact of aging on their efficacy. To address the question of how aging impinges on Ca(2+) homeostasis, we consider potential nodes through which mechanisms regulating Ca(2+) levels interface with molecular pathways known to influence the process of aging and senescent decline. Delineation of this crosstalk would facilitate the development of interventions aiming to fortify neurons against age-associated functional deterioration and death by augmenting Ca(2+) homeostasis.

Alternative splicing: functional diversity among voltage-gated calcium channels and behavioral consequences

Neuronal voltage-gated calcium channels generate rapid, transient intracellular calcium signals in response to membrane depolarization. Neuronal Ca(V) channels regulate a range of cellular functions and are implicated in a variety of neurological and psychiatric diseases including epilepsy, Parkinson's disease, chronic pain, schizophrenia, and bipolar disorder. Each mammalian Cacna1 gene has the potential to generate tens to thousands of Ca(V) channels by alternative pre-mRNA splicing, a process that adds fine granulation to the pool of Ca(V) channel structures and functions. The precise composition of Ca(V) channel splice isoform mRNAs expressed in each cell are controlled by cell-specific splicing factors. The activity of splicing factors are in turn regulated by molecules that encode various cellular features, including cell-type, activity, metabolic states, developmental state, and other factors. The cellular and behavioral consequences of individual sites of Ca(V) splice isoforms are being elucidated, as are the cell-specific splicing factors that control splice isoform selection. Altered patterns of alternative splicing of Ca(V) pre-mRNAs can alter behavior in subtle but measurable ways, with the potential to influence drug efficacy and disease severity. This article is part of a Special Issue entitled: Calcium channels.

Ca(V)1 and Ca(V)2 channels engage distinct modes of Ca(2+) signaling to control CREB-dependent gene expression

Activity-dependent gene expression triggered by Ca(2+) entry into neurons is critical for learning and memory, but whether specific sources of Ca(2+) act distinctly or merely supply Ca(2+) to a common pool remains uncertain. Here, we report that both signaling modes coexist and pertain to Ca(V)1 and Ca(V)2 channels, respectively, coupling membrane depolarization to CREB phosphorylation and gene expression. Ca(V)1 channels are advantaged in their voltage-dependent gating and use nanodomain Ca(2+) to drive local CaMKII aggregation and trigger communication with the nucleus. In contrast, Ca(V)2 channels must elevate [Ca(2+)](i) microns away and promote CaMKII aggregation at Ca(V)1 channels. Consequently, Ca(V)2 channels are ~10-fold less effective in signaling to the nucleus than are Ca(V)1 channels for the same bulk [Ca(2+)](i) increase. Furthermore, Ca(V)2-mediated Ca(2+) rises are preferentially curbed by uptake into the endoplasmic reticulum and mitochondria. This source-biased buffering limits the spatial spread of Ca(2+), further attenuating Ca(V)2-mediated gene expression.

Role of presynaptic metabotropic glutamate receptors in the induction of long-term synaptic plasticity of vesicular release

While postsynaptic ionotropic and metabotropic glutamate receptors have received the lions share of attention in studies of long-term activity-dependent synaptic plasticity, it is becoming clear that presynaptic metabotropic glutamate receptors play critical roles in both short-term and long-term plasticity of vesicular transmitter release, and that they act both at the level of voltage-dependent calcium channels and directly on proteins of the vesicular release machinery. Activation of G protein-coupled receptors can transiently inhibit vesicular release through the release of Gβγ which binds to both voltage-dependent calcium channels to reduce calcium influx, and directly to the C-terminus region of the SNARE protein SNAP-25. Our recent work has revealed that the binding of Gβγ to SNAP-25 is necessary, but not sufficient, to elicit long-term depression (LTD) of vesicular glutamate release, and that the concomitant release of Gα(i) and the second messenger nitric oxide are also necessary steps in the presynaptic LTD cascade. Here, we review the current state of knowledge of the molecular steps mediating short-term and long-term plasticity of vesicular release at glutamatergic synapses, and the many gaps that remain to be addressed. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

GPCR and voltage-gated calcium channels (VGCC) signaling complexes

Voltage-gated ion channels are transmembrane proteins that control nerve impulses and cell homeostasis. Signaling molecules that regulate ion channel activity and density at the plasma membrane must be specifically and efficiently coupled to these channels in order to control critical physiological functions such as action potential propagation. Although their regulation by G-protein receptor activation has been extensively explored, the assembly of ion channels into signaling complexes of GPCRs plays a fundamental role, engaging specific downstream -signaling pathways that trigger precise downstream effectors. Recent work has confirmed that GPCRs can intimately interact with ion channels and serve as -chaperone proteins that finely control their gating and trafficking in subcellular microdomains. This chapter aims to describe examples of GPCR-ion channel co-assembly, focusing mainly on signaling complexes between GPCRs and voltage-gated calcium channels.

PIKfyve and its Lipid products in health and in sickness

PIKfyve, a phosphoinositide 5-kinase synthesizing PtdIns(3,5)P₂ and PtdIns5P in a cellular context, belongs to an evolutionarily ancient gene family of PtdIns(3,5)P₂-synthesizing enzymes that, except for plants, are products of a single-copy gene across species. In the dozen years after its discovery, enormous progress has been made in characterizing the numerous PIKfyve cellular functions and the regulatory mechanisms that govern these functions. It became clear that PIKfyve does not act alone but, rather, it engages the scaffolding regulator ArPIKfyve and the phosphatase Sac3 to make a multiprotein "PAS" complex, so called for the first letters of the protein names. This complex relays antagonistic signals, one for synthesis, another for turnover of PtdIns(3,5)P₂, whose dysregulated coordination is linked to several human diseases. The physiological significance for each protein in the PAS complex is underscored by the early lethality of the mouse models with disruption in any of the three genes. This chapter summarizes our current knowledge of the diverse and complex functionality of PIKfyve and PtdIns(3,5)P₂/PtdIns5P products with particular highlights on recent discoveries of inherited or somatic mutations in PIKfyve and Sac3 linked to human disorders.

Expression and characterization of recombinant kurtoxin, an inhibitor of T-type voltage-gated calcium channels

Kurtoxin, a 63-amino acid peptide stabilized by four disulfide bonds, is the first reported peptide inhibitor of T-type voltage-gated calcium channels. Although T-type calcium channels have been implicated in a number of disease states, including epilepsy, chronic pain, hypertension and cancer, the lack of selective inhibitors has slowed progress in understanding their precise roles. Kurtoxin is a potentially valuable tool with which to study T-type calcium channels. However, because of the limited availability of the native protein, little is known about the structure and molecular mechanism of kurtoxin. Here we report the expression of kurtoxin in Escherichia coli and the structural and functional characterization of the recombinant protein. The disulfide bond pairings and secondary structure of recombinant kurtoxin were characterized through enzymatic cleavage, mass analysis and CD spectroscopy. Recombinant kurtoxin almost completely inhibited the T-type calcium channel in a manner identical to the native toxin. The availability of recombinant kurtoxin that is identical to the native toxin should help in the study of T-type calcium channels and enable development of new strategies for producing even more-selective T-type calcium channel inhibitors and for investigating the molecular basis of the toxin-channel interactions.

Cellular fura-2 manganese extraction assay (CFMEA)

Cellular manganese (Mn) uptake and transport dynamics can be measured using a cellular fura-2 manganese extraction assay (CFMEA). The assay described here uses immortalized murine striatal cell line and primary cortical astrocytes, but the method is equally adaptable to other cultured mammalian cells. An ultrasensitive fluorescent nucleic acid stain for quantification of double-stranded DNA (dsDNA) in solution, Quant-iT PicoGreen, has been utilized for normalization of Mn concentration in the cultured cells, following Mn (II) chloride (MnCl(2)) exposure. Depending on the cell type and density, other methods, e.g., protein determination assays or cell counts, may also be used for normalization. Methods are described for rapidly stopping Mn uptake and transport processes at specified times, extraction, and quantification of cellular Mn content, and normalization of Mn levels to dsDNA concentration.

Tyramine reduces glycinergic transmission by inhibiting presynaptic Ca(2+) channels in the rat trigeminal subnucleus caudalis

We have recently reported that tyramine acts on putative presynaptic trace amine receptors to inhibit glycinergic transmission in substantia gelatinosa (SG) neurons of the rat trigeminal subnucleus caudalis. However, it is still unknown how tyramine elicits presynaptic inhibition of glycine release. In the present study, therefore, we investigated cellular mechanisms underlying the tyramine-induced inhibition of glycinergic transmission in SG neurons using a conventional whole-cell patch clamp technique. Tyramine (100 μM) reversibly and repetitively decreased the amplitude of action potential-dependent glycinergic inhibitory postsynaptic currents (IPSCs), and increased the paired-pulse ratio. Pharmacological data suggest that the tyramine-induced decrease in glycinergic IPSCs was not mediated by the modulation of adenylyl cyclase, protein kinase A and C, or G-protein coupled inwardly rectifying K(+) channels. On the other hand, glycinergic IPSCs were mainly mediated by the Ca(2+) influx passing through presynaptic N-type and P/Q-type Ca(2+) channels. The tyramine-induced decrease in glycinergic IPSCs was completely blocked by ω-conotoxin GVIA, an N-type Ca(2+) channel blocker, but not ω-agatoxin IVA, a P/Q-type Ca(2+) channel blocker. The results suggest that tyramine acts presynaptically to decrease action potential-dependent glycine release onto SG neurons via the selective inhibition of presynaptic N-type Ca(2+) channels. This tyramine-induced inhibition of glycinergic transmission in SG neurons might affect the process of orofacial nociceptive signals.

Neuromuscular synaptic patterning requires the function of skeletal muscle dihydropyridine receptors

Developing skeletal myofibers in vertebrates are intrinsically “pre-patterned” for motor nerve innervation. However, the intrinsic factors that regulate muscle pre-patterning remain unknown. Here we show that a functional skeletal muscle dihydropyridine receptor (DHPR, the L-type Ca²⁺ channel in muscle) is required for muscle pre-patterning during the development of the neuromuscular junction (NMJ). Targeted deletion of the β1 subunit of DHPR (Cacnb1) in mice leads to muscle pre-patterning defects, aberrant innervation and precocious maturation of the NMJ. Reintroducing the Cacnb1 gene into Cacnb1^−/− muscles reverses the pre-patterning defects and restores normal development of the NMJ. The mechanism by which DHPRs govern muscle pre-patterning is independent of their role in excitation-contraction coupling (E-C coupling), but requires Ca²⁺ influx through the L-type Ca²⁺ channel. Our findings demonstrate that the skeletal muscle DHPR retrogradely regulates the patterning and formation of the NMJ.

Presynaptic HCN1 channels regulate Cav3.2 activity and neurotransmission at select cortical synapses

The hyperpolarization-activated cyclic nucleotide-gated (HCN) channels are subthreshold, voltage-gated ion channels that are highly expressed in hippocampal and cortical pyramidal cell dendrites, where they are important for regulating synaptic potential integration and plasticity. We found that HCN1 subunits are also localized to the active zone of mature asymmetric synaptic terminals targeting mouse entorhinal cortical layer III pyramidal neurons. HCN channels inhibited glutamate synaptic release by suppressing the activity of low-threshold voltage-gated T-type (Ca(V)3.2) Ca²(+) channels. Consistent with this, electron microscopy revealed colocalization of presynaptic HCN1 and Ca(V)3.2 subunit. This represents a previously unknown mechanism by which HCN channels regulate synaptic strength and thereby neural information processing and network excitability.

The ß subunit of voltage-gated Ca2+ channels

Calcium regulates a wide spectrum of physiological processes such as heartbeat, muscle contraction, neuronal communication, hormone release, cell division, and gene transcription. Major entryways for Ca(2+) in excitable cells are high-voltage activated (HVA) Ca(2+) channels. These are plasma membrane proteins composed of several subunits, including α(1), α(2)δ, β, and γ. Although the principal α(1) subunit (Ca(v)α(1)) contains the channel pore, gating machinery and most drug binding sites, the cytosolic auxiliary β subunit (Ca(v)β) plays an essential role in regulating the surface expression and gating properties of HVA Ca(2+) channels. Ca(v)β is also crucial for the modulation of HVA Ca(2+) channels by G proteins, kinases, and the Ras-related RGK GTPases. New proteins have emerged in recent years that modulate HVA Ca(2+) channels by binding to Ca(v)β. There are also indications that Ca(v)β may carry out Ca(2+) channel-independent functions, including directly regulating gene transcription. All four subtypes of Ca(v)β, encoded by different genes, have a modular organization, consisting of three variable regions, a conserved guanylate kinase (GK) domain, and a conserved Src-homology 3 (SH3) domain, placing them into the membrane-associated guanylate kinase (MAGUK) protein family. Crystal structures of Ca(v)βs reveal how they interact with Ca(v)α(1), open new research avenues, and prompt new inquiries. In this article, we review the structure and various biological functions of Ca(v)β, with both a historical perspective as well as an emphasis on recent advances.

Rab3-interacting molecule gamma isoforms lacking the Rab3-binding domain induce long lasting currents but block neurotransmitter vesicle anchoring in voltage-dependent P/Q-type Ca2+ channels

Assembly of voltage-dependent Ca(2+) channels (VDCCs) with their associated proteins regulates the coupling of VDCCs with upstream and downstream cellular events. Among the four isoforms of the Rab3-interacting molecule (RIM1 to -4), we have previously reported that VDCC beta-subunits physically interact with the long alpha isoform of the presynaptic active zone scaffolding protein RIM1 (RIM1alpha) via its C terminus containing the C(2)B domain. This interaction cooperates with RIM1alpha-Rab3 interaction to support neurotransmitter exocytosis by anchoring vesicles in the vicinity of VDCCs and by maintaining depolarization-triggered Ca(2+) influx as a result of marked inhibition of voltage-dependent inactivation of VDCCs. However, physiological functions have not yet been elucidated for RIM3 and RIM4, which exist only as short gamma isoforms (gamma-RIMs), carrying the C-terminal C(2)B domain common to RIMs but not the Rab3-binding region and other structural motifs present in the alpha-RIMs, including RIM1alpha. Here, we demonstrate that gamma-RIMs also exert prominent suppression of VDCC inactivation via direct binding to beta-subunits. In the pheochromocytoma PC12 cells, this common functional feature allows native RIMs to enhance acetylcholine secretion, whereas gamma-RIMs are uniquely different from alpha-RIMs in blocking localization of neurotransmitter-containing vesicles near the plasma membrane. Gamma-RIMs as well as alpha-RIMs show wide distribution in central neurons, but knockdown of gamma-RIMs attenuated glutamate release to a lesser extent than that of alpha-RIMs in cultured cerebellar neurons. The results suggest that sustained Ca(2+) influx through suppression of VDCC inactivation by RIMs is a ubiquitous property of neurons, whereas the extent of vesicle anchoring to VDCCs at the plasma membrane may depend on the competition of alpha-RIMs with gamma-RIMs for VDCC beta-subunits.

Fibroblast growth factor 2 induces apoptosis in the early primary culture of rat cortical neurons

In the central nervous system, fibroblast growth factor 2 (FGF2) is known to have important functions in cell survival and differentiation. In addition to its roles as a neurotrophic factor, we found that FGF2 caused cell death in the early primary culture of cortical neurons. FGF2-induced neuronal cell death showed apoptotic characters, e.g., chromatin condensation and DNA fragmentation. The ultrastructural morphology of FGF2-treated neurons indicated apoptotic features such as progressive cell shrinkage, blebbing of the plasma membrane, loss of cytosolic organelles, clumping of chromatin, and fragmentation of DNA. Tyrosine kinase inhibitors significantly rescued neurons from FGF2-induced apoptosis. FGF2 potentiated a marked influx of Ca(2+) into neurons before apoptosis. Both a calcium chelator and L-type voltage-sensitive Ca(2+) channel (L-VSCC) blockers attenuated FGF2-induced apoptosis, whereas other blockers of VSCCs such as N-type and P/Q-types did not. Blockers of L-VSCCs significantly suppressed FGF2-enhanced Ca(2+) influx into neurons. Moreover, FGF2 also generated reactive oxygen species (ROS) before apoptosis. Radical scavengers reduced not only the FGF2-generated ROS, but also the FGF2-induced Ca(2+) influx and apoptosis. In conclusion, we demonstrated that FGF2 caused apoptosis via L-VSCCs in the early neuronal culture.