Channelopathies in Cav1.1, Cav1.3, and Cav1.4 voltage-gated L-type Ca2+ channels

Opto-chemogenetic inhibition of L-type CaV1 channels in neurons through a membrane-assisted molecular linkage

Genetically encoded inhibitors of CaV1 channels that operate via C-terminus-mediated inhibition (CMI) have been actively pursued. Here, we advance the design of CMI peptides by proposing a membrane-anchoring tag that is sufficient to link the inhibitory modules to the target channel as well as chemical and optogenetic modes of system control. We designed and implemented the constitutive and inducible CMI modules with appropriate dynamic ranges for the short and long variants of CaV1.3, both naturally occurring in neurons. Upon optical (near-infrared-responsive nanoparticles) and/or chemical (rapamycin) induction of FRB/FKBP binding, the designed peptides translocated onto the membrane via FRB-Ras, where the physical linkage requirement for CMI could be satisfied. The peptides robustly produced acute, potent, and specific inhibitions on both recombinant and neuronal CaV1 activities, including Ca2+ influx-neuritogenesis coupling. Validated through opto-chemogenetic induction, this prototype demonstrates Ca2+ channel modulation via membrane-assisted molecular linkage, promising broad applicability to diverse membrane proteins.

Natural L-type calcium channels antagonists from Chinese medicine

L-type calcium channels (LTCCs), the largest subfamily of voltage-gated calcium channels (VGCCs), are the main channels for Ca2+ influx during extracellular excitation. LTCCs are widely present in excitable cells, especially cardiac and cardiovascular smooth muscle cells, and participate in various Ca2+-dependent processes. LTCCs have been considered as worthy drug target for cardiovascular, neurological and psychological diseases for decades. Natural products from Traditional Chinese medicine (TCM) have shown the potential as new drugs for the treatment of LTCCs related diseases. In this review, the basic structure, function of LTCCs, and the related human diseases caused by structural or functional abnormalities of LTCCs, and the natural LTCCs antagonist and their potential usages were summarized.

Characterization of two pathological gating-charge substitutions in Cav1.4 L-type calcium channels

Cav1.4 L-type calcium channels are predominantly expressed at the photoreceptor terminals and in bipolar cells, mediating neurotransmitter release. Mutations in its gene, CACNA1F, can cause congenital stationary night-blindness type 2 (CSNB2). Due to phenotypic variability in CSNB2, characterization of pathological variants is necessary to better determine pathological mechanism at the site of action. A set of known mutations affects conserved gating charges in the S4 voltage sensor, two of which have been found in male CSNB2 patients. Here, we describe two disease-causing Cav1.4 mutations with gating charge neutralization, exchanging an arginine 964 with glycine (RG) or arginine 1288 with leucine (RL). In both, charge neutralization was associated with a reduction channel expression also reflected in smaller ON gating currents. In RL channels, the strong decrease in whole-cell current densities might additionally be explained by a reduction of single-channel currents. We further identified alterations in their biophysical properties, such as a hyperpolarizing shift of the activation threshold and an increase in slope factor of activation and inactivation. Molecular dynamic simulations in RL substituted channels indicated water wires in both, resting and active, channel states, suggesting the development of omega (ω)currents as a new pathological mechanism in CSNB2. This sum of the respective channel property alterations might add to the differential symptoms in patients beside other factors, such as genomic and environmental deviations.

Regulation of Cardiac Cav1.2 Channels by Calmodulin

Cav1.2 Ca2+ channels, a type of voltage-gated L-type Ca2+ channel, are ubiquitously expressed, and the predominant Ca2+ channel type, in working cardiac myocytes. Cav1.2 channels are regulated by the direct interactions with calmodulin (CaM), a Ca2+-binding protein that causes Ca2+-dependent facilitation (CDF) and inactivation (CDI). Ca2+-free CaM (apoCaM) also contributes to the regulation of Cav1.2 channels. Furthermore, CaM indirectly affects channel activity by activating CaM-dependent enzymes, such as CaM-dependent protein kinase II and calcineurin (a CaM-dependent protein phosphatase). In this article, we review the recent progress in identifying the role of apoCaM in the channel ‘rundown’ phenomena and related repriming of channels, and CDF, as well as the role of Ca2+/CaM in CDI. In addition, the role of CaM in channel clustering is reviewed.

Case Report: Clinical delineation of CACNA1D mutation: New cases and literature review

Background

Calcium ions are involved in several human cellular processes; nevertheless, the relationship between calcium channelopathies (CCs) and autism spectrum disorder (ASD) or intellectual disability (ID) has been previously investigated. We delineate the spectrum of clinical phenotypes and the symptoms associated with a syndrome caused by an inherited gain-of-function mutation in CACNA1D in a family with a history of neuropsychiatric disorders. We also review the clinical and molecular phenotype of previously reported variants of CACNA1D.

Case presentation

We report the case of a 9-year-old female patient, diagnosed with ASD, severe ID, hyperactivity, and aggressive impulsive behaviors. The father, who was a 65-year-old at the time of his death, had ID and developed major depressive disorder with catatonic features and nihilistic delusion, followed by rapidly progressive dementia. He died after experiencing prolonged seizures followed by post-cardiac arrest. The patient's sister was a 30-year-old woman, known to have a severe ID with aggressive behaviors and sleep disorders. The sister has been diagnosed with bipolar disorder and psychosis. Through whole exome sequencing, a heterozygous previously identified and functionally characterized missense likely pathogenic variant was identified in the CACNA1D gene NM_001128840.3: c.2015C > T (p.Ser672Leu). These findings are consistent with the genetic diagnosis of autosomal dominant primary aldosteronism, seizures, and neurological abnormalities. This variant was found in the heterozygous status in the patient, her father, and her affected sister.

Conclusion

This case report will help to determine the key clinical features of this syndrome, which exhibits variable clinical presentations.

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

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

Selective posttranslational inhibition of CaVβ1-associated voltage-dependent calcium channels with a functionalized nanobody

Ca²⁺ influx through high-voltage-activated calcium channels (HVACCs) controls diverse cellular functions. A critical feature enabling a singular signal, Ca²⁺ influx, to mediate disparate functions is diversity of HVACC pore-forming α₁ and auxiliary Ca_Vβ₁-Ca_Vβ₄ subunits. Selective Ca_Vα₁ blockers have enabled deciphering their unique physiological roles. By contrast, the capacity to post-translationally inhibit HVACCs based on Ca_Vβ isoform is non-existent. Conventional gene knockout/shRNA approaches do not adequately address this deficit owing to subunit reshuffling and partially overlapping functions of Ca_Vβ isoforms. Here, we identify a nanobody (nb.E8) that selectively binds Ca_Vβ₁ SH3 domain and inhibits Ca_Vβ₁-associated HVACCs by reducing channel surface density, decreasing open probability, and speeding inactivation. Functionalizing nb.E8 with Nedd4L HECT domain yielded Chisel-1 which eliminated current through Ca_Vβ₁-reconstituted Ca_V1/Ca_V2 and native Ca_V1.1 channels in skeletal muscle, strongly suppressed depolarization-evoked Ca²⁺ influx and excitation-transcription coupling in hippocampal neurons, but was inert against Ca_Vβ₂-associated Ca_V1.2 in cardiomyocytes. The results introduce an original method for probing distinctive functions of ion channel auxiliary subunit isoforms, reveal additional dimensions of Ca_Vβ₁ signaling in neurons, and describe a genetically-encoded HVACC inhibitor with unique properties.

Intercommunication between Voltage-Gated Calcium Channels and Estrogen Receptor/Estrogen Signaling: Insights into Physiological and Pathological Conditions

Voltage-gated calcium channels (VGCCs) and estrogen receptors are important cellular proteins that have been shown to interact with each other across varied cells and tissues. Estrogen hormone, the ligand for estrogen receptors, can also exert its effects independent of estrogen receptors that collectively constitute non-genomic mechanisms. Here, we provide insights into the VGCC regulation by estrogen and the possible mechanisms involved therein across several cell types. Notably, most of the interaction is described in neuronal and cardiovascular tissues given the importance of VGCCs in these electrically excitable tissues. We describe the modulation of various VGCCs by estrogen known so far in physiological conditions and pathological conditions. We observed that in most in vitro studies higher concentrations of estrogen were used while a handful of in vivo studies used meager concentrations resulting in inhibition or upregulation of VGCCs, respectively. There is a need for more relevant physiological assays to study the regulation of VGCCs by estrogen. Additionally, other interacting receptors and partners need to be identified that may be involved in exerting estrogen receptor-independent effects of estrogen.

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.

Glutamate Signaling and Filopodiagenesis of Astrocytoma Cells in Brain Cancers: Survey and Questions

Astrocytes are non-excitable cells in the CNS that can cause life-threatening astrocytoma tumors when they transform to cancerous cells. Perturbed homeostasis of the neurotransmitter glutamate is associated with astrocytoma tumor onset and progression, but the factors that govern this phenomenon are less known. Herein, we review possible mechanisms by which glutamate may act in facilitating the growth of projections in astrocytic cells. This review discusses the similarities and differences between the morphology of astrocytes and astrocytoma cells, and the role that dysregulation in glutamate and calcium signaling plays in the aberrant morphology of astrocytoma cells. Converging reports suggest that ionotropic glutamate receptors and voltage-gated calcium channels expressed in astrocytes may be responsible for the abnormal filopodiagenesis or process extension leading to astrocytoma cells’ infiltration throughout the brain.

Small Molecules as Modulators of Voltage-Gated Calcium Channels in Neurological Disorders: State of the Art and Perspectives

Voltage-gated calcium channels (VGCCs) are widely expressed in the brain, heart and vessels, smooth and skeletal muscle, as well as in endocrine cells. VGCCs mediate gene transcription, synaptic and neuronal structural plasticity, muscle contraction, the release of hormones and neurotransmitters, and membrane excitability. Therefore, it is not surprising that VGCC dysfunction results in severe pathologies, such as cardiovascular conditions, neurological and psychiatric disorders, altered glycemic levels, and abnormal smooth muscle tone. The latest research findings and clinical evidence increasingly show the critical role played by VGCCs in autism spectrum disorders, Parkinson's disease, drug addiction, pain, and epilepsy. These findings outline the importance of developing selective calcium channel inhibitors and modulators to treat such prevailing conditions of the central nervous system. Several small molecules inhibiting calcium channels are currently used in clinical practice to successfully treat pain and cardiovascular conditions. However, the limited palette of molecules available and the emerging extent of VGCC pathophysiology require the development of additional drugs targeting these channels. Here, we provide an overview of the role of calcium channels in neurological disorders and discuss possible strategies to generate novel therapeutics.

Heterogeneity of glutamatergic synapses: cellular mechanisms and network consequences

Chemical synapses are commonly known as a structurally and functionally highly diverse class of cell-cell contacts specialized to mediate communication between neurons. They represent the smallest "computational" unit of the brain and are typically divided into excitatory and inhibitory as well as modulatory categories. These categories are subdivided into diverse types, each representing a different structure-function repertoire that in turn are thought to endow neuronal networks with distinct computational properties. The diversity of structure and function found among a given category of synapses is referred to as heterogeneity. The main building blocks for this heterogeneity are synaptic vesicles, the active zone, the synaptic cleft, the postsynaptic density, and glial processes associated with the synapse. Each of these five structural modules entails a distinct repertoire of functions, and their combination specifies the range of functional heterogeneity at mammalian excitatory synapses, which are the focus of this review. We describe synapse heterogeneity that is manifested on different levels of complexity ranging from the cellular morphology of the pre- and postsynaptic cells toward the expression of different protein isoforms at individual release sites. We attempt to define the range of structural building blocks that are used to vary the basic functional repertoire of excitatory synaptic contacts and discuss sources and general mechanisms of synapse heterogeneity. Finally, we explore the possible impact of synapse heterogeneity on neuronal network function.

Lighting Up the Plasma Membrane: Development and Applications of Fluorescent Ligands for Transmembrane Proteins

Despite the fact that transmembrane proteins represent the main therapeutic targets for decades, complete and in-depth knowledge about their biochemical and pharmacological profiling is not fully available. In this regard, target-tailored small-molecule fluorescent ligands are a viable approach to fill in the missing pieces of the puzzle. Such tools, coupled with the ability of high-precision optical techniques to image with an unprecedented resolution at a single-molecule level, helped unraveling many of the conundrums related to plasma proteins' life-cycle and druggability. Herein, we review the recent progress made during the last two decades in fluorescent ligand design and potential applications in fluorescence microscopy of voltage-gated ion channels, ligand-gated ion channels and G-coupled protein receptors.

Hydroxysafflor Yellow A Ameliorates Myocardial Ischemia/Reperfusion Injury by Suppressing Calcium Overload and Apoptosis

Myocardial ischemia/reperfusion injury (MI/RI) is an urgent problem with a great impact on health globally. However, its pathological mechanisms have not been fully elucidated. Hydroxysafflor yellow A (HSYA) has a protective effect against MI/RI. This study is aimed at further clarifying the relationship between HSYA cardioprotection and calcium overload as well as the underlying mechanisms. We verified the protective effect of HSYA on neonatal rat primary cardiomyocytes (NPCMs) and human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) from hypoxia-reoxygenation (HR) injury. To explore the cardioprotective mechanism of HSYA, we employed calcium fluorescence, TUNEL assay, JC-1 staining, and western blotting. Finally, cardio-ECR and patch-clamp experiments were used to explain the regulation of L-type calcium channels (LTCC) in cardioprotection mediated by HSYA. The results showed that HSYA reduced the levels of myocardial enzymes and protected NPCMs from HR injury. HSYA also restored the contractile function of hiPSC-CMs and field potential signal abnormalities caused by HR and exerted a protective effect on cardiac function. Further, we demonstrated that HSYA protects cardiomyocytes from HR injury by decreasing mitochondrial membrane potential and inhibiting apoptosis and calcium overload. Patch-clamp results revealed that MI/RI caused a sharp increase in calcium currents, which was inhibited by pretreatment with HSYA. Furthermore, we found that HSYA restored contraction amplitude, beat rate, and field potential duration of hiPSC-CMs, which were disrupted by the LTCC agonist Bay-K8644. Patch-clamp experiments also showed that HSYA inhibits Bay-K8644-induced calcium current, with an effect similar to that of the LTCC inhibitor nisoldipine. Therefore, our data suggest that HSYA targets LTCC to inhibit calcium overload and apoptosis of cardiomyocytes, thereby exerting a cardioprotective effect and reducing MI/RI injury.

Design of an Imaging Probe to Monitor Real-Time Redistribution of L-type Voltage-Gated Calcium Channels in Astrocytic Glutamate Signaling

PURPOSE

In the brain, astrocytes are non-excitable cells that undergo rapid morphological changes when stimulated by the excitatory neurotransmitter glutamate. We developed a chemical probe to monitor how glutamate affects the density and distribution of astrocytic L-type voltage-gated calcium channels (LTCC).

PROCEDURES

The imaging probe FluoBar1 was created from a barbiturate ligand modified with a fluorescent coumarin moiety. The probe selectivity was examined with colocalization analyses of confocal fluorescence imaging in U118-MG and transfected COS-7 cells. Living cells treated with 50 nM FluoBar1 were imaged in real time to reveal changes in density and distribution of astrocytic LTCCs upon exposure to glutamate.

RESULTS

FluoBar1 was synthesized in ten steps. The selectivity of the probe was demonstrated with immunoblotting and confocal imaging of immunostained cells expressing the Ca_V1.2 isoform of LTCCs proteins. Applying FluoBar1 to astrocyte model cells U118-MG allowed us to measure a fivefold increase in fluorescence density of LTCCs upon glutamate exposure.

CONCLUSIONS

Imaging probe FluoBar1 allows the real-time monitoring of LTCCs in living cells, revealing for first time that glutamate causes a rapid increase of LTCC membranar density in astrocyte model cells. FluoBar1 may help tackle previously intractable questions about LTCC dynamics in cellular events.

Effects of selective calcium channel blockers on ions' permeation through the human Cav1.2 ion channel: A computational study

Selective calcium channel antagonists are widely used in the treatment of cardiovascular disorders. They are mainly classified into 1,4-dihydropyridine (1,4-DHPs) and non-DHPs. The non-DHPs class is further classified into phenylalkylamines (PAAs) and benzothiazepines (BZTs) derivatives. These blockers are used for the treatment of hypertension, angina pectoris, and cardiac arrhythmias. Despite their well-established efficiency, the structural basis behind their activity is not very clear. Here we report the use of a near-open confirmation (NOC) model of the Cav1.2 cardiac ion channel to examine the mode of binding of these antagonists within the pore domain as well as the fenestration of the pore-forming domains. Effects of calcium ion permeation in the presence of drug molecules were assessed using steered molecular dynamics (SMD) simulations. These studies reveal that nicardipine, a DHP derivative, shows a strong Cav1.2 blocking activity, requiring more 2500 pN force to pull calcium ion towards the channel's pore in the presence of the compound. Similar blocking activity was observed for verapamil, a PAA derivative, requiring almost 2300 pN of force. The least blocking activity was observed for Diltiazem, a BZT derivative. Our results explain the structural basis and the binding details of 1,4-DHPs, PAAs and BZTs at their distinct Cav1.2 sites and offer detailed insights into their mechanism of action in modulating the Cav1.2 channel.

Calenduloside E suppresses calcium overload by promoting the interaction between L-type calcium channels and Bcl2-associated athanogene 3 to alleviate myocardial ischemia/reperfusion injury

Introduction

Intracellular calcium overload is an important contributor to myocardial ischemia/reperfusion (MI/R) injury. Total saponins of the traditional Chinese medicinal plant Aralia elata (Miq.) Seem. (AS) are beneficial for treating MI/R injury, and Calenduloside E (CE) is the main active ingredient of AS.

Objectives

This study aimed to investigate the effects of CE on MI/R injury and determine its specific regulatory mechanisms.

Methods

To verify whether CE mediated cardiac protection in vivo and in vitro, we performed MI/R surgery in SD rats and subjected neonatal rat ventricular myocytes (NRVMs) to hypoxia-reoxygenation (HR). CE’s cardioprotective against MI/R injury was detected by Evans blue/TTC staining, echocardiography, HE staining, myocardial enzyme levels. Impedance and field potential recording, and patch-clamp techniques of human-induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) were used to detect the function of L-type calcium channels (LTCC). The mechanisms underlying between CE and LTCC was studied through western blot, immunofluorescence, and immunohistochemistry. Drug affinity responsive target stability (DARTS) and co-immunoprecipitation (co-IP) used to further clarify the effect of CE on LTCC and BAG3.

Results

We found that CE protected against MI/R injury by inhibiting calcium overload. Furthermore, CE improved contraction and field potential signals of hiPSC-CMs and restored sarcomere contraction and calcium transient of adult rat ventricular myocytes (ARVMs). Moreover, patch-clamp data showed that CE suppressed increased L-type calcium current (I_Ca,L) caused by LTCC agonist, proving that CE could regulate calcium homeostasis through LTCC. Importantly, we found that CE promoted the interaction between LTCC and Bcl2-associated athanogene 3 (BAG3) by co-IP and DARTS.

Conclusion

Our results demonstrate that CE enhanced LTCC-BAG3 interaction to reduce MI/R induced-calcium overload, exerting a cardioprotective effect.

A Single Amino Acid Determines the Selectivity and Efficacy of Selective Negative Allosteric Modulators of CaV1.3 L-Type Calcium Channels

Ca²⁺ channels with a Ca_V1.3 pore-forming α₁ subunit have been implicated in both neurodegenerative and neuropsychiatric disorders, motivating the development of selective and potent inhibitors of Ca_V1.3 versus Ca_V1.2 channels, the calcium channels implicated in hypertensive disorders. We have previously identified pyrimidine-2,4,6-triones (PYTs) that preferentially inhibit Ca_V1.3 channels, but the structural determinants of their interaction with the channel have not been identified, impeding their development into drugs. By a combination of biochemical, computational, and molecular biological approaches, it was found that PYTs bind to the dihydropyridine (DHP) binding pocket of the Ca_V1.3 subunit, establishing them as negative allosteric modulators of channel gating. Site-directed mutagenesis, based on homology models of Ca_V1.3 and Ca_V1.2 channels, revealed that a single amino acid residue within the DHP binding pocket (M1078) is responsible for the selectivity of PYTs for Ca_V1.3 over Ca_V1.2. In addition to providing direction for chemical optimization, these results suggest that, like dihydropyridines, PYTs have pharmacological features that could make them of broad clinical utility.

Using an integrative machine learning approach utilising homology modelling to clinically interpret genetic variants: CACNA1F as an exemplar

Advances in DNA sequencing technologies have revolutionised rare disease diagnostics and have led to a dramatic increase in the volume of available genomic data. A key challenge that needs to be overcome to realise the full potential of these technologies is that of precisely predicting the effect of genetic variants on molecular and organismal phenotypes. Notably, despite recent progress, there is still a lack of robust in silico tools that accurately assign clinical significance to variants. Genetic alterations in the CACNA1F gene are the commonest cause of X-linked incomplete Congenital Stationary Night Blindness (iCSNB), a condition associated with non-progressive visual impairment. We combined genetic and homology modelling data to produce CACNA1F-vp, an in silico model that differentiates disease-implicated from benign missense CACNA1F changes. CACNA1F-vp predicts variant effects on the structure of the CACNA1F encoded protein (a calcium channel) using parameters based upon changes in amino acid properties; these include size, charge, hydrophobicity, and position. The model produces an overall score for each variant that can be used to predict its pathogenicity. CACNA1F-vp outperformed four other tools in identifying disease-implicated variants (area under receiver operating characteristic and precision recall curves = 0.84; Matthews correlation coefficient = 0.52) using a tenfold cross-validation technique. We consider this protein-specific model to be a robust stand-alone diagnostic classifier that could be replicated in other proteins and could enable precise and timely diagnosis.

Mutations in transmembrane proteins: diseases, evolutionary insights, prediction and comparison with globular proteins

Membrane proteins are unique in that they interact with lipid bilayers, making them indispensable for transporting molecules and relaying signals between and across cells. Due to the significance of the protein's functions, mutations often have profound effects on the fitness of the host. This is apparent both from experimental studies, which implicated numerous missense variants in diseases, as well as from evolutionary signals that allow elucidating the physicochemical constraints that intermembrane and aqueous environments bring. In this review, we report on the current state of knowledge acquired on missense variants (referred to as to single amino acid variants) affecting membrane proteins as well as the insights that can be extrapolated from data already available. This includes an overview of the annotations for membrane protein variants that have been collated within databases dedicated to the topic, bioinformatics approaches that leverage evolutionary information in order to shed light on previously uncharacterized membrane protein structures or interaction interfaces, tools for predicting the effects of mutations tailored specifically towards the characteristics of membrane proteins as well as two clinically relevant case studies explaining the implications of mutated membrane proteins in cancer and cardiomyopathy.

Elementary calcium signaling in arterial smooth muscle

Vascular smooth muscle cells (VSMCs) of small peripheral arteries contribute to blood pressure control by adapting their contractile state. These adaptations depend on the VSMC cytosolic Ca²⁺ concentration, regulated by complex local elementary Ca²⁺ signaling pathways. Ca²⁺ sparks represent local, transient, rapid calcium release events from a cluster of ryanodine receptors (RyRs) in the sarcoplasmic reticulum. In arterial SMCs, Ca²⁺ sparks activate nearby calcium-dependent potassium channels, cause membrane hyperpolarization and thus decrease the global intracellular [Ca²⁺] to oppose vasoconstriction. Arterial SMC Ca_v1.2 L-type channels regulate intracellular calcium stores content, which in turn modulates calcium efflux through RyRs. Ca_v3.2 T-type channels contribute to a minor extend to Ca²⁺ spark generation in certain types of arteries. Their localization within cell membrane caveolae is essential. We summarize present data on local elementary calcium signaling (Ca²⁺ sparks) in arterial SMCs with focus on RyR isoforms, large-conductance calcium-dependent potassium (BK_Ca) channels, and cell membrane-bound calcium channels (Ca_v1.2 and Ca_v3.2), particularly in caveolar microdomains.

De novo CACNA1D Ca2+ channelopathies: clinical phenotypes and molecular mechanism

The identification of rare disease-causing variants in humans by large-scale next-generation sequencing (NGS) studies has also provided us with new insights into the pathophysiological role of de novo missense variants in the CACNA1D gene that encodes the pore-forming α1-subunit of voltage-gated Cav1.3 L-type Ca2+ channels. These CACNA1D variants have been identified somatically in aldosterone-producing adenomas as well as germline in patients with neurodevelopmental and in some cases endocrine symptoms. In vitro studies in heterologous expression systems have revealed typical gating changes that indicate enhanced Ca2+ influx through Cav1.3 channels as the underlying disease-causing mechanism. Here we summarize the clinical findings of 12 well-characterized individuals with a total of 9 high-risk pathogenic CACNA1D variants. Moreover, we propose how information from somatic mutations in aldosterone-producing adenomas could be used to predict the potential pathogenicity of novel germline variants. Since these pathogenic de novo variants can cause a channel-gain-of function, we also discuss the use of L-type Ca2+ channel blockers as a potential therapeutic option.

Targeting Calcium Homeostasis in Myocardial Ischemia/Reperfusion Injury: An Overview of Regulatory Mechanisms and Therapeutic Reagents

Calcium homeostasis plays an essential role in maintaining excitation–contraction coupling (ECC) in cardiomyocytes, including calcium release, recapture, and storage. Disruption of calcium homeostasis may affect heart function, leading to the development of various heart diseases. Myocardial ischemia/reperfusion (MI/R) injury may occur after revascularization, which is a treatment used in coronary heart disease. MI/R injury is a complex pathological process, and the main cause of increased mortality and disability after treatment of coronary heart disease. However, current methods and drugs for treating MI/R injury are very scarce, not ideal, and have limitations. Studies have shown that MI/R injury can cause calcium overload that can further aggravate MI/R injury. Therefore, we reviewed the effects of critical calcium pathway regulators on MI/R injury and drew an intuitive diagram of the calcium homeostasis pathway. We also summarized and analyzed calcium pathway-related or MI/R drugs under research or marketing by searching Therapeutic Target and PubMed Databases. The data analysis showed that six drugs and corresponding targets are used to treat MI/R injury and involved in calcium signaling pathways. We emphasize the relevance of further detailed investigation of MI/R injury and calcium homeostasis and the therapeutic role of calcium homeostasis in MI/R injury, which bridges basic research and clinical applications of MI/R injury.

Gating defects of disease-causing de novo mutations in Cav1.3 Ca2+ channels

Recently, we and others identified somatic and germline de novo gain-of-function mutations in CACNA1D, the gene encoding the α1-subunit of voltage-gated Ca_v1.3 Ca²⁺-channels. While somatic mutations identified in aldosterone producing adenomas (APAs) underlie treatment-resistant hypertension, germline CACNA1D mutations are associated with a neurodevelopmental disorder characterized by a wide symptomatic spectrum, including autism spectrum disorder. The number of newly identified CACNA1D missense mutations is constantly growing, but their pathogenic potential is difficult to predict in silico, making functional studies indispensable to assess their contribution to disease risk.

Here we report the functional characterization of previously identified CACNA1D APA mutations F747L and M1354I using whole-cell patch-clamp electrophysiology upon recombinant expression in tsA-201 cells. We also investigated if alternative splicing of Ca_v1.3 affects the aberrant gating of the previously characterized APA mutation R990H and two mutations associated with autism spectrum disorder (A479G and G407R). Splice-variant dependent gating changes are of particular interest for germline mutations, since the relative expression of Ca_v1.3 splice variants differs across different tissues and within brain regions and might therefore result in tissue-specific phenotypes. Our data revealed a complex gain-of-function phenotype for APA mutation F747L confirming its pathogenic role. Furthermore, we found splice-variant dependent gating changes in R990H, A749G and G407R. M1354I did not change channel function of Ca_v1.3 splice variants and should therefore be considered a rare non-pathogenic variant until further proof for its pathogenicity is obtained. Our new findings together with previously published data allow classification of pathogenic CACNA1D mutations into four categories based on prototypical functional changes.

Rescue of Rod Synapses by Induction of Cav Alpha 1F in the Mature Cav1.4 Knock-Out Mouse Retina

Purpose

Cav1.4 is a voltage-gated calcium channel clustered at the presynaptic active zones of photoreceptors. Cav1.4 functions in communication by mediating the Ca2+ influx that triggers neurotransmitter release. It also aids in development since rod ribbon synapses do not form in Cav1.4 knock-out mice. Here we used a rescue strategy to investigate the ability of Cav1.4 to trigger synaptogenesis in both immature and mature mouse rods.

Methods

In vivo electroporation was used to transiently express Cav α1F or tamoxifen-inducible Cav α1F in a subset of Cav1.4 knock-out mouse rods. Synaptogenesis was assayed using morphologic markers and a vision-guided water maze.

Results

We found that introduction of Cav α1F to knock-out terminals rescued synaptic development as indicated by PSD-95 expression and elongated ribbons. When expression of Cav α1F was induced in mature animals, we again found restoration of PSD-95 and elongated ribbons. However, the induced expression of Cav α1F led to diffuse distribution of Cav α1F in the terminal instead of being clustered beneath the ribbon. Approximately a quarter of treated animals passed the water maze test, suggesting the rescue of retinal signaling in these mice.

Conclusions

These data confirm that Cav α1F expression is necessary for rod synaptic terminal development and demonstrate that rescue is robust even in adult animals with late stages of synaptic disease. The degree of rod synaptic plasticity seen here should be sufficient to support future vision-restoring treatments such as gene or cell replacement that will require photoreceptor synaptic rewiring.

The Transfer Characteristics of Hair Cells Encoding Mechanical Stimuli in the Lateral Line of Zebrafish

Hair cells transmit mechanical information by converting deflection of the hair bundle into synaptic release of glutamate. We have investigated this process in the lateral line of larval zebrafish (male and female) to understand how stimuli are encoded within a neuromast. Using multiphoton microscopy in vivo, we imaged synaptic release of glutamate using the reporter iGluSnFR as well as deflections of the cupula. We found that the neuromast is composed of a functionally diverse population of hair cells. Half the hair cells signaled cupula motion in both directions from rest, either by increasing glutamate release in response to a deflection in the positive direction or by reducing release in the negative direction. The relationship between cupula deflection and glutamate release demonstrated maximum sensitivity at displacements of just ∼40 nm in the positive direction. The remaining hair cells only signaled motion in one direction and were less sensitive, extending the operating range of the neuromast beyond 1 μm. Adaptation of the synaptic output was also heterogeneous, with some hair cells generating sustained glutamate release in response to a steady deflection of the cupula and others generating transient outputs. Finally, a distinct signal encoded a return of the cupula to rest: a large and transient burst of glutamate release from hair cells unresponsive to the initial stimulus. A population of hair cells with these different sensitivities, operating ranges, and adaptive properties will allow the neuromast to encode weak stimuli while maintaining the dynamic range to signal the amplitude and duration of stronger deflections.

SIGNIFICANCE STATEMENT Hair cells transmit information about mechanical stimuli by converting very small deflections of their hair bundle into changes in the release of the neurotransmitter glutamate. We have measured this input/output relation in the live fish using a fluorescent protein and find that different hair cells vary in their mechanical sensitivity and the time course of their response. These variations will allow the fish to sense the timing and duration of both very weak stimuli (∼40 nm deflections) and strong stimuli (∼1 μm), underlying the ability of the fish to avoid predators and maintain its body position in flowing water.

Allosteric regulators selectively prevent Ca2+-feedback of CaV and NaV channels

Calmodulin (CaM) serves as a pervasive regulatory subunit of Ca_V1, Ca_V2, and Na_V1 channels, exploiting a functionally conserved carboxy-tail element to afford dynamic Ca²⁺-feedback of cellular excitability in neurons and cardiomyocytes. Yet this modularity counters functional adaptability, as global changes in ambient CaM indiscriminately alter its targets. Here, we demonstrate that two structurally unrelated proteins, SH3 and cysteine-rich domain (stac) and fibroblast growth factor homologous factors (fhf) selectively diminish Ca²⁺/CaM-regulation of Ca_V1 and Na_V1 families, respectively. The two proteins operate on allosteric sites within upstream portions of respective channel carboxy-tails, distinct from the CaM-binding interface. Generalizing this mechanism, insertion of a short RxxK binding motif into Ca_V1.3 carboxy-tail confers synthetic switching of CaM regulation by Mona SH3 domain. Overall, our findings identify a general class of auxiliary proteins that modify Ca²⁺/CaM signaling to individual targets allowing spatial and temporal orchestration of feedback, and outline strategies for engineering Ca²⁺/CaM signaling to individual targets.

Calcium channel gating

Tuned calcium entry through voltage-gated calcium channels is a key requirement for many cellular functions. This is ensured by channel gates which open during membrane depolarizations and seal the pore at rest. The gating process is determined by distinct sub-processes: movement of voltage-sensing domains (charged S4 segments) as well as opening and closure of S6 gates. Neutralization of S4 charges revealed that pore opening of CaV1.2 is triggered by a "gate releasing" movement of all four S4 segments with activation of IS4 (and IIIS4) being a rate-limiting stage. Segment IS4 additionally plays a crucial role in channel inactivation. Remarkably, S4 segments carrying only a single charged residue efficiently participate in gating. However, the complete set of S4 charges is required for stabilization of the open state. Voltage clamp fluorometry, the cryo-EM structure of a mammalian calcium channel, biophysical and pharmacological studies, and mathematical simulations have all contributed to a novel interpretation of the role of voltage sensors in channel opening, closure, and inactivation. We illustrate the role of the different methodologies in gating studies and discuss the key molecular events leading CaV channels to open and to close.

Role of a conserved glutamine in the function of voltage-gated Ca2+ channels revealed by a mutation in human CACNA1D

Voltage-gated Ca_v Ca²⁺ channels play crucial roles in regulating gene transcription, neuronal excitability, and synaptic transmission. Natural or pathological variations in Ca_v channels have yielded rich insights into the molecular determinants controlling channel function. Here, we report the consequences of a natural, putatively disease-associated mutation in the CACNA1D gene encoding the pore-forming Ca_v1.3 α₁ subunit. The mutation causes a substitution of a glutamine residue that is highly conserved in the extracellular S1-S2 loop of domain II in all Ca_v channels with a histidine and was identified by whole-exome sequencing of an individual with moderate hearing impairment, developmental delay, and epilepsy. When introduced into the rat Ca_v1.3 cDNA, Q558H significantly decreased the density of Ca²⁺ currents in transfected HEK293T cells. Gating current analyses and cell-surface biotinylation experiments suggested that the smaller current amplitudes caused by Q558H were because of decreased numbers of functional Ca_v1.3 channels at the cell surface. The substitution also produced more sustained Ca²⁺ currents by weakening voltage-dependent inactivation. When inserted into the corresponding locus of Ca_v2.1, the substitution had similar effects as in Ca_v1.3. However, the substitution introduced in Ca_v3.1 reduced current density, but had no effects on voltage-dependent inactivation. Our results reveal a critical extracellular determinant of current density for all Ca_v family members and of voltage-dependent inactivation of Ca_v1.3 and Ca_v2.1 channels.

Channeling Vision: CaV1.4-A Critical Link in Retinal Signal Transmission

Voltage-gated calcium channels (VGCC) are key to many biological functions. Entry of Ca2+ into cells is essential for initiating or modulating important processes such as secretion, cell motility, and gene transcription. In the retina and other neural tissues, one of the major roles of Ca2+-entry is to stimulate or regulate exocytosis of synaptic vesicles, without which synaptic transmission is impaired. This review will address the special properties of one L-type VGCC, CaV1.4, with particular emphasis on its role in transmission of visual signals from rod and cone photoreceptors (hereafter called "photoreceptors," to the exclusion of intrinsically photoreceptive retinal ganglion cells) to the second-order retinal neurons, and the pathological effects of mutations in the CACNA1F gene which codes for the pore-forming α1F subunit of CaV1.4.

Bilobal architecture is a requirement for calmodulin signaling to CaV1.3 channels

Calmodulin (CaM) regulation of voltage-gated calcium (Ca_V) channels is a powerful Ca²⁺ feedback mechanism that adjusts Ca²⁺ influx, affording rich mechanistic insights into Ca²⁺ decoding. CaM possesses a dual-lobed architecture, a salient feature of the myriad Ca²⁺-sensing proteins, where two homologous lobes that recognize similar targets hint at redundant signaling mechanisms. Here, by tethering CaM lobes, we demonstrate that bilobal architecture is obligatory for signaling to Ca_V channels. With one lobe bound, Ca_V carboxy tail rearranges itself, resulting in a preinhibited configuration precluded from Ca²⁺ feedback. Reconstitution of two lobes, even as separate molecules, relieves preinhibition and restores Ca²⁺ feedback. Ca_V channels thus detect the coincident binding of two Ca²⁺-free lobes to promote channel opening, a molecular implementation of a logical NOR operation that processes spatiotemporal Ca²⁺ signals bifurcated by CaM lobes. Overall, a unified scheme of Ca_V channel regulation by CaM now emerges, and our findings highlight the versatility of CaM to perform exquisite Ca²⁺ computations.

Transcriptional regulation of voltage-gated Ca2+ channels

The transcriptional regulation of voltage-gated Ca²⁺ (Ca_V ) channels is an emerging research area that promises to improve our understanding of how many relevant physiological events are shaped in the central nervous system, the skeletal muscle and other tissues. Interestingly, a picture of how transcription of Ca_V channel subunit genes is controlled is evolving with the identification of the promoter regions required for tissue-specific expression and the identification of transcription factors that control their expression. These promoters share several characteristics that include multiple transcriptional start sites, lack of a TATA box and the presence of elements conferring tissue-selective expression. Likewise, changes in Ca_V channel expression occur throughout development, following ischaemia, seizures or chronic drug administration. This review focuses on insights achieved regarding the control of Ca_V channel gene expression. To further understand the complexities of expression and to increase the possibilities of detecting Ca_V channel alterations causing human disease, a deeper knowledge on the structure of the 5' upstream regions of the genes encoding these remarkable proteins will be necessary.

Mechanisms Responsible for ω-Pore Currents in Cav Calcium Channel Voltage-Sensing Domains

Mutations of positively charged amino acids in the S4 transmembrane segment of a voltage-gated ion channel form ion-conducting pathways through the voltage-sensing domain, named ω-current. Here, we used structure modeling and MD simulations to predict pathogenic ω-currents in Ca_V1.1 and Ca_V1.3 Ca²⁺ channels bearing several S4 charge mutations. Our modeling predicts that mutations of Ca_V1.1-R1 (R528H/G, R897S) or Ca_V1.1-R2 (R900S, R1239H) linked to hypokalemic periodic paralysis type 1 and of Ca_V1.3-R3 (R990H) identified in aldosterone-producing adenomas conducts ω-currents in resting state, but not during voltage-sensing domain activation. The mechanism responsible for the ω-current and its amplitude depend on the number of charges in S4, the position of the mutated S4 charge and countercharges, and the nature of the replacing amino acid. Functional characterization validates the modeling prediction showing that Ca_V1.3-R990H channels conduct ω-currents at hyperpolarizing potentials, but not upon membrane depolarization compared with wild-type channels.

Src-family tyrosine kinases and the Ca2+ signal

In this review, we shall describe the rich crosstalk between non-receptor Src-family kinases (SFKs) and the Ca²⁺ transient generated in activated cells by a variety of extracellular and intracellular stimuli, resulting in diverse signaling events. The exchange of information between SFKs and Ca²⁺ is reciprocal, as it flows in both directions. These kinases are main actors in pathways leading to the generation of the Ca²⁺ signal, and reciprocally, the Ca²⁺ signal modulates SFKs activity and functions. We will cover how SFKs participate in the generation of the cytosolic Ca²⁺ rise upon activation of a series of receptors and the mechanism of clearance of this Ca²⁺ signal. The role of SFKs modulating Ca²⁺-translocating channels participating in these events will be amply discussed. Finally, the role of the Ca²⁺ sensor protein calmodulin on the activity of c-Src, and potentially on other SFKs, will be outlined as well. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Measuring Ca2+-Dependent Modulation of Voltage-Gated Ca2+ Channels in HEK-293T Cells

Voltage-gated Ca(2+) (Cav) channels regulate a variety of biological processes, such as muscle contraction, gene expression, and neurotransmitter release. Cav channels are subject to diverse forms of regulation, including those involving the Ca(2+) ions that permeate the pore. High voltage-activated Cav channels undergo Ca(2+)-dependent inactivation (CDI) and facilitation (CDF), which can regulate processes such as cardiac rhythm and synaptic plasticity. CDI and CDF differ slightly between Cav1 (L-type) and Cav2 (P/Q-, N-, and R-type) channels. Human embryonic kidney cells transformed with SV40 large T-antigen (HEK-293T) are advantageous for studying CDI and CDF of a particular type of Cav channel. HEK-293T cells do not express endogenous Cav channels, but Cav channels can be expressed exogenously at high levels in these cells by transient transfection. This protocol describes how to characterize and analyze Ca(2+)-dependent modulation of recombinant Cav channels in HEK-293T cells.

Towards a Unified Theory of Calmodulin Regulation (Calmodulation) of Voltage-Gated Calcium and Sodium Channels

Voltage-gated Na and Ca(2+) channels represent two major ion channel families that enable myriad biological functions including the generation of action potentials and the coupling of electrical and chemical signaling in cells. Calmodulin regulation (calmodulation) of these ion channels comprises a vital feedback mechanism with distinct physiological implications. Though long-sought, a shared understanding of the channel families remained elusive for two decades as the functional manifestations and the structural underpinnings of this modulation often appeared to diverge. Here, we review recent advancements in the understanding of calmodulation of Ca(2+) and Na channels that suggest a remarkable similarity in their regulatory scheme. This interrelation between the two channel families now paves the way towards a unified mechanistic framework to understand vital calmodulin-dependent feedback and offers shared principles to approach related channelopathic diseases. An exciting era of synergistic study now looms.

CaV channels and cancer: canonical functions indicate benefits of repurposed drugs as cancer therapeutics

The importance of ion channels in the hallmarks of many cancers is increasingly recognised. This article reviews current knowledge of the expression of members of the voltage-gated calcium channel family (Ca_V) in cancer at the gene and protein level and discusses their potential functional roles. The ten members of the Ca_V channel family are classified according to expression of their pore-forming α-subunit; moreover, co-expression of accessory α2δ, β and γ confers a spectrum of biophysical characteristics including voltage dependence of activation and inactivation, current amplitude and activation/inactivation kinetics. Ca_V channels have traditionally been studied in excitable cells including neurones, smooth muscle, skeletal muscle and cardiac cells, and drugs targeting the channels are used in the treatment of hypertension and epilepsy. There is emerging evidence that several Ca_V channels are differentially expressed in cancer cells compared to their normal counterparts. Interestingly, a number of Ca_V channels also have non-canonical functions and are involved in transcriptional regulation of the expression of other proteins including potassium channels. Pharmacological studies show that Ca_V canonical function contributes to the fundamental biology of proliferation, cell-cycle progression and apoptosis. This raises the intriguing possibility that calcium channel blockers, approved for the treatment of other conditions, could be repurposed to treat particular cancers. Further research will reveal the full extent of both the canonical and non-canonical functions of Ca_V channels in cancer and whether calcium channel blockers are beneficial in cancer treatment.

GDF-15 enhances intracellular Ca2+ by increasing Cav1.3 expression in rat cerebellar granule neurons

GDF-15 (growth/differentiation factor 15) is a novel member of the TGF (transforming growth factor)-β superfamily that has critical roles in the central and peripheral nervous systems. We reported previously that GDF-15 increased delayed rectifier outward K⁺ currents and K_v2.1 α subunit expression through TβRII (TGF-β receptor II) to activate Src kinase and Akt/mTOR (mammalian target of rapamycin) signalling in rat CGNs (cerebellar granule neurons). In the present study, we found that treatment of CGNs with GDF-15 for 24 h increased the intracellular Ca²⁺ concentration ([Ca²⁺]_i) in response to membrane depolarization, as determined by Ca²⁺ imaging. Whole-cell current recordings indicated that GDF-15 increased the inward Ca²⁺ current (I_Ca) without altering steady-state activation of Ca²⁺ channels. Treatment with nifedipine, an inhibitor of L-type Ca²⁺ channels, abrogated GDF-15-induced increases in [Ca²⁺]_i and I_Ca. The GDF-15-induced increase in I_Ca was mediated via up-regulation of the Ca_v1.3 α subunit, which was attenuated by inhibiting Akt/mTOR and ERK (extracellular-signal-regulated kinase) pathways and by pharmacological inhibition of Src-mediated TβRII phosphorylation. Given that Ca_v1.3 is not only a channel for Ca²⁺ influx, but also a transcriptional regulator, our data confirm that GDF-15 induces protein expression via TβRII and activation of a non-Smad pathway, and provide novel insight into the mechanism of GDF-15 function in neurons.

Harnessing the Flow of Excitation: TRP, Voltage-Gated Na(+), and Voltage-Gated Ca(2+) Channels in Contemporary Medicine

Cellular signaling in both excitable and nonexcitable cells involves several classes of ion channels. Some of them are of minor importance, with very specialized roles in physiology, but here we concentrate on three major channel classes: TRP (transient receptor potential channels), voltage-gated sodium channels (Nav), and voltage-gated calcium channels (Cav). Here, we first propose a conceptual framework binding together all three classes of ion channels, a "flow-of-excitation model" that takes into account the inputs mediated by TRP and other similar channels, the outputs invariably provided by Cav channels, and the regenerative transmission of signals in the neural networks, for which Nav channels are responsible. We use this framework to examine the function, structure, and pharmacology of these channel classes both at cellular and also at whole-body physiological level. Building on that basis we go through the pathologies arising from the direct or indirect malfunction of the channels, utilizing ion channel defects, the channelopathies. The pharmacological interventions affecting these channels are numerous. Part of those are well-established treatments, like treatment of hypertension or some forms of epilepsy, but many other are deeply problematic due to poor drug specificity, ion channel diversity, and widespread expression of the channels in tissues other than those actually targeted.

Ribbon Synapses and Visual Processing in the Retina

The first synapses transmitting visual information contain an unusual organelle, the ribbon, which is involved in the transport and priming of vesicles to be released at the active zone. The ribbon is one of many design features that allow efficient refilling of the active zone, which in turn enables graded changes in membrane potential to be transmitted using a continuous mode of neurotransmitter release. The ribbon also plays a key role in supplying vesicles for rapid and transient bursts of release that signal fast changes, such as the onset of light. We increasingly understand how the physiological properties of ribbon synapses determine basic transformations of the visual signal and, in particular, how the process of refilling the active zone regulates the gain and adaptive properties of the retinal circuit. The molecular basis of ribbon function is, however, far from clear.

Novel somatic mutations and distinct molecular signature in aldosterone-producing adenomas

Aldosterone-producing adenomas (APAs) are found in 1.5-3.0% of hypertensive patients in primary care and can be cured by surgery. Elucidation of genetic events may improve our understanding of these tumors and ultimately improve patient care. Approximately 40% of APAs harbor a missense mutation in the KCNJ5 gene. More recently, somatic mutations in CACNA1D, ATP1A1 and ATP2B3, also important for membrane potential/intracellular Ca(2) (+) regulation, were observed in APAs. In this study, we analyzed 165 APAs for mutations in selected regions of these genes. We then correlated mutational findings with clinical and molecular phenotype using transcriptome analysis, immunohistochemistry and semiquantitative PCR. Somatic mutations in CACNA1D in 3.0% (one novel mutation), ATP1A1 in 6.1% (six novel mutations) and ATP2B3 in 3.0% (two novel mutations) were detected. All observed mutations were located in previously described hotspot regions. Patients with tumors harboring mutations in CACNA1D, ATP1A1 and ATP2B3 were operated at an older age, were more often male and had tumors that were smaller than those in patients with KCNJ5 mutated tumors. Microarray transcriptome analysis segregated KCNJ5 mutated tumors from ATP1A1/ATP2B3 mutated tumors and those without mutation. We observed significant transcription upregulation of CYP11B2, as well as the previously described glomerulosa-specific gene NPNT, in ATP1A1/ATP2B3 mutated tumors compared to KCNJ5 mutated tumors. In summary, we describe novel somatic mutations in proteins regulating the membrane potential/intracellular Ca(2) (+) levels, and also a distinct mRNA and clinical signature, dependent on genetic alteration.

Decalmodulation of Cav1 channels by CaBPs

Ca²⁺-dependent inactivation (CDI) is a negative feedback regulation of voltage-gated Ca_v1 and Ca_v2 channels that is mediated by the Ca²⁺ sensing protein, calmodulin (CaM), binding to the pore-forming Ca_v α₁ subunit. David Yue and his colleagues made seminal contributions to our understanding of this process, as well as factors that regulate CDI. Important in this regard are members of a family of Ca²⁺ binding proteins (CaBPs) that are related to calmodulin. CaBPs are expressed mainly in neural tissues and can antagonize CaM-dependent CDI for Ca_v1 L-type channels. This review will focus on the roles of CaBPs as Ca_v1-interacting proteins, and the significance of these interactions for vision, hearing, and neuronal Ca²⁺ signaling events.

Spontaneous ventricular tachyarrhythmias in β2-adrenoceptor transgenic mice in relation to cardiac interstitial fibrosis

Myocardial fibrosis is regarded as a pivotal proarrhythmic substrate, but there have been no comprehensive studies showing a correlation between the severity of fibrosis and ventricular tachyarrhythmias (VTAs). Our purpose was to document this relationship in a transgenic (TG) strain of mice with fibrotic cardiomyopathy. TG mice with cardiac overexpression of β2-adrenoceptors (β2-AR mice) and non-TG (NTG) littermates were studied at 4-12 mo of age. VTA was quantified by ECG telemetry. The effect of pharmacological blockade of β2-ARs on VTA was examined. Myocardial collagen content was determined by hydroxyproline assay. NTG and TG mice displayed circadian variation in heart rate, which was higher in TG mice than in NTG mice (P <0.05). Frequent spontaneous ventricular ectopic beats (VEBs) and ventricular tachycardia (VT) were prominent in TG mice but not present in NTG mice. The frequency of VEB and VT episodes in TG mice increased with age (P < 0.01). Ventricular collagen content was greater in TG mice than in NTG mice (P <0.001) and correlated with age (r = 0.71, P < 0.01). The number of VEBs or VT episodes correlated with age (r = 0.83 and r = 0.73) and the content of total or cross-linked collagen (r = 0.62∼0.66, all P <0.01). While having no effect in younger β2-TG mice, β2-AR blockade reduced the frequency of VTA in old β2-TG mice with more severe fibrosis. In conclusion, β2-TG mice exhibit interstitial fibrosis and spontaneous onset of VTA, becoming more severe with aging. The extent of cardiac fibrosis is a major determinant for both the frequency of VTA and proarrhythmic action of β2-AR activation.

Decreased temporal precision of neuronal signaling as a candidate mechanism of auditory processing disorder

The sense of hearing is the fastest of our senses and provides the first all-or-none action potential in the auditory nerve in less than four milliseconds. Short stimulus evoked latencies and their minimal variability are hallmarks of auditory processing from spiral ganglia to cortex. Here, we review how even small changes in first spike latencies (FSL) and their variability (jitter) impact auditory temporal processing. We discuss a number of mouse models with degraded FSL/jitter whose mutations occur exclusively in the central auditory system and therefore might serve as candidates to investigate the cellular mechanisms underlying auditory processing disorders (APD).

Homeostatic synaptic depression is achieved through a regulated decrease in presynaptic calcium channel abundance

Homeostatic signaling stabilizes synaptic transmission at the neuromuscular junction (NMJ) of Drosophila, mice, and human. It is believed that homeostatic signaling at the NMJ is bi-directional and considerable progress has been made identifying mechanisms underlying the homeostatic potentiation of neurotransmitter release. However, very little is understood mechanistically about the opposing process, homeostatic depression, and how bi-directional plasticity is achieved. Here, we show that homeostatic potentiation and depression can be simultaneously induced, demonstrating true bi-directional plasticity. Next, we show that mutations that block homeostatic potentiation do not alter homeostatic depression, demonstrating that these are genetically separable processes. Finally, we show that homeostatic depression is achieved by decreased presynaptic calcium channel abundance and calcium influx, changes that are independent of the presynaptic action potential waveform. Thus, we identify a novel mechanism of homeostatic synaptic plasticity and propose a model that can account for the observed bi-directional, homeostatic control of presynaptic neurotransmitter release.