Calcium Channel Gene Research Articles

Silencing T-type voltage-gated calcium channel gene reduces the sensitivity of Tetranychus cinnabarinus (Boisduval) to scopoletin

Tetranychus cinnabarinus (Boisduval) is a major pest that harms crops and vegetables worldwide. Scopoletin is a promising acaricidal compound. Our previous study demonstrated that the acaricidal mechanism of scopoletin may be via disrupting intracellular Ca2+ homeostasis and calcium signaling pathway. However, the mechanism underlying the specific target location of scopoletin against T. cinnabarinus remains unclear. In this study, the full-length cDNA of the calcium channel (TcT-VDCC) gene from T. cinnabarinus was cloned and characterized. The TcT-VDCC gene is expressed at all developmental stages of T. cinnabarinus but is highly expressed in the larval and nymphal stages. The TcT-VDCC gene was significantly upregulated after treatment with scopoletin, and the RNAi method was used to feed the dsRNA in T. cinnabarinus to silence the TcT-VDCC gene and reduce its sensitivity to scopoletin. The results showed that the acaricidal mechanism of scopoletin on T. cinnabarinus may be related to TcT-VDCC.

Atrial fibrillation risk loci interact to modulate Ca2+-dependent atrial rhythm homeostasis.

Atrial fibrillation (AF), defined by disorganized atrial cardiac rhythm, is the most prevalent cardiac arrhythmia worldwide. Recent genetic studies have highlighted a major heritable component and identified numerous loci associated with AF risk, including the cardiogenic transcription factor genes TBX5, GATA4, and NKX2-5. We report that Tbx5 and Gata4 interact with opposite signs for atrial rhythm controls compared with cardiac development. Using mouse genetics, we found that AF pathophysiology caused by Tbx5 haploinsufficiency, including atrial arrhythmia susceptibility, prolonged action potential duration, and ectopic cardiomyocyte depolarizations, were all rescued by Gata4 haploinsufficiency. In contrast, Nkx2-5 haploinsufficiency showed no combinatorial effect. The molecular basis of the TBX5/GATA4 interaction included normalization of intra-cardiomyocyte calcium flux and expression of calcium channel genes Atp2a2 and Ryr2. Furthermore, GATA4 and TBX5 showed antagonistic interactions on an Ryr2 enhancer. Atrial rhythm instability caused by Tbx5 haploinsufficiency was rescued by a decreased dose of phospholamban, a sarco/endoplasmic reticulum Ca2+-ATPase inhibitor, consistent with a role for decreased sarcoplasmic reticulum calcium flux in Tbx5-dependent AF susceptibility. This work defines a link between Tbx5 dose, sarcoplasmic reticulum calcium flux, and AF propensity. The unexpected interactions between Tbx5 and Gata4 in atrial rhythm control suggest that evaluating specific interactions between genetic risk loci will be necessary for ascertaining personalized risk from genetic association data.

Inhibitory effect of octyl-phenol and bisphenol A on calcium signaling in cardiomyocyte differentiation of mouse embryonic stem cells.

Endocrine-disrupting chemicals (EDCs) have structures similar to steroid hormones and can interfere with hormone synthesis and normal physiological functions of reproductive organs. For example, sex steroid hormones influence calcium signaling of the cardiac muscle in early embryo development. To confirm the effect of progesterone (P4), octyl-phenol (OP), and bisphenol A (BPA) on early differentiation of mouse embryonic stem cells (mESCs) into cardiomyocytes, mESCs were treated with P4, OP, and BPA two days after attachment and media were replaced every two days. In addition, cells were treated with mifepristone (RU486), a synthetic steroid that has an affinity for progesterone receptor (Pgr), for one day starting on day 11. Beating ratio was decreased with P4, OP, and BPA treatment. The Pgr mRNA level was significantly increased in the P4-, OP- and BPA-treated groups. However, the mRNA level of the calcium channel gene (Trpv2), contraction-related genes (Ryr2, Cam2, and Mylk3) and cardiac development and morphogenesis genes (Rbp4, Ly6e, and Gata4) were significantly decreased in the P4-, OP-, and BPA-treated groups. Interestingly, treatment with RU486 rescued the altered calcium channel gene, contraction-related genes, and cardiac development and morphogenesis genes. P4, OP, and BPA treatments reduced the intracellular calcium level. Taken together, these results indicate that EDCs (OP and BPA) has a structure similar to that of endogenous steroid hormones such as progesterone and estrogen, and OP and BPA act like progesterone to inhibit and disrupt cardiomyocyte differentiation of mESCs.

Age- and Nicotine-Associated Gene Expression Changes in the Hippocampus of APP/PS1 Mice.

The etiology of Alzheimer's disease (AD) has been intensively studied. However, little is known about the molecular alterations in early-stage and late-stage AD. Hence, we performed RNA sequencing and assessed differentially expressed genes (DEGs) in the hippocampus of 18-month and 7-month-old APP/PS1 mice. Moreover, the DEGs induced by treatment with nicotine, the nicotinic acetylcholine receptor agonist that is known to improve cognition in AD, were also analyzed in old and young APP/PS1 mice. When comparing old APP/PS1 mice with their younger littermates, we found an upregulation in genes associated with calcium overload, immune response, cancer, and synaptic function; the transcripts of 14 calcium ion channel subtypes were significantly increased in aged mice. In contrast, the downregulated genes in aged mice were associated with ribosomal components, mitochondrial respiratory chain complex, and metabolism. Through comparison with DEGs in normal aging from previous reports, we found that changes in calcium channel genes remained one of the prominent features in aged APP/PS1 mice. Nicotine treatment also induced changes in gene expression. Indeed, nicotine augmented glycerolipid metabolism, but inhibited PI3K and MAPK signaling in young mice. In contrast, nicotine affected genes associated with cell senescence and death in old mice. Our study suggests a potential network connection between calcium overload and cellular signaling, in which additional nicotinic activation might not be beneficial in late-stage AD.

Genes, biomarkers, and clinical features associated with the course of bipolar disorder

There is considerable variability in the severity of bipolar disorder, e.g., in terms of the frequency of inpatient episodes. The long-term progression also differs, where some patients are sensitised with progressively shorter healthy intervals. Little is known about the proportion of patients being sensitised, their clinical characteristics, and biological underpinnings. We analysed long-term progression of bipolar disorder in relation to clinical characteristics (N = 3074), serum biomarkers (N = 745), and genetic variants (N = 1401) in a cohort of Swedish bipolar disorder patients. We took advantage of the National Patient Register, providing reliable data on 35,973 psychiatric inpatient care episodes in Sweden since 1973. First, one third of the cohort cluster together with a maximum of one inpatient episode per year, while the remaining two thirds had >1 episode per year. These groups did not differ with respect to clinical features or biomarkers. Second, among patients with at least five inpatient episodes (defined as severely ill), we find one group with progressively shorter cycle-lengths (one fifth of the total cohort, N = 550). Compared with those with a stable or recuperant trajectory, these patients featured lower functioning, more antidepressant treatment, as well as reduced levels of inflammatory markers in serum. Third, sensitisation was associated with a common genetic variant near the calcium channel gene CACNA2D3 at genome-wide significance. These results suggest the potential for translational research aimed at preventive actions.

The cardiovascular toxicity induced by high doses of gatifloxacin and ciprofloxacin in zebrafish

As a new type of pollutant, fluoroquinolones (FQs) antibiotics are ubiquitous in environment and have some threat to human health and ecological environment. Their ecological toxicity to the environment urgently need to be assessed. Therefore, we firstly explored the toxic effects and possible mechanism of cardiovascular toxicity induced by gatifloxacin (GTFX) and ciprofloxacin (CPFX) using zebrafish model. After 24 h exposure, the zebrafish treated with GTFX showed pericardial edema which was further investigated by histopathological examination, while CPFX exposure did not induce morphological abnormalities. However, both of them induced cardiac dysfunction, such as decreased heart rate and cardiac output which was showed a positive correlation with the concentration. To better understand the possible molecular mechanisms underlying cardiovascular toxicity in zebrafish, we investigated the transcriptional level of genes related to calcium signaling pathway and cardiac muscle contraction. The results indicated that the expression of ATPase (atp2a1l) and cardiac troponin C (tnnc1a) genes were significantly inhibited, the expression of calcium channel (cacna1ab) gene showed slight promoted trend after CPFX exposure. For zebrafish treated with GTFX, the expression of atp2a1l genes was also significantly inhibited, while the expression of tnnc1a genes was slightly inhibited and cacna1ab genes expression had no obvious effect. The present study firstly revealed that GTFX exposure can induce morphological and functional abnormalities on the cardiovascular system of zebrafish. Though CPFX exposure did not induce morphological abnormalities, the function of cardiovascular system was still damaged. Mechanistically, this toxicity might result from the pressure of down-regulation of genes associated with calcium signaling pathway and cardiac muscle contraction. The results of this study can provide a valuable theoretical basis for the establishment of FQs environmental quality standards in water environment, environmental drug regulation and risk management.

Dravet Syndrome: An Overview.

Dravet syndrome (DS), also known as severe myoclonic epilepsy of infancy (SMEI), is one of the rare early childhood intractable epileptic encephalopathies associated with pleomorphic seizure activity, cognitive decline, motor, and behavioral abnormalities. The convulsive seizure is the most common type seen in DS. After the first episode of seizure-like activity, behavioral disorders and cognitive decline are progressive and long-lasting. The most common etiology identified in patients with DS is a de-novo genetic mutation alpha-1 subunit of voltage-gated calcium channel gene (SCN1A). DS is diagnosed clinically and if unclear, genetic testing is recommended. DS treatment options include anti-epileptic drugs and cannabinoids; ketogenic diet therapy and surgical options such as the deep brain and vagal nerve stimulation. Due to drug-refractory epilepsy in DS, many more therapies are being investigated to increase the longevity of patients.

TRPV2 Calcium Channel Gene Expression and Outcomes in Gastric Cancer Patients: A Clinically Relevant Association.

Gastric cancer (GC) is characterized by poor efficacy and the modest clinical impact of current therapies. Apoptosis evasion represents a causative factor for treatment failure in GC as in other cancers. Since intracellular calcium homeostasis regulation has been found to be associated with apoptosis resistance, the aberrant expression of intracellular calcium regulator genes (CaRGs) could have a prognostic value in GC patients. We analyzed the association of the expression levels of 98 CaRGs with prognosis by the log-rank test in a collection of 1524 GC samples from four gene expression profiling datasets. We also evaluated differential gene expression in comparison with normal stomach tissue, and then we crossed results with tissue microarrays from the Human Protein Atlas. Among the investigated CaRGs, patients with high levels of TRPV2 expression were characterized by a shorter overall survival. TRPV2 expression was found to increase according to tumor stage. Both mRNA and protein levels were significantly higher in tumor than normal stomach samples. TRPV2 was also associated with poor prognosis in the Lauren’s intestinal type GC and in patients treated with adjuvant therapy. Overall, we highlighted the relevance of TRPV2 not only as a prognostic biomarker but also as a potential therapeutic target to improve GC treatment efficacy.

CACNA1C (rs1006737) may be a susceptibility gene for schizophrenia: An updated meta-analysis.

IntroductionSchizophrenia is a serious mental illness with a genetic predisposition. Genome‐wide association studies (GWAS) have identified the α‐1C subunit of the L‐type voltage‐gated calcium channel (CACNA1C) gene as a significant risk gene for schizophrenia. However, there are inconsistent conclusions in case–control studies.MethodsWe performed a comprehensive meta‐analysis of all available samples from existing studies under four different genetic models (recessive model, dominant model, additive model and allele model) to further confirm whether CACNA1C rs1006737 is an authentic risk single nucleotide polymorphism (SNP) for schizophrenia.ResultsA statistically significant difference under the four models (all p < 0.05) was observed by pooling nine Asian and European studies, including a total of 12,744 cases and 16,460 controls. For European‐decent samples, a significant difference was identified between patients and controls for the four models (all p < 0.05). We observed a significant difference between patients and controls for the recessive model and allele model (GG vs. GA + AA: p < 0.00001; G vs. A: p < 0.00001) using a fixed effect model, but the dominant model (GG + GA vs. AA: OR: p = 0.15) and additive model (GG vs. AA: p = 0.11) showed no significant difference between patients and controls in the Asian samples.ConclusionOur findings provide important evidence for the establishment of CACNA1C as a susceptibility gene for schizophrenia across world populations, but its roles in the pathogenesis of schizophrenia need to be further investigated.

Entrainment of Circadian Rhythms to Temperature Reveals Amplitude Deficits in Fibroblasts from Patients with Bipolar Disorder and Possible Links to Calcium Channels

Bipolar disorder (BD) is characterized by recurrent mood episodes, and circadian rhythm disturbances. Past studies have identified calcium channel genes as risk loci for BD. CACNA1C encodes an L-type calcium channel (LTCC) involved in the entrainment of circadian rhythms to light. Another calcium channel, i.e., the ryanodine receptor (RYR), is involved in ­circadian phase delays. It is unknown whether variants in CACNA1C or other calcium channels contribute to the circadian phenotype in BD. We hypothesized that, by using temperature cycles, we could model circadian entrainment in fibroblasts from BD patients and controls to interrogate the circadian functions of LTCCs. Using Per2-luc, a bioluminescent reporter, we verified that cells entrain to temperature rhythms in vitro. Under constant temperature conditions, the LTCC antagonist verapamil shortened the circadian period, and the RYR antagonist dantrolene lengthened the period. However, neither drug affected temperature entrainment. Fibroblasts from BD patients and controls also entrained to temperature. In cells from BD patients, the rhythm amplitude was lower under entrained, but not constant, conditions. Temperature entrainment was otherwise similar between BD and control cells. However, the CACNA1C genotype among BD cells predicted the degree to which cells entrained. We conclude that assessment of rhythms under entrained conditions reveals additional rhythm abnormalities in BD that are not observable under constant temperature conditions.

α1ACT Is Essential for Survival and Early Cerebellar Programming in a Critical Neonatal Window

Postnatal cerebellar development is a precisely regulated process involving well-orchestrated expression of neural genes. Neurological phenotypes associated with CACNA1A gene defects have been increasingly recognized, yet the molecular principles underlying this association remain elusive. By characterizing a dose-dependent CACNA1A gene deficiency mouse model, we discovered that α1ACT, as a transcription factor and secondary protein of CACNA1A mRNA, drives dynamic gene expression networks within cerebellar Purkinje cells and is indispensable for neonatal survival. Perinatal loss of α1ACT leads to motor dysfunction through disruption of neurogenesis and synaptic regulatory networks. However, its elimination in adulthood hasminimal effect on the cerebellum. These findingsshed light on the critical role of α1ACT in facilitating neuronal development in both mice and humans and support a rationale for gene therapies for calcium-channel-associated cerebellar disorders. Finally, we show that bicistronic expression may be common to the voltage-gated calcium channel (VGCC) gene family and may help explain complex genetic syndromes.

The Oxford study of Calcium channel Antagonism, Cognition, Mood instability and Sleep (OxCaMS): study protocol for a randomised controlled, experimental medicine study

BackgroundThe discovery that voltage-gated calcium channel genes such as CACNA1C are part of the aetiology of psychiatric disorders has rekindled interest in the therapeutic potential of L-type calcium channel (LTCC) antagonists. These drugs, licensed to treat hypertension and angina, have previously been used in bipolar disorder, but without clear results. Neither is much known about the broader effects of these drugs on the brain and behaviour.MethodsThe Oxford study of Calcium channel Antagonism, Cognition, Mood instability and Sleep (OxCaMS) is a high-intensity randomised, double-blind, placebo-controlled experimental medicine study on the effect of the LTCC antagonist nicardipine in healthy young adults with mood instability. An array of cognitive, psychiatric, circadian, physiological, biochemical and neuroimaging (functional magnetic resonance imaging and magnetoencephalography) parameters are measured during a 4-week period, with randomisation to drug or placebo on day 14. We are interested in whether nicardipine affects the stability of these measures, as well as its overall effects. Participants are genotyped for the CACNA1C risk polymorphism rs1006737.DiscussionThe results will clarify the potential of LTCC antagonists for repurposing or modification for use in psychiatric disorders in which cognition, mood and sleep are affected.Trial registrationISRCTN, ISRCTN33631053. Retrospectively registered on 8 June 2018 (applied 17 May 2018).

Association between single nucleotide polymorphism (rs4252424) in TRPV5 calcium channel gene and lead poisoning in Chinese workers.

BackgroundLead (Pb) is broadly used in various industries and causes irreversible damage to human tissues, organs, and systems. Studies have revealed that lead exerts toxic effects via interfering with calcium channel.MethodsIn the present study, we investigated whether single nucleotide polymorphisms (SNPs) in TRPV5, a calcium channel‐related gene, were associated with lead exposure susceptibility. By using TaqMan SNP genotyping, we performed genotyping of eight TRPV5 tag‐SNPs in 1,130 lead‐exposed Chinese workers with similar lead exposure level.ResultsSingle nucleotide polymorphism rs4252424 was significantly associated with lead susceptibility, measured by blood lead level (BLL) (β = −0.069, p linear = 0.029). However, there was no significant association between any other seven SNPs and BLL. The further expression Quantitative Trait Loci displayed that CC genotype of rs4252424 is significant associated with higher BLL than CT (p < 0.0001).ConclusionWe conclude that SNP rs4252424 has the potential to evaluate lead susceptibility in the Chinese occupational population, and further enhance lead exposure prevention and intervention.

The T-type calcium channel antagonist, Z944, alters social behavior in Genetic Absence Epilepsy Rats from Strasbourg

Abnormalities in social behavior are a co-morbid symptom of idiopathic generalized epilepsies such as childhood absence epilepsy. The Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model is a spontaneously occurring absence epilepsy phenotype closely correlated to that of human absence epilepsies. Similar to the human conditions, GAERS display social abnormalities. Previous studies have only demonstrated social abnormalities in female GAERS, whereas social problems are observed in male and female patients. Seizures in GAERS result in part due to a gain-of-function missense mutation in the Cav3.2 T-type calcium channel gene. This study examined the effects of the pan-T-type calcium channel antagonist, Z944, on social interaction behaviors in male and female GAERS using an open field social interaction test. A second objective of this study was to examine the effects of Z944 on anxiety-like behavior in an open field locomotion test and elevated plus maze. Results showed a decrease in social activity in GAERS relative to non-epileptic control (NEC) rats. Acute, systemic Z944 (5 mg/kg; i.p.) consistently reduced introductory and aggressive behaviors in both GAERS and NECs whereas strain effects were observed for over-and-under crawl behaviors. In the open field locomotion test and elevated plus maze, Z944 increased anxiety-like behaviors in GAERS, whereas, Z944 produced inconsistent effects on anxiety-like behaviors in NECs. The results of this study suggest that the regulation of T-type calcium channel activity may be a useful strategy for the development of new therapeutic approaches for the treatment of social and affective abnormalities observed in absence epilepsy disorders.

190 Effects of endocrine-disrupting chemical on calcium signalling in cardiomyocyte differentiation from mouse embryonic stem cells

Endocrine-disrupting chemicals (EDC) are substances similar to steroid hormones that can disturb normal physiological functions of male and female reproductive organs. Endocrine-disrupting chemicals tend to bind to steroid hormone receptors. Sex steroid hormones modulate calcium signalling in the cardiac muscle in early embryo development. Among the steroid hormones, progesterone (P4) has been reported to affect blood pressure and other aspects of the cardiovascular system. The EDC that have similar structure to P4, such as octyl-phenol (OP) and bisphenol A (BPA), are potentially harmful to development of the heart. To confirm the effect of OP and BPA on early differentiation of mouse embryonic stem cells (mES) into cardiomyocytes, the hanging-drop method with mESC cell line (ES-E14TG2a) was used for forming embryoid bodies. Pluripotent mESC were cultured in basal medium with leukemia inhibitory factor and grown on mitomycin C-treated mouse embryonic fibroblasts in a 60-mm plate at 37°C in a 5% CO2 humidified tissue culture incubator with basal medium consisting of DMEM/F-12 supplemented with nonessential amino acids, 10% heat-inactivated and certified fetal bovine serum (FBS), 2-mercaptoethanol, penicillin, and streptomycin. The mouse embryoid bodies (mEB) were suspended onto 6-well plates and cultured with differentiation medium containing steroid-free FBS without leukemia inhibitory factor. Progesterone, OP, and BPA were added on Day 2 from mEB attachment. In addition, mifepristone (RU486), an antagonist for progesterone receptor (PR), was used to confirm the effect of P4 through PR. To determine whether RU486 is capable of attenuating the inhibition effect of P4, RU486 was added for 1 day starting on Day 11. Assessment of cardiomyocyte differentiation was determined by checking the number of beating cell populations divided by the total number of attached mEB. Total RNA was extracted using Trizol reagent and synthesised to cDNA using Moloney murine leukemia virus (MMLV) reverse transcriptase. Messenger RNA level was assessed using quantitative real-time PCR. To investigate calcium signalling, the mRNA levels of calcium channel gene Trpv2 and contraction-related genes Ryr2, Cam2, and Mylk3 were analysed. Beating ratio was decreased in P4, OP, and BPA treatments. Data were analysed by one-way ANOVA followed by Tukey’s multiple comparison tests, and P&amp;lt;0.05 was considered statistically significant in least 3 different replicates. The mRNA level of Pgr was significantly increased in P4, OP, and BPA-treated group. However, the mRNA level of calcium channel gene Trpv2 was significantly decreased in the P4, OP, and BPA-treated group. Expression of contraction-related genes such as Ryr2, Cam2, and Mlck3 were significantly decreased in the P4, OP, and BPA-treated group. In addition, treatment with RU486 rescues altered calcium channel gene and contraction-related genes. Taken together, these results suggest that OP and BPA may affect the differentiation of mESC into cardiomyocyte and disrupts differentiation of cardiomyocytes.

Bifid T waves on the ECG and genetic variation in calcium channel voltage-dependent beta 2 subunit gene (CACNB2) in acute Kawasaki disease.

We previously described the association of genetic variants in calcium channel genes and susceptibility to Kawasaki disease (KD), an acute, self-limited vasculitis, and the most common cause of acquired cardiac disease in children. Abnormal repolarization of cardiomyocytes and changes in T wave morphology have been reported in KD but have not been studied systematically. We analyzed acute and convalescent ECG T wave morphology in two independent cohorts of KD subjects and studied the association between bifid T waves and genetic variants in previously reported genes with SNVs associated with cardiac repolarization. Bifid T waves in limb leads were identified in 24% and 27% of two independent cohorts of acute KD subjects. Calcium channel voltage-dependent beta 2 subunit gene (CACNB2) (rs1409207) showed association with bifid T waves in both cohorts (nominal P = .04 and P = .0003, respectively). This CACNB2 polymorphism also showed association with KD susceptibility in a previously published KD genome wide association study data (nominal P = .009). This genotype/phenotype association study uncovered a variant in CACNB2 that may be associated with both KD susceptibility and bifid T waves, a novel signature of altered myocardial repolarization. The present study combined with published reports suggests that genetic variants in calcium channels and intracellular calcium signaling play a prominent role in shaping susceptibility to KD.

Characterization of a Human-Specific Tandem Repeat Associated with Bipolar Disorder and Schizophrenia

Bipolar disorder (BD) and schizophrenia (SCZ) are highly heritable diseases that affect more than 3% of individuals worldwide. Genome-wide association studies have strongly and repeatedly linked risk for both of these neuropsychiatric diseases to a 100 kb interval in the third intron of the human calcium channel gene CACNA1C. However, the causative mutation is not yet known. We have identified a human-specific tandem repeat in this region that is composed of 30bp units, often repeated hundreds of times. This large tandem repeat is unstable using standard polymerase chain reaction and bacterial cloning techniques, which may have resulted in its incorrect size in the human reference genome. The large 30-mer repeat region is polymorphic in both size and sequence in human populations. Particular sequence variants of the 30-mer are associated with risk status at several flanking single-nucleotide polymorphisms in the third intron of CACNA1C that have previously been linked to BD and SCZ. The tandem repeat arrays function as enhancers that increase reporter gene expression in a human neural progenitor cell line. Different human arrays vary in the magnitude of enhancer activity, and the 30-mer arrays associated with increased psychiatric disease risk status have decreased enhancer activity. Changes in the structure and sequence of these arrays likely contribute to changes in CACNA1C function during human evolution and may modulate neuropsychiatric disease risk in modern human populations.

1,25-Dihydroxyvitamin D3 enhances glucose-stimulated insulin secretion in mouse and human islets: a role for transcriptional regulation of voltage-gated calcium channels by the vitamin D receptor

AimVitamin D deficiency in rodents negatively affects glucose-stimulated insulin secretion (GSIS) and human epidemiological studies connect poor vitamin D status with type 2 diabetes. Previous studies performed primarily in rat islets have shown that vitamin D can enhance GSIS. However the molecular pathways linking vitamin D and insulin secretion are currently unknown. Therefore, experiments were undertaken to elucidate the transcriptional role(s) of the vitamin D receptor (VDR) in islet function. MethodsHuman and mouse islets were cultured with vehicle or 1,25-dihydroxyvitamin-D3 (1,25D3) and then subjected to GSIS assays. Insulin expression, insulin content, glucose uptake and glucose-stimulated calcium influx were tested. Microarray analysis was performed. In silico analysis was used to identify VDR response elements (VDRE) within target genes and their activity was tested using reporter assays. ResultsVdr mRNA is abundant in islets and Vdr expression is glucose-responsive. Preincubation of mouse and human islets with 1,25D3 enhances GSIS and increases glucose-stimulated calcium influx. Microarray analysis identified the R-type voltage-gated calcium channel (VGCC) gene, Cacna1e, which is highly upregulated by 1,25D3 in human and mouse islets and contains a conserved VDRE in intron 7. Results from GSIS assays suggest that 1,25D3 might upregulate a variant of R-type VGCC that is resistant to chemical inhibition. ConclusionThese results suggest that the role of 1,25D3 in regulating calcium influx acts through the R-Type VGCC during GSIS, thereby modulating the capacity of beta cells to secrete insulin.

Variation within voltage-gated calcium channel genes and antipsychotic treatment response in a South African first episode schizophrenia cohort

Voltage-gated calcium channels have been implicated in schizophrenia aetiology; however, little is known about their involvement in antipsychotic treatment response. This study investigated variants within the calcium channel subunit genes for association with antipsychotic treatment response in a first episode schizophrenia cohort. Twelve regulatory variants within seven genes were shown to be significantly associated with treatment outcome. Most notably, the CACNA1B rs2229949 CC genotype was associated with improved negative symptomology, where the C allele was predicted to abolish a miRNA-binding site (has-mir-5002-3p), suggesting a possible mechanism of action through which this variant may have an effect. These results implicate the calcium channel subunits in antipsychotic treatment response and suggest that increased activation of these channels may be explored to enhance or predict antipsychotic treatment outcome.

Does thyrotoxic periodic paralysis have a genetic predisposition? A case report.

Thyrotoxic periodic paralysis is a rare complication of hyperthyroidism where increased influx of potassium into skeletal muscle cells leads to profound hypokalaemia and paralysis. Most cases arise sporadically in Asians; however, it is being increasingly reported in Caucasians. It is regarded as a channelopathy where a genetic and/or acquired defect in the sodium-potassium (Na/K-ATPase) pump renders it more sensitive to excess thyroid hormone in susceptible individuals. Because the clinical presentation is similar to familial hypokalaemic periodic paralysis, genes implicated in this autosomal-dominant condition became candidates for thyrotoxic periodic paralysis, particularly if they were known to have thyroid hormone-responsive elements. These include the voltage-gated calcium (CACNA1S) and sodium (SCN4A) channel genes, KCNJ18 which encodes the inwardly rectifying potassium channel Kir2.6, and subunits of the Na/K-ATPase genes. Although no single pathogenetic mutation has been identified in thyrotoxic periodic paralysis, several single-nucleotide polymorphisms in these genes have been associated with it. We describe a 27-year-old Caucasian Irish male who presented with acute onset limb paralysis and severe hypokalaemia. He was diagnosed as having thyrotoxic periodic paralysis secondary to Graves' disease based on clinical presentation, biochemical findings and rapid response to intravenous potassium. Genetic analysis identified heterozygous variants in three candidate genes: KCNJ18 (c.576G>C), SCN4A (c.2341G>A) and CACNA1S (c.1817G>A). Since these variants are not disease causing and occur at high prevalences of 50%, 2-3% and 1%, respectively, in the normal population, they do not explain the clinical phenotype in our patient suggesting that acquired environmental triggers or as-yet unidentified gene mutations remain as leading pathogenetic co-factors in thyrotoxic periodic paralysis.