Human Alpha-subunit Research Articles

Detection of interferon alpha and beta receptor subunit 1 (IFNAR1) loss-of-function Glu386∗ variant by tri-allelic genotyping

Mutations of the human interferon alpha and beta receptor subunit 1 (IFNAR1) gene are associated with severe viral infections. Individuals homozygous for the Glu386∗ variant have impaired type I interferon signalling and can suffer severe illness when exposed to certain viruses and live attenuated virus vaccines. Glu386∗ heterozygotes are clinically unaffected, but can pass the variant allele to their descendants. We aimed to develop an assay that can identify IFNAR1 Glu386∗ homozygotes and heterozygotes to support urgent clinical diagnosis, and that can use dried blood spots (DBS) sent at ambient temperature to overcome geographical logistical challenges in the South Pacific region. The tri-allelic genotyping assay interrogates a single nucleotide polymorphism (rs201609461) located in IFNAR1. The reference allele G encodes for wild-type IFNAR1. Minor alleles A (c.1156G>A) and T (c.1156G>T) encode for Glu386Lys and a truncated IFNAR1 protein (p.Glu386∗), respectively. Synthetic oligonucleotides were mixed in equal molar ratio to create six different genotypes which were randomly assigned to 960 genotyping reactions by R software. Three different fluorescence probes were designed to discriminate the three alleles (G, T and A) within a pair of flanking primers in a single genotyping reaction. The assay discriminated all three alleles using DBS from Guthrie cards randomly spiked with synthetic oligonucleotides. We correctly identified all the different genotypes in 960 reactions in these blinded experiments. These findings validate the genotyping assay for rapidly identifying the IFNAR1 Glu386∗ variant from DBS.

Interaction of the antiarrhythmic drug Amiodarone with the sodium channel Nav1.5 depends on the extracellular pH

IntroductionAmiodarone (AMD) is a clinically used drug to treat arrhythmias with significant effect upon the cardiac sodium channel Nav1.5. AMD has a pKa of 6.56, and changes in extracellular pH (pHe) may alter its pharmacological properties. Here we explored how changes in pHe impacts the pharmacological properties of AMD upon human-Nav1.5-sodium-current (INa) and in ex vivo rat hearts. MethodsEmbryonic-human-kidney-cells (HEK293) were used to transiently express the human alpha-subunit of NaV1.5 channels and the isolated heart of Wistar rats were used. Patch-Clamp technique was deployed to study INa and for electrocardiogram (ECG) evaluation the ex vivo heart preparation in the Langendorff system was applied. ResultsThe potency of AMD upon peak INa was ∼25x higher in pHe 7.0 when compared to pHe 7.4. Voltage dependence for activation did not differ among all groups. AMD shifted the steady-state inactivation curve to more hyperpolarized potentials, with similar magnitudes for both pHes. The recovery from INa inactivation was delayed in the presence of AMD with similar profile in both pHes. Interestingly, the use-dependent properties of AMD was distinct at pHe 7.0 and 7.4. Finally, AMD was able to change the ex vivo ECG profile, however at pHe 7.0+AMD a larger increase in the RR and QRS duration and in the QT interval when compared to pHe 7.4 was found. ConclusionsThe pharmacological properties of AMD upon NaV1.5 and isolated heart preparation depends on the pHe and its use in vivo during extracellular acidosis may cause a distinct biological response in the heart tissue.

Thyroid Dysfunction in Pregnancy: A Literature Review

Due to structural similarities between HCG and thyroid-stimulating hormone, thyroid stimulation during pregnancy starts in the first trimester (TSH). The volume of thyroid hormone distribution increases along with placental metabolism, maternal thyroxine transport, and estrogen-mediated changes in thyroxine-binding globulin (TBG), all of which cause a 20–40% rise in early pregnancy thyroid hormone demand. Due to the human chorionic gonadotropin alpha subunit's cross-reactivity with the TSH receptor, the reference range of laboratory values for TSH is lower. High serum protein levels may alter estimates rather than direct measurements of free thyroxine (FT4), leading to reported results that are inaccurate. The clinical range of thyroid dysfunction during pregnancy can include both hyperthyroidism (Graves' disease and transitory gestational thyrotoxicosis) and hypothyroidism (overt hypothyroidism, subclinical hypothyroidism, and autoimmune thyroid disease). The risk of preterm and infant respiratory distress syndrome is increased by this malfunction.

Stability of Maleimide-PEG and Mono-Sulfone-PEG Conjugation to a Novel Engineered Cysteine in the Human Hemoglobin Alpha Subunit.

In order to use a Hemoglobin Based Oxygen Carrier as an oxygen therapeutic or blood substitute, it is necessary to increase the size of the hemoglobin molecule to prevent rapid renal clearance. A common method uses maleimide PEGylation of sulfhydryls created by the reaction of 2-iminothiolane at surface lysines. However, this creates highly heterogenous mixtures of molecules. We recently engineered a hemoglobin with a single novel, reactive cysteine residue on the surface of the alpha subunit creating a single PEGylation site (βCys93Ala/αAla19Cys). This enabled homogenous PEGylation by maleimide-PEG with >80% efficiency and no discernible effect on protein function. However, maleimide-PEG adducts are subject to deconjugation via retro-Michael reactions and cross-conjugation to endogenous thiol species in vivo. We therefore compared our maleimide-PEG adduct with one created using a mono-sulfone-PEG less susceptible to deconjugation. Mono-sulfone-PEG underwent reaction at αAla19Cys hemoglobin with > 80% efficiency, although some side reactions were observed at higher PEG:hemoglobin ratios; the adduct bound oxygen with similar affinity and cooperativity as wild type hemoglobin. When directly compared to maleimide-PEG, the mono-sulfone-PEG adduct was significantly more stable when incubated at 37°C for seven days in the presence of 1 mM reduced glutathione. Hemoglobin treated with mono-sulfone-PEG retained > 90% of its conjugation, whereas for maleimide-PEG < 70% of the maleimide-PEG conjugate remained intact. Although maleimide-PEGylation is certainly stable enough for acute therapeutic use as an oxygen therapeutic, for pharmaceuticals intended for longer vascular retention (weeks-months), reagents such as mono-sulfone-PEG may be more appropriate.

Identification and semi-relative quantification of intact glycoforms of human chorionic gonadotropin alpha and beta subunits by nano liquid chromatography-Orbitrap mass spectrometry

The human chorionic gonadotropin (hCG) protein belongs to a family of glycoprotein hormones called gonadotropins. It is a heterodimer made of two non-covalently linked subunits. The α-subunit structure, hCGα, has 2 N-glycosylation sites, while the beta subunit, hCGβ, has 2 N- and 4 O-glycosylation sites. This leads to numerous glycoforms. A method based on the analysis of hCG glycoforms at the intact level by nano-reversed phase liquid chromatography coupled to high resolution mass spectrometry (nanoLC-HRMS) with an Orbitrap analyzer was previously developed using a recombinant hCG-based drug, Ovitrelle®, as standard. It allowed the detection of about 30 hCGα glycoforms, but didn't allow the detection of hCGβ glycoforms. This method was thus here significantly modified (addition of a pre-concentration step of the sample to increase the sample volume from 70 nl to 1 µl, optimization of the gradient slope and the nature and content of the acidic additive in the mobile phase). It led to an improvement of the separation of hCGα and hCGβ glycoforms, which allowed for the first time the detection of 33 hCGβ glycoforms at intact level. In addition, a higher number of hCGα glycoforms (42 in total, i.e. a 40% increase) was detected. The figures of merit of this new method were next assessed. The relative standard deviations (RSDs) of the retention time ranged between 0.02 and 0.95% (n = 3), with an average value of 0.36% for the alpha glycoforms and between 0.01 and 1.08% (n = 3) with an average value of 0.23% for the beta glycoforms. The RSDs of the relative peak area measured on the extracted ion chromatogram of each glycoform were below 20% (n = 3), with an average value of 9.8%, thus allowing semi-relative quantification. Therefore, this method has a high potential for rapid quality control aiming for the detection and comparison of glycoforms present in glycoprotein-based pharmaceutical preparations.

Enrichment of ovine gonadotropes via adenovirus gene targeting enhances assessment of transcriptional changes in response to estradiol-17 beta†.

Gonadotropes represent approximately 5-15% of the total endocrine cell population in the mammalian anterior pituitary. Therefore, assessing the effects of experimental manipulation on virtually any parameter of gonadotrope biology is difficult to detect and parse from background noise. In non-rodent species, applying techniques such as high-throughput ribonucleic acid (RNA) sequencing is problematic due to difficulty in isolating and analyzing individual endocrine cell populations. Herein, we exploited cell-specific properties inherent to the proximal promoter of the human glycoprotein hormone alpha subunit gene (CGA) to genetically target the expression of a fluorescent reporter (green fluorescent protein [GFP]) selectively to ovine gonadotropes. Dissociated ovine pituitary cells were cultured and infected with an adenoviral reporter vector (Ad-hαCGA-eGFP). We established efficient gene targeting by successfully enriching dispersed GFP-positive cells with flow cytometry. Confirming enrichment of gonadotropes specifically, we detected elevated levels of luteinizing hormone (LH) but not thyrotropin-stimulating hormone (TSH) in GFP-positive cell populations compared to GFP-negative populations. Subsequently, we used next-generation sequencing to obtain the transcriptional profile of GFP-positive ovine gonadotropes in the presence or absence of estradiol 17-beta (E2), a key modulator of gonadotrope function. Compared to non-sorted cells, enriched GFP-positive cells revealed a distinct transcriptional profile consistent with established patterns of gonadotrope gene expression. Importantly, we also detected nearly 200 E2-responsive genes in enriched gonadotropes, which were not apparent in parallel experiments on non-enriched cell populations. From these data, we conclude that CGA-targeted adenoviral gene transfer is an effective means for selectively labeling and enriching ovine gonadotropes suitable for investigation by numerous experimental approaches.

Molecular biology of gonadotrophins

Regulation of gonadotrophin synthesis involves a complex interaction between hypothalamic and gonadal hormones. Chronic administration of oestrogens and androgens to gonadectomized animals blocked the postcastration rise in amounts of mRNA encoding gonadotrophin subunits. Removal of endogenous GnRH decreased amounts of mRNA encoding gonadotrophin subunits. Pulsatile administration of GnRH to GnRH-deficient animals increased amounts of mRNA encoding gonadotrophin subunits. Studies using transgenic mice and transient transfection assays identified at least eight cis-acting DNA sequences in the proximal 350 bp of 5' flanking sequence of the human alpha subunit gene that directed expression to gonadotrophs or conferred responsiveness to oestrogens, androgens or GnRH. Unique DNA-binding proteins were also identified which directed expression of the human alpha subunit gene specifically to the pituitary. Pituitary cell lines that express bovine gonadotrophin subunit genes are not currently available; thus, relatively little is known about the molecular mechanisms that regulate expression of bovine gonadotrophin subunit genes. Recent studies with transgenic mice harbouring bovine alpha, LH beta, or FSH beta subunit transgenes revealed that DNA sequences important for gonadotroph-specific expression and hormonal regulation resided within the proximal 5' flanking sequences.

A Novel Di-Leucine Motif at the N-Terminus of Human Organic Solute Transporter Beta Is Essential for Protein Association and Membrane Localization.

The heteromeric membrane protein Organic Solute Transporter alpha/beta is the major bile acid efflux transporter in the intestine. Physical association of its alpha and beta subunits is essential for their polarized basolateral membrane localization and function in the transport of bile acids and other organic solutes. We identified a highly conserved acidic dileucine motif (-EL20L21EE) at the extracellular amino-tail of organic solute transporter beta from multiple species. To characterize the role of this protein interacting domain in the association of the human beta and alpha subunits and in membrane localization of the transporter, Leu20 and Leu21 on the amino-tail of human organic solute transporter beta were replaced with alanines by site-directed mutagenesis. Co-immunoprecipitation study in HEK293 cells demonstrated that substitution of the leucine residues with alanines prevented the interaction of the human beta mutant with the alpha subunit. Membrane biotinylation demonstrated that the LL/AA mutant eliminated membrane expression of both subunits. Computational-based modelling of human organic solute transporter beta suggested that the LL/AA mutation substantially alters both the structure and lipophilicity of the surface, thereby not only affecting the interaction with the alpha subunit but also possibly impacting the capacity of the beta subunit to traffick through the cell and interact with the membrane. In summary, our findings indicate that the dileucine motif in the extracellular N-terminal region of human organic solute transporter beta subunit plays a critical role in the association with the alpha subunit and in its polarized plasma membrane localization.

A Putative Non-Canonical Ras-Like GTPase from P. falciparum: Chemical Properties and Characterization of the Protein.

During its development the malaria parasite P. falciparum has to adapt to various different environmental contexts. Key cellular mechanisms involving G-protein coupled signal transduction chains are assumed to act at these interfaces. Heterotrimeric G-proteins are absent in Plasmodium. We here describe the first cloning and expression of a putative, non-canonical Ras-like G protein (acronym PfG) from Plasmodium. PfG reveals an open reading frame of 2736 bp encoding a protein of 912 amino acids with a theoretical pI of 8.68 and a molecular weight of 108.57 kDa. Transcript levels and expression are significantly increased in the erythrocytic phase in particular during schizont and gametocyte formation. Most notably, PfG has GTP binding capacity and GTPase activity due to an EngA2 domain present in small Ras-like GTPases in a variety of Bacillus species and Mycobacteria. By contrast, plasmodial PfG is divergent from any human alpha-subunit. PfG was expressed in E. coli as a histidine-tagged fusion protein and was stable only for 3.5 hours. Purification was only possible under native conditions by Nickel-chelate chromatography and subsequent separation by Blue Native PAGE. Binding of a fluorescent GTP analogue BODIPY® FL guanosine 5’O-(thiotriphosphate) was determined by fluorescence emission. Mastoparan stimulated GTP binding in the presence of Mg2+. GTPase activity was determined colorimetrically. Activity expressed as absolute fluorescence was 50% higher for the human paralogue than the activity of the parasitic enzyme. The PfG protein is expressed in the erythrocytic stages and binds GTP after immunoprecipitation. Immunofluorescence using specific antiserum suggests that PfG localizes to the parasite cytosol. The current data suggest that the putitative, Ras-like G-protein might be involved in a non-canonical signaling pathway in Plasmodium. Research on the function of PfG with respect to pathogenesis and antimalarial chemotherapy is currently under way.

A Common Polymorphism of the Human Cardiac Sodium Channel Alpha Subunit (SCN5A) Gene Is Associated with Sudden Cardiac Death in Chronic Ischemic Heart Disease.

Cardiac death remains one of the leading causes of mortality worldwide. Recent research has shed light on pathophysiological mechanisms underlying cardiac death, and several genetic variants in novel candidate genes have been identified as risk factors. However, the vast majority of studies performed so far investigated genetic associations with specific forms of cardiac death only (sudden, arrhythmogenic, ischemic etc.). The aim of the present investigation was to find a genetic marker that can be used as a general, powerful predictor of cardiac death risk. To this end, a case-control association study was performed on a heterogeneous cohort of cardiac death victims (n=360) and age-matched controls (n=300). Five single nucleotide polymorphisms (SNPs) from five candidate genes (beta2 adrenergic receptor, nitric oxide synthase 1 adaptor protein, ryanodine receptor 2, sodium channel type V alpha subunit and transforming growth factor-beta receptor 2) that had previously been shown to associate with certain forms of cardiac death were genotyped using sequence-specific real-time PCR probes. Logistic regression analysis revealed that the CC genotype of the rs11720524 polymorphism in the SCN5A gene encoding a subunit of the cardiac voltage-gated sodium channel occurred more frequently in the highly heterogeneous cardiac death cohort compared to the control population (p=0.019, odds ratio: 1.351). A detailed subgroup analysis uncovered that this effect was due to an association of this variant with cardiac death in chronic ischemic heart disease (p=0.012, odds ratio = 1.455). None of the other investigated polymorphisms showed association with cardiac death in this context. In conclusion, our results shed light on the role of this non-coding polymorphism in cardiac death in ischemic cardiomyopathy. Functional studies are needed to explore the pathophysiological background of this association.

711. Intravenous Neonatal Gene Therapy Corrects GM2 Gangliosidosis in Sandhoff Mice for Long-Term, By Using AAV Viral Vector Expressing a New Hexosaminidase Variant

GM2 gangliosidosis is a group of neurodegenerative disorders, characterized by the malfunctioning Hexosaminidase A (HexA) enzyme, for which there is no treatment. HexA is composed of two similar, but non-identical subunits, the alpha and the beta, which must interact with the GM2 activator protein, a substrate-specific cofactor, to hydrolyze GM2. Mutation in either subunit (or the activator) results in the development of GM2 gangliosidosis. In these diseases, the malfunctioning protein is unable to play its role in cleaving GM2 ganglioside, whose accumulation within the neurons of the central nervous system is ultimately toxic. The resulting neuronal death induces the primary symptoms of the disease; motor impairment, seizures, and sensory impairments. The aim of this study is to observe the long-term in vivo effects of a novel treatment in a Sandhoff (beta deficient) mouse model. The treatment utilized a new Hex isoenzyme, Hex M, which functions as a homodimer in the treatment of GM2 gangliosidosis. The HexM subunit is a variant of the human Hex alpha subunit containing critical beta-components that allow it to form stable homodimers and interact with the GM2 activator protein to reduce substrate storage. Our methods include intravenous injections of the neonatal mice with a self-complementary vector (with a synthetic promoter) expressing HexM at day 0-1. We monitored one cohort for 8 weeks and another cohort long-term (>40 weeks) for biochemical, behavioural and molecular analyses. Through the enzymatic and GM2 ganglioside lipid analyses, we see that with a slight increase in enzyme activity, there is a significant increase in the clearance of GM2 gangliosides. On behavioural tests, the treated mice outperform their knockout age matched controls. While the untreated controls die before the age of 15 weeks, treated animals have survived to more than 40 weeks and are still being monitored. The molecular analyses reveal a uniform distribution of the vector between brain and spinal cord regions. In conclusion, the neonatal delivery of our newly synthesized viral vector expressing HexM to the Sandhoff mice provided long-term correction of the disease. This study will have implications not only for treatment of Sandhoff, but also Tay-Sachs disease (alpha deficiency).

In search of the protein kinase A phosphorylation sites on the human cardiac L-type calcium channel alpha subunit

In search of the protein kinase A phosphorylation sites on the human cardiac L-type calcium channel alpha subunit

SY35-2 * DORSAL STRIATAL INDIRECT PATHWAY REGULATES THE PERFORMANCE OF AUDITORY CONDITIONAL DISCRIMINATION

The dorsal striatum, which contains the dorsolateral striatum (DLS) and dorsomedial striatum (DMS), is known to be involved in the performance of discrimination learning. The dorsal striatum regulates the basal ganglia circuitry through direct and indirect pathways. However the mechanism by which the striatopallidal pathway regulates the learning processes of discriminative actions remains unclear. To induce selective elimination of the striatopallidal pathway by injecting the recombinant immunotoxin into the DLS or DMS, we used transgenic rats that expressed human interleukin-2 receptor alpha-subunit under the control of dopamine D2 receptor gene promoter. Intrastriatal immunotoxin treatment induced a selective elimination of the striatopallidal neurons while persisting normally the number of other striatal neuronal types. Ablation of the DLS- or DMS-derived striatopallidal pathway transiently impaired the performance of conditional discrimination, showing a marked reduction in the selection accuracy of learned motor responses. In addition, the probability of perseverative errors was significantly increased in the animals lacking the striatopallidal pathway from the DMS, but not from the DLS. Although there is a distinct role in modulating perseverative behavior between the DLS- and DMS-derived striatopallidal pathways, these two pathways are necessary for controlling the accuracy of response selection.

C-terminus of Human BKca Channel Alpha Subunit Enhances the Permeability of the Brain Endothelial Cells by Interacting with Caveolin-1 and Triggering Caveolin-1 Intracellular Trafficking

The blood-tumor barrier (BTB) significantly limits the delivery of chemotherapeutic drugs to brain tumors. In this study, we found a significant increase in the permeability of BTB by mediating the association of the C-terminus of alpha subunit of human large-conductance calcium-activated potassium channels (hSlo1c) with caveolin-1 (Cav-1). We present evidence for the first time that hSlo1c associates with Cav-1 in human brain microvascular endothelial cells (HBMECs). A 57-amino acid (966-1022) fragment in hSlo1c was identified to be critical for hSlo1c/Cav-1 interaction. Activation of HBMECs transfected with fusion plasmids of pCMV-hSlo1c containing aa966-1022 by NS1619 selectively enhanced BTB permeability in a BTB model from the co-culture of HBMECs and U87 MG cells but not if the fusion plasmid lacks this fragment. This effect was attenuated by filipin, an agent disrupting caveolae or deletion of the potential interaction fragment, suggesting hSlo1c/Cav-1 association is crucial for regulating the permeability of BTB. Furthermore, we found that hSlo1c/Cav-1 association boosted Cav-1 transferring from the cell membrane to the cytoplasm of HBMECs. Our study indicates that cytoplasmic hSlo1c not only associates with Cav-1 but also has functional consequences on the permeability of BTB by triggering the intracellular trafficking of its interacting protein partner, Cav-1.

0265: A novel SCN5A mutation associated with exercise-induced polymorphic ventricular arrhythmias resembling CPVT

Cardiac sodium channel is a complex which includes the poreforming alpha subunit and regulatory proteins that allow sodium influx during the depolarization phase of the ventricular action potential. The alpha subunit, Nav1.5, is encoded by SCN5A . Mutations in this gene are responsible for a wide spectrum of hereditary arrhythmias such as cardiac conduction disease and atrial fibrillation. A mutation in SCN5A , leading to a p.I141V substitution, was identified in a large multigenerational family with an arrhythmia syndrome resembling catecholaminergic polymorphic ventricular tachycardia through whole-exome sequencing. The purpose of this study was to identify the molecular mechanisms linking the p.I141V mutation to this arrhythmia. To evaluate the incidence of this substitution on Nav1.5 function, whole-cell patch-clamp experiments were performed on HEK293 cells transfected with the human alpha and beta subunits. The presence of the p.I141V mutation shifted the voltage-dependence of steady state activation towards more negative potentials. Thus, we studied the effect of this mutation on the sodium window current. Compared to the WT, the p.I141V window current exhibited a larger peak and this peak was shifted towards more negative potentials. To investigate the functional consequences of the cardiac hyperexcitability due to the p.I141V mutation, we incorporated biophysical properties of the mutant into atrial, Purkinje and ventricular cell models. The computational analyses imply that the biophysical changes caused by the p.I141V mutation accelerates the spontaneous rate in the Purkinje cell model, and reduce the excitation threshold leading to an increase of the excitability of the cardiac cells. In conclusion, the present study demonstrates that mutations in SCN5A also may result in exercise-induced polymorphic ventricular premature complexes and tachycardia resembling CPVT.

PM376 Direct phosphorylation of the human cardiac L-type calcium channel alpha subunit by cAMP-dependent protein kinase alters function

PM376 Direct phosphorylation of the human cardiac L-type calcium channel alpha subunit by cAMP-dependent protein kinase alters function

Determining the Site of Phosphorylation on the Human Cardiac L-type Calcium Channel Alpha Subunit by cAMP-Dependent Protein Kinase

Determining the Site of Phosphorylation on the Human Cardiac L-type Calcium Channel Alpha Subunit by cAMP-Dependent Protein Kinase

Intragenic suppressor mutations of a constitutively active allele of Gs alpha

Heterotrimeric G‐proteins cycle between an active/GTP‐bound conformation and an inactive/GDP‐bound conformation. Reduction in GTP hydrolysis by the G‐protein alpha subunit results in constitutive activity of the protein. McCune‐Albright Syndrome (MAS) is a human genetic disorder caused by a mutation that constitutively activates the Gs alpha subunit by inhibiting GTP hydrolysis. Arginine 201 substitutions with histidine, serine, or cysteine have been reported in biopsies from MAS patients. Previous work in this laboratory modeled the MAS mutation in a yeast system, and identified an intragenic suppressor of the MAS mutation, which substituted two residues in the GTP‐binding site. The homologous mutations (F222P, D223V) in the human Gs alpha subunit also suppressed the constitutive activity of the MAS mutation when the protein was expressed in human cells. To extend these studies, F222 and D223 were mutated to a variety of other amino acids to determine the structural requirements for suppression of the MAS mutation. Basal and receptor‐stimulated cAMP levels were measured in HEK293 cells transfected with the different alleles of Gs alpha. While some single mutations at either F222 or D223 were able to suppress the MAS R201H mutation, a range of levels of suppression were observed.

Localization of ion-regulatory epithelia in embryos and hatchlings of two cephalopods

The tissue distribution and ontogeny of Na(+)/K(+)-ATPase has been examined as an indicator for ion-regulatory epithelia in whole animal sections of embryos and hatchlings of two cephalopod species: the squid Loligo vulgaris and the cuttlefish Sepia officinalis. This is the first report of the immunohistochemical localization of cephalopod Na(+)/K(+)-ATPase with the polyclonal antibody alpha (H-300) raised against the human alpha1-subunit of Na(+)/K(+)-ATPase. Na(+)/K(+)-ATPase immunoreactivity was observed in several tissues (gills, pancreatic appendages, nerves), exclusively located in baso-lateral membranes lining blood sinuses. Furthermore, large single cells in the gill of adult L. vulgaris specimens closely resembled Na(+)/K(+)-ATPase-rich cells described in fish. Immunohistochemical observations indicated that the amount and distribution of Na(+)/K(+)-ATPase in late cuttlefish embryos was similar to that found in juvenile and adult stages. The ion-regulatory epithelia (e.g., gills, excretory organs) of the squid embryos and paralarvae exhibited less differentiation than adults. Na(+)/K(+)-ATPase activities for whole animals were higher in hatchlings of S. officinalis (157.0 +/- 32.4 micromol g (FM) (-1) h(-1)) than in those of L. vulgaris (31.8 +/- 3.3 micromol g (FM) (-1) h(-1)). S. officinalis gills and pancreatic appendages achieved activities of 94.8 +/- 18.5 and 421.8 +/- 102.3 micromol(ATP) g (FM) (-1) h(-1), respectively. High concentrations of Na(+)/K(+)-ATPase in late cephalopod embryos might be important in coping with the challenging abiotic conditions (low pH, high pCO(2)) that these organisms encounter inside their eggs. Our results also suggest a higher sensitivity of squid vs. cuttlefish embryos to environmental acid-base disturbances.

Mutation of Cardiac Nav1.5 in an Hisian-Type Arrhythmia, Associated with Dilated Cardiomayopathy

Cardiac sodium channels are complexes including alpha and beta1 subunits allowing sodium influx during the depolarization phase of the ventricular action potential. The pore-forming alpha subunit, Nav1.5, is encoded by SCN5A. Using a candidate-gene approach, we detected a variant of SCN5A, leading to the R222Q substitution by screening one family with cardiac arrhythmia resulting in frequent premature ventricular contractions, non sustained ventricular tachycardia and dilated cardiomyopathy. Arrhythmia mechanisms involved ectopic foci originating from the proximal part of the His-Purkinje system. To evaluate the incidence of this substitution on Nav1.5 function, whole-cell patch-clamp experiments were performed on COS-7 cells transfected with the human alpha and beta1 subunits. The presence of the mutation at the heterozygous or homozygous state did not modify the sodium current density. In contrast, the activation curve was shifted toward more negative potentials (V1/2act, WT: −30.6±2.1 mV, n=11; R222Q: −42.3±1 mV, n=11, p<0.001; heterozygous: −37.2±1.6 mV, n=9; p<0.05) and the slope was changed in the heterozygous condition only (WT: 5.7±0.3 mV, R222Q: 6.5±0.4 mV, heterozygous: 7.1±0.3 mV; p<0.01). Activation kinetics were also accelerated in mutant homozygous condition only (p<0.001, versus WT). Inactivation voltage sensitivity was also changed (V1/2inact, WT: −79.6±0.7 mV, n=10; R222Q: −84.6±0.7 mV, n=8, p<0.001; heterozygous: −82.2±1 mV, n=9; p<0.05), its kinetics accelerated (p<0.001 versus WT for both mutant and heterozygous conditions) and the slope was changed in the mutant homozygous condition only (WT: 5.6±0.2 mV; R222Q: 4.8±0.2 mV; p<0.01; heterozygous: 5.3±0.1 mV). Finally, recovery from inactivation was not modified by the R222Q mutation. We studied the impact of the current biophysical changes in cellular models of the Purkinje and ventricular action potentials. The premature ventricular contractions are explained by the appearance of electrical abnormalities rather in Purkinje fibers than in ventricular cardiomyocytes.