Novel avian paramyxovirus isolated from gulls in Caspian seashore in Kazakhstan

Three isolates APMV/gull/Kazakhstan/5976/2014, APMV/gull/Kazakhstan/ 5977/2014 and APMV/gull/Kazakhstan/5979/2014, were obtained from independent samples during annual surveillance for avian influenza and paramyxoviruses in wild birds from the Caspian Sea coast in Western Kazakhstan, and were initially identified as putative paramyxoviruses on the basis of electron microscopy. Hemagglutination Inhibition Assays with antisera to nine known APMV serotypes (APMV1-9) indicated no relation to any of them. Next generation sequencing of whole genome sequences indicated the three isolates were genetically identical, and had a nucleotide structure typical for all APMVs, consisting of six genes 3'-NP-P-M-F-HN-L-5'. Phylogenetic analyses, and assessment of amino acid identities, suggested the most closely related lineages to be APMV-2, 8, 10 and 15, but the novel isolate had less than 64% identity to them and all other known avian paramyxoviruses. This value was above levels considered to generally define other APMV serotypes. Estimates of the evolutionary divergence of the nucleotide sequences of the genomes of APMVs have shown that novel Kazakhstan APMV strain was closest to APMV-2, APMV-8, APMV-10 and APMV-15, with calculated distance values of 2.057, 2.058, 2.026 and 2.286 respectively, which is above values considered to differentiate other serotypes (observed minimum was 1.108 between APMV-1 and recently isolated APMV/UPO216/Korea). Together, the data suggest that isolate APMV/gull/Kazakhstan/5976/2014 and other two should be considered as the first representative of a novel APMV-20 group, and is the first time that avian paramyxoviruses have been found infecting members of the gull family, extending the known taxonomic host range.

m6aViewer: software for the detection, analysis, and visualization of N6-methyladenosine peaks from m6A-seq/ME-RIP sequencing data

Recent methods for transcriptome-wide N⁶-methyladenosine (m⁶A) profiling have facilitated investigations into the RNA methylome and established m⁶A as a dynamic modification that has critical regulatory roles in gene expression and may play a role in human disease. However, bioinformatics resources available for the analysis of m⁶A sequencing data are still limited. Here, we describe m6aViewer-a cross-platform application for analysis and visualization of m⁶A peaks from sequencing data. m6aViewer implements a novel m⁶A peak-calling algorithm that identifies high-confidence methylated residues with more precision than previously described approaches. The application enables data analysis through a graphical user interface, and thus, in contrast to other currently available tools, does not require the user to be skilled in computer programming. m6aViewer and test data can be downloaded here: http://dna2.leeds.ac.uk/m6a.

Quality of deli-style turkey enriched with plant sterols

Low-fat meat products could be excellent carriers for plant sterols, known for their cholesterol-lowering properties. In this study, we developed a protocol for the manufacture of a deli-style turkey enriched with plant sterols (S) at a level sufficient to deliver the maximum plant sterols amount recommended for cholesterol reduction by the European Food Safety Authority (3 g of plant sterols per day) in a 70 g portion. We investigated the stability of the plant sterols and the effects of their addition on the product quality. Plant sterols remained stable during the seven-day storage period. The addition of plant sterols significantly affected some texture parameters, shear force, lipid oxidation, L values and water-holding capacity compared with control (C). Sensory analysis was carried out by an untrained panel (32) using the difference-from-control test between C and S samples to evaluate first the extent of the overall sensory difference and then the extent of sensory difference on colour, texture and flavour. Results indicated that panellists considered the intensity of the difference between C and S samples to be ‘small’. Plant sterols could be used as a potential health-promoting meat ingredient with no effect on plant sterol stability but with some effects on texture and sensory characteristics.

A Chromosome 7 Pericentric Inversion Defined at Single-Nucleotide Resolution Using Diagnostic Whole Genome Sequencing in a Patient with Hand-Foot-Genital Syndrome

Next generation sequencing methodologies are facilitating the rapid characterisation of novel structural variants at nucleotide resolution. These approaches are particularly applicable to variants initially identified using alternative molecular methods. We report a child born with bilateral postaxial syndactyly of the feet and bilateral fifth finger clinodactyly. This was presumed to be an autosomal recessive syndrome, due to the family history of consanguinity. Karyotype analysis revealed a homozygous pericentric inversion of chromosome 7 (46,XX,inv(7)(p15q21)x2) which was confirmed to be heterozygous in both unaffected parents. Since the resolution of the karyotype was insufficient to identify any putatively causative gene, we undertook medium-coverage whole genome sequencing using paired-end reads, in order to elucidate the molecular breakpoints. In a two-step analysis, we first narrowed down the region by identifying discordant read-pairs, and then determined the precise molecular breakpoint by analysing the mapping locations of “soft-clipped” breakpoint-spanning reads. PCR and Sanger sequencing confirmed the identified breakpoints, both of which were located in intergenic regions. Significantly, the 7p15 breakpoint was located 523 kb upstream of HOXA13, the locus for hand-foot-genital syndrome. By inference from studies of HOXA locus control in the mouse, we suggest that the inversion has delocalised a HOXA13 enhancer to produce the phenotype observed in our patient. This study demonstrates how modern genetic diagnostic approach can characterise structural variants at nucleotide resolution and provide potential insights into functional regulation.

Deficiency of the myogenic factor MyoD causes a perinatally lethal fetal akinesia

Background

Lethal fetal akinesia deformation sequence (FADS) describes a clinically and genetically heterogeneous phenotype that includes fetal akinesia, intrauterine growth retardation, arthrogryposis and developmental anomalies. Affected babies die as a result of pulmonary hypoplasia. We aimed to identify the underlying genetic cause of this disorder in a family in which there were three affected individuals from two sibships.

Methods

Autosomal-recessive inheritance was suggested by a family history of consanguinity and by recurrence of the phenotype between the two sibships. We performed exome sequencing of the affected individuals and their unaffected mother, followed by autozygosity mapping and variant filtering to identify the causative gene.

Results

Five autozygous regions were identified, spanning 31.7 Mb of genomic sequence and including 211 genes. Using standard variant filtering criteria, we excluded all variants as being the likely pathogenic cause, apart from a single novel nonsense mutation, c.188C>A p.(Ser63*) (NM_002478.4), in MYOD1. This gene encodes an extensively studied transcription factor involved in muscle development, which has nonetheless not hitherto been associated with a hereditary human disease phenotype.

Conclusions

We provide the first description of a human phenotype that appears to result from MYOD1 mutation. The presentation with FADS is consistent with a large body of data demonstrating that in the mouse, MyoD is a major controller of precursor cell commitment to the myogenic differentiation programme.

Enhanced diagnostic yield in Meckel-Gruber and Joubert syndrome through exome sequencing supplemented with split-read mapping

Background

The widespread adoption of high-throughput sequencing technologies by genetic diagnostic laboratories has enabled significant expansion of their testing portfolios. Rare autosomal recessive conditions have been a particular focus of many new services. Here we report a cohort of 26 patients referred for genetic analysis of Joubert (JBTS) and Meckel-Gruber (MKS) syndromes, two clinically and genetically heterogeneous neurodevelopmental conditions that define a phenotypic spectrum, with MKS at the severe end.

Methods

Exome sequencing was performed for all cases, using Agilent SureSelect v5 reagents and Illumina paired-end sequencing. For two cases medium-coverage (9×) whole genome sequencing was subsequently undertaken.

Results

Using a standard analysis pipeline for the detection of single nucleotide and small insertion or deletion variants, molecular diagnoses were confirmed in 12 cases (4 %). Seeking to determine whether our cohort harboured pathogenic copy number variants (CNV), in JBTS- or MKS-associated genes, targeted comparative read-depth analysis was performed using FishingCNV. These analyses identified a putative intragenic AHI1 deletion that included three exons spanning at least 3.4 kb and an intergenic MPP4 to TMEM237 deletion that included exons spanning at least 21.5 kb. Whole genome sequencing enabled confirmation of the deletion-containing alleles and precise characterisation of the mutation breakpoints at nucleotide resolution. These data were validated following development of PCR-based assays that could be subsequently used for “cascade” screening and/or prenatal diagnosis.

Conclusions

Our investigations expand the AHI1 and TMEM237 mutation spectrum and highlight the importance of performing CNV screening of disease-associated genes. We demonstrate a robust increasingly cost-effective CNV detection workflow that is applicable to all MKS/JBTS referrals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12881-015-0265-z) contains supplementary material, which is available to authorized users.

OVA: integrating molecular and physical phenotype data from multiple biomedical domain ontologies with variant filtering for enhanced variant prioritization

MOTIVATION

Exome sequencing has become a de facto standard method for Mendelian disease gene discovery in recent years, yet identifying disease-causing mutations among thousands of candidate variants remains a non-trivial task.

RESULTS

Here we describe a new variant prioritization tool, OVA (ontology variant analysis), in which user-provided phenotypic information is exploited to infer deeper biological context. OVA combines a knowledge-based approach with a variant-filtering framework. It reduces the number of candidate variants by considering genotype and predicted effect on protein sequence, and scores the remainder on biological relevance to the query phenotype.We take advantage of several ontologies in order to bridge knowledge across multiple biomedical domains and facilitate computational analysis of annotations pertaining to genes, diseases, phenotypes, tissues and pathways. In this way, OVA combines information regarding molecular and physical phenotypes and integrates both human and model organism data to effectively prioritize variants. By assessing performance on both known and novel disease mutations, we show that OVA performs biologically meaningful candidate variant prioritization and can be more accurate than another recently published candidate variant prioritization tool.

AVAILABILITY AND IMPLEMENTATION

OVA is freely accessible at http://dna2.leeds.ac.uk:8080/OVA/index.jsp.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

CONTACT

umaan@leeds.ac.uk.

Rapid Detection of Rare Deleterious Variants by Next Generation Sequencing with Optional Microarray SNP Genotype Data

Autozygosity mapping is a powerful technique for the identification of rare, autosomal recessive, disease‐causing genes. The ease with which this category of disease gene can be identified has greatly increased through the availability of genome‐wide SNP genotyping microarrays and subsequently of exome sequencing. Although these methods have simplified the generation of experimental data, its analysis, particularly when disparate data types must be integrated, remains time consuming. Moreover, the huge volume of sequence variant data generated from next generation sequencing experiments opens up the possibility of using these data instead of microarray genotype data to identify disease loci. To allow these two types of data to be used in an integrated fashion, we have developed AgileVCFMapper, a program that performs both the mapping of disease loci by SNP genotyping and the analysis of potentially deleterious variants using exome sequence variant data, in a single step. This method does not require microarray SNP genotype data, although analysis with a combination of microarray and exome genotype data enables more precise delineation of disease loci, due to superior marker density and distribution.

Robust diagnostic genetic testing using solution capture enrichment and a novel variant-filtering interface

Targeted hybridization enrichment prior to next-generation sequencing is a widespread method for characterizing sequence variation in a research setting, and is being adopted by diagnostic laboratories. However, the number of variants identified can overwhelm clinical laboratories with strict time constraints, the final interpretation of likely pathogenicity being a particular bottleneck. To address this, we have developed an approach in which, after automatic variant calling on a standard unix pipeline, subsequent variant filtering is performed interactively, using AgileExomeFilter and AgilePindelFilter (http://dna.leeds.ac.uk/agile), tools designed for clinical scientists with standard desktop computers. To demonstrate the method's diagnostic efficacy, we tested 128 patients using (1) a targeted capture of 36 cancer-predisposing genes or (2) whole-exome capture for diagnosis of the genetically heterogeneous disorder primary ciliary dyskinesia (PCD). In the cancer cohort, complete concordance with previous diagnostic data was achieved across 793 variant genotypes. A high yield (42%) was also achieved for exome-based PCD diagnosis, underscoring the scalability of our method. Simple adjustments to the variant filtering parameters further allowed the identification of a homozygous truncating mutation in a presumptive new PCD gene, DNAH8. These tools should allow diagnostic laboratories to expand their testing portfolios flexibly, using a standard set of reagents and techniques.

Diagnostic whole genome sequencing and split-read mapping for nucleotide resolution breakpoint identification in CNTNAP2 deficiency syndrome

Whole genome sequencing (WGS) has the potential to report on all types of genetic abnormality, thus converging diagnostic testing on a single methodology. Although WGS at sufficient depth for robust detection of point mutations is still some way from being affordable for diagnostic purposes, low-coverage WGS is already an excellent method for detecting copy number variants ("CNVseq"). We report on a family in which individuals presented with a presumed autosomal recessive syndrome of severe intellectual disability and epilepsy. Array comparative genomic hybridization (CGH) analysis had revealed a homozygous deletion apparently lying within intron 3 of CNTNAP2. Since this was too small for confirmation by FISH, CNVseq was used, refining the extent of this mutation to approximately 76.8 kb, encompassing CNTNAP2 exon 3 (an out-of-frame deletion). To characterize the precise breakpoints and provide a rapid molecular diagnostic test, we resequenced the CNVseq library at medium coverage and performed split read mapping. This yielded information for a multiplex polymerase chain reaction (PCR) assay, used for cascade screening and/or prenatal diagnosis in this family. This example demonstrates a rapid, low-cost approach to converting molecular cytogenetic findings into robust PCR-based tests.

Simple and efficient identification of rare recessive pathologically important sequence variants from next generation exome sequence data

Massively parallel ("next generation") DNA sequencing (NGS) has quickly become the method of choice for seeking pathogenic mutations in rare uncharacterized monogenic diseases. Typically, before DNA sequencing, protein-coding regions are enriched from patient genomic DNA, representing either the entire genome ("exome sequencing") or selected mapped candidate loci. Sequence variants, identified as differences between the patient's and the human genome reference sequences, are then filtered according to various quality parameters. Changes are screened against datasets of known polymorphisms, such as dbSNP and the 1000 Genomes Project, in the effort to narrow the list of candidate causative variants. An increasing number of commercial services now offer to both generate and align NGS data to a reference genome. This potentially allows small groups with limited computing infrastructure and informatics skills to utilize this technology. However, the capability to effectively filter and assess sequence variants is still an important bottleneck in the identification of deleterious sequence variants in both research and diagnostic settings. We have developed an approach to this problem comprising a user-friendly suite of programs that can interactively analyze, filter and screen data from enrichment-capture NGS data. These programs ("Agile Suite") are particularly suitable for small-scale gene discovery or for diagnostic analysis.

Mapping the minimal regions within the ORF73 protein required for herpesvirus saimiri episomal persistence

Herpesvirus saimiri (HVS) establishes a persistent infection in which the viral genome persists as a circular non-integrated episome. ORF73 tethers HVS episomes to host mitotic chromosomes, allowing episomal persistence via an interaction with the chromosome-associated protein, MeCP2. Here we demonstrate that ORF73 also interacts with the linker histone H1 via its C terminus, suggesting it associates with multiple chromosome-associated proteins. In addition, we show that the C terminus is also required for the ability of ORF73 to bind the terminal repeat region of the HVS genome. These results suggest that the ORF73 C terminus contains all the necessary elements required for HVS episomal persistence. Using a range of ORF73 C terminus deletions to rescue the episomal maintenance properties of a HVSDelta73 recombinant virus, we show that a C terminus region comprising residues 285-407 is sufficient to maintain the HVS episome in a dividing cell population.

Kaposi's sarcoma-associated herpesvirus (KSHV) Rta and cellular HMGB1 proteins synergistically transactivate the KSHV ORF50 promoter

Kaposi's sarcoma-associated herpesvirus 'replication transcriptional activator' (Rta) plays a critical role in the switch from latency to lytic replication. Rta upregulates several lytic KSHV genes, including its own, through multiple mechanisms. We demonstrate that cellular HMGB1 binds and synergistically upregulates the ORF50 promoter in conjunction with Rta. No direct interaction between Rta and HMGB1 was observed, however a ternary complex is formed in the presence of Oct1. Furthermore, deletion of an Oct-1 binding site within the ORF50 promoter ablates the HMGB1-mediated synergistic response. These results suggest Rta autostimulation may be mediated by a transient complex involving Oct1 and HMGB1.

Lithium chloride inhibits the coronavirus infectious bronchitis virus in cell culture

The avian coronavirus infectious bronchitis virus (IBV) is a major economic pathogen of domestic poultry that, despite vaccination, causes mortality and significant losses in production. During replication of the RNA genome there is a high frequency of mutation and recombination, which has given rise to many strains of IBV and results in the potential for new and emerging strains. Currently the live-attenuated vaccine gives poor cross-strain immunity. Effective antiviral agents may therefore be advantageous in the treatment of IBV. Lithium chloride (LiCl) is a potent inhibitor of the DNA virus herpes simplex virus but not RNA viruses. The effect of LiCl on the replication of IBV was examined in cell culture using two model cell types; Vero cells, an African Green monkey kidney-derived epithelial cell line; and DF-1 cells, an immortalized chicken embryo fibroblast cell line. When treated with a range of LiCl concentrations, IBV RNA and protein levels and viral progeny production were reduced in a dose-dependent manner in both cell types, and the data indicated that inhibition was a cellular rather than a virucidal effect. Host cell protein synthesis still took place in LiCl-treated cells and the level of a standard cellular housekeeping protein remained unchanged, indicating that the effect of LiCl was specifically against IBV.

Cell cycle dependent nucleolar localization of the coronavirus nucleocapsid protein

The nucleolus is a dynamic sub-nuclear structure which is involved in ribosome subunit biogenesis, modulation of cell growth and response to cell stress. The nucleolar proteome varies particularly with regard to the cell cycle. Viral proteins can localise to the nucleolus and using the coronavirus nucleocapsid (N) protein as a model, the cell cycle dependent trafficking of viral proteins to the nucleolus was investigated. Cell synchronisation studies coupled to live cell confocal microscopy indicated that nucleolar localisation of N protein was greater in the G2/M phase of the cell cycle than at other stages. This result was reinforced when FRAP and FLIP analysis indicated that N protein was more mobile within the nucleoplasm and nucleolus in the G2/M phase of the cell cycle. The data suggested that viral nucleolar proteins can also localise to the nucleolus in a cell cycle dependent manner and this may be related to dynamic trafficking.

Characterization of the nuclear export signal in the coronavirus infectious bronchitis virus nucleocapsid protein

The nucleocapsid (N) protein of infectious bronchitis virus (IBV) localizes to the cytoplasm and nucleolus and contains an eight-amino-acid nucleolar retention motif. In this study, a leucine-rich nuclear export signal (NES) (291-LQLDGLHL-298) present in the C-terminal region of the IBV N protein was analyzed by using alanine substitution and deletion mutagenesis to investigate the relative contributions that leucine residues make to nuclear export and where these residues are located on the structure of the IBV N protein. The analysis indicated that Leu296 and Leu298 are required for efficient nuclear export of the protein. Structural information indicated that both of these amino acids are available for interaction with protein complexes involved in this process. However, export of N protein from the nucleus/nucleolus was not inhibited by leptomycin B treatment, indicating that N protein nuclear export is independent of the CRM1-mediated export pathway.

Characterisation of cyclin D1 down-regulation in coronavirus infected cells

The positive strand RNA coronavirus, infectious bronchitis virus (IBV), induces a G2/M phase arrest and reduction in the G1 and G1/S phase transition regulator cyclin D1. Quantitative real-time RT-PCR and Western blot analysis demonstrated that cyclin D1 was reduced post-transcriptionally within infected cells independently of the cell-cycle stage at the time of infection. Confocal microscopy revealed that cyclin D1 decreased in IBV-infected cells as infection progressed and inhibition studies indicated that a population of cyclin D1 could be targeted for degradation by a virus mediated pathway. In contrast to the SARS-coronavirus, IBV nucleocapsid protein did not interact with cyclin D1.

Negative inotropic effects of tumour necrosis factor-alpha and interleukin-1beta are ameliorated by alfentanil in rat ventricular myocytes

BACKGROUND AND PURPOSE

Serum levels of tumour necrosis factor-alpha (TNF-alpha) and interleukin-1beta (IL-1beta) increase during an inflammatory response and have been reported to induce a negative inotropic effect on the myocardium. Alfentanil, an opioid analgesic often used in the critical care of patients with sepsis, has been shown to enhance ventricular contractility. This study characterised the effects of TNF-alpha and IL-1beta on contraction and the Ca(2+) transient and investigated whether depressed ventricular function was ameliorated by alfentanil.

EXPERIMENTAL APPROACH

Isolated rat ventricular myocytes were loaded with fura-2 and electrically stimulated at 1 Hz. Contraction and Ca(2+) transients were measured after 60, 120 and 180 min incubations in TNF-alpha (0.05 ng ml(-1)) and IL-1beta (2 ng ml(-1)). The effects of 10 microM alfentanil on contractility and Ca(2+) transients of TNF-alpha and IL-1beta treated cells were determined.

KEY RESULTS

After 180 min of TNF-alpha and IL-1beta treatment, the amplitude of contraction, the Ca(2+) transient and sarcoplasmic reticulum (SR) Ca(2+) content were significantly reduced. Alfentanil significantly increased contraction of TNF-alpha and IL-1beta treated cells via a small increase in the Ca(2+) transient and a larger increase in myofilament Ca(2+) sensitivity, effects that were not blocked by 10 microM naloxone, a broad spectrum opioid receptor antagonist.

CONCLUSIONS AND IMPLICATIONS

TNF-alpha and IL-1beta induce a significant negative inotropic effect on ventricular myocytes in a time dependent manner through disruption of SR Ca(2+) handling and the Ca(2+) transient. This negative inotropic effect was ameliorated by alfentanil, but this response may not be mediated via opioid receptors.

A pinch elastometer for soft tissue

A prototype compression elastometer suited to the characterisation of soft tissue is analysed and tested by application to various elastomers. The test material is pinched between two rigid cylinders and the compression force and displacement interpreted to yield a measure of "effective" stiffness or to calibrate a simple non-linear-elastic material model (Neo-Hookean). This deformation suits the testing of bulk soft tissue since it effectively isolates the test material from boundary conditions such as other soft tissue, ligaments and bones. These can be highly variable in the body and can affect results greatly when employing other types of tests to determine the elastic nature of tissue. A simple linear-material analysis, based on established solutions to two-dimensional problems, is extended to take into account various geometrical complexities. This analysis permits immediate inversion of the readings from the device to yield the elastic properties of the material, without the need for complex numerical analysis. Finite element analysis is also employed to determine the range of reliable application of the linear-elastic model. In particular, this analysis permits the extension of the linear-elastic analysis to include simple forms of non-linear-material behaviour. The method is demonstrated using three elastomers having significantly different material properties. A viable range of application of the device is identified in which it yields results with reasonable precision and accuracy. The prototype device was able to measure the effective elastic modulus of the test materials with a maximum error of 13% for three material types (N=25). Repeatability error was less than 7% in all cases. Further refinement of the device and measuring system will reduce this uncertainty.

Halothane and sevoflurane inhibit Na/Ca exchange current in rat ventricular myocytes

BACKGROUND

The electrogenic Na+/Ca2+ exchanger (NCX) represents the main extrusion pathway for Ca2+ in ventricular muscle and therefore plays an important role in the regulation of cytosolic Ca2+ and contraction. Halothane and sevoflurane modulate cytosolic Ca2+ regulation and at steady state are negatively inotropic, however, the involvement of anaesthetic-induced changes in NCX activity in these effects requires further study.

METHODS

Ventricular myocytes were isolated using a standard collagenase/protease dispersion technique and superfused with a physiological salt solution at 30 degrees C. Whole-cell patch-clamp technique was used to control membrane voltage. I(NCX) (identified as Ni2+ sensitive current) was recorded using a ramp clamp protocol under conditions to inhibit contaminating currents.

RESULTS

With 0.6 mM sevoflurane, outward I(NCX) at positive voltages (> or = 0 mV) and inward I(NCX) at voltages negative to -60 mV was significantly reduced (P<0.05, n=13; I(NCX) reduced by 48% at +50 and 65% of control at -120 mV). Halothane (0.6 mM) inhibited outward I(NCX) at voltages positive to -10 mV and inward I(NCX) at voltages negative to -80 mV (P<0.05, n=10; I(NCX) reduced by 64% at +50 and 65% of control at -120 mV). Anaesthetic-induced inhibition of both inward and outward current was not voltage-dependent.

CONCLUSIONS

Inhibition of Ca2+ efflux via NCX (i.e. inward I(NCX)) during an exposure to halothane or sevoflurane would be expected to limit the negative inotropic effects of these agents and help maintain SR Ca2+ content.

Transient and sustained changes in myofilament sensitivity to Ca2+ contribute to the inotropic effects of sevoflurane in rat ventricle

BACKGROUND

The volatile anaesthetics isoflurane and sevoflurane induce both negative and positive inotropic effects in ventricular myocytes, the mechanisms of which are not fully understood. Previous data suggest that changes in myofilament Ca(2+) sensitivity contribute to their sustained negative inotropic effects. In this study, the role of changes in myofilament Ca(2+) sensitivity in both positive and negative inotropic effects of these agents was examined in intact ventricular myocytes.

METHODS

Contractility and cytosolic Ca(2+) (fura-2) were recorded optically in ventricular myocytes stimulated electrically (1 Hz) at 30 degrees C. Myofilament Ca(2+) sensitivity was assessed from plots of cell length against fura-2 fluorescence ratio (Fr) from individual twitches at various points before, during and after a 1 or 4 min exposure to 0.6 mM anaesthetic.

RESULTS

Isoflurane reduced mean (sd) myofilament Ca(2+) sensitivity from 10.3 (1.9) to 5.9 (1.6) microm Fr(-1) (P<0.001) throughout a 1 min exposure, which returned to control on removal. In contrast, on initial exposure to sevoflurane, Ca(2+) sensitivity was reduced from 10.8 (1.3) to 4.3 (0.9) microm Fr(-1) (P<0.001) but this recovered partially towards control over 3 min. On removal, sensitivity was increased above control (to 17.7 (2.2) microm Fr(-1); P<0.001) before preanaesthetic levels were restored.

CONCLUSIONS

These data show that both isoflurane and sevoflurane reduce apparent myofilament Ca(2+) sensitivity at steady state. However, sevoflurane (but not isoflurane) induced transient changes in apparent myofilament Ca(2+) sensitivity, which would contribute to its inotropic profile.

LPA1 receptor-deficient mice have phenotypic changes observed in psychiatric disease

Several psychiatric diseases, including schizophrenia, are thought to have a developmental aetiology, but to date no clear link has been made between psychiatric disease and a specific developmental process. LPA(1) is a G(i)-coupled seven transmembrane receptor with high affinity for lysophosphatidic acid. Although LPA(1) is expressed in several peripheral tissues, in the nervous system it shows relatively restricted temporal expression to neuroepithelia during CNS development and to myelinating glia in the adult. We report the detailed neurological and behavioural analysis of mice homozygous for a targeted deletion at the lpa(1) locus. Our observations reveal a marked deficit in prepulse inhibition, widespread changes in the levels and turnover of the neurotransmitter 5-HT, a brain region-specific alteration in levels of amino acids, and a craniofacial dysmorphism in these mice. We suggest that the loss of LPA(1) receptor generates defects resembling those found in psychiatric disease.

Effects of halothane on contraction and intracellular calcium in ventricular myocytes from streptozotocin-induced diabetic rats

BACKGROUND

Some of the cellular targets affected by volatile anaesthetics (e.g. halothane) which contribute to the negative inotropic effects of these agents are also affected during the progression of diabetic cardiomyopathy. A previous report suggested that halothane inhibited contraction to a lesser extent in papillary muscle from diabetic animals and so the aim of this study was to investigate possible mechanisms underlying this effect.

METHODS

Contractility and cytosolic calcium ion (Ca(2+)) transients were measured (fura-2) in ventricular myocytes isolated from control and streptozotocin (STZ)-induced diabetic rats in the absence and presence of halothane 0.6 mmol litre(-1) at 1 Hz stimulation. Sarcoplasmic reticulum (SR) Ca(2+) content was assessed by rapid application of caffeine. All experiments were carried out at 36-37 degrees C.

RESULTS

The amplitude of shortening, the electrically evoked Ca(2+) transient, SR Ca(2+) content and myofilament Ca(2+) sensitivity, though not altered by STZ treatment, were significantly reduced by halothane to a similar extent in control and STZ myocytes. The time course of contraction and Ca(2+) transient were prolonged in myocytes from STZ-treated rats compared with controls but this was not altered further by halothane. STZ treatment appeared to reduce Ca(2+) efflux from the cell, an effect reversed by halothane.

CONCLUSIONS

In contrast to a previous report, we could find no evidence of amelioration of the negative inotropic effect of halothane in myocytes from the STZ-induced diabetic rat. Contractility, the cytosolic Ca(2+) transient, SR Ca(2+) content and myofilament Ca(2+) sensitivity were qualitatively similar in control and STZ myocytes and were all depressed to the same extent by halothane.

Effects of halothane on action potential configuration in sub-endocardial and sub-epicardial myocytes from normotensive and hypertensive rat left ventricle

BACKGROUND

Halothane shortens ventricular action potential duration (APD), as a consequence of its inhibitory effects on a variety of membrane currents, an effect that is greater in sub-endocardial than sub-epicardial myocytes. In hypertrophied ventricle, APD is prolonged as a consequence of electrical remodelling. In this study, we compared the effects of halothane on transmural APD in myocytes from normal and hypertrophied ventricle.

METHODS

Myocytes were isolated from the sub-endocardium and sub-epicardium of the left ventricle of spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. Action potentials were recorded before, during, and after a 1-min exposure to 0.6 mM halothane and APD measured from the peak of the action potential to repolarization at -50 mV (APD(-50 mV)). Data are presented as mean (SEM).

RESULTS

In WKY myocytes, halothane reduced APD(-50 mV) from 21 (2) to 18 (2) ms (P<0.001, n=15) in sub-epicardial myocytes but abbreviated APD(-50 mV) to a greater extent in sub-endocardial myocytes (37 (4) to 28 (3) ms; P<0.001, n=14). In SHR myocytes, APD(-50 mV) values were prolonged compared with WKY and APD(-50 mV) was reduced by halothane from 36 (6) to 27 (4) ms (P<0.016) and from 77 (10) to 38 (4) ms (P<0.001) in sub-epicardial and sub-endocardial myocytes, respectively.

CONCLUSIONS

In the SHR, hypertrophic remodelling was not homogeneous; APD(-50 mV) was prolonged to a greater extent in sub-endocardial than sub-epicardial cells. Halothane reduced APD to a greater extent in sub-endocardium than sub-epicardium in both WKY and SHR but this effect was larger proportionately in SHR myocytes. The transmural gradient of repolarization was reduced in WKY and effectively abolished in SHR by halothane, which might disturb normal ventricular repolarization.

Different regional effects of voluntary exercise on the mechanical and electrical properties of rat ventricular myocytes

Short-term (6 weeks) voluntary wheel running exercise in young female rats that were in an active growth phase resulted in whole-heart hypertrophy and myocyte concentric hypertrophy, when compared to sedentary controls. The cross-sectional area of ventricular myocytes from trained rats was significantly greater than for those isolated from sedentary rats, with the greatest change in morphology seen in sub-endocardial cells. There was no statistically significant effect of training on cell shortening in the absence of external mechanical loading, in [Ca2+](i) transients, or in myofilament Ca2+ sensitivity (assessed during re-lengthening following tetanic stimulation). Under the external mechanical load of carbon fibres, absolute force developed in myocytes from trained rats was significantly greater than in those from sedentary rats. This suggests that increased myocyte cross-sectional area is a major contractile adaptation to exercise in this model. Training did not alter the passive mechanical properties of myocytes or the relative distribution of titin isomers, which was exclusively of the short, N2B form. However, training did increase the steepness of the active tension-sarcomere length relationship, suggesting an exercise-induced modulation of the Frank-Starling mechanism. This effect would be expected to enhance cardiac contractility. Training lengthened the action potential duration of sub-epicardial myocytes, reducing the transmural gradient in action potential duration. This observation may be important in understanding the cellular causes of T-wave abnormalities found in the electrocardiograms of some athletes. Our study shows that voluntary exercise modulates the morphological, mechanical and electrical properties of cardiac myocytes, and that this modulation is dependent upon the regional origin of the myocytes.

Halothane inhibits contraction and action potential duration to a greater extent in subendocardial than subepicardial myocytes from the rat left ventricle

BACKGROUND

Halothane inhibits the 4-aminopyridine-sensitive transient outward K(+) current (I(to)) which in many species, including humans, plays an important role in determining action potential duration. As I(to) is greater in the ventricular subepicardium than subendocardium, halothane may have differential effects on action potential duration and, therefore, contraction in cells isolated from these two regions.

METHODS

Myocytes were isolated from the subendocardium and subepicardium of the rat left ventricle. Myocytes from each region were electrically stimulated at 1 Hz to measure contractions and action potentials and exposed to 0.6 mm halothane (approximately 2 x minimum alveolar concentration(50) for the rat) for 1 min. The time from the peak of the action potential to repolarization at 0 and -50 mV was measured to assess the effects of halothane on action potential duration.

RESULTS

Halothane inhibited contraction to a significantly (P = 0.002) greater extent in subendocardial myocytes than in subepicardial myocytes: the amplitude of contraction during control conditions was 3.6 +/- 0.4 microm and 3.2 +/- 0.7 microm in subendocardial and subepicardial cells, respectively, and this was reduced to 1.1 +/- 0.2 microm (29 +/- 2% of control, P < 0.0001, n = 10) and 1.4 +/- 0.3 microm (46 +/- 3% of control, P = 0.007, n = 7), respectively, after a 1-min exposure to 0.6 mm halothane. Control action potential duration (at -50 mV) was 67 +/- 10 and 28 +/- 4 ms in subendocardial and subepicardial myocytes, respectively, and these values were reduced to 39 +/- 6 ms (58 +/- 3% of control, P < 0.001) and 20 +/- 3 ms (73 +/- 5% of control, P = 0.009) by halothane, respectively.

CONCLUSIONS

Action potential duration was reduced to a greater extent in subendocardial than subepicardial myocytes, which would contribute to the greater negative inotropic effect of halothane in the subendocardium. Furthermore, the transmural difference in action potential duration was reduced by halothane, which could contribute to its arrhythmogenic properties.

Regional effects of voluntary exercise on cell size and contraction-frequency responses in rat cardiac myocytes

A model of voluntary exercise, in which rats are given free access to a running wheel over a 14-week period, led to left ventricular hypertrophy. To test whether the hypertrophic response to exercise was uniformly distributed across the ventricular wall, single ventricular myocytes were isolated from the sub-epicardium (EPI) and sub-endocardium (ENDO) of exercised rats and from sedentary rats for comparison. Cellular hypertrophy (approximately 20 % greater cell volume) was seen in ENDO cells from exercised animals, but no significant changes were observed in EPI cells when compared with sedentary controls. This regional effect of exercise may be a response to transmural changes in ventricular wall stress and/or strain. Cell contraction was measured as cell shortening in ENDO and EPI cells at stimulation frequencies between 1 and 9 Hz at 37 degrees C. Exercise training had no effect on cell shortening. Positive and negative contraction-frequency relationships (CFRs) were found in both EPI and ENDO cells between 1 and 5 Hz; at higher frequencies (5–9 Hz), all myocytes displayed a negative CFR. The CFR of a myocyte was, therefore, independent of regional origin and unaffected by exercise. These results suggest that, in vivo, the rat heart displays a negative CFR. We conclude that increased cell size may be a more important adaptive response to exercise than a modification of excitation-contraction coupling.

Sp5, a new member of the Sp1 family, is dynamically expressed during development and genetically interacts with Brachyury

We describe the identification, biochemical characterisation, and mutation of a novel mouse gene: Sp5. Sp5 encodes a protein having a C-terminal C(2)H(2) zinc finger domain closely related to that of the transcription factor Sp1. In vitro, DNA binding studies show that it binds to the GC box, a DNA motif present in the promoter of a very large number of genes, including Brachyury, and recognised by members of the Sp1 family. However, outside of its DNA binding domain, Sp5 has little homology with any other member of the Sp1 family. In contrast to the ubiquitous expression of Sp1, Sp5 exhibits a remarkably dynamic pattern of expression throughout early development. This is suggestive of a role in numerous tissue patterning events, including gastrulation and axial elongation; differentiation and patterning of the neural tube, pharyngeal region, and somites; and formation of skeletal muscle in the body and limbs. Mice homozygous for a targeted mutation in Sp5 show no overt phenotype. However, the enhancement of the T/+ phenotype in compound mutant mice (Sp5(lacZ)/Sp5(lacZ), T/+) indicates a genetic interaction between Sp5 and Brachyury. These observations are consistent with a role for Sp5 in the coordination of changes in transcription required to generate pattern in the developing embryo.

Effects of isoflurane, sevoflurane, and halothane on myofilament Ca2+ sensitivity and sarcoplasmic reticulum Ca2+ release in rat ventricular myocytes

BACKGROUND

The aim of this study was to describe and compare the effects of isoflurane, sevoflurane, and halothane at selected concentrations (i.e., concentrations that led to equivalent depression of the electrically evoked Ca2+ transient) on myofilament Ca2+ sensitivity, sarcoplasmic reticulum (SR) Ca2+ content, and the fraction of SR Ca2+ released during electrical stimulation (fractional release) in rat ventricular myocytes.

METHODS

Single rat ventricular myocytes loaded with fura-2 were electrically stimulated at 1 Hz, and the Ca2+ transients and contractions were recorded optically. Cells were exposed to each anesthetic for 1 min. Changes in myofilament Ca2+ sensitivity were assessed by comparing the changes in the Ca2+ transient and contraction during exposure to anesthetic and low Ca2+. SR Ca2+ content was assessed by exposure to 20 mm caffeine.

RESULTS

Isoflurane and halothane caused a depression of myofilament Ca2+ sensitivity, unlike sevoflurane, which had no effect on myofilament Ca2+ sensitivity. All three anesthetics decreased the electrically stimulated Ca2+ transient. SR Ca2+ content was reduced by both isoflurane and halothane but was unchanged by sevoflurane. Fractional release was reduced by both isoflurane and sevoflurane, but was unchanged by halothane.

CONCLUSIONS

Depressed myofilament Ca2+ sensitivity contributes to the negative inotropic effects of isoflurane and halothane but not sevoflurane. The decrease in the Ca2+ transient is either responsible for or contributory to the negative inotropic effects of all three anesthetics and is either primarily the result of a decrease in fractional release (isoflurane and sevoflurane) or primarily the result of a decrease in SR Ca2+ content (halothane).

Levels of nerve growth factor and neurotrophin-3 are affected differentially by the presence of p75 in sympathetic neurons in vivo

The development and survival of sympathetic neurons is critically dependent on the related neurotrophic factors nerve growth factor (NGF) and neurotrophin-3 (NT3), the actions of which must be executed appropriately despite spatial and temporal overlaps in their activities. The tyrosine receptor kinases, trkA and trkC, are the cognate receptors for NGF and NT3, respectively. The p75 neurotrophin receptor has been implicated in neurotrophin binding and signaling for both NGF and NT3. In this study, the authors used mice that overexpressed NGF (NGF-OE) or NT3 (NT3-OE) in skin and mice that lacked p75 (p75(-/-)) to understand the dynamics of sympathetic neuron response to each neurotrophin and to address the role of p75. NGF and NT3 were measured in sympathetic ganglia and skin (a major target of sympathetic neurons) by using the enzyme-linked immunosorbent assay (ELISA) technique. A three- to four-fold increase in skin NT3 was seen in both NT3-OE and p75(-/-) mice. Moreover, both mouse lines exhibited a three-fold increase in ganglionic NT3. However, the increase in ganglionic NT3 was accompanied by a decrease in ganglionic NGF in p75(-/-) mice but not in NT3-OE mice. This indicated that p75 plays an important role in determining the level of NGF within sympathetic neurons. In NGF-OE mice, the overexpression of NGF was correlated with increased ganglionic NGF and increased ganglionic expression of p75 mRNA. In addition, in NGF-OE mice, ganglionic trkC expression was decreased, as was the amount of NT3 present within sympathetic ganglia. These results indicate that the level of p75 is integral in determining the level of sympathetic NGF and that NGF competes with NT3 by increasing the expression of p75 and decreasing the expression of trkC.

The concentration-dependent effects of propofol on rat ventricular myocytes

Whether propofol contributes a direct negative inotropic effect is controversial. Our principal aim in this study was to determine whether negative inotropic effects of propofol occur at clinically relevant concentrations. We constructed the concentration-response relationship for the negative inotropic effects on intact, isolated, stimulated rat ventricular myocytes. Contraction was measured as cell shortening by using an optical system. Propofol was applied as dilutions of the commercial preparation in physiological saline solution. The drug vehicle had a minimal effect on myocyte contractility. Propofol produced a concentration-dependent reduction in evoked contraction at concentrations greater than 5 microM. The maximum effect was observed at >100 microM, with the K(0.5) calculated to be 34.5 microM (95% CI, 21.8-54.7 microM). In further experiments, we investigated the relationship between changes in contractility and changes in Ca(2+) transient (measured by using fura-2 fluorescence) after the application of propofol. By using the shift in the relationship of the cell length to fura-2 fluorescence ratio in the relaxation phase of a contraction as an index of Ca(2+) response of the myofilaments, we demonstrated that some of the negative inotropic effect of propofol may be caused by a reduction in myofilament Ca(2+) sensitivity. We confirmed this by comparing the reduction in contractility in the presence of propofol with that caused by reducing the extracellular Ca(2+) concentration. We observed that, for a decrease in the fura-2 fluorescence ratio of 21%, propofol caused a 12% (95% CI, 2% to 22%) greater reduction in contractility than predicted from reducing the extracellular Ca(2+) concentration. However, the K(0.5) for the negative inotropic effect of propofol we observed is more than 80 times the 50% effective concentration value for anesthesia. The potential relevance of these findings for clinical use of propofol in humans is discussed.

IMPLICATIONS

By using intact, isolated rat heart ventricle cells, we investigated the mechanisms and concentration dependence of the depressant effect of propofol on contractility of the heart. We conclude that direct effects of propofol on the heart are unlikely to be of significance at the clinical dosage usually given.

Quantitative analysis of Na+-Ca2+ exchanger expression in guinea-pig heart

In previous studies, regional variations in the expression of the Na+-Ca2+ exchanger (NCX) have been examined qualitatively in human heart using the C2C12 monoclonal antibody [Wang, J., Schwinger, R.H., Frank, K., Muller-Ehmsen, J., Martin-Vasallo, P., Pressley, T.A., Xiang, A., Erdmann, E. & McDonough, A.A. (1996) J. Clin. Invest. 98, 1650-1658]. Although NCX expression was found to be significantly lower in the atria compared to the septum, no significant differences were found between atrial and ventricular tissue. NCX has been located in the general sarcolemma and t-tubules of ventricular muscle and as t-tubules are sparse in atrial tissue compared to ventricular tissue, it is surprising that NCX expression was found to be similar in both atria and ventricles [Wang et al. (1996)]. To reinvestigate this, we have used SDS/PAGE and a quantitative Western blotting technique to determine the pattern of expression of NCX in guinea-pig heart in tissue samples from left atrium, right atrium, septum, left ventricle and right ventricle. NCX protein expression was 17.5 +/- 3.9 pmol.mg-1 of protein in the left atrium and 29.2 +/- 6.1 pmol.mg-1 of protein in the right atrium, which were both significantly lower (P < 0.05) than NCX expression in the septum, left ventricle and right ventricle (64.7 +/- 15.2, 76.8 +/- 19.5 and 69.4 +/- 14.1 pmol.mg-1 of protein, respectively, n = 7). These differences in NCX expression may reflect variations in the cellular location of NCX protein in these regions. To study this, we used confocal immunofluorescence of single isolated myocytes to examine differences in the proportion of fluorescent staining on the general surface membrane compared with the interior of the cell (which presumably reflects a t-tubular location). We found that the general membrane staining was 79.0 +/- 1.2% in cells from the atria which was significantly higher (P < 0. 001) than that seen in cells from the septum, left ventricle and right ventricle, with 48.1 +/- 1.1%, 48.2 +/- 1.8% and 45.6 +/- 1.3%, respectively (n = 20). These results illustrate a similar pattern of NCX expression in guinea-pig and human, with expression in atrial tissue significantly lower than in ventricular tissue. However, the cellular location of NCX differs regionally; in atrial tissue, the majority of the NCX protein is located in the general sarcolemma whereas in ventricular and septal tissue, approximately 50% of NCX protein is located within the cell (presumably at the level of the t-tubules).

Concentration-dependent inotropic effects of halothane, isoflurane and sevoflurane on rat ventricular myocytes

We have described the concentration-dependent inotropic effects of halothane, isoflurane and sevoflurane on rat ventricular cells and investigated the role of the sarcoplasmic reticulum (SR) in these inotropic actions. Single ventricular myocytes, isolated from rat hearts, were stimulated electrically at 1 Hz and contractions recorded optically. Cells were exposed to a range of concentrations of halothane, isoflurane or sevoflurane for a period of 1 min to determine the concentration-dependency of their inotropic actions. For each anaesthetic, the peak negative inotropic action was determined early during an exposure, and sustained negative inotropic action was measured at steady-state just before wash-off. In some experiments, cells were equilibrated with ryanodine 1 mumol litre-1 to investigate the role of the SR in these intropic effects. Halothane caused a concentration-dependent initial increase in contractions (to mean 130 (SEM 28)% at 10 mmol litre-1) followed by rapid onset of a negative inotropic effect (K0.5 0.34 mmol litre-1 for peak effect; K0.5 0.46 mmol litre-1 for sustained effect). Exposure to isoflurane induced a small potentiation of contractions in some cells, followed by a concentration-dependent decrease in contraction in all cells (K0.5 0.85 mmol litre-1 for peak effect; K0.5 1.92 mmol litre-1 for sustained effect); contractions recovered partially during a 1-min exposure. On wash-off, contractions were increased transiently above control. Sevoflurane caused a large initial decrease in contraction which then returned rapidly towards control (K0.5 0.2 mmol litre-1 for peak effect; K0.5 2.57 mmol litre-1 for sustained effect). In common with isoflurane, removal of sevoflurane caused a transient increase in contractions above control. After exposure to ryanodine, the positive inotropic effects of halothane and isoflurane did not occur, and recovery of contractions during exposure to isoflurane and sevoflurane was abolished as was the transient increase in contractions seen on wash-off, indicating that these effects were mediated via the SR. Halothane had the most potent sustained negative inotropic effect but there was little difference between the negative inotropic effects of isoflurane and sevoflurane at clinically relevant concentrations. At higher concentrations, sevoflurane caused a less potent negative inotropic effect than isoflurane. The SR plays a major role in the effects of all three anaesthetics. One possible mechanism underlying the initial potentiation of contraction by halothane (and isoflurane) may be sensitization of the Ca(2+)-induced Ca(2+)-release process of the SR.

Mechanisms underlying the inotropic action of halothane on intact rat ventricular myocytes

The mechanisms contributing to the negative inotropic effect of halothane were studied in isolated rate ventricular myocytes. Contraction and intracellular Ca2+ transients were measured optically in these cells. The initial application of halothane (2% or 0.5 mmol litre-1) led to short-lived increases in the Ca2+ transient and contraction, which were abolished by ryanodine. Continued application of halothane led to a sustained decrease in contraction: this resulted from: (i) a decrease in myofilament Ca2+ sensitivity; (ii) a decrease in the Ca2+ transient; and (iii) a decrease in the Ca2+ content of the sarcoplasmic reticulum. Although halothane reduced action potential duration, the sustained negative inotropic effect was similar when action potentials or voltage clamp pulses of constant duration were used to trigger contractions. In cells exposed to nifedipine 0.5 mumol litre-1 (which decreases the L-type Ca2+ current, ICa), Ca2+ transients, sarcoplasmic reticulum Ca2+ content and fractional release (the fraction of sarcoplasmic reticulum Ca2+ content released during each stimulus) were reduced. Halothane 0.5 mmol litre-1 (which also decreases ICa) decreased Ca2+ transients to a lesser extent and reduced sarcoplasmic reticulum Ca2+ content to a greater extent than nifedipine, whereas fractional release was unchanged compared with control. These data suggest that halothane sensitizes Ca(2+)-induced Ca2+ release from the sarcoplasmic reticulum in addition to reducing ICa.

Changes in contraction, cytosolic Ca2+ and pH during metabolic inhibition and upon restoration of mitochondrial respiration in rat ventricular myocytes

Exposure of cardiac muscle to metabolic poisons reduces the availability of cellular ATP and cardiac dysfunction ensues. In this study rat ventricular myocytes were exposed to 2-deoxyglucose, iodoacetate and cyanide to induce complete metabolic blockade. Changes in contraction, cytosolic Ca2+ and pH were determined during metabolic blockade and following restoration of mitochondrial ATP production. Metabolic blockade resulted in a rapid failure of contractions and Ca2+ transients, a rise of diastolic Ca2+, a cytosolic acidosis and ultimately a rigor contracture. Washing out cyanide during the development of the rigor contracture led to a rapid relaxation of the contracture, a fall in cytosolic Ca2+ and a rapid, partial reversal of the cytosolic acidosis. The partial reversal of the cytosolic acidosis and fall of cytosolic Ca2+ were abolished in the presence of oligomycin. This suggests that the rapid partial recovery of cytosolic acidosis could result from the rephosphorylation of ADP to ATP by the mitochondrial F1,F0-ATPase (a reaction that consumes protons).

A method for reversible permeabilization of isolated rat ventricular myocytes

A method is described that enables the cell membrane of isolated rat ventricular myocytes to be permeabilized and resealed while maintaining cell viability. Streptolysin O, a cholesterol-binding cytolysin, was used to form pores in the surface membrane; subsequent incubation with 5% fetal bovine serum was used to reverse this permeabilization. The efficacy of membrane permeabilization and resealing was ascertained using a simultaneous double-staining technique using propidium iodide, a marker for cells with permeabilized membranes, and fluorescein diacetate, a marker for viable cells. This procedure allowed a distinction to be made between dead cells, unpermeabilized cells and viable cells that had been successfully permeabilized and resealed. The accessibility of the cell interior during permeabilization was investigated by including fluorescein isothiocyanate (FITC)-labelled dextrans (11, 38 and 148 kDa) and bovine serum albumin (67 kDa) in the permeabilization buffer, and localizing the FITC label using confocal microscopy following resealing. The confocal images showed that these molecules entered the cells and were retained after resealing. Following the permeabilization-resealing protocol, cells appeared to have both normal morphology and response to electrical stimulation. Thus this appears to be a cheap, simple and effective method to introduce relatively large molecules into cardiac myocytes.

Cell death during development of testis and cerebellum in the mutant mouse weaver

The murine mutation weaver confers early death during development on cells in testes, cerebellum, and midbrain. The results reported here support the hypothesis that the action of weaver is intrinsic to testes and independent of Sertoli cells: germ cells are the only testicular cell type seen to die in weaver homozygotes, while Sertoli cell-dependent development of the blood testis barrier is normal. This report includes characterization of patterns of germ cell death and cerebellar granule cell death in homozygous weavers with respect to that seen during normal development by in situ end-labeling of DNA and high-magnification light microscopy. Comparison of the spatial distribution of dying cells in the weaver's cerebellum with that of dividing cells revealed disarray in the external germinal zone. The results show that cells vulnerable to weaver die by apoptotic and nonapoptotic mechanisms and indicate that weaver-induced cell death is not the consequence of extended naturally occurring developmental cell death, although their timing overlaps. Thus, although the death of cells in each region is likely to be caused by the same mutation, a base pair substitution in the G protein-coupled inwardly rectifying potassium channel 2 gene, the cell death program activated differs depending on cell type.

The effect of temperature on the rate-dependent decrease of the rat ventricular calcium current

We have investigated the effect of temperature upon the rate-dependent decrease in the L-type Ca2+ current (iCa) in isolated rat ventricular myocytes. Increasing the rate of stimulation from 0.5 to 3.0 Hz for 30s induced a reversible decrease in iCa which was temperature dependent. Compared to control (0.5 Hz), the first beat at 3 Hz was decreased by 38 +/- 7% at 22 degrees C and by 9 +/- 1% at 37 degrees C (mean +/- S.E.M., n = 5, P < 0.05) and, after 30 s of 3 Hz stimulation, iCa was reduced by a further 26 +/- 4 and 21 +/- 2% at 22 and 37 degrees C, respectively. The magnitude of this secondary decline was not significantly different at the two temperatures (P = 0.29). Corroboratory results were obtained from cell-attached patches which also illustrated that the rate-dependent decrease in iCa resulted from a reduction of open channel probability. Paired pulse experiments showed that the greater initial rate-dependent decrease in iCa at 22 degrees C occurred as a result of slower recovery from fast inactivation processes at 22 than at 37 degrees C. Recovery of the channel from fast inactivation was very temperature sensitive with a Q10 of 5.6. In contrast, the secondary, progressive decrease in iCa, which results from incomplete recovery from ultra-slow voltage-dependent inactivation, was similar at the two temperatures and appears to be much less temperature dependent.

The role of Na(+)-Ca2+ exchange current in electrical restitution in ferret ventricular cells

1. The mechanisms underlying electrical restitution (recovery of action potential duration after a preceding beat) were investigated in ferret ventricular cells. The time to 80% recovery (t80) of action potential duration was approximately 204 ms. 2. At a holding potential of -80 mV, the Ca2+ current (ICa) reactivated and the delayed rectifier K+ current (IK) deactivated very rapidly (t80: approximately 32 and approximately 93 ms, respectively). The kinetics of both currents are too fast to account for electrical restitution alone. 3. The putative inward Na(+)-Ca2+ exchange current (INa-Ca) produced by the Na(+)-Ca2+ exchanger in response to the intracellular Ca2+ transient reprimed (t80: 189 ms) with the same time course as mechanical restitution (recovery of contraction) and with a similar time course to electrical restitution. 4. Substantial reduction of inward INa-Ca, by buffering intracellular Ca2+ with the acetyl methyl ester form of BAPTA, shortened the action potential and greatly altered the electrical restitution curve. Subsequent addition of nifedipine (to block ICa) or 4-aminopyridine (4-AP) (to block the transient outward current, ITO) further altered the electrical restitution curve. 5. Any time-dependent current that contributes to the action potential is likely to affect the time course of electrical restitution. Although ICa, IK and ITO were previously thought to be the only currents involved in electrical restitution, we conclude that inward INa-Ca also plays an important role.

Mouse Dll3: a novel divergent Delta gene which may complement the function of other Delta homologues during early pattern formation in the mouse embryo

Mouse delta-like 3 (Dll3), a novel vertebrate homologue of the Drosophila gene Delta was isolated by a subtracted library screen. In Drosphila, the Delta/Notch signalling pathway functions in many situations in both embryonic and adult life where cell fate specification occurs. In addition, a patterning role has been described in the establishment of the dorsoventral compartment boundary in the wing imaginal disc. Dll3 is the most divergent Delta homologue identified to date. We confirm that Dll3 can inhibit primary neurogenesis when ectopically expressed in Xenopus, suggesting that it can activate the Notch receptor and therefore is a functional Delta homologue. An extensive expression study during gastrulation and early organogenesis in the mouse reveals a diverse and dynamic pattern of expression. The three major sites of expression implicate Dll3 in somitogenesis and neurogenesis and in the production of tissue from the primitive streak and tailbud. A careful comparison of Dll3 and Dll1 expression by double RNA in situ hybridisation demonstrates that these genes have distinct patterns of expression, but implies that together they operate in many of the same processes. We postulate that during somitogenesis Dll3 and Dll1 coordinate in establishing the intersomitic boundaries. We confirm that, during neurogenesis in the spinal cord, Dll1 and Dll3 are expressed by postmitotic cells and suggest that expression is sequential such that cells express Dll1 first followed by Dll3. We hypothesise that Dll1 is involved in the release of cells from the precursor population and that Dll3 is required later to divert neurons along a specific differentiation pathway.

Attempt to correlate urine arsenic excretion with clinical course during melarsoprol therapy of patients with Rhodesian trypanosomiasis

This study enrolled 28 CNS-involved patients with Trypanosoma brucei rhodesiense at the Kenya Trypanosomiasis Research Institute (Alupe, Kenya) to examine treatment efficacy and toxicity of melarsoprol in relation to renal excretion/dose relationships. This study complied with World Health Organization treatment recommendations, initially treating with suramin followed by three courses of melarsoprol. Traced study patients had a relapse rate of 4.1%. The toxicity and crude death rate was 7.1%. Total urine arsenic output was measured between 24 and 48 hr after the last dose for each course. The range of means of total urine arsenic output between the three treatment courses was 356-511 micrograms. There was no correlation comparing melarsoprol dose, estimated creatine clearance, or urine arsenic output. Urinary pharmacokinetic parameters are not predictive of toxicity or therapeutic efficacy.

The role of inward Na(+)-Ca2+ exchange current in the ferret ventricular action potential

1. Inward Na(+)-Ca2+ exchange current (iNaCa) was either blocked in ferret ventricular cells by replacing extracellular Na+ with Li+ or substantially reduced by the almost complete elimination of the Ca2+ transient by buffering intracellular Ca2+ with the acetoxymethyl ester form of BAPTA (BAPTA AM). 2. During square wave voltage clamp pulses to 0 mV, replacing extracellular Na+ with Li+ or buffering intracellular Ca2+ with BAPTA AM resulted in the loss of a transient inward current. This current was increased by the application of isoprenaline (expected to increase the underlying Ca2+ transient) and displayed the voltage-dependent characteristics of inward iNaCa. 3. Replacing extracellular Na+ with Li+ or buffering intracellular Ca2+ caused a significant shortening of the action potential (at -65 mV, 44 +/- 2% with Li+ and 20 +/- 2% with BAPTA AM). The shortening can be explained by changes in iNaCa. 4. The action potential clamp technique was used to measure the BAPTA-sensitive current (putative iNaCa) and the Ca2+ current (ica; measured using nifedipine) during the action potential. Under control conditions, the inward BAPTA-sensitive current makes approximately the same contribution as iCa during much of the action potential plateau. These results suggest an important role for inward iNaCa in the ferret ventricular action potential.

Neuropeptide changes persist in spinal cord despite resolving hyperalgesia in a rat model of mononeuropathy

We have previously described the changes in spinal cord neuropeptides in the unilateral sciatic chronic constriction injury (CCI) model of Bennett and Xie [Pain, 33 (1988) 87-108] at 28 days, a time of maximum mechanical hyperalgesia. In this study we examine the same model 100-120 days post injury by which time resolution of the hyperalgesia and peripheral nerve injury has occurred according to previous studies. Rats underwent either CCI of the sciatic nerve (n = 12) or else sham operation (n = 8) which involved exposure but no ligation of the nerve. Mechanical hyperalgesia was assessed with a Ugo-Basile analgesymeter and immunohistochemistry performed on the spinal cord sections of the animals and quantified using a confocal microscope. At this late time point CCI rats were no longer significantly mechanically hyperalgesic compared to the sham animals (P > or = 0.09). However, examination of the lumbar spinal cord revealed the following changes. (i) The neuropeptides substance P (SP) (P < 0.0001) and galanin (P < 0.003) both showed decreases of about 30% ipsilaterally in immunoreactivity in laminae 1 and 2 of the dorsal horn compared to the sham operated animals. (ii) Calcitonin gene-related peptide (CGRP) and neuropeptide Y (NPY) in laminae 1 and 2 showed no significant changes compared to sham animals. (iii) NPY levels in laminae 3 and 4 of the spinal cord showed a 15% increase in immunoreactivity compared to sham animals (P = 0.008). These results indicate that changes in neuronal markers in the spinal cord can persist after apparent resolution of a peripheral nerve injury. We suggest that these changes may form a substrate for subsequent development of abnormal pain states.

Neuron death in the substantia nigra of weaver mouse occurs late in development and is not apoptotic

Weaver is a spontaneous mutation in mice characterized by the postnatal loss of external granule cells in the cerebellum and dopaminergic neurons of the midbrain, especially in the substantia nigra. We have shown previously that natural cell death with the morphology of apoptosis occurs in the substantia nigra of normal rodents during postnatal development. We therefore sought to determine whether the loss of dopaminergic neurons in homozygous weaver mice occurs during the period of natural cell death in the substantia nigra and whether it has the morphology of apoptosis. We have found, using a silver stain technique, that although apoptotic cell death does occur early postnatally in homozygous weaver substantia nigra, it also does so with equal magnitude in wild-type and heterozygous weaver littermates. Unique to homozygous weavers is the occurrence of degenerating neurons in the nigra that are not apoptotic. These degenerating neurons are observed at postnatal day 7, and they are most abundant on postnatal days 24-25. The nonapoptotic nature of this cell death is confirmed by negative in situ end labeling of nuclear DNA fragmentation and by ultrastructural analysis. Ultrastructural studies reveal irregular chromatin aggregates in the nucleus, as well as marked cytoplasmic changes, including the formation of vacuoles and distinctive stacks of dilated cisternae of endoplasmic reticulum. We interpret these changes as indicative of either a variant morphology of programmed cell death or a pathological degenerative process mediated by an as yet unknown mechanism related to the recently described mutation in the GIRK2 potassium channel.

Comparison of ultra-slow, voltage-dependent inactivation of the cardiac L-type Ca2+ channel with Ca2+ or Ba2+ as the charge carrier in ferret ventricular myocytes

The whole-cell patch clamp technique was used to investigate the effect of different charge carriers upon ultra-slow voltage-dependent inactivation of L-type Ca2+ channel current in ferret ventricular myocytes at 37 degrees C. Intracellular Ca2+ was buffered with 10 mM EGTA and the membrane potential held at -40 mV. With Ba2+ as the charge carrier, the L-type current decayed throughout 20 s pulses to 0 mV as a result of ultra-slow voltage-dependent inactivation. In contrast, with Ca2+ as the charge carrier, there was no such slow decay of the current as the current decayed almost completely in the first approximately 100 ms as a result of Ca(2+)-dependent inactivation. However, with Ca2+ as the charge carrier it is still possible that ultra-slow voltage-dependent inactivation occurs. A conditioning-test pulse protocol and a second protocol were used to test for the development of ultra-slow inactivation during 20 or 30 s pulses to 0 mV with Ca2+ as the charge carrier. Ultra-slow inactivation did occur and it was qualitatively similar to that with Ba2+ as the charge carrier. The onset of ultra-slow inactivation with Ca2+ as the charge carrier could be described by the sum of two exponentials with time constants of 0.3 and 6.7 s. Recovery from ultra-slow inactivation with Ca2+ as the charge carrier was also measured with a conditioning-test pulse protocol and was best described by the sum of two exponentials with time constants of 0.5 and 6.2 s. We conclude that ultra-slow inactivation of the L-type current does occur with the physiological charge carrier, Ca2+, but it is normally masked by Ca(2+)-dependent inactivation.

Mn2+ can substitute for Ca2+ in causing catecholamine secretion but not for increasing tyrosine hydroxylase phosphorylation in bovine adrenal chromaffin cells

The ability of the divalent cation manganese (Mn2+) to substitute for calcium (Ca2+) both in triggering catecholamine release and in stimulating catecholamine synthesis, as indicated by an increase in tyrosine hydroxylase (TOH) phosphorylation, has been determined in bovine adrenal medullary chromaffin cells maintained in tissue culture. Mn2+ was found to enter chromaffin cells through pathways activated by nicotinic receptor stimulation and potassium depolarisation, and via the Na1:Ca0 exchange mechanism in Na(+)-loaded cells. Like Ca2+, entry of Mn2+ through these pathways triggered immediate catecholamine release and, like Ca2+, maintained quantitatively comparable release at least up to 40 min. Unlike Ca2+, Mn2+ did not stimulate an increase in TOH phosphorylation in intact chromaffin cells, even over a prolonged time course, but Mn2+ did stimulate increased TOH phosphorylation in lysed cell preparations showing that its lack of effect in the intact cells was not due to inhibition of the specific phosphorylation pathway. In lysed cell preparations, Mn2+ stimulated also phosphorylation of a different spectrum of proteins to Ca2+, and of the same proteins to different extents. In particular, P80 (MARCKS protein) was more intensely phosphorylated in the presence of Mn2+ than in the presence of Ca2+. Since TOH phosphorylation always occurs when intracellular Ca2+ is increased, the absence of an increase with Mn2+ indicates that none of its intracellular effects could have occurred as a consequence of Mn2+ mobilisation of intracellular Ca2+. In summary, the data show that Mn2+ is a surrogate for Ca2+ in triggering and maintaining catecholamine release, but does not substitute for Ca2+ in stimulating TOH phosphorylation.

Tyrosine hydroxylase phosphorylation in bovine adrenal chromaffin cells. Clonidine stimulates basal but inhibits nicotinic receptor evoked phosphorylation

Clonidine inhibited the uptake of calcium and the overall phosphorylation of tyrosine hydroxylase induced by nicotinic receptor activation in bovine adrenal medullary chromaffin cells in culture. However, clonidine did not inhibit the increase in these parameters that accompanied K+ depolarisation of the cells. There was also no effect of clonidine on the overall phosphorylation of tyrosine hydroxylase when cells were stimulated by muscarine. Nicotinic receptor activation increased the phosphorylation of Ser-19, Ser-31, and Ser-40 on tyrosine hydroxylase, and this was inhibited by clonidine in a concentration-dependent manner. On the other hand, clonidine had no effect on calcium uptake, yet increased the phosphorylation of Ser-19 under basal conditions. Using calcium and calmodulin-stimulated protein kinase II obtained from rat brain clonidine increased the autophosphorylation of the alpha-subunit of the kinase by 37%, and also its activity against an exogenous peptide substrate by 29%. These data are consistent with the hypothesis that clonidine inhibits nicotinic receptor-induced tyrosine hydroxylase phosphorylation by decreasing calcium influx into chromaffin cells, perhaps by an action at the nicotinic receptor. Clonidine also increases the basal phosphorylation of tyrosine hydroxylase at Ser-19, perhaps by directly activating calcium and calmodulin-stimulated protein kinase II.