Modulation of K+ channels by hydrogen peroxide.

External application of hydrogen peroxide (H2O2) was found to inhibit the time-dependent fast inactivation process of three cloned voltage-gated K+ channels expressed in Xenopus oocytes: KShIIIC, KShIIID and HukII. As expected from kinetic models where some channels are still opening while a significant fraction of channels is already inactivated there was a large increase in current magnitude concomitant to inactivation block. The channels otherwise functioned normally. The effects of H2O2 were specific (other cloned voltage-gated K+ channels were not affected), and reversible, the currents returned to normal upon removal of the H2O2. H2O2 is produced during normal metabolism; it could act as a modulator of excitability through effects on K+ channels if effective local concentrations are reached in neuronal regions close to the channel. KShIIIC and KShIIID currents are very similar to an O2-sensitive K+ current present in type I cells of the carotid body which is believed to underlie the modulation of excitability of these cells by changes in arterial O2 pressure. H2O2 has been proposed as an intermediary between O2 and cellular response in the carotid body; our results provide support for this model.     

Plasma selenium levels in healthy blood bank donors in the central-eastern part of Belgium

Graphite furnace atomic absorption spectrometry, with Zeeman background correction and after improved matrix modification, was used to measure the plasma selenium content of healthy blood bank donors in the central part of Belgium.

The mean plasma selenium concentration of 80 men and 80 women was 79.7±4.4 ng/mL with a range of 55.0–117.4 ng/mL.

There was no gender difference observed. Plasma selenium level was significantly highest for the adult group, aged 45–64 years, compared to the others, except the young adults (18–24 years).

The mean plasma selenium concentration measured corresponded well with literature data for Belgium. The obtained values were found to be in the medium range, compared with recent literature values for the European countries.     

Managing anabolic steroids in pre-hibernating Arctic ground squirrels: obtaining their benefits and avoiding their costs

Androgens have benefits, such as promoting muscle growth, but also significant costs, including suppression of immune function. In many species, these trade-offs in androgen action are reflected in regulated androgen production, which is typically highest only in reproductive males. However, all non-reproductive Arctic ground squirrels, irrespective of age and sex, have high levels of androgens prior to hibernating at sub-zero temperatures. Androgens appear to be required to make muscle in summer, which, together with lipid, is then catabolized during overwinter. By contrast, most hibernating mammals catabolize only lipid. We tested the hypothesis that androgen action is selectively enhanced in Arctic ground squirrel muscle because of an upregulation of androgen receptors (ARs). Using Western blot analysis, we found that Arctic ground squirrels have AR in skeletal muscle more than four times that of Columbian ground squirrels, a related southern species that overwinters at approximately 0°C and has low pre-hibernation androgen levels. By contrast, AR in lymph nodes was equivalent in both species. Brain AR was also modestly but significantly increased in Arctic ground squirrel relative to Columbian ground squirrel. These results are consistent with the hypothesis that tissue-specific AR regulation prior to hibernation provides a mechanism whereby Arctic ground squirrels obtain the life-history benefits and mitigate the costs associated with high androgen production.     

A computer-based simulation of childbirth using the partial Dirichlet–Neumann contact method with total Lagrangian explicit dynamics on the GPU

During physiological or ‘natural’ childbirth, the fetal head follows a distinct motion pattern—often referred to as the cardinal movements or ‘mechanisms’ of childbirth—due to the biomechanical interaction between the fetus and maternal pelvic anatomy. The research presented in this paper introduces a virtual reality-based simulation of physiological childbirth. The underpinning science is based on two numerical algorithms including the total Lagrangian explicit dynamics method to calculate soft tissue deformation and the partial Dirichlet–Neumann contact method to calculate the mechanical contact interaction between the fetal head and maternal pelvic anatomy. The paper describes the underlying mathematics and algorithms of the solution and their combination into a computer-based implementation. The experimental section covers first a number of validation experiments on simple contact mechanical problems which is followed by the main experiment of running a virtual reality childbirth. Realistic mesh models of the fetus, bony pelvis and pelvic floor muscles were subjected to the intra-uterine expulsion forces which aim to propel the virtual fetus through the virtual birth canal. Following a series of simulations, taking variations in the shape and size of the geometric models into account, we consistently observed the cardinal movements in the simulator just as they happen in physiological childbirth. The results confirm the potential of the simulator as a predictive tool for problematic childbirths subject to patient-specific adaptations.

     

Variation in Wolbachia cidB gene,but not cidA,is associated with cytoplasmic incompatibility mod phenotype diversity in Culex pipiens

Endosymbiotic Wolbachia bacteria are, to date, considered the most widespread symbionts in arthropods and are the cornerstone of major biological control strategies. Such a high prevalence is based on the ability of Wolbachia to manipulate their hosts' reproduction. One manipulation called cytoplasmic incompatibility (CI) is based on the death of the embryos generated by crosses between infected males and uninfected females or between individuals infected with incompatible Wolbachia strains. CI can be seen as a modification‐rescue system (or mod‐resc) in which paternal Wolbachia produce mod factors, inducing embryonic defects, unless the maternal Wolbachia produce compatible resc factors. Transgenic experiments in Drosophila melanogaster and Saccharomyces cerevisiae converged towards a model where the cidB Wolbachia gene is involved in the mod function while cidA is involved in the resc function. However, as cidA expression in Drosophila males was required to observe CI, it has been proposed that cidA could be involved in both resc and mod functions. A recent correlative study in natural Culex pipiens mosquito populations has revealed an association between specific cidA and cidB variations and changes in mod phenotype, also suggesting a role for both these genes in mod diversity. Here, by studying cidA and cidB genomic repertoires of individuals from newly sampled natural C. pipiens populations harbouring wPipIV strains from North Italy, we reinforce the link between cidB variation and mod phenotype variation fostering the involvement of cidB in the mod phenotype diversity. However, no association between any cidA variants or combination of cidA variants and mod phenotype variation was observed. Taken together our results in natural C. pipiens populations do not support the involvement of cidA in mod phenotype variation.     

Variations in carotenoid content and acyl chain composition in exponential,stationary and biofilm states of Staphylococcus aureus,and their influence on membrane biophysical properties

Bacteria are often found in close association with surfaces, resulting in the formation of biofilms. In Staphylococcus aureus (S. aureus), biofilms are implicated in the resilience of chronic infections, presenting a serious clinical problem world-wide. Here, S. aureus biofilms are grown under flow within clinical catheters at 37 °C. The lipid composition and biophysical properties of lipid extracts from these biofilms are compared with those from exponential growth and stationary phase cells. Biofilms show a reduction in iso and anteiso branching compensated by an increase in saturated fatty acids compared to stationary phase. A drastic reduction in carotenoid levels is also observed during biofilm formation. Thermotropic measurements of Laurdan GP and DPH polarization, show a reduction of lipid packing at 37 °C for biofilms compared to stationary phase. We studied the effects of carotenoid content on DMPG and DPPG model membranes showing trends in thermotropic behavior consistent with those observed in bacterial isolates, indicating that carotenoids participate in modulating lipid packing. Additionally, bending elastic constant (k_c) measurements using vesicle fluctuation analysis (VFA) show that the presence of carotenoids can increase membrane bending rigidity. The antimicrobial peptide Magainin H2 was less activity on liposomes composed of stationary phase compared to biofilms or exponential growth isolates. This study contributes to an understanding of how Staphylococcus aureus modulates the composition of its membrane lipids, and how those changes affect the biophysical properties of membranes, which in turn may play a role in its virulence and its resistance to different membrane-active antimicrobial agents.     

Ecological restoration of rich fens in Europe and North America: from trial and error to an evidence‐based approach

Fens represent a large array of ecosystem services, including the highest biodiversity found among wetlands, hydrological services, water purification and carbon sequestration. Land‐use change and drainage has severely damaged or annihilated these services in many parts of North America and Europe; restoration plans are urgently needed at the landscape level. We review the major constraints on the restoration of rich fens and fen water bodies in agricultural areas in Europe and disturbed landscapes in North America: (i) habitat quality problems: drought, eutrophication, acidification, and toxicity, and (ii) recolonization problems: species pools, ecosystem fragmentation and connectivity, genetic variability, and invasive species; and here provide possible solutions. We discuss both positive and negative consequences of restoration measures, and their causes. The restoration of wetland ecosystem functioning and services has, for a long time, been based on a trial‐and‐error approach. By presenting research and practice on the restoration of rich fen ecosystems within agricultural areas, we demonstrate the importance of biogeochemical and ecological knowledge at different spatial scales for the management and restoration of biodiversity, water quality, carbon sequestration and other ecosystem services, especially in a changing climate. We define target processes that enable scientists, nature managers, water managers and policy makers to choose between different measures and to predict restoration prospects for different types of deteriorated fens and their starting conditions.