Age-related changes in neuromuscular function of the quadriceps muscle in physically active adults

Substantial evidence exists for the age-related decline in maximal strength and strength development. Despite the importance of knee extensor strength for physical function and mobility in the elderly, studies focusing on the underlying neuromuscular mechanisms of the quadriceps muscle weakness are limited.The aim of this study was to investigate the contributions of age-related neural and muscular changes in the quadriceps muscle to decreases in isometric maximal voluntary torque (iMVT) and explosive voluntary strength. The interpolated twitch technique and normalized surface electromyography (EMG) signal during iMVT were analyzed to assess changes in neural drive to the muscles of 15 young and 15 elderly volunteers. The maximal rate of torque development as well as rate of torque development, impulse and neuromuscular activation in the early phase of contraction were determined. Spinal excitability was estimated using the H reflex technique. Changes at the muscle level were evaluated by analyzing the contractile properties and lean mass.The age-related decrease in iMVT was accompanied by a decline in voluntary activation and normalized surface EMG amplitude. Mechanical parameters of explosive voluntary strength were reduced while the corresponding muscle activation remained primarily unchanged. The spinal excitability of the vastus medialis was not different while M wave latency was longer. Contractile properties and lean mass were reduced.In conclusion, the age-related decline in iMVT of the quadriceps muscle might be due to a reduced neural drive and changes in skeletal muscle properties. The decrease in explosive voluntary strength seemed to be more affected by muscular than by neural changes.     

Moths in fragments: insights into the biology and ecology of the Australian endangered golden sun moth Synemon plana (Lepidoptera: Castniidae) in natural temperate and exotic grassland remnants

The conservation and management of endangered species requires an adequate understanding of their biology and ecology. Although there has been an increasing appreciation in Australia of the need for greater efforts to conserve insects, there is only limited information available that can be used to underpin conservation efforts. The endangered golden sun moth, Synemon plana (Lepidoptera: Castniidae) is a flagship species endemic to natural temperate grassland in south-eastern Australia. Most populations of this species are at considerable risk from habitat loss, weed invasion and inadequate management. Despite the considerable knowledge that exists about the species biology and ecology, efforts to improve the species conservation status are hampered because there are still critical gaps in our understanding of the species’ natural history. In particular, the ecology of the larvae is not known. Our study examined the abundance, population structure and reproductive biology of the moths in a broad sample of both natural temperate and exotic grassland remnants in and near Canberra in the Australian Capital Territory (ACT) in south-eastern Australia. The results fill critical gaps in the knowledge needed to achieve effective conservation management. From our findings, it is clear that the species inhabits grasslands dominated by a mixture of native wallaby grasses (Rytidosperma spp. (formerly Austrodanthonia)) and spear grasses (Austrostipa spp.). In contrast to earlier suggestions that S. plana is entirely confined to natural temperate grassland, mature and immature life stages of the species were also present in grasslands comprised entirely of the exotic Chilean needlegrass (Nassella neesiana). Most of the S. plana populations surveyed in the ACT were characterised by low relative abundance with only very few large populations being recorded. The conservation of exotic grasslands as substitute habitat for S. plana is discussed and suggestions regarding future monitoring and research of the species are provided.     

Very rapid phosphorylation kinetics suggest a unique role for Lhcb2 during state transitions in Arabidopsis

Light‐harvesting complex II (LHCII) contains three highly homologous chlorophyll‐a/b‐binding proteins (Lhcb1, Lhcb2 and Lhcb3), which can be assembled into both homo‐ and heterotrimers. Lhcb1 and Lhcb2 are reversibly phosphorylated by the action of STN7 kinase and PPH1/TAP38 phosphatase in the so‐called state‐transition process. We have developed antibodies that are specific for the phosphorylated forms of Lhcb1 and Lhcb2. We found that Lhcb2 is more rapidly phosphorylated than Lhcb1: 10 sec of ‘state 2 light’ results in Lhcb2 phosphorylation to 30% of the maximum level. Phosphorylated and non‐phosphorylated forms of the proteins showed no difference in electrophoretic mobility and dephosphorylation kinetics did not differ between the two proteins. In state 2, most of the phosphorylated forms of Lhcb1 and Lhcb2 were present in super‐ and mega‐complexes that comprised both photosystem (PS)I and PSII, and the state 2‐specific PSI–LHCII complex was highly enriched in the phosphorylated forms of Lhcb2. Our results imply distinct and specific roles for Lhcb1 and Lhcb2 in the regulation of photosynthetic light harvesting.     

Postnatal remains of the foetal membranes affect growth and survival of wild European rabbit pups

During a long-term study on reproduction of the European rabbit (Oryctolagus cuniculus L.) that was carried out on a population living under semi-natural conditions, occasionally single pups per litter were discovered being stuck in remnants of the foetal membranes. Here we describe this so far unknown phenomenon, quantify the occurrence, and investigate the consequences for the individual growth rate and for survival. Furthermore, we tested if maternal social rank and age were correlated with the occurrence of this phenomenon. Pups comprising the described adherence of the foetal membranes had lower growth rates than their unaffected litter siblings, and usually died during the nestling period or short after emergence above ground. Our findings point out that there was an individual predisposition of the mother for having affected litters. However, an impact of maternal social rank or age on the occurrence of this feature in their offspring was not supported by our data. Nevertheless, a pathological background also has to be considered as a possible cause.     

L-ascorbic acid potentiates endothelial nitric oxide synthesis via a chemical stabilization of tetrahydrobiopterin

Ascorbic acid has been shown to stimulate endothelial nitric oxide (NO) synthesis in a time- and concentration-dependent fashion without affecting NO synthase (NOS) expression or l-arginine uptake. The present study investigates if the underlying mechanism is related to the NOS cofactor tetrahydrobiopterin. Pretreatment of human umbilical vein endothelial cells with ascorbate (1 microm to 1 mm, 24 h) led to an up to 3-fold increase of intracellular tetrahydrobiopterin levels that was concentration-dependent and saturable at 100 microm. Accordingly, the effect of ascorbic acid on Ca(2+)-dependent formation of citrulline (co-product of NO) and cGMP (product of the NO-activated soluble guanylate cyclase) was abolished when intracellular tetrahydrobiopterin levels were increased by coincubation of endothelial cells with sepiapterin (0.001-100 microm, 24 h). In contrast, ascorbic acid did not modify the pterin affinity of endothelial NOS, which was measured in assays with purified tetrahydrobiopterin-free enzyme. The ascorbate-induced increase of endothelial tetrahydrobiopterin was not due to an enhanced synthesis of the compound. Neither the mRNA expression of the rate-limiting enzyme in tetrahydrobiopterin biosynthesis, GTP cyclohydrolase I, nor the activities of either GTP cyclohydrolase I or 6-pyruvoyl-tetrahydropterin synthase, the second enzyme in the de novo synthesis pathway, were altered by ascorbate. Our data demonstrate that ascorbic acid leads to a chemical stabilization of tetrahydrobiopterin. This was evident as an increase in the half-life of tetrahydrobiopterin in aqueous solution. Furthermore, the increase of tetrahydrobiopterin levels in intact endothelial cells coincubated with cytokines and ascorbate was associated with a decrease of more oxidized biopterin derivatives (7,8-dihydrobiopterin and biopterin) in cells and cell supernatants. The present study suggests that saturated ascorbic acid levels in endothelial cells are necessary to protect tetrahydrobiopterin from oxidation and to provide optimal conditions for cellular NO synthesis.     

Abnormal etioplast development in barley seedlings infected with BSMV by seed transmission

The effect of barley stripe mosaic hordeivirus (BSMV) was studied on the ultrastructure of etioplasts, protochlorophyllide forms and the greening process of barley ( Hordeum vulgare cv. Pannónia) plants infected by seed transmission. The leaves of 7- to 11-day-old etiolated seedlings were examined by transmission electron microscopy, fluorescence and absorption spectroscopy. The etioplasts of infected seedlings contained smaller prolamellar bodies with less regular membrane structure, while prothylakoid content was higher than in the control. The protochlorophyllide content of virus-infected seedlings was reduced to 74% of the control. In the 77 K fluorescence spectra the relative amount of 655 nm emitting photoactive protochlorophyllide form decreased, and the amount of the 645 and 633 nm emitting forms increased in the infected leaves. A characteristic effect was observed in the process of the Shibata-shift: 40 min delay was observed in the infected leaves. The results of this work proved that BSMV infection delays or inhibits plastid development and the formation of photosynthetic apparatus.     

Position of eukaryotic initiation factor eIF5B on the 80S ribosome mapped by directed hydroxyl radical probing

Eukaryotic translation initiation factor eIF5B is a ribosome-dependent GTPase that mediates displacement of initiation factors from the 40S ribosomal subunit in 48S initiation complexes and joining of 40S and 60S subunits. Here, we determined eIF5B's position on 80S ribosomes by directed hydroxyl radical cleavage. In the resulting model, eIF5B is located in the intersubunit cleft of the 80S ribosome: domain 1 is positioned near the GTPase activating center of the 60S subunit, domain 2 interacts with the 40S subunit (helices 3, 5 and the base of helix 15 of 18S rRNA and ribosomal protein (rp) rpS23), domain 3 is sandwiched between subunits and directly contacts several ribosomal elements including Helix 95 of 28S rRNA and helix 44 of 18S rRNA, domain 4 is near the peptidyl-transferase center and its helical subdomain contacts rpL10E. The cleavage data also indicate that binding of eIF5B might induce conformational changes in both subunits, with ribosomal segments wrapping around the factor. Some of these changes could also occur upon binding of other translational GTPases, and may contribute to factor recognition.     

Activation of estrogen receptor-beta by a special extract of Rheum rhaponticum (ERr 731), its aglycones and structurally related compounds

The special extract ERr 731^® from the roots of Rheum rhaponticum is the major constituent of Phytoestrol^® N which is used for the treatment of climacteric symptoms in menopausal women. However, the molecular mode of action of ERr 731^® was unknown. For the first time, ERr 731^® and its aglycones trans-rhapontigenin and desoxyrhapontigenin were investigated with regard to the activation of the estrogen receptor- or estrogen receptor-β (ER, ERβ). The related hydroxystilbenes cis-rhapontigenin, resveratrol and piceatannol were studied as comparators. As controls, 17β-estradiol or the selective ER-(propylpyrazoltriol) or ERβ-agonists (diarylpropionitril) were used. Neither in ER-expressing yeast cells, in the ER-responsive Ishikawa cells, nor in human endometrial HEC-1B cells transiently transfected with the ER an activation of ER by ERr 731^® or the other single compounds was detected. Furthermore, an antiestrogenic effect was not observed. In contrast in human endometrial HEC-1B cells transiently transfected with the ERβ, 100 ng/ml ERr 731^® and the single compounds significantly induced the ERβ-coupled luciferase activity in a range comparable to 10⁻⁸ M 17β-estradiol. All effects were abolished with the pure ER antagonist ICI 182780, indicating an ER-specific effect. The ERβ agonistic activity by ERr 731^® could be of importance for its clinical use, as central functions relevant to climacteric complaints are proposed to be mediated via ERβ activation.