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991.
992.
The purpose of this study was to investigate changes in motor unit firing behavior during prolonged contractions in young and older adults. Motor unit activity was recorded from the tibialis anterior of 16 subjects (8 young and 8 older), while they performed isometric dorsiflexion at 50% MVC until task failure. Mean motor unit firing rate, the standard deviation (SD), and coefficient of variation (CV) of the interspike intervals, and number of doublet discharges were calculated for a total of 52 motor units, tracked for an average of 92.9 ± 68.6 s. There was no age-related difference in the time to task failure. A modest decline in firing rate was observed in 71% of the motor units, with no significant age-related difference. The SD and CV of the interspike interval had a positive slope in 65% and 69% of the motor units, respectively, with no significant age-related differences. The number of doublet discharges remained stable throughout the contraction. Both groups exhibited motor unit dropout (discharge cessation) during the contraction. Thus, a fatiguing task producing modest changes in firing rate in young and older adults is accompanied by an appreciable increase in firing rate variability. The incidence of doublet discharges is not increased during fatiguing contractions. 相似文献
993.
Stefanie D. Krämer Dario Lombardi Adriana Primorac Anita V. Thomae Heidi Wunderli‐Allenspach 《化学与生物多样性》2009,6(11):1900-1916
Lipid‐bilayer permeation is determinant for the disposition of xenobiotics in the body. It controls the pharmacokinetic behavior of drugs and is, in many cases, a prerequisite for intracellular targeting. Permeation of in vivo barriers is in general predicted from lipophilicity and related parameters. This article goes beyond the empirical correlations, and elucidates the processes and their interplay determining bilayer permeation. A flip‐flop model for bilayer permeation, which considers the partitioning rate constants beside the translocation rate constants, is compared with the diffusion model based on Fick's first law. According to the flip‐flop model, the ratios of aqueous volumes to barrier area can determine whether partitioning or translocation is rate‐limiting. The flip‐flop model allows permeation of anions and cations, and expands our understanding of pH‐dependent permeation kinetics. Some experimental evidences for ion‐controlled permeation at pH 7 are also included in this work. 相似文献
994.
995.
996.
Molecule of fullerene, having a spherical or ellipsoidal shape, is made of rings consisting of five or six carbon atoms, combined with conjugated pi bonds. Delocalization of pi electrons in the molecule of fullerene makes it easy to scavenge free radicals. But, despite being the effective antioxidants and radical scavengers fullerenes may be prooxidants by reactive oxygen species generation. Mammalian cells consist mainly of water (about 70%). Thus, the radical and non-radical products of water radiolysis are the basic sources of radiation damage to biomolecules. Reactive oxygen species, such as hydroxyl (HO*) and superoxide (O2-*) radicals and hydrogen peroxide (H2O2), are responsible for radiation-induced damage in aerated systems. Free radical mechanism of radiation damage suggests that scavengers of free radicals should protect cellular structures against damage. Electron donor compounds should also exhibit protective properties towards oxidized functional groups by reducing them. However, the electron transfer from fullerene to oxygen may generate superoxide radical. The shape of fullerenes allows them to act as carriers of radioactive atoms of isotopes used in the therapy and medical diagnostics. Fullerenes and their derivatives due to its properties are new promising chemicals for application in radiobiology. Fullerenes may be radioprotectors, radiosensitizer or auxiliary compounds in diagnostic imaging. What they are depends on the experimental system used. 相似文献
997.
998.
Wei-Qiang Chen Anita Salmazo Matti Myllykoski Björn Sjöblom Martin Bidlingmaier Arnold Pollak Peter Baumgärtel Kristina Djinovic-Carugo Petri Kursula Gert Lubec 《Amino acids》2010,39(3):859-869
Most protein preparations require purification steps prior to biophysical analysis assessing protein stability, secondary
structure and degree of folding. It was, therefore, the aim of this study to develop a system to separate and purify a protein
from a commercially available medicinal product, recombinant human growth hormone (rhGH) and show preservation of conformation
and function following the gel-based procedure. The rhGH was run on clear native (CN) gels and recovered from the gels by
electroelution using D-Tube Dialyzer Midi under rigorous cooling. Melting point studies indicated preservation of the structural
integrity. This finding was confirmed by synchrotron radiation circular dichroism spectroscopy (SRCD) revealing an identical
folding pattern for the sample before and after electrophoretic separation and purification. Synchrotron small-angle X-ray
scattering (SAXS) indicated that the sample was folded and monomeric, both before and after separation and purification, and
that its shape corresponded well to the known crystal structure of GH. Binding properties of rhGH to a receptor-model system
before and after clear native electrophoresis were comparable. This analytical and preparative approach to purify and concentrate
a protein preserving conformation and function may be helpful for many applications in analytical, protein and stereochemistry. 相似文献
999.
1000.
Anita C. Risch Sven Wirthner Matt D. Busse Deborah S. Page-Dumroese Martin Schütz 《Oecologia》2010,164(3):773-784
Interest in soil C storage and release has increased in recent years. In addition to factors such as climate/land-use change,
vertebrate animals can have a considerable impact on soil CO2 emissions. To date, most research has considered herbivores, while the impact of omnivorous animals has rarely been investigated.
Our goal was to determine how European wild boars (Sus scrofa L.), large omnivores that consume soil-inhabiting animals and belowground plant parts by grubbing in the soil, affect soil
C dynamics. We measured soil respiration (CO2), temperature, and moisture on paired grubbed and non-grubbed plots in six hardwood forest stands for a 3-year period and
sampled fine root and microbial biomass at the beginning and after 2 years of the study. We also measured the percentage of
freshly disturbed forest soil within the larger surroundings of each stand and used this information together with hunting
statistics and forest cover data to model the total amount of CO2 released from Swiss forest soils due to grubbing during 1 year. Soil CO2 emissions were significantly higher on grubbed compared to non-grubbed plots during the study. On average 23.1% more CO2 was released from these plots, which we associated with potential alterations in CO2 diffusion rates, incorporation of litter into the mineral soil and higher fine root/microbial biomass. Thus, wild boars considerably
increased the small-scale heterogeneity of soil properties. Roughly 1% of Switzerland’s surface area is similar to our sites
(boar density/forest cover). Given the range of forest soil disturbance of 27–54% at our sites, the geographic information
system model predicted that boar grubbing would lead to the release of an additional 49,731.10–98,454.74 t CO2 year−1. These values are relatively small compared to total soil emissions estimated for Swiss hardwood forests and suggest that
boars will have little effect on large-scale emissions unless their numbers increase and their range expands dramatically. 相似文献