3,943 research outputs found
Abnormally high content of free glucosamine residues identified in a preparation of commercially available porcine intestinal heparan sulfate
Heparan sulfate (HS) polysaccharides are ubiquitous in animal tissues as components of proteoglycans, and they participate in many important biological processes. HS carbohydrate chains are complex and can contain rare structural components such as N-unsubstituted glucosamine (GlcN). Commercially available HS preparations have been invaluable in many types of research activities. In the course of preparing microarrays to include probes derived from HS oligosaccharides, we found an unusually high content of GlcN residue in a recently purchased batch of porcine intestinal mucosal HS. Composition and sequence analysis by mass spectrometry of the oligosaccharides obtained after heparin lyase III digestion of the polysaccharide indicated two and three GlcN in the tetrasaccharide and hexasaccharide fractions, respectively. (1)H NMR of the intact polysaccharide showed that this unusual batch differed strikingly from other HS preparations obtained from bovine kidney and porcine intestine. The very high content of GlcN (30%) and low content of GlcNAc (4.2%) determined by disaccharide composition analysis indicated that N-deacetylation and/or N-desulfation may have taken place. HS is widely used by the scientific community to investigate HS structures and activities. Great care has to be taken in drawing conclusions from investigations of structural features of HS and specificities of HS interaction with proteins when commercial HS is used without further analysis. Pending the availability of a validated commercial HS reference preparation, our data may be useful to members of the scientific community who have used the present preparation in their studies
Mapping the cellular electrophysiology of rat sympathetic preganglionic neurones to their roles in cardiorespiratory reflex integration:A whole cell recording study in situ
Sympathetic preganglionic neurones (SPNs) convey sympathetic activity flowing from the CNS to the periphery to reach the target organs. Although previous in vivo and in vitro cell recording studies have explored their electrophysiological characteristics, it has not been possible to relate these characteristics to their roles in cardiorespiratory reflex integration. We used the working heartâbrainstem preparation to make whole cell patch clamp recordings from T3â4 SPNs (n = 98). These SPNs were classified by their distinct responses to activation of the peripheral chemoreflex, diving response and arterial baroreflex, allowing the discrimination of muscle vasoconstrictor-like (MVC(like), 39%) from cutaneous vasoconstrictor-like (CVC(like), 28%) SPNs. The MVC(like) SPNs have higher baseline firing frequencies (2.52 ± 0.33 Hz vs. CVC(like) 1.34 ± 0.17 Hz, P = 0.007). The CVC(like) have longer after-hyperpolarisations (314 ± 36 ms vs. MVC(like) 191 ± 13 ms, P < 0.001) and lower input resistance (346 ± 49  MΩ vs. MVC(like) 496 ± 41 MΩ, P < 0.05). MVC(like) firing was respiratory-modulated with peak discharge in the late inspiratory/early expiratory phase and this activity was generated by both a tonic and respiratory-modulated barrage of synaptic events that were blocked by intrathecal kynurenate. In contrast, the activity of CVC(like) SPNs was underpinned by rhythmical membrane potential oscillations suggestive of gap junctional coupling. Thus, we have related the intrinsic electrophysiological properties of two classes of SPNs in situ to their roles in cardiorespiratory reflex integration and have shown that they deploy different cellular mechanisms that are likely to influence how they integrate and shape the distinctive sympathetic outputs
Divergence in Dialogue
Copyright: 2014 Healey et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.This work was supported by the Economic and Social Research Council (ESRC; http://www.esrc.ac.uk/) through the DynDial project (Dynamics of Conversational Dialogue, RES-062-23-0962) and the Engineering and Physical Sciences Research Council (EPSRC; http://www.epsrc.ac.uk/) through the RISER
project (Robust Incremental Semantic Resources for Dialogue, EP/J010383/1). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
Modelling the vascular response to sympathetic postganglionic nerve activity
AbstractThis paper explores the influence of burst properties of the sympathetic nervous system on arterial contractility. Specifically, a mathematical model is constructed of the pathway from action potential generation in a sympathetic postganglionic neurone to contraction of an arterial smooth muscle cell. The differential equation model is a synthesis of models of the individual physiological processes, and is shown to be consistent with physiological data.The model is found to be unresponsive to tonic (regular) stimulation at typical frequencies recorded in sympathetic efferents. However, when stimulated at the same average frequency, but with repetitive respiratory-modulated burst patterns, it produces marked contractions. Moreover, the contractile force produced is found to be highly dependent on the number of spikes in each burst. In particular, when the model is driven by preganglionic spike trains recorded from wild-type and spontaneously hypertensive rats (which have increased spiking during each burst) the contractile force was found to be 10-fold greater in the hypertensive case. An explanation is provided in terms of the summative increased release of noradrenaline. Furthermore, the results suggest the marked effect that hypertensive spike trains had on smooth muscle cell tone can provide a significant contribution to the pathology of hypertension
Vertical stratification of iron in atmospheres of blue horizontal-branch stars
The aim of this study is to search for observational evidence of vertical
iron stratification in the atmosphere of fourteen blue horizontal-branch (BHB)
stars. We have found from our numerical simulations that five BHB stars: B22,
B186 in the globular cluster NGC 288, WF2-820, WF2-2692 in M13 and B203 in M15
show clear signatures of the vertical stratification of iron whose abundance
increases toward the lower atmosphere. Two other BHB stars (B334 in M15 and
B176 in M92) also show possible iron stratification in their atmosphere. A
dependence of the slope of iron stratification on the effective temperature was
also discovered. It is found that the vertical stratification of iron is
strongest in BHB stars with Teff around 11,500K. The slope of iron abundance
decreases as Teff increases and becomes negligible for the BHB stars with Teff=
14,000K. These results support the hypothesis regarding the efficiency of
atomic diffusion in the stellar atmospheres of BHB stars with Teff > 11,500K.Comment: 6 pages, 2 figures, 3 table
Vertical abundance stratification in the blue horizontal branch star HD135485
It is commonly believed that the observed overabundances of many chemical
species relative to the expected cluster metallicity in blue horizontal branch
(BHB) stars appear as a result of atomic diffusion in the photosphere. The slow
rotation of BHB stars (with T_eff > 11,500K), typically v sin{i} < 10 km/s, is
consistent with this idea. In this work we search for observational evidence of
vertical chemical stratification in the atmosphere of HD135485. If this
evidence exists, it will demonstrate the importance of atomic diffusion
processes in the atmospheres of BHB stars. We undertake an extensive abundance
stratification analysis of the atmosphere of HD135485, based on recently
acquired high resolution and S/N CFHT ESPaDOnS spectra and a McDonald-CE
spectrum. Our numerical simulations show that nitrogen and sulfur reveal
signatures of vertical abundance stratification in the stellar atmosphere. It
appears that the abundances of these elements increase toward the upper
atmosphere. This fact cannot be explained by the influence of microturbulent
velocity, because oxygen, carbon, neon, argon, titanium and chromium do not
show similar behavior and their abundances remain constant throughout the
atmosphere. It seems that the iron abundance may increase marginally toward the
lower atmosphere. This is the first demonstration of vertical abundance
stratification of metals in a BHB star.Comment: 8 pages, 5 figures, accepted to A&
Search for vertical stratification of metals in atmospheres of blue horizontal-branch stars
The observed abundance peculiarities of many chemical species relative to the
expected cluster metallicity in blue horizontal-branch (BHB) stars presumably
appear as a result of atomic diffusion in the photosphere. The slow rotation
(typically 10 km s) of BHB stars with effective temperatures
11,500 K supports this idea since the diffusion mechanism is
only effective in a stable stellar atmosphere. In this work we search for
observational evidence of vertical chemical stratification in the atmospheres
of six hot BHB stars: B84, B267 and B279 in M15 and WF2-2541, WF4-3085 and
WF4-3485 in M13. We undertake an abundance stratification analysis of the
stellar atmospheres of the aforementioned stars, based on acquired Keck HIRES
spectra. We have found from our numerical simulations that three stars (B267,
B279 and WF2-2541) show clear signatures of the vertical stratification of iron
whose abundance increases toward the lower atmosphere, while the other two
stars (B84 and WF4-3485) do not. For WF4-3085 the iron stratification results
are inconclusive. B267 also shows a signature of titanium stratification. Our
estimates for radial velocity, and overall iron, titanium and
phosphorus abundances agree with previously published data for these stars
after taking the measurement errors into account. The results support the
hypothesis regarding the efficiency of atomic diffusion in the stellar
atmospheres of BHB stars with 11,500 K.Comment: 8 pages, 12 figures, accepted for publication in Astronomy and
Astrophysic
A Far Ultraviolet Study of the Old Nova V841 Oph
We have carried out a synthetic spectral analysis of archival IUE spectra of
the old nova V841 Oph (Nova Oph 1848) taken 15 years apart. The spectra reveal
a rising continuum shortward of 1560\AA, a C {\sc iv} P-Cygni profile
indicative of wind outflow associated with disk accretion in one spectrum, a
deep Ly profile, and strong N {\sc v} (1238\AA, 1242\AA) and O {\sc v}
(1371\AA) wind/coronal absorption lines. Numerous sharp interstellar resonance
lines are also present. A grid of high gravity atmospheres and accretion disk
models, spanning a wide range of inclinations, accretion rates and white dwarf
masses was compared to the de-reddened spectra. We find that, for a steady
state accretion disk model to account for the FUV spectra, the accretion rate
is only 3 10 M_{\sun}/yr, 147 years after its outburst
in 1848, with an implied distance within 300 pc. The accretion rate at
147 years post-outburst is smaller than expected for an old nova.Comment: 6 b/w figures, 2 tables, preprint accepted in the November 2005 issue
of PAS
Planning, implementation, and first results of the Tropical Composition, Cloud and Climate Coupling Experiment (TC4)
The Tropical Composition, Cloud and Climate Coupling Experiment (TC4), was based in Costa Rica and Panama during July and August 2007. The NASA ER-2, DC-8, and WB-57F aircraft flew 26 science flights during TC4. The ER-2 employed 11 instruments as a remote sampling platform and satellite surrogate. The WB-57F used 25 instruments for in situ chemical and microphysical sampling in the tropical tropopause layer (TTL). The DC-8 used 25 instruments to sample boundary layer properties, as well as the radiation, chemistry, and microphysics of the TTL. TC4 also had numerous sonde launches, two ground-based radars, and a ground-based chemical and microphysical sampling site. The major goal of TC4 was to better understand the role that the TTL plays in the Earth's climate and atmospheric chemistry by combining in situ and remotely sensed data from the ground, balloons, and aircraft with data from NASA satellites. Significant progress was made in understanding the microphysical and radiative properties of anvils and thin cirrus. Numerous measurements were made of the humidity and chemistry of the tropical atmosphere from the boundary layer to the lower stratosphere. Insight was also gained into convective transport between the ground and the TTL, and into transport mechanisms across the TTL. New methods were refined and extended to all the NASA aircraft for real-time location relative to meteorological features. The ability to change flight patterns in response to aircraft observations relayed to the ground allowed the three aircraft to target phenomena of interest in an efficient, well-coordinated manner
Influence of age on respiratory modulation of muscle sympathetic nerve activity, blood pressure and baroreflex function in humans
New Findings What is the central question of this study? Does ageing influence the respiratoryârelated bursting of muscle sympathetic nerve activity (MSNA) and the association between the rhythmic fluctuations in MSNA and blood pressure (TraubeâHering waves) that occur with respiration? What is the main finding and its importance? Despite the ageârelated elevation in MSNA, the cyclical inhibition of MSNA during respiration is similar between young and older individuals. Furthermore, central respiratoryâsympathetic coupling plays a role in the generation of TraubeâHering waves in both young and older humans. Healthy ageing and alterations in respiratoryâsympathetic coupling have been independently linked with heightened sympathetic neural vasoconstrictor activity. We investigated how age influences the respiratoryârelated modulation of muscle sympathetic nerve activity (MSNA) and the association between the rhythmic fluctuations in MSNA and blood pressure that occur with respiration (TraubeâHering waves; THW). Ten young (22 ± 2 years; mean ± SD) and 10 older healthy men (58 ± 6 years) were studied while resting supine and breathing spontaneously. MSNA, blood pressure and respiration were recorded simultaneously. Resting values were ascertained and respiratory cycleâtriggered averaging of MSNA and blood pressure measurements performed. The MSNA burst incidence was higher in older individuals [22.7 ± 9.2 versus 42.2 ± 13.7 bursts (100 heart beats)â1, P < 0.05], and was reduced to a similar extent in the inspiratory to postinspiratory period in young and older subjects (by âŒ25% compared with midâ to late expiration). A similar attenuation of MSNA burst frequency (in bursts per minute), amplitude and total activity (burst frequency Ă mean burst amplitude) was also observed in the inspiratory to postinspiratory period in both groups. A significant positive correlation between respiratoryârelated MSNA and the magnitude of TraubeâHering waves was observed in all young (100%) and most older subjects (80%). These data suggest that the strength of the cyclical inhibition of MSNA during respiration is similar between young and older individuals; thus, alterations in respiratoryâsympathetic coupling appear not to contribute to the ageârelated elevation in MSNA. Furthermore, central respiratoryâsympathetic coupling plays a role in the generation of TraubeâHering waves in both healthy young and older humans
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