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1.
The purpose of these studies was to identify the rheologic properties of polyacrylic acid gels necessary for optimal reductions
in mucociliary clearance. The mucociliary transport of 2 bioadhesive polyacrylic acid polymers, polycarbophil and carbopol,
was assessed in vitro by measuring their clerance rates across explants of ciliated bovine tracheal tissue. The viscoelastic
properties of polymer gels were measured in the presence of mucus using controlled stress rheometry. Combinations of apparent
viscosity (η) and complex modulus (G*) were found to be the most useful parameters in the identification of polyacrylic acid formulations capable of decreasing
mucociliary transport rate (MTR). A narrow range of η and G* values suitable for reducing mucociliary clearance, while remaining sufficiently fluid for intranasal administration, were
identified. The correlations between the rheologic parameters of the polycarbophil gels and their mucociliary transport rates
were used to identify other polyacrylic acid gels that also had suitable mucociliary clearance properties, demonstrating that
these parameters can be used to direct the optimization of formulations using simple in vitro rheologic testing.
Published: April 20, 2007 相似文献
2.
Adaucto B. Pereira-Netto Carmem L. O. Petkowicz Claudia T. A. Cruz-Silva Mariana T. Gazzoni Arianne F. P. Mello Joana L. M. Silveira 《In vitro cellular & developmental biology. Plant》2007,43(4):356-363
Shoots of the marubakaido apple rootstock grown in culture medium containing BBL agar presented significantly lower multiplication
rate (MR) compared to MRs found for shoots grown in medium containing A-7002, A-7921, Select, and Phytagar as gelling agents.
In addition, significant hyperhydricity was found for shoots grown in Phytagar and A-7921 agar-containing media. Analysis
of elastic (G′) and viscous (G″) modulus showed that for all of the five agar brands used in this study, G′ was always much
higher, i.e., typically one order of magnitude higher than G″, which characterizes a strong gel. G′ changed randomly with
time for all of the agar brands studied, except for BBL, which presented progressive decline in G′ throughout the culture
cycle. Examination of G′, within the same week, showed that Select agar always had the smallest G′, while Phytagar always
had the highest G′. Analysis of the loss tangent (tan δ = G″/G′), a better indicator for gel behavior compared to G′ isolated, showed that tan δ for Select and Phytagar were always
between tan δ values found for A-7002 and BBL. In addition, analysis of tan δ also indicated that BBL and Select agars showed a significantly weaker gel network, compared to Phytagar, A-7002 and A-7921
agars after the third week of culture. When seen together, these results indicate that shoot performance for the marubakaido
rootstock is not related to agar gel strength. In addition, the high hyperhydricity rate found for shoots grown on agars A-7921
and Phytagar could not be related to agar gel strength, as well. Analysis of HPSEC profiles indicated that the best performance,
i.e., multiplication rate, of marubakaido shoots in agars A-7002 and A-7921 is likely to be related to their lower polydispersity
and/or smaller amount of high molecular weight fractions, compared to BBL, Phytagar, and Select agars. 相似文献
3.
Neutral xyloglucan was purified from the cell walls of suspension-cultured rose (Rosa sp. `Paul's Scarlet') cells by alkali extraction, ethanol precipitation and anion-exchange chromatography on `Q-Sepharose
FastFlow'. The procedure recovered 70% of the total xyloglucan at about 95% purity in the neutral fraction. The remaining
30% of the xyloglucan was anionic, as demonstrated both by anion-exchange chromatography at pH 4.7 and by high-voltage electrophoresis
at pH 6.5. Alkali did not cause neutral xyloglucan to become anionic, indicating that the anionic nature of the rose xyloglucan
was not an artefact of the extraction procedure. Pre-incubation of neutral [3H]xyloglucan with any of ten non-radioactive acidic polysaccharides did not cause the radioactive material to become anionic
as judged by electrophoresis, indicating that stable complexes between neutral xyloglucan and acidic polysaccharides were
not readily formed in vitro. The anionic xyloglucan did not lose its charge in the presence of 8 M urea or after a second
treatment with NaOH, indicating that its anionic nature was not due to hydrogen-bonding of xyloglucan to an acidic polymer.
Proteinase did not affect the anionic xyloglucan, indicating that it was not associated with an acidic protein. Cellulase
converted the anionic xyloglucan to the expected neutral nonasaccharide and heptasaccharide, indicating that the repeat-units
of the xyloglucan did not contain acidic residues. Endo-polygalacturonase converted about 40% of the anionic xyloglucan to
neutral material. Arabinanase and galactanase also converted appreciable proportions of the anionic xyloglucan to neutral
material. These results show that about 30% of the xyloglucan in the cell walls of suspension-cultured rose cells exists in
covalently-linked complexes with acidic pectins.
Received: 5 November 1999 / Accepted: 18 January 2000 相似文献
4.
Erika Silletti Monique H. Vingerhoeds George A. van Aken Willem Norde 《Food biophysics》2008,3(3):318-328
In this paper, we studied the effect of saliva on the rheological properties of β-lactoglobulin- and lysozyme-stabilized emulsions,
prepared at pH = 6.7 in relation to variation of emulsions- and saliva-related parameters. The effect of oil–volume fraction
(2.5% w/w to 10% w/w), salivary protein concentration (0.1 to 0.8 mg ml−1), and the use of both stimulated and unstimulated saliva was investigated. Viscosity and storage modulus were measured before
(η
emul and G′emul, respectively) and after addition of saliva (η
mix and G′mix). To better estimate the changes due to saliva-induced flocculation of the emulsions, the ratios η
mix/η
emul, G′mix/G′emul were calculated. In addition, tan δ (=the ratio of the loss and storage moduli) was investigated to evaluate the viscoelastic behavior of the emulsion/saliva
mixtures. Increasing the oil–volume fraction and salivary protein concentration resulted in an increase in η
mix/η
emul and G′mix/G′emul, while a decrease in tan δ of the emulsion/saliva mixtures is occurring. When compared with unstimulated saliva, mixing β-lactoglobulin-stabilized emulsions
with stimulated saliva led to a reduction in η
mix/η
emul and G′mix/G′emul, and an augment of tan δ at all measured deformations. In case of lysozyme-stabilized emulsions, the use of stimulated saliva increased G′mix/G′emul for γ < 3 when compared to unstimulated saliva. The effect of stimulated saliva on the η
mix/η
emul and tan δ in this mixture is similar to that of unstimulated saliva. These results indicate that the influence of stimulated saliva
on the rheological parameters of emulsion/saliva mixtures largely depends on the type of emulsions. To conclude, our findings
demonstrate that the rheological behavior of emulsions upon mixing with saliva is greatly affected by both saliva and emulsion
properties. 相似文献
5.
C. T. Andrade E. G. Azero L. Luciano M. P. Gonalves 《International journal of biological macromolecules》2000,27(5)
Mixed gels of κ-carrageenan (κ-car) from Hypnea musciformis and galactomannans (Gal) from Cassia javanica (CJ) and locust bean gum (LBG) were compared using dynamic viscoelastic measurements and compression tests. Mixed gels at 5 g/l of total polymer concentration in 0.1 M KCl showed a synergistic maximum in viscoelastic measurements for κ-car/CJ and κ-car/LBG at 2:1 and 4:1 ratios, respectively. The synergistic maximum obtained from compression tests carried out for mixed gels at 10 g/l of total polymer concentration in 0.25 M KCl was the same for both κ-car/CJ and κ-car/LBG gels. An enhancement in the storage modulus (G′) and the loss modulus (G″) was observed in the mechanical spectra for the mixtures in relation to κ-car. The proportionally higher increase in G″ compared with G′, as indicated by the values of the loss tangent (tan δ), suggests that the Gal adhere non-specifically to the κ-car network. 相似文献
6.
To better understand the frog palate model of mucociliary transport, we measured the transport rate of mucus (MTR) from the leopard frog, Rana pipiens, and from the bullfrog, R. catesbeiana, recorded the stability of the MTR over a period of hours and days and over the course of 1 yr, and measured the viscoelasticity, percent solid composition, and spinnability (filance) of mucus from both species. Bullfrog mucus was less rigid than leopard frog mucus (log G* at 1 rad/s 2.09 vs. 2.61; P less than 0.01) and had a higher viscosity-to-elasticity ratio (tan delta at 1 rad/s 0.36 vs. 0.26; P less than 0.05). It also had a lower solids content (8.71 vs. 13.72%; P = 0.02), and there was a trend to lower spinnability for bullfrog mucus (filance 26.7 vs. 33.5 mm). These data suggest that bullfrog mucus has viscoelastic properties similar to normal mammalian respiratory mucus and leopard frog mucus has viscoelasticity similar to sputum samples. MTR was significantly slower in the winter than in the summer months (17 vs. 30 mm/min; P less than 0.0001). Although the leopard frog palate could be used for at least 7 consecutive days without exhaustion, bullfrog palates could be used for only 5 days. Palates of either species could generally be tested for 6 h/day without a significant decrease in MTR. These data clarify some of the sources of variability in the use of this system and suggest methods of standardization. 相似文献
7.
Ricardo N. Pereira Federico Gómez Galindo António A. Vicente Petr Dejmek 《Food biophysics》2009,4(3):229-239
We have investigated whether transient permeabilization caused by the application of pulsed electric field would give rise
to transient changes in the potato tissue viscoelastic properties. Potato tissue was subjected to nominal field strengths
(E) ranging from 30 to 500 V/cm, with a single rectangular pulse of 10−5, 10−4, or 10−3 s. The changes on the viscoelastic properties of potato tissue during pulsed electric fields (PEF) were monitored through
small amplitude oscillatory dynamic rheological measurements. The elastic (G′) and viscous moduli (G″) were measured every 30 s after the delivery of the pulse and the loss tangent change (tan-δ) was calculated. The results were correlated with measurements of changes on electrical resistance during the delivery of
the pulse. Results show a drastic increase of tan-δ in the first 30 s after the application of the pulse, followed by a decrease 1 min after pulsation. This response is strongly
influenced by pulsing conditions and is independent of the total permeabilization achieved by the pulse. Our results, supported
by similar measurements on osmotically dehydrated control samples, clearly show that PEF causes a rapid change of the viscoelastic
properties of the tissue that could be attributed to a partial loss in turgor pressure. This would be an expected consequence
of electroporation. The recovery of tan-δ to values similar to those before pulsation strongly suggests recovery of cell membrane properties and turgor, pointing at
reversible permeabilization of the cells. A slight increase of stiffness traduced by a negative change of tan-δ after application of certain PEF conditions may also give an indication of events occurring on cell wall structure due to
stress responses. This study set the basis for further investigations on the complex cell stress physiology involving both
cell membrane functional properties and cell wall structure that would influence tissue physical properties upon PEF application. 相似文献
8.
Phase behaviour and crystallinity of plant cuticular waxes studied by Fourier transform infrared spectroscopy 总被引:1,自引:0,他引:1
The phase behaviour of cuticular waxes from leaves of Hedera helix L. and Juglans regia L. was studied by Fourier transform infrared spectroscopy. For this purpose reconstituted waxes, isolated cuticular membranes,
dewaxed polymer matrix membranes and whole leaves were studied in the horizontal attenuated total reflection and transmission
modes. Melting curves of cuticular waxes were derived from temperature-dependent changes in the absorption maximum of the
symmetric stretching mode of CH2 groups (νs, at approx. 2856–2848 cm−1). With increasing temperature absorption band doublets due to CH2 scissoring (δsciss) and rocking (δrock) movements (at approx. 1473–1471 and 730–720 cm−1, respectively) indicative of an orthorhombic arrangement of alkyl chains merged into a single peak. The area ratio of the
peaks at approx. 720 and 730 cm−1 was used as a measure for aliphatic crystallinity of plant cuticular waxes at a given temperature. The investigations of
reconstituted cuticular waxes and those still embedded in isolated cuticles or in situ on the leaf produced comparable results.
The findings are discussed in terms of the properties of the cuticular transport barrier.
Received: 21 March 1997 / Accepted: 25 April 1997 相似文献
9.
Meloxicam gel was designed based on the matching of the solubility parameter (δ) of the drug with that of the polymer and subsequently with skin for improved dermal delivery of meloxicam. The δ of meloxicam (11.48 (cal/cm3)0.5) determined by solubility measurement was matched statistically to the solubility parameter of monomers, n-vinyl-2-pyrrolidone, polyvinyl alcohol (PVA), hydroxyl ethyl methacrylate, ethylene glycol methacrylate (EGMA) determined
by intrinsic viscosity measurement. Consequently gels were formulated by polymerization in selected solvent blend of water/ethyl
acetate (20:80) in which the drug showed maximum solubility. Thus, F1–F16 formulations designed were evaluated for physicochemical
properties, textural analysis, and in vitro drug release. On the basis of optimum characteristics, F2 (PVA, δ = 16.96 (cal/cm3)0.5) and F8 (EGMA, δ = 18.35 (cal/cm3)0.5) formulated by suspension polymerization were selected and subjected to skin irritation and topical anti-inflammatory studies.
The formulation F8 demonstrated significant (p < 0.05) of anti-inflammatory activity in comparison to marketed piroxicam gel and was free from irritation. 相似文献
10.
Relevance of Rheological Properties of Sodium Alginate in Solution to Calcium Alginate Gel Properties 总被引:2,自引:0,他引:2
Fu S Thacker A Sperger DM Boni RL Buckner IS Velankar S Munson EJ Block LH 《AAPS PharmSciTech》2011,12(2):453-460
The purpose of this study is to determine whether sodium alginate solutions’ rheological parameters are meaningful relative
to sodium alginate’s use in the formulation of calcium alginate gels. Calcium alginate gels were prepared from six different
grades of sodium alginate (FMC Biopolymer), one of which was available in ten batches. Cylindrical gel samples were prepared
from each of the gels and subjected to compression to fracture on an Instron Universal Testing Machine, equipped with a 1-kN
load cell, at a cross-head speed of 120 mm/min. Among the grades with similar % G, (grades 1, 3, and 4), there is a significant correlation between deformation work (L
E) and apparent viscosity (η
app). However, the results for the partial correlation analysis for all six grades of sodium alginate show that L
E is significantly correlated with % G, but not with the rheological properties of the sodium alginate solutions. Studies of the ten batches of one grade of sodium
alginate show that η
app of their solutions did not correlate with L
E while tan δ was significantly, but minimally, correlated to L
E. These results suggest that other factors—polydispersity and the randomness of guluronic acid sequencing—are likely to influence
the mechanical properties of the resultant gels. In summary, the rheological properties of solutions for different grades
of sodium alginate are not indicative of the resultant gel properties. Inter-batch differences in the rheological behavior
for one specific grade of sodium alginate were insufficient to predict the corresponding calcium alginate gel’s mechanical
properties. 相似文献
11.
A hypothesis describing the mechanism of photoactive protochlorophyllide (P) photoreduction in vivo, relating mainly to the molecular nature of the intermediates, is proposed. The hypothesis is compatible with currently published
experimental data. After illumination of etiolated barley leaves at 143 to 153 K, the absorption of P remains essentially
unchanged, but a new absorption band at 690 nm is observed. Appearance of this new intermediate enables to distinguish between
light and dark stages of the photoconversion reaction. When returned to the higher temperature in the dark, the treated leaves
begin accumulating chlorophyllide (Chlide), concomitant with the disappearance of the 690-nm band. The decay time of the excited
P (P*) is estimated at 300 ps, which approximates the time constant of photoinduced electron transfer (ET). It is suggested that
the charge-transfer complex (CTC) in its ground state (GS) (ground state of CTC formed by the partial (δ) electron transfer),
i.e. (Pδ−•••H–Dδ+), between P and NADPH – the electron and proton donor (H–D) – accumulates in the following sequence: P* + H–D → (P*•••H–D)→[(P*•••H–D)←(P−•••H–D+)] → 1(P−•••H–D+)] → 3(P−•••H–D+) → (Pδ−•••H–D δ+), where an equilibrium state (ES) – [(P*•••H–D)←(P−•••H–D+)] – with a lifetime of about 1 to 2 ns, exists between the local excited (LE) and ET states. The existence of a triplet ET
state – 3(P−•••H–D+) – is proposed because the time interval between recording of the ES and appearance of the CTC GS (35–250 ns) does not fit
the lifetime of the singlet excited complex (exciplex). It is feasible that apart from NADPH, other intermediate proton carriers
are contemporaneously involved in the dark reaction (Pδ−•••H–Dδ+) → Chlide, because proton binding to the C7–C8 bond in vivo takes place in the trans-configuration. The hydride ion may approach the C7–C8 bond from one side by heterolytic fission and an additional proton, donated by the protein group, may be simultaneously added
to this bond from the opposite side of the porphyrin nucleus surface.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
12.
Previously reported results obtained for the elastoviscous properties of some thermoreversible gels formed from anionic polysaccharides (high methoxyl pectin, furcellaran and κ-carrageenan) and also gelatin and maltodextrin are discussed and some conclusions about the structure of the gels are presented.The rate at which the relaxation processes take place in the gel is independent of the polymer concentration suggesting that the gels are structurally inhomogeneous.If the helical conformation of the individual macromolecule is stable the standard enthalpy change on crosslink breakdown is less than 45 kJ mol?1. A relatively small decrease in standard enthalpy is sufficient for network stability because of the low standard entropy loss on gelation which is typical of semi-rigid chain polymers. If, however, the helical conformation is unstable the gelation process is cooperative and the standard enthalpy change on crosslink breakdown exceeds 200 kJ mol?1. 相似文献
13.
Size effects of large magnitude are observed in the torsional shear modulus and damping of bovine plexiform bone. Damping
increases and stiffness decreases with specimen size over all sizes studied. Measurements were conducted in torsion using
a laser-based micromechanics apparatus capable of viscoelastic studies over a range of frequencies up to 100 kHz, upon samples
of various size, with no parasitic friction or other errors that could mimic any size effect. Torsional tan δ at 1 Hz varies
by about a factor of five over the size range 2.8–6.2 mm thick, and is more dependent on specimen thickness at 1 Hz than it
is at higher frequency. The size effects are attributed to compliance and viscoelasticity of the interfaces between laminae.
These laminae must be substantially stiffer than whole bone. Observed size effects are likely to play a role in understanding
scaling laws of bones in living organisms.
Received: 12 February 2002 / Accepted: 22 November 2002
R.S. Lakes is also at the Department of Biomedical Engineering, Department of Engineering Physics, Materials Science Program
and Rheology Research Center all at the University of Wisconsin.
We thank the Whitaker foundation for their support of this work. 相似文献
14.
A feeding trial was performed in the laboratory with the catfish species Pterygoplichthys disjunctivus to determine stable carbon (13C) and nitrogen (15 N) turnover rates and discrimination factors in non-lethally sampled tissues (red blood cells, plasma solutes, and fin).
A second feeding trial was conducted to determine what P. disjunctivus could assimilate from low-quality wood-detritus—refractory polysaccharides (e.g., cellulose), or soluble wood-degradation products inherent in wood-detritus. This was performed
by feeding the fish an artificial wood-detritus diet with fibrous (δ13C = −26.36‰; δ15
N = 2.13‰) and soluble portions (δ13C = −11.82‰; δ15
N = 3.39‰) that had different isotopic signatures and monitoring the dynamics of isotopic incorporation in the different tissues
over time. Plasma solutes turned over more quickly than red blood cells for 13C and 15 N. However, in contrast to previous studies of juvenile fishes, C and N incorporation was primarily driven by catabolic tissue
turnover as opposed to growth rate. Tissue-diet discrimination factors for 15 N varied from 4.08 to 5.17‰, whereas they were <2‰ for 13C (and less than 0.3‰ for plasma and red blood cells). The results of trial two suggested that P. disjunctivus could not assimilate refractory polysaccharides. Moreover, the δ13C and δ15 N signatures of wild-caught P. disjunctivus from Florida confirmed their detrital trophic standing in Floridian aquatic ecosystems. 相似文献
15.
Other than the fact that the cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel can be activated by cAMP dependent kinase (PKA), little is known about the signal transduction pathways regulating
CFTR. Since G-proteins play a principal role in signal transduction regulating several ion channels [4, 5, 9], we sought to
test whether G-proteins control CFTR Cl− conductance (CFTR G
Cl
) in the native sweat duct (SD). We permeabilized the basolateral membrane with α-toxin so as to manipulate cytosolic nucleotides.
We activated G-proteins and monitored CFTR G
Cl
activity as described earlier [20, 23, 25]. We now show that activating G-proteins with GTP-γ-S (100 μm) also activates CFTR G
Cl
in the presence of 5 mm ATP alone (without exogenous cAMP). GTP-γ-S increased CFTR G
Cl
by 44 ± 20 mS/cm2 (mean ±se; n= 7). GDP (10 mm) inhibited G-protein activation of CFTR G
Cl
even in the presence of GTP-γ-S. The heterotrimeric G-protein activator (AlF4
−) in the cytoplasmic bath activated CFTR G
Cl
(increased by 51.5 ± 9.4 mS/cm2 in the presence of 5 mm ATP without cAMP, n= 6), the magnitude of which was similar to that induced by GTP-γ-S. Employing immunocytochemical-labeling techniques, we
localized Gαs, Gαi, Gαq, and Gβ at the apical membranes of the sweat duct. Further, we showed that the mutant CFTR G
Cl
in ducts from cystic fibrosis (CF) subjects could be partially activated by G-proteins. The magnitude of mutant CFTR G
Cl
activation by G-proteins was smaller as compared to non-CF ducts but comparable to that induced by cAMP in CF ducts. We conclude
that heterotrimeric G-proteins are present in the apical membrane of the native human sweat duct which may help regulate salt
absorption by controlling CFTR G
Cl
activity.
Received: 9 June 2000/Revised: 5 October 2000 相似文献
16.
A 200-year coral stable oxygen isotope record from a high-latitude reef off Western Australia 总被引:4,自引:0,他引:4
H. Kuhnert J. Pätzold B. Hatcher K.-H. Wyrwoll A. Eisenhauer L. B. Collins Z. R. Zhu G. Wefer 《Coral reefs (Online)》1999,18(1):1-12
A core from a coral colony of Porites lutea was analysed for stable oxygen isotopic composition*. A 200-year proxy record of sea surface temperatures from the Houtman Abrolhos Islands off west Australia was obtained from
coral δ18O. At 29′S, the Houtman Abrolhos are the southernmost major reef complex of the Indian Ocean. They are located on the path
of the Leeuwin Current, a southward flow of warm, tropical water, which is coupled to Indonesian throughflow. Coral δ18O primarily reflects local oceanographic and climatic variability, which is largely determined by spatial variability of the
Leeuwin Current. However, coherence between coral δ18O and the current strength itself is relatively weak. Evolutionary spectral and singular spectrum analyses of coral δ18O demonstrate a high variability in spectral composition through time. Oscillations in the 5–7-y, 14–15-y, and quasi-biennial
bands reflect teleconnections of local sea surface temperature (SST) to tropical Pacific climate variability. Deviations between
local (coral-based) and regional (instrument) SST contain a cyclic component with a period of 15 y. Coral δ18O suggests a rise in SST by 0.6 ′C since AD 1944, consistent with available instrumental SST records. A long-term warming
by 1.4 ′C since AD 1795 is inferred from the coral record.
Accepted: 3 July 1998 相似文献
17.
Common carp is cheap and prolific in Australian waters and is regarded as an aquatic environmental pest. In order to add value
to this fish species, surimi and kamaboko was prepared from common carp and its rheological and microstructure characteristics
were compared with those produced from Alaska pollock and threadfin bream. Temperature sweep tests were run under 100-Pa stress
and 0.1-Hz frequency, obtained from linear viscoelastic ranges of all tested fish gels. Storage modulus (G′) thermographs of all samples consisted of two positive peaks and a plateau zone in between. The sol-gel transition was completed
at about 53 and 61 °C for these Alaska pollock and threadfin bream gels, respectively, whereas it was recorded at about 69 °C
for common carp gel. At these temperatures, G′ of Alaska pollock gel was recorded at 330 kPa, which was 71% and 88% greater than that from threadfin bream and common carp
gels, respectively. Furthermore, Alaska pollock and threadfin bream gels had greater gel strength than the gel prepared from
common carp surimi. Textural quality could be associated with cross-linking in the gel network. From scanning electron microscopy
studies, the microstructure of Alaska pollock gel matrix had about 15,450 polygonal structures per square millimeter with
an average area of about 9 μm2. For threadfin bream and common carp gels, the polygonal structures were larger and 12% and 39% fewer, respectively, than
those of Alaska pollock gel. However, these results cannot be only attributed to the species variation among tested fish as
some other factors such as harvest location, physiological state, handling and processing method, etc. were not considered
in this study. 相似文献
18.
D. R. Bowling W. J. Massman S. M. Schaeffer S. P. Burns R. K. Monson M. W. Williams 《Biogeochemistry》2009,95(1):37-59
Considerable research has recently been devoted to understanding biogeochemical processes under winter snow cover, leading
to enhanced appreciation of the importance of many winter ecological processes. In this study, a comprehensive investigation
of the stable carbon isotope composition (δ13C) of CO2 within a high-elevation subalpine forest snowpack was conducted. Our goals were to study the δ13C of biological soil respiration under snow in winter, and to assess the relative importance of diffusion and advection (ventilation
by wind) for gas transport within snow. In agreement with other studies, we found evidence of an active microbial community
under a roughly 1-m deep snowpack during winter and into spring as it melted. Under-snow CO2 mole fractions were observed up to 3,500 μmol mol−1, and δ13C of CO2 varied from ~−22 to ~−8‰. The δ13C of soil respiration calculated from mixing relationships was −26 to −24‰, and although it varied in time, it was generally
close to that of the bulk organic horizon (−26.0‰). Subnivean CO2 and δ13C were quite dynamic in response to changes in soil temperature, liquid water availability, and wind events. No clear biologically-induced
isotopic changes were observed during periods when microbial activity and root/rhizosphere activity were expected to vary,
although such changes cannot be eliminated. There was clear evidence of isotopic enrichment associated with diffusive transport
as predicted by theory, but simple diffusive enrichment (4.4‰) was not observed. Instead, ventilation of the snowpack by sustained
wind events in the forest canopy led to changes in the diffusively-enriched gas profile. The isotopic influence of diffusion
on gases in the snowpack and litter was greatest at greater depths, due to the decreased relative contribution of advection
at depth. There were highly significant correlations between the apparent isotopic content of respiration from the soil with
wind speed and pressure. In summary, physical factors influencing gas transport substantially modified and potentially obscured
biological factors in their effects on δ13C of CO2 within this subalpine forest snowpack. 相似文献
19.
We present a theory describing how the δ15N values of the nitrogen (N) pools in a vascular plant depend on that of its source N (nitrate), on 15N/14N fractionations during N assimilation, and on N transport within and N loss from the plant. The theory allows measured δ15N values to be interpreted in terms of physiological processes. The δ15N values of various N pools are calculated using three rules: (1) when a pool divides without transformation, there is no
change in the δ15N values of the N entering the resulting pools; (2) when nitrate is assimilated by nitrate reductase, the δ15N values of the resulting pools (product and residual substrate) are described by a Rayleigh equation; (3) when two N pools
mix, the δ15N value of the mixture is a weighted average of the δ15N values of the component pools. The theory is written as a spreadsheet and solved numerically. Potentially, it has multiple
solutions. Some contravene physiological reality and are rejected. The remainder are distinguished, where possible, using
additional physiological information. The theory simulated independent measurements of δ15N in N pools of Brassica campestris L. var. rapa (komatsuna) and Lycopersicon esculentum Mill. cv. T-5 (tomato).
Received: 27 October 1997 / Accepted: 13 January 1998 相似文献
20.
Chakraborti S Mandal A Das S Chakraborti T 《Molecular and cellular biochemistry》2005,280(1-2):107-117
Treatment of bovine pulmonary artery smooth muscle with the O2•− generating system hypoxanthine plus xanthine oxidase stimulated MMP-2 activity and PKC activity; and inhibited Na+ dependent Ca2+ uptake in the microsomes. Pretreatment of the smooth muscle with SOD (the O2•− scavenger) and TIMP-2 (MMP-2 inhibitor) prevented the increase in MMP-2 activity and PKC activity, and reversed the inhibition
of Na+ dependent Ca2+ uptake in the microsomes. Pretreatment with calphostin C (a general PKC inhibitor) and rottlerin (a PKCδ inhibitor) prevented
the increase in PKC activity and reversed O2•− caused inhibition of Na+ dependent Ca2+ uptake without causing any change in MMP-2 activity in the microsomes of the smooth muscle. Treatment of the smooth muscle
with the O2•− generating system revealed, respectively, 36 kDa RACK-1 and 78 kDa PKCδ immunoreactive protein profile along with an additional
38 kDa immunoreactive fragment in the microsomes. The 38 kDa band appeared to be the proteolytic fragment of the 78 kDa PKCδ
since pretreatment with TIMP-2 abolished the increase in the 38 kDa immunoreactive fragment. Co-immunoprecipitation of PKCδ
and RACK-1 demonstrated O2•− dependent increase in PKCδ-RACK-1 interaction in the microsomes. Immunoblot assay elicited an immunoreactive band of 41 kDa
Giα in the microsomes. Treatment of the smooth muscle tissue with the O2•− generating system causes phosphorylation of Giα in the microsomes and pretreatment with TIMP-2 and rottlerin prevented the phosphorylation. Pretreatment of the smooth muscle
tissue with pertussis toxin reversed O2•− caused inhibition of Na+ dependent Ca2+ uptake without affecting the protease activity and PKC activity in the microsomes. We suggest the existence of a pertussis
toxin sensitive G protein mediated mechanism for inhibition of Na+ dependent Ca2+ uptake in microsomes of bovine pulmonary artery smooth muscle under O2•− triggered condition, which is regulated by PKCδ dependent phosphorylation and sensitive to TIMP-2 for its inhibition. (Mol
Cell Biochem xxx: 107–117, 2005) 相似文献