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排序方式: 共有159条查询结果,搜索用时 31 毫秒
51.
Clunes MT Lindsay SL Roussa E Quinton PM Bovell DL 《Journal of molecular histology》2004,35(4):339-345
The localisation of the vacuolar proton pump (V-H+ -ATPase) and the enzyme carbonic anhydrase II (CAII) was investigated in the human eccrine sweat gland employing standard immunohistochemical techniques after antigen retrieval using microwave heat treatment and high pressure. The high-pressure antigen retrieval unmasked the presence of V-H+ -ATPase in the clear cells of the secretory coil, with a distribution similar to that previously observed for CAII. However, the dark cells were unreactive to both antibodies. In addition, heat and high-pressure antigen retrieval demonstrated the presence of CAII in the apical zone of luminal cells of the reabsorptive duct, a location not previously reported. The localisation of V-H+ -ATPase and CAII in the secretory coil clear cells suggests that the formation of HCO3- and H+ by carbonic anhydrase II and the transport of H+ by V-H+ -ATPase may play an role in sweat fluid secretion. Their presence at the apex of the duct cells indicates involvement in ductal ion reabsorption. 相似文献
52.
Summary Growth, substrate utilization and product formation forLactobacillus xylosus on glucose, xylose and a mixture of both substrates was modeled during batch fermentations. The yield of lactate on glucose was 0.88 g/g (55% of theoretical) and the yield on xylose was 0.41 g/g (69% of theoretical). When grown on both substrates,L. xylosus consumed no xylose at glucose concentrations exceeding 3.3 g/l. 相似文献
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Jake K Nikota Fernando M Botelho Carla MT Bauer Manel Jordana Anthony J Coyle Alison A Humbles Martin R Stampfli 《Respiratory research》2011,12(1):39
Background
While the presence of the chitinase-like molecule YKL40 has been reported in COPD and asthma, its relevance to inflammatory processes elicited by cigarette smoke and common environmental allergens, such as house dust mite (HDM), is not well understood. The objective of the current study was to assess expression and function of BRP-39, the murine equivalent of YKL40 in a murine model of cigarette smoke-induced inflammation and contrast expression and function to a model of HDM-induced allergic airway inflammation.Methods
CD1, C57BL/6, and BALB/c mice were room air- or cigarette smoke-exposed for 4 days in a whole-body exposure system. In separate experiments, BALB/c mice were challenged with HDM extract once a day for 10 days. BRP-39 was assessed by ELISA and immunohistochemistry. IL-13, IL-1R1, IL-18, and BRP-39 knock out (KO) mice were utilized to assess the mechanism and relevance of BRP-39 in cigarette smoke- and HDM-induced airway inflammation.Results
Cigarette smoke exposure elicited a robust induction of BRP-39 but not the catalytically active chitinase, AMCase, in lung epithelial cells and alveolar macrophages of all mouse strains tested. Both BRP-39 and AMCase were increased in lung tissue after HDM exposure. Examining smoke-exposed IL-1R1, IL-18, and IL-13 deficient mice, BRP-39 induction was found to be IL-1 and not IL-18 or IL-13 dependent, while induction of BRP-39 by HDM was independent of IL-1 and IL-13. Despite the importance of BRP-39 in cellular inflammation in HDM-induced airway inflammation, BRP-39 was found to be redundant for cigarette smoke-induced airway inflammation and the adjuvant properties of cigarette smoke.Conclusions
These data highlight the contrast between the importance of BRP-39 in HDM- and cigarette smoke-induced inflammation. While functionally important in HDM-induced inflammation, BRP-39 is a biomarker of cigarette smoke induced inflammation which is the byproduct of an IL-1 inflammatory pathway. 相似文献56.
The relationships between the vulnerability of stem xylem to cavitation, stomatal conductance, stomatal density, and leaf and stem water potential were examined in six hybrid poplar (P38P38, Walker, Okanese, Northwest, Assiniboine and Berlin) and balsam poplar (Populus balsamifera) clones. Stem xylem cavitation resistance was examined with the Cavitron technique in well-watered plants grown in the greenhouse. To investigate stomatal responses to drought, plants were subjected to drought stress by withholding watering for 5 (mild drought) and 7 (severe drought) days and to stress recovery by rewatering severely stressed plants for 30 min and 2 days. The clones varied in stomatal sensitivity to drought and vulnerability to stem xylem cavitation. P38P38 reduced stomatal conductance in response to mild stress while the balsam poplar clone maintained high leaf stomatal conductance under more severe drought stress conditions. Differences between the severely stressed clones were also observed in leaf water potentials with no or relatively small decreases in Assiniboine, P38P38, Okanese and Walker. Vulnerability to drought-induced stem xylem embolism revealed that balsam poplar and Northwest clones reached loss of conductivity at lower stem water potentials compared with the remaining clones. There was a strong link between stem xylem resistance to cavitation and stomatal responsiveness to drought stress in balsam poplar and P38P38. However, the differences in stomatal responsiveness to mild drought suggest that other drought-resistant strategies may also play a key role in some clones of poplars exposed to drought stress. 相似文献
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Cavitation of water in xylem vessels followed by embolism formation has been authenticated for more than 40 years. Embolism formation involves the gradual buildup of bubble pressure (air) to atmospheric pressure as demanded by Henry’s law of equilibrium between gaseous and liquid phases. However, the tempo of pressure increase has not been quantified. In this report, we show that the rate of pressurization of embolized vessels is controlled by both fast and slow kinetics, where both tempos are controlled by diffusion but over different spatial scales. The fast tempo involves a localized diffusion from endogenous sources: over a distance of about 0.05 mm from water-filled wood to the nearest embolized vessels; this process, in theory, should take <2 min. The slow tempo involves diffusion of air from exogenous sources (outside the stem). The latter diffusion process is slower because of the increased distance of diffusion of up to 4 mm. Radial diffusion models and experimental measurements both confirm that the average time constant is >17 h, with complete equilibrium requiring 1 to 2 d. The implications of these timescales for the standard methods of measuring percentage loss of hydraulic conductivity are discussed in theory and deserve more research in future.Vulnerability curves (VCs) have been used as a measure of drought resistance of woody plants, and many methods have been used and evaluated to construct VCs (Cochard et al., 2013). Vessels cavitate in response to increasing drought stress and immediately fill with a mixture of water vapor and air. Henry’s law of gas solubility in water demands that, eventually, the air pressure in an embolized vessel will equal atmospheric pressure provided that the surrounding water pressure remains low enough. Most presumed, until recently, that the air pressure builds up to atmospheric pressure in 10 to 20 min (Sperry and Tyree, 1988; Tyree and Zimmermann, 2002). In contrast, research has shown that dissolving of air bubbles in stem takes many hours (10–100) depending on water pressure applied and stem diameter (Tyree and Yang, 1992; Yang and Tyree, 1992), but how long it takes to fully embolize a vessel remains unknown. Recently, cavitron methods have been developed to estimate average bubble pressure by measuring the impact of the water tension on stem hydraulic conductivity when the water pressure adjacent to a bubble changes, causing bubble expansion or compression (Wang et al., 2014b, 2015).Subatmospheric bubble pressure in vessels makes the measurements of hydraulic conductivity of stems, kh, inaccurate when measured at or near atmospheric pressure, because bubble collapse will cause an increase in kh as shown by traditional measurements (Tyree and Yang, 1992; Yang and Tyree, 1992) and modern cavitron methods (Wang et al., 2015). Intuitively, if embolized vessels have subatmospheric air pressure, then the air bubbles ought to collapse in volume as the surrounding water tension increases to zero (atmospheric pressure). A collapsing air bubble will result in a vessel partly filled with water, and a partly water-filled vessel is capable of conducting water if it contacts adjacent water-filled vessels. Bubble pressure will also increase with time because of Henry’s law, and the time required to fully embolize the vessels depends on the penetration rate of air through the xylem as governed by Fick’s law of diffusion. Where does the air come from, and how long does it take to fully embolize a vessel?
Open in a separate windowTo answer the questions, some insights can be gained through some theoretical analyses and calculations before conducting experiments. Embolized vessels serve as a sink of air, and there are two main sources of air: (1) an endogenous source, which is the air dissolved in liquid phase inside the stem, and (2) an exogenous source, which is the air in atmospheric phase outside the stem. Air dissolved in water in the stem would be drawn out very quickly to fill recently cavitated vessels because of the very short distance between newly cavitated vessels and the surrounding water. For example, if one-half of the vessels cavitate quickly, the approximate distance between cavitation voids will be 0.05 mm (Wang et al., 2015), but ambient air beyond the bark boundary has to move a comparatively long way (many millimeters) into the cavitated vessels through the bark and wood. The reason for the longer time for exogenous air to move follows from the relationship between the median distance that a molecule can diffuse, x, and the time for the diffusion, t. The relationship is x2 = 2Dt, where D is the diffusion coefficient of air molecules in water. In a recent article (Wang et al., 2015), it was argued that the time for endogenous bubble pressure equilibrium was ≤10 s over diffusional distances of 0.05 to 0.1 mm. Hence, it follows that, if distances are 102 more, the time will be 104 more for diffusion from exogenous sources (i.e. 1–2 d versus 10 s). However, Wang et al. (2015) used an inappropriate value for D equal to air diffusion in pure water. Using a more appropriate value actually measured in wood (Sorz and Hietz, 2006), the recomputed time is nearly 1 min (Supplemental Fig. S1; Supplemental Theory S1). The original model (Wang et al., 2015) has not changed, except for the use of a more accurate value of D. However, the qualitative argument that some bubble pressurization is fast and that the rest is slow is still correct.It could be argued theoretically that, based on Fick’s law of diffusion, the ideal gas law of air bubbles, and Henry’s law of solubility of air in water, the time for exogenous bubble pressure equilibrium could be even more than 1 d. However, a technically valid, experimental verification of equilibrium time constant is always preferable to theory alone. Hence, the objective of this study is to first measure experimentally the time constant of exogenous equilibration and second, explain by theory why the time constant should be the value measured experimentally.Readers should consult the work by Wang et al. (2015) for details about the theoretical and experimental approaches used in this study, but the basic idea is easy to explain without rigorous theory. It is well known that stem kh increases if bubbles dissolve or otherwise grow smaller (Tyree and Yang, 1992; Yang and Tyree, 1992); therefore, information about bubble size or pressure can be deduced from repeated measurements of kh. In brief, bubbles in vessels can be compressed when bubble pressure is lower than the sum of water pressure and capillary pressure, and water will partly refill the vessel as bubbles collapse. Partly refilled vessels enhance stem conductivity provided that the water is in contact through pit membranes with adjacent water-filled vessels. In this article, we use a centrifuge technique (Wang et al., 2014b) to manipulate the water pressure or tension, T, adjacent to embolized vessels. If the initial bubble pressure, Pb*, is low, the bubbles will collapse more as tension decreases toward zero than if Pb* is high. Wang et al. (2015) showed that Pb* can be computed by fitting functions of kh versus T in a cavitron. Hence, by doing repeated measurements over many hours of kh versus T, one can determine the tempo of Pb* change. 相似文献
Table I.
Table of abbreviationsAbbreviation | Meaning |
---|---|
D, Dw | Coefficient of diffusion of gas in water and wood, respectively |
kh | Hydraulic conductivity of the stem |
kmax | Maximum hydraulic conductivity of the stem |
Lv, Lb | Length of vessel and bubble, respectively |
τ | Time constant in an exponential process |
T | Tension in xylem |
Tc | Central tension in stem that spins in a centrifuge |
PLC | PLC of stem |
P50, P63 | Xylem pressure when stem loss is 50% or 63% of its maximum conductivity, respectively |
VC | Vulnerability curve |
Cavitron | Cochard’s cavitron (Cochard rotor) that both spins stem and measures conductivity in the centrifuge |
Sperry rotor | Standard centrifuge method that spins stem in the centrifuge and measures kh in conductivity apparatus out of the centrifuge |
Pb* | Bubble pressure in stem before bubble collapse |
59.
Ewa Przybytkowski Elizabeth Lenkiewicz Michael T Barrett Kathleen Klein Sheida Nabavi Celia MT Greenwood Mark Basik 《BMC genomics》2014,15(1)