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排序方式: 共有126条查询结果,搜索用时 15 毫秒
1.
An optode device for net-photosynthesis measurements, based on oxygen-depending quenching of fluorescence from O2-specific sensors, and PAM fluorometry have been used to study diurnal courses of net-photosynthesis and the Fv/Fm ratio of the submerged plant Lagarosiphon major. Plants were pre-cultivated and studied in large mesocosm flow-through outdoor tanks under 50% and 80% shade cloth, respectively. Growth under the different shade cloths resulted in similar light compensation points (∼20 μmol photons m−2 s−1), but strongly different light saturation levels, with about 150 μmol m−2 s−1 for plants grown under 80% shade cloth and about 350 μmol m−2 s−1 for plants grown under 50% shade cloth. Plants under both growth conditions showed a transient reduction of the maximum Fv/Fm value in the afternoon (down to 70% of the morning control values under 80% shade cloth and down to 85% under 50% shade cloth), which was not accompanied by a reduction of the net photosynthetic rate. This indicated that the fluorescence parameter Fv/Fm must not be a reliable indicator of the rate of photosynthesis under all conditions. The new photo-optical device became evidenced as a valuable tool not only for laboratory experiments, but also for field studies of gas exchange of submerged plants. 相似文献
2.
Images of human erythrocytes from a healthy donor were recorded under differential interference contrast (DIC) microscopy;
they were acquired rapidly (~336 Hz) and the intensity of the centermost pixel of each cell was recorded for ~60 s (20,000
values). Various techniques were used to analyze the data, including detrended fluctuation analysis (DFA) and multiscale entropy
(MSE); however, power spectrum analysis was deemed the most appropriate for metrifying and comparing results. This analysis
was used to compare cells from young and old populations, and after perturbing normal conditions, with changes in temperature,
adenosine triphosphate (ATP) concentration (using NaF, an inhibitor of glycolysis, and α-toxin, a pore-forming molecule used
to permeabilize red cells to ATP), and water transport rates [using glycerol, and p-chloromercuriphenylsulfonic acid (pCMBS) to inhibit aquaporins, AQPs]. There were measurable differences in the membrane
fluctuation characteristics in populations of young and old cells, but there was no significant change in the flickering time
series on changing the temperature of an individual cell, by depleting it of ATP, or by competing with the minor water exchange
pathway via AQP3 using glycerol. However, pCMBS, which inhibits AQP1, the major water exchange pathway, inhibited flickering
in all cells, and yet it was restored by the membrane intercalating species dibutyl phthalate (DBP). We developed a computer
model to simulate acquired displacement spectral time courses and to evaluate various methods of data analysis, and showed
how the flexibility of the membrane, as defined in the model, affects the flickering time course. 相似文献
3.
Neuronal growth cones are motile structures located at the end of axons that translate extracellular guidance information into directional movements. Despite the important role of growth cones in neuronal development and regeneration, relatively little is known about the topography and mechanical properties of distinct subcellular growth cone regions under live conditions. In this study, we used the AFM to study the P domain, T zone, and C domain of live Aplysia growth cones. The average height of these regions was calculated from contact mode AFM images to be 183 ± 33, 690 ± 274, and 1322 ± 164 nm, respectively. These findings are consistent with data derived from dynamic mode images of live and contact mode images of fixed growth cones. Nano-indentation measurements indicate that the elastic moduli of the C domain and T zone ruffling region ranged between 3-7 and 7-23 kPa, respectively. The range of the measured elastic modulus of the P domain was 10-40 kPa. High resolution images of the P domain suggest its relatively high elastic modulus results from a dense meshwork of actin filaments in lamellipodia and from actin bundles in the filopodia. The increased mechanical stiffness of the P and T domains is likely important to support and transduce tension that develops during growth cone steering. 相似文献
4.
Many promising therapeutics are currently awaiting their clinical application. Due to their low capability of cell membrane crossing, these compounds do not reach their site of action. One way to overcome this problem might be the fusion of these agents to cell-penetrating peptides (CPP), which are able to shuttle various cargoes across cellular membranes. One disadvantage in using CPP in drug delivery is their low metabolic stability. The aim of our work was to increase the proteolytic resistance of the CPP hCT(9-32), a truncated C-terminal fragment of human calcitonin. Thus, we synthesised six modified N-terminally carboxyfluorescein labelled hCT(9-32) derivatives by replacing positions 12 and/or 16 of hCT(9-32) with either N-methylphenylalanine or d-phenylalanine, respectively. By using confocal laser scanning microscopy we showed that the modifications did neither affect the peptide internalisation efficiency in HeLa nor HEK 293T cells. The metabolic stability of the peptides was investigated in human blood plasma and HEK 293T cell culture supernatant. To analyse the degradation patterns, we used RP-HPLC and MALDI-TOF mass spectrometry. However, we found for all of the new derivatives high metabolic stabilities. In blood plasma, the half-lives for five of the six peptides increased compared to unmodified hCT(9-32). The degradation patterns showed a distinct stabilisation in the N-terminal part of the modified peptides, in the C-terminal part, we found some cleavage to a minor extent. Furthermore, we studied the conformation of the peptides by CD spectroscopy and demonstrated that they possess no cell toxicity. Since our metabolically more stable compounds are still able to pass the cell membrane they provide powerful tools as drug delivery vectors. 相似文献
5.
Tim Salditt 《生物化学与生物物理学报:生物膜》2006,1758(9):1483-1498
The conformation and correlations of amphiphilic and antimicrobial peptides and the associated changes of lipid bilayers can be studied in oriented lipid membranes deposited on solid substrates. Here we review recent work on these systems, as studied by modern interface-sensitive X-ray and neutron scattering methods. Density profile, short range order of acyl chains and molecular conformations of peptides and lipids are probed in the fluid state of the bilayer. With an emphasis on technical aspects, we review recent work illustrating the potential of the methods and discuss its potential in the field. 相似文献
6.
6例竹叶青蛇咬伤致DIC治疗体会 总被引:1,自引:1,他引:0
1995年初至2003年底,我院采用活血化瘀,凉血止血,佐以清热解毒等方法为主的综合疗法治疗竹叶青蛇咬伤致DIC6例,疗效显著。现总结报告如下。 相似文献
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9.
Haruki Hasegawa Carla ForteIrene Barber Shanon TurnbaughJanelle Stoops Min ShenAi Ching Lim 《Biochimica et Biophysica Acta (BBA)/Molecular Cell Research》2014
Crystalline bodies (CBs) can develop in the endoplasmic reticulum (ER) of antibody-producing cells. Although this phenotype is often reported in association with plasma cell dyscrasias and other hematological disorders, the details of CB biogenesis and CB's roles in pathophysiology remain poorly understood. Using an imaging-based screening method, we identified a secretion-competent human IgG2/λ clone that develops spindle-shaped intracellular crystals in transiently-transfected HEK293 cells upon Brefeldin A treatment. When stably overexpressed from CHO cells, the IgG2/λ clone spontaneously produced spindle-shaped CBs in the ER. Some CBs were released to the extracellular space while remaining enclosed by the membranes of secretory pathway origin. Structural modeling on the variable-region did not uncover prominent surface characteristics such as charge clusters. In contrast, alterations to the constant domain-encoded properties revealed their modulatory roles in CB-inducing propensities and CB morphology. For example, deletion of the entire Fc domain changed the morphology of CBs into thin filaments. Elimination of an N-linked glycan by a N297A mutation promoted Russell body biogenesis accompanied by marked reduction in IgG secretion. Isotype class switching from the original IgG2 to IgG1 and IgG4 changed the crystal morphology from spindle-shaped to long needle and acicular shaped, respectively. The IgG3 version, in contrast, suppressed the CB formation. Either the HC or LC alone or the Fc-domain alone did not trigger CB biogenesis. An IgG's in vivo crystal morphology and crystallization propensity can thus be modulated by the properties genetically and biochemically encoded in the HC constant region. 相似文献
10.