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Chemical Gradients (chemical + gradient)

Distribution by Scientific Domains

Life Sciences	53%
Polymers and Materials Science	30%

Selected Abstracts

Rapid Generation of Biologically Relevant Hydrogels Containing Long-Range Chemical Gradients

ADVANCED FUNCTIONAL MATERIALS, Issue 1 2010
Jiankang He
Abstract Many biological processes are regulated by gradients of bioactive chemicals. Thus, the generation of materials with embedded chemical gradients may be beneficial for understanding biological phenomena and generating tissue-mimetic constructs. Here a simple and versatile method to rapidly generate materials containing centimeter-long gradients of chemical properties in a microfluidic channel is described. The formation of a chemical gradient is initiated by a passive-pump-induced forward flow and further developed during an evaporation-induced backward flow. The gradient is spatially controlled by the backward flow time and the hydrogel material containing the gradient is synthesized via photopolymerization. Gradients of a cell-adhesion ligand, Arg-Gly-Asp-Ser (RGDS), are incorporated in poly(ethylene glycol)-diacrylate (PEG-DA) hydrogels to test the response of endothelial cells. The cells attach and spread along the hydrogel material in a manner consistent with the RGDS-gradient profile. A hydrogel containing a PEG-DA concentration gradient and constant RGDS concentration is also shown. The morphology of cells cultured on such hydrogel changes from round in the lower PEG-DA concentration regions to well-spread in the higher PEG-DA concentration regions. This approach is expected to be a valuable tool to investigate the cell,material interactions in a simple and high-throughput manner and to design graded biomimetic materials for tissue engineering applications. [source]

A High-Throughput Assay of Cell-Surface Interactions using Topographical and Chemical Gradients,

ADVANCED MATERIALS, Issue 3 2009
Jing Yang
Orthogonal wettability and topographical gradients in a combinatorial sample format are fabricated using plasma-polymer-coated microgrooved surfaces. Preferred cell proliferation is found on specific combinations of topography and chemistry. This proof-of-concept study demonstrates the potential applications of this sample format for investigating the relationship between multiple surface properties on cellular response in a high-throughput manner. [source]

Rapid Generation of Biologically Relevant Hydrogels Containing Long-Range Chemical Gradients

Characterization of Arginine Transport in Helicobacter pylori

HELICOBACTER, Issue 4 2003
George L. Mendz
ABSTRACT Background. The amino acid L-arginine is an essential requirement for growth of Helicobacter pylori. Several physiological roles of this amino acid have been identified in the bacterium, but very little is known about the transport of L-arginine and of other amino acids into H. pylori. Methods. Radioactive tracer techniques using L-(U- 14C) arginine and the centrifugation through oil method were employed to measure the kinetic parameters, temperature dependence, substrate specificity, and effects of analogues and inhibitors on L-arginine transport. Results. The transport of arginine at millimolar concentrations was saturable with a Km of 2.4 ± 0.3 mM and Vmax of 1.3 ± 0.2 pmole min,1 (µl cell water),1 or 31 ± 3 nmole per minute (mg protein),1 at 20°C, depended on temperature between 4 and 40°C, and was susceptible to inhibitors. These characteristics suggested the presence of one or more arginine carriers. The substrate specificity of the transport system was studied by measuring the effects of L-arginine analogues and amino acids on the rates of transport of L-arginine. The absence of inhibition in competition experiments with L-lysine and L-ornithine indicated that the transport system was not of the Lysine-Arginine-Ornithine or Arginine-Ornithine types. The presence of different monovalent cations did not affect the transport rates. Several properties of L-arginine transport were elucidated by investigating the effects of potential inhibitors. Conclusions. The results provided evidence that the transport of L-arginine into H. pylori cells was carrier-mediated transport with the driving force supplied by the chemical gradient of the amino acid. [source]

Prostate carcinoma cells selected by long-term exposure to reduced oxygen tension show remarkable biochemical plasticity via modulation of superoxide, HIF-1, levels, and energy metabolism

JOURNAL OF CELLULAR PHYSIOLOGY, Issue 3 2007
Jeanne Bourdeau-Heller
Cancer cells are able to tolerate levels of O2 that are damaging or lethal to normal cells; we hypothesize that this tolerance is the result of biochemical plasticity which maintains cellular homeostasis of both energy levels and oxidation state. In order to examine this hypothesis, we used different O2 levels as a selective agent during long-term culture of DU145 prostate cancer cells to develop three isogenic cell lines that grow in normoxic (4%), hyperoxic (21%), or hypoxic (1%) O2 conditions. Growth characteristics and O2 consumption differed significantly between these cell lines without changes in ATP levels or altered sensitivity to 2-deoxy- D -glucose, an inhibitor of glycolysis. O2 consumption was significantly higher in the hyperoxic line as was the level of endogenous superoxide. The hypoxic cell line regulated the chemical gradient of the proton motive force (PMF) independent of the electrical component without O2 -dependent changes in Hif-1, levels. In contrast, the normoxic line regulated Hif-1, without tight regulation of the chemical component of the PMF noted in the hypoxic cell line. From these studies, we conclude that selection of prostate cancer cells by long-term exposure to low ambient levels of O2 resulted in cells with unique biochemical properties in which energy metabolism, reactive oxygen species (ROS), and HIF-1, levels are modulated to allow cell survival and growth. Thus, cancer cells exhibit remarkable biochemical plasticity in response to various O2 levels. J. Cell. Physiol. 212:744,752, 2007. © 2007 Wiley-Liss, Inc. [source]

Effects of cold-girdling on flows in the transport phloem in Ricinus communis: is mass flow inhibited?

PLANT CELL & ENVIRONMENT, Issue 1 2006
ANDREAS D. PEUKE
ABSTRACT The effects of cold girdling of the transport phloem at the hypocotyl of Ricinus communis on solute and water transport were investigated. Effects on the chemical composition of saps of phloem and xylem as well as of stem tissue were studied by conventional techniques and the water flow in the phloem was investigated by NMR imaging. Cold girdling reduced the concentration of sucrose but not that of inorganic solutes or amino acids in phloem saps. The possibility that cold treatment inhibited the retrieval of sucrose into the phloem, following leaching from the sieve tubes along a chemical gradient is discussed. Leaching of other solutes did not occur, as a result of missing promoting gradients in stem tissue. Following 3 d of cold girdling, sugar concentration increased and starch was synthesized and accumulated in stem tissue above the cold girdling region and along the cold-treated phloem pathway due to leaching of sugars from the phloem. Only in the very first period of cold girdling (< 15,30 min) was mass flow inhibited, but recovered in the rest of cold treatment period to values similar to the control period before and the recovery period after the cold treatment. It is concluded that cold treatment affected phloem transport through two independent and reversible processes: (1) a permanent leaching of sucrose from the phloem stem without normal retrieval during cold treatment, and (2) a short-term inhibition of mass flow at the beginning of cold treatment, possibly involving P proteins. Possible further mechanisms for reversible inhibition of water flow are discussed. [source]

Symmetry-breaking in mammalian cell cohort migration during tissue pattern formation: Role of random-walk persistence

CYTOSKELETON, Issue 4 2005
S. Huang
Abstract Coordinated, cohort cell migration plays an important role in the morphogenesis of tissue patterns in metazoa. However, individual cells intrinsically move in a random walk-like fashion when studied in vitro. Hence, in the absence of an external orchestrating influence or template, the emergence of cohort cell migration must involve a symmetry-breaking event. To study this process, we used a novel experimental system in which multiple capillary endothelial cells exhibit spontaneous and robust cohort migration in the absence of chemical gradients when cultured on micrometer-scale extracellular matrix islands fabricated using microcontact printing. A computational model suggested that directional persistence of random-walk and dynamic mechanical coupling of adjacent cells are the critical control parameters for this symmetry-breaking behavior that is induced in spatially-constrained cell ensembles. The model predicted our finding that fibroblasts, which exhibit a much shorter motility persistence time than endothelial cells, failed to undergo symmetry breaking or produce cohort migration on the matrix islands. These findings suggest that cells have intrinsic motility characteristics that are tuned to match their role in tissue patterning. Our results underscore the importance of studying cell motility in the context of cell populations, and the need to address emergent features in multicellular organisms that arise not only from cell-cell and cell-matrix interactions, but also from properties that are intrinsic to individual cells. Cell Motil. Cytoskeleton 61:201,213, 2005. © 2005 Wiley-Liss, Inc. [source]

A novel, multi-layered methanotrophic microbial mat system growing on the sediment of the Black Sea

ENVIRONMENTAL MICROBIOLOGY, Issue 8 2008
Martin Krüger
Summary A novel microbially diverse type of 1- to 5-cm-thick mat performing anaerobic oxidation of methane (AOM) and covering several square metres of the seafloor was discovered in the Black Sea at 180 m water depth. Contrary to other AOM-mat systems of the Black Sea these floating mats are not associated to free gas and are not stabilized by authigenic carbonates. However, supply of methane is ensured by the horizontal orientation of the mats acting as a cover of methane enriched fluids ascending from the underlying sediments. Thorough investigation of their community composition by molecular microbiology and lipid biomarkers, metabolic activities and elemental composition showed that the mats provide a clearly structured system with extracellular polymeric substances (EPS) building the framework of the mats. The top black zone, showing high rates of AOM (15 ,mol gdw,1 day,1), was dominated by ANME-2, while the following equally active pink layer was dominated by ANME-1 Archaea. The lowest AOM activity (2 ,mol gdw,1 day,1) and cell numbers were found in the greyish middle part delimited towards the sediment by a second pink, ANME-1-dominated and sometimes a black outer layer (ANME-2). Our work clearly shows that the different microbial populations are established along defined chemical gradients such as methane, sulfate or sulfide. [source]

Colonization of nascent, deep-sea hydrothermal vents by a novel Archaeal and Nanoarchaeal assemblage

ENVIRONMENTAL MICROBIOLOGY, Issue 1 2006
Elizabeth A. McCliment
Summary Active deep-sea hydrothermal vents are areas of intense mixing and severe thermal and chemical gradients, fostering a biotope rich in novel hyperthermophilic microorganisms and metabolic pathways. The goal of this study was to identify the earliest archaeal colonizers of nascent hydrothermal chimneys, organisms that may be previously uncharacterized as they are quickly replaced by a more stable climax community. During expeditions in 2001 and 2002 to the hydrothermal vents of the East Pacific Rise (EPR) (9°50,N, 104°17,W), we removed actively venting chimneys and in their place deployed mineral chambers and sampling units that promoted the growth of new, natural hydrothermal chimneys and allowed their collection within hours of formation. These samples were compared with those collected from established hydrothermal chimneys from EPR and Guaymas Basin vent sites. Using molecular and phylogenetic analysis of the 16S rDNA, we show here that at high temperatures, early colonization of a natural chimney is dominated by members of the archaeal genus Ignicoccus and its symbiont, Nanoarchaeum. We have identified 19 unique sequences closely related to the nanoarchaeal group, and five archaeal sequences that group closely with Ignicoccus. These organisms were found to colonize a natural, high temperature protochimney and vent-like mineral assemblages deployed over high temperature outflows within 92 h. When compared phylogenetically, several of these colonizing organisms form a unique clade independent of those found in mature chimneys and low-temperature mineral chamber samples. As a model ecosystem, the identification of pioneering consortia in deep-sea hydrothermal vents may help advance the understanding of how early microbial life forms gained a foothold in hydrothermal systems on early Earth and potentially on other planetary bodies. [source]

Rapid Generation of Biologically Relevant Hydrogels Containing Long-Range Chemical Gradients

Priming the productivity pump: flood pulse driven trends in suspended algal biomass distribution across a restored floodplain

FRESHWATER BIOLOGY, Issue 8 2006
DYLAN S. AHEARN
Summary 1. Chlorophyll a (Chl a) distribution across a 0.36 km2 restored floodplain (Cosumnes River, California) was analysed throughout the winter and spring flood season from January to June 2005. In addition, high temporal-resolution Chl a measurements were made in situ with field fluorometers in the floodplain and adjacent channel. 2. The primary objectives were to characterise suspended algal biomass distribution across the floodplain at various degrees of connection with the channel and to correlate Chl a concentration and distribution with physical and chemical gradients across the floodplain. 3. Our analysis indicates that periodic connection and disconnection of the floodplain with the channel is vital to the functioning of the floodplain as a source of concentrated suspended algal biomass for downstream aquatic ecosystems. 4. Peak Chl a levels on the floodplain occurred during disconnection, reaching levels as high as 25 ,g L,1. Chl a distribution across the floodplain was controlled by residence time and local physical/biological conditions, the latter of which were primarily a function of water depth. 5. During connection, the primary pond on the floodplain exhibited low Chl a (mean = 3.4 ,g L,1) and the shallow littoral zones had elevated concentrations (mean = 4.6 ,g L,1); during disconnection, shallow zone Chl a increased (mean = 12.4 ,g L,1), but the pond experienced the greatest algal growth (mean = 14.7 ,g L,1). 6. Storm-induced floodwaters entering the floodplain not only displaced antecedent floodplain waters, but also redistributed floodplain resources, creating complex mixing dynamics between parcels of water with distinct chemistries. Incomplete replacement of antecedent floodplain waters led to localised hypoxia in non-flushed areas. 7. The degree of complexity revealed in this analysis makes clear the need for high-resolution spatial and temporal studies such as this to begin to understand the functioning of dynamic and heterogeneous floodplain ecosystems. [source]

The Fountain Hills unique CB chondrite: Insights into thermal processes on the CB parent body

METEORITICS & PLANETARY SCIENCE, Issue 6 2009
Dante S. LAURETTA
This meteorite is closely related to the CBa class. Mineral compositions and O-isotopic ratios are indistinguishable from other members of this group. However, many features of Fountain Hills are distinct from the other CB chondrites. Fountain Hills contains 23 volume percent metal, significantly lower than other members of this class. In addition, Fountain Hills contains porphyritic chondrules, which are extremely rare in other CBa chondrites. Fountain Hills does not appear to have experienced the extensive shock seen in other CB chondrites. The chondrule textures and lack of fine-grained matrix suggests that Fountain Hills formed in a dust-poor region of the early solar system by melting of solid precursors. Refractory siderophiles and lithophile elements are present in near-CI abundances (within a factor of two, related to the enhancement of metal). Moderately volatile and highly volatile elements are significantly depleted in Fountain Hills. The abundances of refractory siderophile trace elements in metal grains are consistent with condensation from a gas that is reduced relative to solar composition and at relatively high pressures (10,3bars). Fountain Hills experienced significant thermal metamorphism on its parent asteroid. Combining results from the chemical gradients in an isolated spinel grain with olivine-spinel geothermometry suggests a peak temperature of metamorphism between 535 °C and 878 °C, similar to type-4 ordinary chondrites. [source]

Biodiversity effects on ecosystem functioning: emerging issues and their experimental test in aquatic environments

OIKOS, Issue 3 2004
Paul S. Giller
Recent experiments, mainly in terrestrial environments, have provided evidence of the functional importance of biodiversity to ecosystem processes and properties. Compared to terrestrial systems, aquatic ecosystems are characterised by greater propagule and material exchange, often steeper physical and chemical gradients, more rapid biological processes and, in marine systems, higher metazoan phylogenetic diversity. These characteristics limit the potential to transfer conclusions derived from terrestrial experiments to aquatic ecosystems whilst at the same time provide opportunities for testing the general validity of hypotheses about effects of biodiversity on ecosystem functioning. Here, we focus on a number of unique features of aquatic experimental systems, propose an expansion to the scope of diversity facets to be considered when assessing the functional consequences of changes in biodiversity and outline a hierarchical classification scheme of ecosystem functions and their corresponding response variables. We then briefly highlight some recent controversial and newly emerging issues relating to biodiversity-ecosystem functioning relationships. Based on lessons learnt from previous experimental and theoretical work, we finally present four novel experimental designs to address largely unresolved questions about biodiversity-ecosystem functioning relationships. These include (1) investigating the effects of non-random species loss through the manipulation of the order and magnitude of such loss using dilution experiments; (2) combining factorial manipulation of diversity in interconnected habitat patches to test the additivity of ecosystem functioning between habitats; (3) disentangling the impact of local processes from the effect of ecosystem openness via factorial manipulation of the rate of recruitment and biodiversity within patches and within an available propagule pool; and (4) addressing how non-random species extinction following sequential exposure to different stressors may affect ecosystem functioning. Implementing these kinds of experimental designs in a variety of systems will, we believe, shift the focus of investigations from a species richness-centred approach to a broader consideration of the multifarious aspects of biodiversity that may well be critical to understanding effects of biodiversity changes on overall ecosystem functioning and to identifying some of the potential underlying mechanisms involved. [source]