bluuebunny/crossref_metadata_2025 huggingface dataset:
ENHANCED GROWTH OF CARBON NANOTUBES ON SELECTED AREA USING AN AQUEOUS CATALYST
Authors: TSAI J. T. H. , CHEN K. H.
Published: December 2005

This paper describes the work carried out to produce patterned arrays of multi-wall carbon nanotubes (MWCNTs) using a liquid catalyst and a microwave plasma technique. By this method we can control the CNT growth on selective sites by engineering the substrate surface and yet maintain a very high CNT growth rate (~10 μm per minute). The catalyst is made by hydrochloric acid solution which contains high concentration of ferromagnetic metal ions. Upon dispersing the liquid catalyst on a silicon nitride substrate containing exposed silicon patterns, the catalyst only precipitates on the hydrophilic sites (i.e. silicon surface). After performing the CNT growth in a microwave reactor with CH 4/ N 2 mixture plasma, nanotubes can only be found to grow on exposed silicon surface instead of the main area covered by silicon nitride. This method allows us to produce multi-wall carbon nanotubes on the selective area as in the silicon trenches, concavities and thin film edges.
IN VITRO EXPERIMENT STUDY ON ABLATION PARAMETERS IN FEMTOSECOND LASER-OCULAR TISSUE INTERACTION
Authors: NGOI K. A. , HOU D. X. , HOH S. T. , KOH L. H. K. , DENG Y. Z.
Published: December 2005

In order to apply femtosecond laser technology in ophthalmology, especially in glaucoma treatment, femtosecond laser-ocular tissue interaction research was conducted. Focusing angle, output power, irradiance duration are three important laser parameters for ophthalmic microsurgery. In our work, the relationship of the three different laser parameter versus cutting effect was investigated respectively by an in-vitro experiment using an 800 nm-wavelength 150 fs-pulse-length laser system. This experiment aims to minimize the effects of thermal damage, while at the same time maximizing the speed or quality of the tissue ablation process. The experiment result shows that there is a great potential to optimize the surgical effects using femtosecond laser compared to that using a longer pulse laser.
OXIDATION OF CYCLOHEXENE IN A SIMPLE CAPILLARY-MICROREACTOR
Authors: BASHEER CHANBASHA , VETRICHELVAN MUTHALAGU , PERERA AGAMPODI PROMODA P. , VALIYAVEETTIL SURESH , LEE HIAN KEE
Published: December 2005

A simple glass capillary-microreactor for studying the epoxidation of cyclohexene is described in this paper. Reaction conditions were optimized to achieve high reaction yield. The microreactor is easy to fabricate, fast and easy way for reliable catalyst screening in studying homogeneous oxidation reactions. Four different catalysts (i.e. manganese(II) and copper(II) metal complexes of Schiff and reduced Schiff base ligands) were synthesized and used. The reaction products were monitored by gas chromatography/mass spectrometry. The reaction performance was compared with conventional (batch scale) reaction. In both cases, catalytic activities and the product yields were found to be relatively higher for the copper(II) complexes when compared with the conventional route.
A STUDY ON MICROSTRUCTURAL AND MECHANICAL PROPERTIES OF NANOCRYSTALLINE NICKEL
Authors: MOHANKUMAR KATTA , SIOW K. S. , JAYAGANTHAN RENGASWAMY , TAY ANDREW A. O. , KRIPESH VAIDYANATHAN
Published: December 2005

The microstructural characteristics and mechanical property of the Nanocrystalline Nickel ( Nc -Nickel), produced by Electrodeposition (ED) and Mechanical milling (MM), were investigated in the present work. From the nanoindentation study, we observed that MM - Nc - Ni showed lower hardness than ED - Nc - Ni and Microcrystalline ( Mc )- Ni . ED - Nc - Ni showed a significant improvement in hardness. All the Nc -Nickel samples, regardless of processing methods and grain sizes, showed comparable elastic moduli. The lower hardness of MM - Nc - Ni is due to the presence of microcrystalline Nc - Ni .
CHARACTERISTICS OF CdS NANOPARTICLES SYNTHESIZED BY SOLVOTHERMAL ROUTE WITH DIFFERENT RATIOS OF ETHYLENEDIAMINE/WATER
Authors: YAO JIANXI , HONG LI , ZHAO GAOLING , WENG WENJIAN , HAN GAORONG
Published: December 2005

CdS nanoparticles with various size and shape were synthesized through solvothermal route using different ratios of ethylenediamine/water. X-ray diffraction and transmission electron microscopy results revealed that CdS nanorods were formed by using ethylenediamine and the mixture of ethylenediamine and water as solvents. The CdS nanorods had [002] preferential orientation. When water was used as the solvent, irregular shape particles and typical XRD patterns of hexagonal CdS were observed. The produced nanoparticles displayed interesting photoluminescence feature, which were found to be sensitive to the ratio of ethylenediamine/water. It is suggested that the different coordination ability with Cd 2+ and dielectric constant of ethylenediamine and water caused different formation mechanism of CdS and led to the difference in the shape, crystallinity and optical properties of produced CdS particles.
NANOSTRUCTURED TiO2 FILMS IN DYE-SENSITIZED SOLAR CELLS
Authors: MENZIES D. B. , HART J. N. , CHENG Y.-B. , SIMON G. P. , DAI Q. , SPICCIA L.
Published: December 2005

The need for cost-effective renewable energy technology is of ever-increasing importance with the diminishing stock of raw materials for traditional non-renewable energy production. The dye-sensitized solar cell (DSSC) is a relatively new device that offers the potential of economically feasible conversion of solar energy to electricity. This approach to photovoltaic technology is a promising development in that it offers reasonable efficiencies, while using cheap materials and relatively simple manufacturing techniques. The aim of this paper is to provide a general background to DSSCs, an understanding of the components that make up the cell and an overview of the current research objectives.
PRODUCTION AND GRAIN STABILITY OF NANOCRYSTALLINE Fe-Si POWDERS AND THE EFFECTS OF ALUMINIUM ADDITION
Authors: ZUO B. , SARASWATI N. , SRITHARAN T. , HNG H. H.
Published: December 2005

The present work studied the production of nanocrystalline Fe 90 Si 10, Fe 75 Si 25 and Fe 75 Si 15 Al 10 alloys via a high-energy ball milling technique and their grain growth responses to high-temperature annealing treatments. The grain sizes of the resulting powders were determined by X-ray diffraction peak broadening and were also confirmed by transmission electron microscopy. A minimum crystallite size of 13-17 nm could be achieved in Fe 90 Si 10, Fe 75 Si 25 and Fe 75 Si 15 Al 10 alloys. The lattice parameters of as-milled Fe 90 Si 10, Fe 75 Si 25 and Fe 75 Si 15 Al 10 attained minimum values of about 0.2860, 0.2842 and 0.2862 nm respectively after 60 h, and thereafter remained constant for prolonged milling times. The grain size of Fe 90 Si 10 increased from approximately 17 nm to about 35 nm after annealing at 873 K. Fe 75 Si 25 exhibited some stability against grain growth at low temperatures but not above 673 K. Fe 75 Si 15 Al 10 grains showed better stability with no significant grain growth until 873 K. For Fe 75 Si 25 and Fe 75 Si 15 Al 10 alloys annealing at 773 K, 873 K and 973 K resulted in the formation of ordered DO 3 structure.
A NEW SCHEME TO REALIZE THE MEASUREMENT STANDARD OF MICROFORCE
Authors: YEH HSIEN-CHI , YEO SWEE HOCK , PAN SHEAU-SHI , LUO JUN
Published: December 2005

To increase the accuracy of mechanical characterizations of microstructures and nanomaterials on the molecular- and nano-scale, the measurement standard of microforce ranging from 10-6 N to 10-9 N must be realized for calibrating the testing and measuring instruments. In this paper, a new scheme based on the equal-arm torsion balance is proposed. This precision torsion balance detects accurately the gravitational force between two mass standards, and links the small force measurement to the International System of Units and Newtonian gravitational constant G. Such a balance might serve as a force standard machine operating in the regime below 10-6 N with an accuracy of 0.1%.
MORPHOLOGY EVOLUTION OF AN ASYMMETRIC DIBLOCK COPOLYMER P(S-b-MMA) AS A FUNCTION OF FILM THICKNESS AND ANNEALING TIME
Authors: WANG H. , DJURIŠIĆ A. B. , XIE M. H. , CHAN W. K. , KUTSAY O.
Published: December 2005

We studied the morphology evolution of asymmetric diblock copolymer poly (styrene-b-methyl methacrylate) P(S-b-MMA) films as a function of film thickness and annealing time on Si /native oxide substrate. We also investigated other factors affecting the morphology in addition to film thickness and annealing time, such as substrate cleaning procedures. Ion etching was employed to probe the structure inside the films. The obtained results confirm that there is a range of thicknesses where perpendicular cylinder orientation is obtained on a preferential surface, in agreement with theoretical predictions.
PERFORMANCE OF PMMA FOR NANODOT PATTERNING USING ELECTRON BEAM LITHOGRAPHY
Authors: NARAYANAN T. V. , SINGH SOHAN , TANOTO HENDRIX , THE MY , YOON SOON FATT
Published: December 2005

The performance of a positive tone resist, PMMA, for sub 100 nm patterning of nano-dots using electron beam lithography is to be studied. This optimization is done on a JEOL JBX-6000 FS System. The various parameters such as beam current, resist thickness, dose and electron energies are optimized. This patterning involves greater control over beam parameters so as to reduce aberrations that might arise due to astigmatism. In this respect, the optimization of the beam current parameters is very important, as a narrower beam will minimize scattering effects. These structures will be particularly significant for the fabrication of quantum dot based devices. Nano-dot arrays of dimensions 70 nm with equal spacings of 70 nm were obtained at 100 pA beam current at 50 KeV for a dose of 170 μC/cm2.
THE EVALUATION AND MODELING OF THE CMP REMOVAL RATE FOR POLYSILICON
Authors: WANG SIM KIT , BUTLER DAVID LEE , LIU DONG SENG , CHEN FENG
Published: December 2005

Polysilicon chemical mechanical planarization (CMP) is an area of research, which has largely been ignored until recently. With the development of bipolar complementary metal oxide semiconductor (BiCMOS), polysilicon has become of increasing importance as the preferred material for filling of deep trench. In this paper, study of removal rates of Polysilicon CMP will be discussed. Traditional models for predicting the polishing rate are typically based on Preston's equation. Here we present a new empirical polishing rate (EPR) model, which is statistically evaluated by cross-validation method, which assess the predictive ability of the model. The study also reveals inadequacies of Preston's equation in describing the polysilicon removal rate in the CMP process.
SINGLE MOLECULE IMMOBILIZATION OF π-CONJUGATED MOLECULES ON Au USING DENDRIMER-BASED TEMPLATES
Authors: BELAISSAOUI ABDELHAK , TOKUHISA HIDEO , KOYAMA EMIKO , KANESATO MASATOSHI
Published: December 2005

We demonstrate that immobilization of a π-conjugated molecule containing a bipyridine moiety as a hydrogen bond acceptor on Au using a dendrimer-based template with 3,4-dihydroxybenzene moiety at the core as a hydrogen bond donor. The hydrogen bond interaction was used for the linkage between the conjugated molecule and the template to improve the method to fabricate single-molecule arrays we reported before.1 Although the binding constant is small ( K = 120 ± 20 M -1) in CDCl 3, it was demonstrated that the dendrimer spacer serves as a template to isolate the π-conjugated molecule, and is removable simply with a CH 2 Cl 2 rinsing by surface FTIR spectroscopy.
EQUIVALENT CONTINUUM MODELING OF GRAPHENE SHEETS
Authors: REDDY C. D. , RAJENDRAN S. , LIEW K. M.
Published: December 2005

Carbon nanotubes have drawn tremendous interest due to their excellent mechanical and electronic properties. Carbon nanotubes have a similar molecular structure as that of graphene sheets. Hence, characterization of mechanical properties of graphene sheet based on equivalent continuum modelling is of considerable importance. Our initial studies are carried out on a single carbon ring/cell. The ring is then modelled as a truss (finite) element assemblage and equivalent Young's modulus is computed for a few fundamental modes. Next, these studies have been extended to model graphene sheet as a planar continuum to determine the mechanical properties (Young's modulus, shear modulus and Poisson's ratio) for typical modes of deformation. Further research is in progress to investigate how this set of different values can be integrated together towards a meaningful continuum characterization of the inherent discrete structure.
DISSIPATION OF CHARGES IN SILICON NANOCRYSTALS EMBEDDED IN SiO2 DIELECTRIC FILMS: AN ELECTROSTATIC FORCE MICROSCOPY STUDY
Authors: NG C. Y. , LAU H. W. , CHEN T. P. , TAN O. K. , LIM V. S. W.
Published: December 2005

In this paper, we report a mapping of charge transport in silicon nanocrystals ( nc - Si ) embedded in SiO 2 dielectric films with electrostatic force microscopy (EFM). By using contact EFM mode, positive and negative charges can be deposited on nc - Si . We found that the charge diffusion from the charged nc - Si to the surrounding neighboring uncharged nc - Si is the dominant mechanism during charge decay. A longer decay time was observed for a wider area of stored charge (i.e. 3 charged spots) due to the diffusion of charges being blocked by the surrounding charged nc - Si . This result is consistent with the increase of charge cloud size during the charge decay and the lower charge change percentage for 3 charged spots.
IN-PROCESS MONITORING OF FEMTOSECOND LASER MATERIAL PROCESSING
Authors: DENG Y. Z. , ZHENG H. Y. , MURUKESHAN V. M. , WANG X. C. , LIM G. C. , NGOI B. K. A.
Published: December 2005

Recent research and development on the femtosecond laser has shown that it is a powerful tool for high precision micromachining. However, the femtosecond laser-material interaction is fast and complex due to its ultrashort pulse duration. Consequently, it is not an easy task to optimize process parameters and to ensure high-quality fabrication. In this context, we propose an in-line monitoring technique based on plasma plume diagnostics. By analyzing the spectra of the femtosecond laser-induced plasma, which was detected and analyzed using a spectrometer, the plasma temperature of the copper sample was estimated. As drilling holes and cutting lines are two common applications in industry, the relationship between the emission light and the geometry of the fabricated structure was investigated based on the time-varying signals from the photodetector. These results will help us to understand the mechanism of femtosecond laser ablation so as to achieve high quality micromachining.
PHYSICAL AND CHEMICAL NANOLITHOGRAPHY TECHNIQUES: CHALLENGES AND PROSPECTS
Authors: WEI J. , WONG C. K.
Published: December 2005

The fabrication of nanodevices and nanosystems having dimensions smaller than 100 nm requires the ability to produce, control, manipulate, and modify structures at the nanometer scale. Physical and chemical nanolithography techniques have been demonstrated to be promising because of the low cost and high throughput. Although the physical and chemical nanolithography techniques can pattern small features on single chips or across an entire wafer, there are considerable challenges when dealing with complex nanostructures, alignment and multilevel stacks. In this paper, the problems are reviewed and potential solutions suggested.
NANOPATTERNED CROSSBAR STRUCTURES FOR MOLECULAR ELECTRONICS
Authors: DENG JIE , SAW BENG TIAM , LAU K. H. AARON , WILHELMI OLIVER , MOSER HERBERT O. , O'SHEA SEAN
Published: December 2005

Nano-patterned crossbar structures were fabricated as test structures for the development of nanoelectronic devices based on functional molecules. The crossbar structures serve as a platform for testing electronic properties of molecules and their interface to metal electrodes. The fabrication of the crossbar structures involved electron-beam lithography of sub-100-nm features aligned to electrodes pre-patterned by UV lithography and the deposition of and pattern transfer into an intermediate layer. The molecules to be tested were self-assembled as a monolayer on the nano-patterned area. The top electrode structures were subsequently deposited on top of the intermediate layer. The crossbar architecture allows measuring the current-voltage characteristics across the molecules for each crossing point individually.
IMPEDANCE CHARACTERIZATION OF DIELECTRIC AND SEMICONDUCTING MATERIALS WITH ORGANIC CAPACITORS FOR ORGANIC TRANSISTORS
Authors: LI C. M. , PAN L. K. , SUN C. Q. , ZHANG J. , GAMOTA DAN
Published: December 2005

A new characterization method based on impedance frequency response analysis at different temperatures has been developed to assess and identify the dielectric and semiconductor materials for organic field-effect transistors (OFET). This method can not only characterize simultaneously dielectric and conductive behaviors of materials but also distinguish individual contributions to electrical conduction or to polarization from layers such as dielectric layer, semiconductor layer, and interfaces in OFET. Two kinds of materials, Urathan and DuPont 5018A as dielectric materials have been used to make a multilayer organic capacitor. It has been observed that Urathan, due to its lower conductivity, non-metallic conduction behavior at high temperature, and lower interfacial resistance, is more suitable as dielectric layer for OFET. Urathan appears an enhancement in conductivity by heating following an Arrhenius law with an activation energy transition from 0.002 to 0.24 eV at ~307 K, which originates from band tail hopping that occurs around the Fermi edge. At ~314 K, a dielectric transition also occurs, which is interpreted as a combination of electron polarization associated to the band tail hopping. The materials were used to fabricate OEFT, which performance was in agreement with that obtained from impedance analysis of the organic capacitor.
MECHANOCHEMICAL SYNTHESIS OF NANOCRYSTALLINE FLUORINATED HYDROXYAPATITE
Authors: RAMESHBABU N. , SAMPATH KUMAR T. S. , MURUGAN R. , PRASAD RAO K.
Published: December 2005

Synthetic hydroxyapatite ( Ca 10( PO 4)6( OH )2, HA ) is an important material used for orthopaedic and dental implant applications. The biological hydroxyapatite in the human bone and tooth is of nano size and differs in composition from the stiochiometric HA by the presence of other ions such as carbonate, magnesium and fluoride, etc. Osseointegration is enhanced by using nanocrystalline HA . This stimulates the interest in synthesizing nanocrystalline HA by different routes and among the methods, mechanochemical seems to form fine grain size and uniform characteristic nanocrystalline materials. Fluorinated hydroxyapatite ( FHA , Ca 10( PO 4)6( OH )2-x F x) possesses higher corrosion resistance in biofluids than pure HA and reduces the risk of dental caries. The present work deals with the synthesis of nanocrystalline FHAs by mechanochemical processing. The nanomaterials were characterized using X-ray powder diffraction (XRD) and transmission electron microscopy (TEM) methods. Nano FHA of about 27-46 nm size was observed. The functional groups present in the FHA powders were ascertained by Fourier transform infrared spectroscopy (FT-IR) and Laser Raman spectroscopy. A gradual decrease in intensity of the OH - band at 655 and 3572 cm-1 has been observed with increasing fluorine substitution. The TEM micrograph shows that the powder is highly agglomerated and particle size is below 50 nm.
NANOTIPS COLD-END CONTACT FOR MICROCOOLING SYSTEMS
Authors: TAN KWONG-LUCK , ILIESCU CIPRIAN , TAY FRANCIS , CHUA HUI-TONG , MIAO JIANMIN
Published: December 2005

The paper presents the fabrication of nanotips cold-end contact for microcooling system. The fabrication process is based on an optimized isotropic plasma etching in SF 6/ O 2 using an ICP-deep RIE system from STS. We managed to fabricate the radius of the nanotips which are below 50 nm.
Cytokine stimulation of pregnancy-associated plasma protein A expression in human coronary artery smooth muscle cells: inhibition by resveratrol
Authors: Conover Cheryl A. , Bale Laurie K. , Harrington Sean C. , Resch Zachary T. , Overgaard Michael T. , Oxvig Claus
Published: December 2005

Through specific cleavage of proteins that bind and inhibit insulin-like growth factor-I (IGF-I), pregnancy-associated plasma protein-A (PAPP-A) enhances local IGF-I availability, and, consequently, receptor activation. PAPP-A expression is increased in experimental models of vascular injury and in human atherosclerotic plaque; however, little is known about the regulation of PAPP-A gene expression in vascular cells. In this study, we tested the hypothesis that proinflammatory cytokines involved in the vascular injury response stimulate PAPP-A gene expression in human coronary artery smooth muscle cells (hCASMC) in culture. Tumor necrosis factor (TNF)-α and interleukin (IL)-1β stimulated PAPP-A gene expression in a time- and dose-dependent manner. The effect of these cytokines appears to be at the level of transcription because actinomycin D completely prevented the induction of PAPP-A gene expression. Accumulation of PAPP-A in cell-conditioned medium paralleled mRNA synthesis, as did proteolytic activity against IGF binding protein-4 (IGFBP-4). Interestingly, pretreatment of hCASMC with resveratrol, a polyphenol found in the skin of grapes and in red wine purported to underlie the “French paradox,” inhibited TNF-α- and IL-1β-induced PAPP-A expression and, hence, its IGFBP-4 proteolytic activity. Resveratrol had no effect on basal PAPP-A expression and protease activity. Our finding that PAPP-A gene expression in hCASMC is stimulated by TNF-α and IL-1β suggests a mechanism for the regulation of PAPP-A in response to vascular injury that may contribute to the enhanced IGF-I bioactivity in intimal hyperplasia and atherosclerotic plaque development. Our results also suggest that PAPP-A may be a target of the cardiovascular system-protective effects of resveratrol.
Protein kinase C mediates erythrocyte “programmed cell death” following glucose depletion
Authors: Klarl Barbara A. , Lang Philipp A. , Kempe Daniela S. , Niemoeller Olivier M. , Akel Ahmad , Sobiesiak Malgorzata , Eisele Kerstin , Podolski Marlis , Huber Stephan M. , Wieder Thomas , Lang Florian
Published: December 2005

Glucose depletion of erythrocytes leads to activation of Ca2+-permeable cation channels, Ca2+ entry, activation of a Ca2+-sensitive erythrocyte scramblase, and subsequent exposure of phosphatidylserine at the erythrocyte surface. Ca2+ entry into erythrocytes was previously shown to be stimulated by phorbol esters and to be inhibited by staurosporine and chelerythrine and is thus thought to be regulated by protein phosphorylation/dephosphorylation, presumably via protein kinase C (PKC) and the corresponding phosphoserine/threonine phosphatases. The present experiments explored whether PKC could contribute to effects of energy depletion on erythrocyte phosphatidylserine exposure and cell volume. Phosphatidylserine exposure was estimated from annexin binding and cell volume from forward scatter in fluorescence-activated cell sorter analysis. Removal of extracellular glucose led to depletion of cellular ATP, stimulated PKC activity, led to translocation of PKCα, enhanced serine phosphorylation of membrane proteins, decreased cell volume, and increased annexin binding, the latter effect being blunted but not abolished in the presence of 1 μM staurosporine or 50 nM calphostin C. The PKC stimulator phorbol-12-myristate-13-acetate (3 μM) and the phosphatase inhibitor okadaic acid (1–10 μM) mimicked the effect of glucose depletion and similarly led to translocation of PKCα and enhanced serine phosphorylation, increased annexin binding, and decreased forward scatter, the latter effects being abrogated by PKC inhibitor staurosporine (1 μM). Fluo-3 fluorescence measurements revealed that okadaic acid also enhanced erythrocyte Ca2+ activity. The present observations suggest that protein phosphorylation and dephosphorylation via PKC and the corresponding protein phosphatases contribute to phosphatidylserine exposure and cell shrinkage after energy depletion.
Role of N- and O-glycans in polarized biosynthetic sorting
Authors: Potter Beth A. , Hughey Rebecca P. , Weisz Ora A.
Published: December 2005

The maintenance of proper epithelial function requires efficient sorting of newly synthesized and recycling proteins to the apical and basolateral surfaces of differentiated cells. Whereas basolateral protein sorting signals are generally confined to their cytoplasmic regions, apical targeting signals have been identified that localize to luminal, transmembrane, and cytoplasmic aspects of proteins. In the past few years, both N- and O-linked glycans have been identified as apical sorting determinants. Glycan structures are extraordinarily diverse and have tremendous information potential. Moreover, because the oligosaccharides added to a given protein can change depending on cell type and developmental stage, the potential exists for altering sorting pathways by modulation of the expression pattern of enzymes involved in glycan synthesis. In this review, we discuss the evidence for glycan-mediated apical sorting along the biosynthetic pathway and present possible mechanisms by which these common and heterogeneous posttranslational modifications might function as specific sorting signals.
Effect of prior hyperglycemia on IL-6 responses to exercise in children with type 1 diabetes
Authors: Galassetti P. R. , Iwanaga K. , Pontello A. M. , Zaldivar F. P. , Flores R. L. , Larson J. K.
Published: December 2005

The proinflammatory cytokine interleukin-6 (IL-6) may modulate the onset and progression of complications of diabetes. As this cytokine increases after exercise, and many other exercise responses are altered by prior glycemic fluctuations, we hypothesized that prior hyperglycemia might exacerbate the IL-6 response to exercise. Twenty children with type 1 diabetes (12 boys/8 girls, age 12–15 yr) performed 29 exercise studies (30-min intermittent cycling at ∼80% peak O2 uptake). Children were divided into four groups based on highest morning glycemic reading [blood glucose (BG) < 150, BG 151–200, BG 201–300, or BG > 300 mg/dl]. All exercise studies were performed in the late morning, after hyperglycemia had been corrected and steady-state conditions (plasma glucose <120 mg/dl, basal insulin infusion) had been maintained for ≥90 min. Blood samples for IL-6, growth factors, and counterregulatory hormones were drawn at pre-, end-, and 30 min postexercise time points. At all time points, circulating IL-6 was lowest in BG < 150 and progressively higher in the other three groups. The exercise-induced increment also followed a similar dose-response pattern (BG < 150, 0.6 ± 0.2 ng/ml; BG 151–200, 1.2 ± 0.8 ng/ml; BG 201–300, 2.1 ± 1.1 ng/ml; BG > 300, 3.2 ± 1.4 ng/ml). Other measured variables (growth hormone, IGF-I, glucagon, epinephrine, cortisol) were not influenced by prior hyperglycemia. Recent prior hyperglycemia markedly influenced baseline and exercise-induced levels of IL-6 in a group of peripubertal children with type 1 diabetes. While exercise is widely encouraged and indeed often considered part of diabetic management, our data underscore the necessity to completely understand all adaptive mechanisms associated with physical activity, particularly in the context of the developing diabetic child.
The AT1Areceptor “gain-of-function” mutant N111S/Δ329 is both constitutively active and hyperreactive to angiotensin II
Authors: Billet Sandrine , Bardin Sabine , Tacine Rachida , Clauser Eric , Conchon Sophie
Published: December 2005

The renin-angiotensin-aldosterone system (RAAS) is central to cardiovascular and renal physiology. However, there is no animal model in which the activation of the RAAS only reflects the activation of the angiotensin II (ANG II) AT1receptor. As a first step to developing such a model, we characterized a gain-of-function mutant of the mouse AT1Areceptor. This mutant carries two mutations: N111S predicted to activate the receptor constitutively and a COOH-terminal deletion, Δ329, expected to reduce receptor internalization and desensitization. We expressed this double mutant (AT1A-N111S/Δ329) in heterologous cells. It showed a pharmacological profile consistent with that of other constitutively active mutants. Furthermore, it increased basal production of inositol phosphates, as well as basal cytosolic and nuclear ERK activities. Basal proliferation of cells expressing the mutant was also greater than that of the wild type. The double mutant was poorly internalized and failed to recruit β-arrestin 2 in the presence of ANG II. It also showed hypersensitive and hyperreactive responses to ANG II for both inositol phosphate production and ERK activation. The additivity of the phenotypes of the two mutations makes this mutant an appropriate candidate to test the physiological consequences of the AT1Areceptor activation itself in transgenic animal models.
Efferent arterioles exclusively express the subtype 1A angiotensin receptor: functional insights from genetic mouse models
Authors: Harrison-Bernard Lisa M. , Monjure Christopher J. , Bivona Benjamin J.
Published: December 2005

Angiotensin (ANG) type 1A (AT1A) receptor-null (AT1A−/−) mice exhibit reduced afferent arteriolar (AA) constrictor responses to ANG II compared with wild-type (WT) mice, whereas efferent arteriolar (EA) responses are absent (Harrison-Bernard LM, Cook AK, Oliverio MI, and Coffman TM. Am J Physiol Renal Physiol 284: F538–F545, 2003). In the present study, the renal arteriolar constrictor responses to norepinephrine (NE) and/or ANG II were determined in blood-perfused juxtamedullary nephrons from kidneys of AT1A−/−, AT1B receptor-null (AT1B−/−), and WT mice. Baseline AA diameter in AT1A−/− mice was not different from that in WT mice (13.1 ± 0.9 and 12.6 ± 0.9 μm, n = 7 and 8, respectively); however, EA diameters were significantly larger (17.3 ± 1.4 vs. 11.7 ± 0.4 μm, n = 10 and 8) in AT1A−/− than in WT mice. Constriction of AA (−40 ± 8 and −51 ± 6% at 1 μM NE) and EA (−29 ± 6 and −38 ± 3% at 1 μM NE) in response to 0.1–1 μM NE was similar in AT1A−/− and WT mice. Baseline diameters of AA (13.5 ± 0.7 and 14.2 ± 0.9 μm, n = 9 and 10) and EA (15.4 ± 1.0 and 15.0 ± 0.7 μm, n = 11 and 9) and ANG II (0.1–10 nM) constrictor responses of AA (−25 ± 4 and −31 ± 5% at 10 nM) and EA (−32 ± 6 and −35 ± 7% at 10 nM) were similar in AT1B−/− and WT mice, respectively. ANG II-induced constrictions were eliminated by AT1 receptor blockade with 4 μM candesartan. Taken together, our data demonstrate that AA and EA responses to NE are unaltered in the absence of AT1A receptors, and ANG II responses remain intact in the absence of AT1B receptors. Therefore, we conclude that AT1A and AT1B receptors are functionally expressed on the AA, whereas the EA exclusively expresses the AT1A receptor.
Lithium-induced NDI in rats is associated with loss of α-ENaC regulation by aldosterone in CCD
Authors: Nielsen Jakob , Kwon Tae-Hwan , Frøkiær Jørgen , Knepper Mark A. , Nielsen Søren
Published: December 2005

Lithium-induced nephrogenic diabetes insipidus (Li-NDI) is associated with increased urinary sodium excretion and decreased responsiveness to aldosterone and vasopressin. Dysregulation of the epithelial sodium channel (ENaC) is thought to play an important role in renal sodium wasting. The effect of 7-day aldosterone and spironolactone treatment on regulation of ENaC in rat kidney cortex was investigated in rats with 3 wk of Li-NDI. Aldosterone treatment of rats with Li-NDI decreased fractional excretion of sodium (0.83 ± 0.02), whereas spironolactone did not change fractional excretion of sodium (1.10 ± 0.11) compared with rats treated with lithium alone (1.11 ± 0.05). Plasma lithium concentration was decreased by aldosterone (0.31 ± 0.03 mmol/l) but unchanged with spironolactone (0.84 ± 0.18 mmol/l) compared with rats treated with lithium alone (0.54 ± 0.04 mmol/l). Immunoblotting showed increased protein expression of α-ENaC, the 70-kDa form of γ-ENaC, and the Na-Cl cotransporter (NCC) in kidney cortex in aldosterone-treated rats, whereas spironolactone decreased α-ENaC and NCC compared with control rats treated with lithium alone. Immunohistochemistry confirmed increased expression of α-ENaC in the late distal convoluted tubule and connecting tubule and also revealed increased apical targeting of all three ENaC subunits (α, β, and γ) in aldosterone-treated rats compared with rats treated with lithium alone. Aldosterone did not, however, affect α-ENaC expression in the cortical collecting duct (CCD), which showed weak and dispersed labeling similar to that in rats treated with lithium alone. Spironolactone did not affect ENaC targeting compared with rats treated with lithium alone. This study shows a segment specific lack of aldosterone-mediated α-ENaC regulation in the CCD affecting both α-ENaC protein expression and trafficking, which may explain the increased sodium wasting associated with chronic lithium treatment.
Expression of P2X and P2Y receptors in the intramural parasympathetic ganglia of the cat urinary bladder
Authors: Ruan Huai Zhen , Birder Lori A. , Xiang Zhenghua , Chopra Bikramjit , Buffington Tony , Tai Changfeng , Roppolo James R. , de Groat William C. , Burnstock Geoffrey
Published: December 2005

The distribution and function of P2X and P2Y receptor subtypes were investigated on intact or cultured intramural ganglia of the cat urinary bladder by immunocytochemistry and calcium-imaging techniques, respectively. Neurons were labeled by all seven P2X receptor subtype antibodies and antibodies for P2Y2, P2Y4, P2Y6, and P2Y12receptor subtypes with a staining intensity of immunoreactivity in the following order: P2X3=P2Y2=P2Y4=P2Y6=P2Y12>P2X1=P2X2=P2X4>P2X5=P2X6=P2X7. P2Y1receptor antibodies labeled glial cells, but not neurons. P2X3and P2Y4polyclonal antibodies labeled ∼95 and 40% of neurons, respectively. Double staining showed that 100, 48.8, and 97.4% of P2X3receptor-positive neurons coexpressed choline acetyl transferase (ChAT), nitric oxide synthase (NOS), and neurofilament 200 (NF200), respectively, whereas 100, 59.2, and 97.6% of P2Y4receptor-positive neurons coexpressed ChAT, NOS, and NF200, respectively. Application of ATP, α,β-methylene ATP, and uridine triphosphate elevated intracellular Ca2+concentration in a subpopulation of dissociated cultured cat intramural ganglia neurons, demonstrating the presence of functional P2Y4and P2X3receptors. This study indicates that P2X and P2Y receptor subtypes are expressed by cholinergic parasympathetic neurons innervating the urinary bladder. The neurons were also stained for NF200, usually regarded as a marker for large sensory neurons. These novel histochemical properties of cholinergic neurons in the cat bladder suggest that the parasympathetic pathways to the cat bladder may be modulated by complex purinergic synaptic mechanisms.
Distinctive role of Stat3 and Erk-1/2 activation in mediating interferon-γ inhibition of TGF-β1action
Authors: Giannopoulou Myrto , Iszkula Steven C. , Dai Chunsun , Tan Xiaoyue , Yang Junwei , Michalopoulos George K. , Liu Youhua
Published: December 2005

Interferon-γ (IFN-γ) is a multifunctional cytokine that elicits antifibrotic activity in a variety of organs. In this study, we investigated the potential role and mechanism of IFN-γ in modulating the fibrogenic action of transforming growth factor (TGF)-β1in tubular epithelial cells. Incubation of human proximal tubular epithelial (HKC) cells with IFN-γ inhibited TGF-β1-mediated α-smooth muscle actin (α-SMA) expression. IFN-γ also abolished TGF-β1-induced fibronectin and plasminogen activator inhibitor-1 (PAI-1) expression. To explore the mechanisms by which INF-γ inhibits TGF-β1action, the signaling pathways that are critical for mediating the antifibrotic activity of IFN-γ were studied. Stimulation of HKC cells with IFN-γ triggered a sustained activation of Erk-1/2 and signal transducer and activator of transcription-3 (Stat3). Blockade of Erk-1/2 activation with an Mek1 inhibitor abolished the inhibitory effect of IFN-γ on α-SMA expression, whereas inhibition of Stat3 activation had no influence. Constitutive activation of Erk-1/2 by ectopic expression of activated Mek1 mimicked IFN-γ and suppressed TGF-β1-mediated α-SMA expression. Interestingly, inhibition of Stat3 activation abolished the ability of IFN-γ to attenuate TGF-β1-mediated PAI-1 and fibronectin expression in HKC cells. These findings indicate that IFN-γ is capable of antagonizing the fibrogenic actions of TGF-β1in renal tubular epithelial cells. The antifibrotic action of IFN-γ appears to be mediated through a coordinated activation of both Erk-1/2 and Stat3 signal pathways in a mutually independent fashion.
Sepsis induces changes in the expression and distribution of Toll-like receptor 4 in the rat kidney
Authors: El-Achkar Tarek M. , Huang Xiaoping , Plotkin Zoya , Sandoval Ruben M. , Rhodes Georges J. , Dagher Pierre C.
Published: December 2005

Toll-like receptors (TLRs) are now recognized as the major receptors for microbial pathogens on cells of the innate immune system. Recently, TLRs were also identified in many organs including the kidney. However, the cellular distribution and role of these renal TLRs remain largely unknown. In this paper, we investigated the expression of TLR4 in a cecal ligation and puncture (CLP) model of sepsis in Sprague-Dawley rats utilizing fluorescence microscopy. In sham animals, TLR4 was expressed predominantly in Tamm-Horsfall protein (THP)-positive tubules. In CLP animals, TLR4 expression increased markedly in all tubules (proximal and distal), glomeruli, and the renal vasculature. The staining showed a strong apical distribution in all tubules. A moderately less intense cellular signal colocalized partially with the Golgi apparatus. In addition, kidneys from septic rats showed increased expression of CD14 and THP. They each colocalized strongly with TLR4, albeit in different tubular segments. We also imaged the kidneys of live septic animals with two-photon microscopy after fluorescent lipopolysaccharide (LPS) injection. Within 10 min, LPS was seen at the brush border of some proximal tubules. Within 60 min, LPS was fully cytoplasmic in proximal tubules. Conversely, distal tubules showed no LPS uptake. We conclude that TLR4, CD14, and THP have specific renal cellular and tubular expression patterns that are markedly affected by sepsis. Systemic endotoxin can freely access the tubular and cellular sites where these proteins are present. Therefore, locally expressed TLRs and other interacting proteins could potentially modulate the renal response to systemic sepsis.
Phase-Locked Responses to Pure Tones in the Inferior Colliculus
Authors: Liu Liang-Fa , Palmer Alan R. , Wallace Mark N.
Published: December 2005

In the auditory system, some ascending pathways preserve the precise timing information present in a temporal code of frequency. This can be measured by studying responses that are phase-locked to the stimulus waveform. At each stage along a pathway, there is a reduction in the upper frequency limit of the phase-locking and an increase in the steady-state latency. In the guinea pig, phase-locked responses to pure tones have been described at various levels from auditory nerve to neocortex but not in the inferior colliculus (IC). Therefore we made recordings from 161 single units in guinea pig IC. Of these single units, 68% (110/161) showed phase-locked responses. Cells that phase-locked were mainly located in the central nucleus but also occurred in the dorsal cortex and external nucleus. The upper limiting frequency of phase-locking varied greatly between units (80−1,034 Hz) and between anatomical divisions. The upper limits in the three divisions were central nucleus, >1,000 Hz; dorsal cortex, 700 Hz; external nucleus, 320 Hz. The mean latencies also varied and were central nucleus, 8.2 ± 2.8 (SD) ms; dorsal cortex, 17.2 ms; external nucleus, 13.3 ms. We conclude that many cells in the central nucleus receive direct inputs from the brain stem, whereas cells in the external and dorsal divisions receive input from other structures that may include the forebrain.
Distal Gap Junctions and Active Dendrites Can Tune Network Dynamics
Authors: Saraga Fernanda , Ng Leo , Skinner Frances K.
Published: December 2005

Gap junctions allow direct electrical communication between CNS neurons. From theoretical and modeling studies, it is well known that although gap junctions can act to synchronize network output, they can also give rise to many other dynamic patterns including antiphase and other phase-locked states. The particular network pattern that arises depends on cellular, intrinsic properties that affect firing frequencies as well as the strength and location of the gap junctions. Interneurons or GABAergic neurons in hippocampus are diverse in their cellular characteristics and have been shown to have active dendrites. Furthermore, parvalbumin-positive GABAergic neurons, also known as basket cells, can contact one another via gap junctions on their distal dendrites. Using two-cell network models, we explore how distal electrical connections affect network output. We build multi-compartment models of hippocampal basket cells using NEURON and endow them with varying amounts of active dendrites. Two-cell networks of these model cells as well as reduced versions are explored. The relationship between intrinsic frequency and the level of active dendrites allows us to define three regions based on what sort of network dynamics occur with distal gap junction coupling. Weak coupling theory is used to predict the delineation of these regions as well as examination of phase response curves and distal dendritic polarization levels. We find that a nonmonotonic dependence of network dynamic characteristics (phase lags) on gap junction conductance occurs. This suggests that distal electrical coupling and active dendrite levels can control how sensitive network dynamics are to gap junction modulation. With the extended geometry, gap junctions located at more distal locations must have larger conductances for pure synchrony to occur. Furthermore, based on simulations with heterogeneous networks, it may be that one requires active dendrites if phase-locking is to occur in networks formed with distal gap junctions.
Comparative and evolutionary analysis of genes encoding small GTPases and their activating proteins in eukaryotic genomes
Authors: Jiang Shu-Ye , Ramachandran Srinivasan
Published: December 2005

Both small GTPase and its activating protein (GAP) superfamilies exist in various eukaryotes. The small GTPases regulate a wide variety of cellular processes by cycling between active GTP- and inactive GAP-bound conformations. The GAPs promote GTPase inactivation by stimulating the GTP hydrolysis. In this study, we identified 111 small GTPases and 85 GAPs in rice, 65 GAPs in Arabidopsis, 90 small GTPases in Drosophila melanogaster, and 35 GAPs in Saccharomyces cerevisiaeby genome-wide analysis. We then analyzed and compared a total of 498 small GTPases and 422 GAPs from these four eukaryotic and human genomes. Both animals and yeast genomes contained five families of small GTPases and their GAPs. However, plants had only four of these five families because of a lack of the Ras and RasGAP genes. Small GTPases were conserved with common motifs, but GAPs exhibited higher and much more rapid divergence. On the basis of phylogenetic analysis of all small GTPases and GAPs in five eukaryotic organisms, we estimated that their ancestors had small sizes of small GTPases and GAPs and their large-scale expansions occurred after the divergence from their ancestors. Further investigation showed that genome duplications represented the major mechanism for such expansions. Nonsynonymous substitutions per site ( Ka) and synonymous substitutions per site ( Ks) analyses showed that most of the divergence due to a positive selection occurred in common ancestors, suggesting a major functional divergence in an ancient era.
Lack of Cardiac Differentiation in c-kit-Enriched Porcine Bone Marrow and Spleen Hematopoietic Cell Cultures Using 5-Azacytidine
Authors: Ramirez M.L. , McMorrow I.M. , Sanderson T.M. , Lancos C.J. , Tseng Y.-L. , Cooper D.K.C. , Dor F.J.M.F.
Published: December 2005

The adult spleen is a source of early hematopoietic stem cells (HSC). We therefore studied whether culturing spleen or bone marrow (BM) HSC in medium containing 5-azacytidine could induce a cardiac phenotype. c-kit enrichment and depletion of adult pig spleen and BM mononuclear cells were obtained by magnetic bead separation using biotinylated pig stem cell factor (c-kit ligand). Cells were incubated with 5-azacytidine for 24 h and refreshed with 5-azacytidine-free medium every 48 h. Western blot was used to detect cardiac troponin and myosin heavy chains. Although 5-azacytidine treatment led to the formation of ball-like cell clusters in both c-kit-enriched populations, these clusters showed no rhythmic contractions (beating), as observed by others. Furthermore, neither cardiac troponin nor myosin was detected in cells derived from either source. Our methodology and treatment with 5-azacytidine did not induce cardiac gene expression in porcine HSC derived from either pig spleen or BM.
Population Genetics of Wild-Type CAG Repeats in the Machado-Joseph Disease Gene in Portugal
Authors: Lima M. , Costa M.C. , Montiel R. , Ferro A. , Santos C. , Silva C. , Bettencourt C. , Sousa A. , Sequeiros J. , Coutinho P. , Maciel P.
Published: December 2005

Objective: To gain insights on the molecular mechanisms of mutation that led to the emergence of expanded alleles in the MJD gene, by studying the behavior of wild-type alleles and testing the association of its distribution with the representation of the disease. Methods: The number of CAG motifs in the MJD gene was determined in a representative sample of 1000 unrelated individuals. Associations between the repeat size and the epidemiological representation of MJD were tested. Results: The allelic profile of the total sample was in the normal range (13–41 repeats), with mode (CAG)23. No intermediate alleles were present. Allelic size distribution showed a negative skew. The correlation between the epidemiological representation of MJD in each district and the frequency of small, medium and large normal alleles was not significant. Further correlations performed grouping the districts also failed to produce significant results. Conclusions: The absence of association between the size of the repeats and the representation of MJD demonstrates that prevalence is not an indirect reflection of the frequency of large normal alleles. Globally the results obtained are in accordance with a model that postulates the occurrence of a few mutations on the basis of most of the MJD cases worldwide.