bluuebunny/crossref_metadata_2025_split huggingface dataset:
Multichannel Surface EMG for the Non-Invasive Assessment of the Anal Sphincter Muscle
Authors: Merletti R. , Bottin A. , Cescon C. , Farina D. , Gazzoni M. , Martina S. , Mesin L. , Pozzo M. , Rainoldi A. , Enck P. 
Published: April 2004

<i>Background/Aims:</i> This work focuses on recording, processing and interpretation of multichannel surface EMG detected from the external anal sphincter muscle. The aim is to describe the information that can be extracted from signals recorded with such a technique. <i>Methods:</i> The recording of many signals from different locations on a muscle allows the extraction of additional information on muscle physiology and anatomy with respect to that obtained by classic bipolar recordings. Multichannel EMG methods have been recently developed for the assessment of the external anal sphincter. An anal probe was used in this study to record signals at different depths within the anal canal during contractions at different effort levels. The plug is 150 mm in length and 14 mm in diameter, holding a circumferential array of 16 equally spaced silver bar electrodes, located at a distance of 20 mm from the probe tip and aligned with the probe axis. <i>Results:</i> Information about localization of the innervation zone, fiber length, EMG amplitude, muscle fiber conduction velocity and single motor unit analysis can be obtained from the signals recorded with the circumferential array by means of innovative signal processing techniques. <i>Conclusions:</i> The type of information extracted from multichannel surface EMG signals cannot be obtained with other currently available techniques. The technological innovation described in this work is promising for a further insight into the investigation of pelvic floor pathologies and rehabilitation treatments.
The role of muscarinic receptors and intracellular Ca2+ in the spectral reflectivity changes of squid iridophores
Authors: Mäthger Lydia M. , Collins Toby F. T. , Lima Pedro A. 
Published: April 2004

SUMMARYIn this paper we describe changes in spectral reflectivity of the light reflectors (iridophores) of the squid Alloteuthis subulata. The spectral changes that can be seen in living squid, can also be brought about by superfusing whole skin preparations with acetylcholine (ACh) (20 μmol l-1) and muscarine (30 μmol l-1) but not nicotine (up to 50 mmol l-1), suggesting that cholinergic muscarinic receptors are involved. Changing the osmolarity of the external solution had no effect on spectral reflectivity. To study the iridophores at the cellular level,iridophores were isolated enzymatically. Lucifer Yellow filled the iridophores uniformly, showing cellular individuality. Isolated iridophore cells were loaded with Fura-2 AM and cytoplasmic Ca2+ was recorded ratiometrically. Intracellular Ca2+ (resting concentration at 66.16 nmol l-1) increased transiently after addition of ACh (50 μmol l-1), muscarine (25 μmol l-1), but not nicotine (up to 5 mmol l-1). Ca2+ also increased when superfused with potassium chloride (10 mmol l-1) and caffeine (2.5 mmol l-1). Hypo- and hyperosmotic solutions had no effects on the cytoplasmic Ca2+. By presenting direct evidence that iridophores are polarised cellular structures containing Ca2+ stores and that they are activated via cholinergic muscarinic receptors, we demonstrate that Ca2+ is involved in the reflectivity changes of the iridophores of A. subulata. Specimens were prepared for transmission electron microscopy. It was found that the orientations of the plates with respect to the skin surface are in good agreement with the expected orientations based on the prediction that the iridophores act as multilayer reflectors.
The transepithelial voltage of the isolated anterior stomach of mosquito larvae (Aedes aegypti): pharmacological characterization of the serotonin-stimulated cells
Authors: Onken H. , Moffett S. B. , Moffett D. F. 
Published: April 2004

SUMMARYThe lumen-negative transepithelial voltage (Vte) of the isolated and perfused anterior stomach of mosquito larvae (Aedes aegypti) was studied with a `semi-open' preparation in which one end of the gut was ligated onto a perfusion pipette and the other end remained open to the bath. All experiments were performed with serotonin-stimulated preparations. Vte was abolished after addition of 2.5 mmol l-1 dinitrophenol and depended on the presence of Cl-. Na+ substitution experiments showed that a major part of Vte depended on the presence of this cation in the hemolymph side of the epithelium. Addition of 10 μmol l-1concanamycin (78±6% inhibition) or 2.5 mmol l-1 ouabain(15±2% inhibition) to the bath partially inhibited Vte. DPC (0.5 mmol l-1) or DIDS (0.1 mmol l-1) reduced Vte when applied to the hemolymph side of the epithelium (to 49±8% or 78±3% of the control,respectively). When present on both sides of the epithelium, these inhibitors caused further Vte reductions (to 23±4% or 35±4% of the control, respectively). Hemolymph-side furosemide (0.1 mmol l-1) or BaCl2 (5 mmol l-1) reduced Vte by 13±3% or 23±4% of the control,respectively. When applied to the hemolymph side of the epithelium, amiloride(0.2 mmol l-1) significantly decreased Vte by 35±6% of the control, whereas the drug caused no further effect when it was subsequently also applied to the luminal side of the epithelium. The above results are the basis for an extended model for the cellular mechanisms of NaHCO3 secretion/HCl absorption involved in alkalization of the anterior stomach of mosquito larvae.
The regulation and importance of glucose uptake in the isolated Atlantic cod heart: rate-limiting steps and effects of hypoxia
Authors: Clow Kathy A. , Rodnick Kenneth J. , MacCormack Tyson J. , Driedzic William R. 
Published: April 2004

SUMMARY
This study investigated the regulation of glucose uptake in Atlantic cod(Gadus morhua) hearts. Isolated hearts were perfused with or without glucose in the medium, under either normoxic or severely hypoxic conditions. Working at basal levels, hearts did not require extracellular glucose to maintain power under aerobic conditions. However, cardiac performance was significantly reduced without exogenous glucose under oxygen-limiting conditions. The addition of the glucose transporter inhibitor cytochalasin B caused hypoxic hearts to fail early, and hearts perfused with a glucose analogue, 2-deoxyglucose (2-DG), increased glucose uptake 3-fold under hypoxia. The uptake of 2-DG was only partially inhibited when cytochalasin B was added to the medium. Isolated ventricle strips were also incubated in the presence of 2-DG and the extracellular marker mannitol. Glucose uptake(glucose transport plus intracellular phosphorylation) was assessed by measuring the initial rate of 2-deoxyglucose-6-phosphate (2-DG-6-P)accumulation. At 1 mmol l-1 2-DG, the rate of 2-DG uptake remained linear for 60 min, and 2-DG-6-P, but not free 2-DG, accumulation was increased. The fact that intracellular 2-DG did not increase indicates that glucose transport is the rate-limiting step for glucose utilization in non-stimulated cardiac tissue. Replacement of Na+ by choline in the incubation medium did not affect 2-DG uptake, providing evidence that Na+-coupled glucose transport is absent in cod cardiac tissue. Similar to cytochalasin B, glucose uptake was also inhibited by phloridzin,suggesting that facilitated, carrier-mediated glucose transport occurs in cod hearts. Under the conditions employed in these experiments, it is clear that(1) activation of glucose transport is required to support hypoxic performance, (2) the rate-limiting step for glucose utilization is glucose transport rather than glucose phosphorylation, (3) 2-DG uptake accurately reflects glucose transport activity and (4) glucose uptake in cod hearts does not involve an Na+-dependent mechanism.
Surface pauses in relation to dive duration in imperial cormorants; how much time for a breather?
Authors: Wilson Rory P. , Quintana Flavio 
Published: April 2004

SUMMARYAir-breathing animals diving to forage can optimize time underwater by diving with just enough oxygen for the projected performance underwater. By so doing they surface with minimal body oxygen levels, which leads to maximal rates of oxygen uptake. We examined whether imperial cormorants Phalacrocorax atriceps adhere to this by examining dive:pause ratios in birds diving for extended, continuous periods to constant depths, assuming that the oxygen used underwater was exactly replenished by the periods at the surface. Examination of the cumulative time spent in surface pauses relative to the cumulative time spent in diving showed that surface pauses increase according to a power curve function of time spent in the dive or water depth. In a simplistic model we considered the rate at which birds expended energy underwater to be constant and that the rate of oxygen replenishment during the surface pause was directly proportional to the oxygen deficit. We then worked out values for the rate constant for the surface pause before using this constant to examine bird body oxygen levels immediately pre- and post dive. The model predicted that imperial cormorants do not submerge with just enough oxygen to cover their projected dive performance but rather dive with substantial reserves, although these reserves decrease with increasing dive depth/duration. We speculate that these oxygen reserves may be used to enhance bird survival when rare events, such as the appearance of predators or discovery of large prey requiring extended handling time, occur. The form of the oxygen saturation curve over time at the surface means that the time costs for maintaining constant oxygen reserves become particularly onerous for long,deep dives, so the observed decrease in reserves with increasing dive duration is expected in animals benefiting by optimizing for time.
The hydrodynamics of eel swimming
Authors: Tytell Eric D. , Lauder George V. 
Published: April 2004

SUMMARYEels undulate a larger portion of their bodies while swimming than many other fishes, but the hydrodynamic consequences of this swimming mode are poorly understood. In this study, we examine in detail the hydrodynamics of American eels (Anguilla rostrata) swimming steadily at 1.4 Ls-1 and compare them with previous results from other fishes. We performed high-resolution particle image velocimetry (PIV) to quantify the wake structure, measure the swimming efficiency, and force and power output. The wake consists of jets of fluid that point almost directly laterally,separated by an unstable shear layer that rolls up into two or more vortices over time. Previously, the wake of swimming eels was hypothesized to consist of unlinked vortex rings, resulting from a phase offset between vorticity distributed along the body and vorticity shed at the tail. Our high-resolution flow data suggest that the body anterior to the tail tip produces relatively low vorticity, and instead the wake structure results from the instability of the shear layers separating the lateral jets, reflecting pulses of high vorticity shed at the tail tip. We compare the wake structure to large-amplitude elongated body theory and to a previous computational fluid dynamic model and note several discrepancies between the models and the measured values. The wake of steadily swimming eels differs substantially in structure from the wake of previously studied carangiform fishes in that it lacks any significant downstream flow, previously interpreted as signifying thrust. We infer that the lack of downstream flow results from a spatial and temporal balance of momentum removal (drag) and thrust generated along the body, due to the relatively uniform shape of eels. Carangiform swimmers typically have a narrow caudal peduncle, which probably allows them to separate thrust from drag both spatially and temporally. Eels seem to lack this separation, which may explain why they produce a wake with little downstream momentum while carangiform swimmers produce a wake with a clear thrust signature.
Thermolimit respirometry: an objective assessment of critical thermal maxima in two sympatric desert harvester ants,Pogonomyrmex rugosusandP. californicus
Authors: Lighton John R. B. , Turner Robbin J. 
Published: April 2004

SUMMARYThe critical thermal maxima (CTmax) of two sympatric,diurnal, thermophilic harvester ants from the Mojave Desert, USA(Pogonomyrmex rugosus and P. californicus) were measured by ramping their temperature upwards at a rate of 0.25°C min-1during flow-through respirometry with optical activity detection. Rates of CO2 emission(V̇CO2) increased exponentially to plateau values that were twice as high in P. californicus as P. rugosus on a mass-specific basis. V̇CO2 then fell sharply, during which gross motor activity (measured optically) and spiracular control (measured from V̇CO2 variation)abruptly ceased, yielding two independent measures of CTmax. As determined by loss of muscular coordination, the CTmax of Pogonomyrmex rugosus was 51.57±0.38°C (mean ± s.d., while that of Pogonomyrmex californicus was 51.74±0.25°C. As determined by loss of spiracular control, the CTmax of Pogonomyrmex rugosus was 51.59±0.35°C, while that of Pogonomyrmex californicus was 51.78±0.37°C. In each species a pronounced post-mortal peak of V̇CO2 was observed. The major ecological and behavioral differences of the two species are not reflected in their CTmax values, which do not differ significantly. `Thermolimit respirometry' allows CTmax to be estimated objectively with coefficients of variation (s.d./mean) &lt;1%, lending confidence to comparisons between species or treatment groups.
Control of planula migration by LWamide and RFamide neuropeptides inHydractinia echinata
Authors: Katsukura Yuki , Ando Hiroshi , David Charles N. , Grimmelikhuijzen Cornelis J. P. , Sugiyama Tsutomu 
Published: April 2004

SUMMARYPlanula larvae of Hydractinia echinata (Cnidaria) settled on a substratum migrate toward light. We observed that planula migration is not a continuous process. Instead, it consists of repeating cycles of active migration (about 8 min on average) and inactive resting periods (about 26 min on average). This pattern of periodic migration is regulated by LWamide and RFamide neuropeptides. LWamide (10-8 mol l-1)stimulates migration primarily by making the active periods longer, whereas RFamide (10-7 mol l-1) inhibits migration by blocking the initiation and also shortening the length of the active periods. Since sensory neurons containing LWamides and RFamides are present in planula larvae, it appears likely that planula migration is regulated by the release of endogenous neuropeptides in response to environmental cues.
Molecular adsorption of n‐alkyl amines, carboxylic acids, and amides onto well‐defined, polar organic surfaces
Authors: Lee Seok‐Won , Laibinis Paul E. 
Published: April 2004

AbstractThis paper details the formation of oriented monolayer films by the solution‐phase adsorption of n‐alkyl‐chained adsorbates (CH3(CH2)n‐1Y) onto the polar surfaces of terminally‐substituted self‐assembled monolayers (SAMs; Au/S(CH2)mX). The polar tail groups (X and Y) of the adsorbate and SAM included amine, carboxylic acid, and amide groups, and the formation of the adsorbed monomolecular films on the SAMs relied on non‐covalent interactions between X and Y. Highly organized monomolecular adlayers could be produced on the SAM surface that were as densely packed as the underlying alkanethiolate SAMs comprising the first layer. The quality of the adsorbed monolayers was related to the identities of the tail groups X and Y.
Isolation of directed evolution mutants of chloroperoxidase resistant to suicide inactivation by primary olefins
Authors: Rai Gyan P. , Zong Qin , Hager Lowell P. 
Published: April 2004

AbstractWild‐type chloroperoxidase catalyzes the efficient chiral epoxidation of secondary olefins but is rapidly inactivated in a mechanism‐based suicide reaction when incubated with hydrogen peroxide and primary olefins. Directed evolution mutants of chloroperoxidase have now been isolated that are resistant to suicidal inactivation. Plasmid vectors containing error‐prone copies of the chloroperoxidase gene and a hygromycin B resistance marker gene have been used to transform Caldariomyces fumago spheroplasts and produce mutant libraries. The mutant library clones were screened for their ability to resist mechanism‐based inactivation by allylbenzene. Four generations of PCR‐based random mutagenesis and screening yielded mutants that were completely resistant to the suicide‐inactivation reaction. Rather surprisingly, the fourth generation mutant developed enhanced epoxidation activity in addition to resistance to allylbenzene inactivation. These initial results suggest that the directed evolution technique can be used to produce chloroperoxidase variants that can further exploit the potential of chloroperoxidase for the synthesis of chiral intermediates.
Cyclodextrin‐based carbohydrate clusters by amide bond formation
Authors: Fulton David A. , Pease Anthony R. , Stoddart J. Fraser 
Published: April 2004

AbstractPer‐6‐amino‐2,3‐dimethyl‐ß‐cyclodextrin was prepared very efficiently as its hydrochloride salt from native ß‐cyclodextrin in four steps and 89% overall yield. O‐Acetyl‐protected ß‐D‐thioglucose and ß‐D‐thiolactose derivatives, containing short spacer arms terminated with carboxylic acid functions, were prepared by the BF3·OEt2‐catalyzed thioglycosylation of ß‐D‐glucose pentaacetate and ß‐lactose octaacetate with 3‐mercaptopropionic acid, respectively. Utilizing amide bond formation as the key step, these thio‐ß‐D‐glucosyl and lactosyl derivatives were coupled to per‐6‐amino‐2,3‐dimethyl‐ß‐cyclodextrin to afford, after deprotection, perfunctionalized ß‐cyclodextrin‐based clusters containing seven thio‐ß‐D‐glucosyl and seven ß‐lactosyl appendages, respectively. Molecular modeling of both these ß‐cyclodextrin‐based clusters revealed the glucose and lactose clusters to be approximately 23 Å and 27 Å in diameter, respectively, and approximately 19 Å in height in both cases. The association constants for the complexation of the anti‐inflammatory drug naproxen by ß‐cyclodextrin, per‐2,3‐dimethyl‐ß‐cyclodextrin, and the lactose cluster of ß‐cyclodextrin in 0.01 M phosphate buffered saline solution (pH 7.4) were found by UV‐vis spectrophotometric titration to be 374 ± 75 M−1, 351 ± 70 M−1, and 165 ± 33 M−1, respectively.
Catalytic Behavior of Bis(Pyrrolide‐Imine) and Bis(Phenoxy‐Imine) Titanium Complexes for the Copolymerization of Ethylene with Propylene, 1‐Hexene, or Norbornene
Authors: Yoshida Yasunori , Nakano Takashi , Tanaka Hidetsugu , Fujita Terunori 
Published: April 2004

AbstractThis contribution reports the catalytic behavior of bis(pyrrolide‐imine)Ti complexes 1 and 2, [2‐(RNCH)‐C4H3N]2TiCl2 (1, R = Ph; 2, R = cyclohexyl), and bis(phenoxy‐imine)Ti complex 3, [2‐(Ph‐NCH)‐3‐t Bu‐C6H3O]2TiCl2 for the copolymerization of ethylene with propylene, 1‐hexene, or norbornene. An inspection of the X‐ray structures of complexes 1–3 suggested that complexes 1 and 2 with pyrrolide‐imine ligands would provide more space for olefin polymerization than complex 3 with phenoxy‐imine ligands. In addition, DFT calculations also showed that active species derived from complexes 1 and 2 possess higher electrophilicity of the Ti center compared to that from complex 3. Complexes 1 and 2 on activation with methylalumoxane (MAO) had higher affinity for propylene and 1‐hexene and incorporated higher amounts of propylene (1; 30.5 mol%, 2; 23.4 mol%) and 1‐hexene (1; 1.9 mol%, 2; 1.7 mol%) than complex 3 (propylene; 4.5 mol%, 1‐hexene; 0.4 mol%). The incorporation levels of propylene and 1‐hexene displayed by complexes 1 and 2 were lower than those for Cp2TiCl2 (propylene; 41.6 mol%, 1‐hexene; 5.1 mol%) under identical conditions. In contrast, complexes 1 and 2 exhibited higher incorporation ability for norbornene and produced copolymers with much higher norbornene contents (1; 32.0 mol%, 2; 26.5 mol%) than Cp2TiCl2 (1.2 mol%) under the same conditions. Additionally, complex 3 also promoted higher norbornene incorporation (4.3 mol%) than Cp2TiCl2 and provided a copolymer with extremely narrow molecular weight distribution (Mw/Mn 1.14). A correlation exists between electrophilicity of the Ti center in active species and norbornene incorporation.
Stepwise synthesis of cellodextrins assisted by a mutant cellulase
Authors: Fort Sébastien , Christiansen Lars , Schülein Martin , Cottaz Sylvain , Drigueza Hugues 
Published: April 2004

AbstractA 4II‐protected α‐cellobiosyl fluoride is an efficient donor for the enzymatic stepwise condensations onto methyl ß‐D‐glycoside acceptors. These reactions, catalyzed by the Cel7B E197A glycosynthase from Humicola insolens, gave cellodextrins from degree of polymerization 3 to 6 in high yields.
Interaction of heparin with Ca2+: A model study with a synthetic heparin‐like hexasaccharide
Authors: Angulo Jesús , De Paz José‐Luis , Nieto Pedro M. , Martín‐Lomas Manuel 
Published: April 2004

AbstractThe binding of Ca2+ to synthetic hexasaccharide 1, containing the structural motifs of the regular region of heparin, has been investigated using NMR spectroscopy and molecular modeling. The NMR data of the calcium salt of 1 indicate the existence of specific Ca2+ binding, and molecular modeling results predict three different types of binding sites with different negative potential and preorganized geometry. The presence of Ca2+ does not seem to affect the overall helical structure of hexasaccharide 1, although it seems to have a marked influence on the flexibility of the oligosaccharide backbone.
Hydrolysis of chlorpyrifos in aqueous and colloidal systems
Authors: Wu Jigang , Laird David A. 
Published: April 2004

AbstractHydrolysis of chlorpyrifos [O,O‐diethyl O‐(3,5,6‐trichloro‐2‐pyridyl) phosphorothioate] to TCP (3,5,6‐trichloro‐2‐pyridinol) is an important degradation process influencing the fate of chlorpyrifos in aquatic environments. The effects of water chemistry and suspended colloids (smectites, humic acid, and river sediment) on the hydrolysis of chlorpyrifos were investigated in this study. Chlorpyrifos was incubated in various aqueous and colloidal systems at 23 ± 2 °C for up to 100 days, and aqueous phase concentrations of chlorpyrifos and TCP were determined using solid phase extraction‐high performance liquid chromatography (SPE‐HPLC). Chlorpyrifos degraded in the aqueous solutions with half‐lives ranging from 27 to 158 days, depending on the initial concentration of chlorpyrifos and the chemistry of the aqueous solutions. The rate of degradation was slower in systems containing low concentrations of suspended colloids (1 g L−1 in 0.01 M CaCl2) than in the control (0.01 M CaCl2, with no colloids), and negligible hydrolysis of chlorpyrifos was found for concentrated colloidal systems (20 g L−1 in 0.01 M CaCl2). Total recoveries of chlorpyrifos for the concentrated colloidal systems ranged from 78% to 97%, with a tendency to decrease with incubation time. The study indicates that the formation of chlorpyrifos‐colloid complexes inhibits the hydrolysis of chlorpyrifos in aqueous systems and that chlorpyrifos‐colloid complexes may act as a buffer by slowly releasing chlorpyrifos to the aqueous phase.
Resonant laser excitation of molecular wires
Authors: Kohler Sigmund , Lehmann Jörg , Camalet Sébastien , Hänggi Peter 
Published: April 2004

AbstractWe investigate the influence of external laser excitations on the average current through bridged molecules. For the computation of the current, we use a numerically very efficient formalism that is based on the Floquet solutions of the time‐dependent molecule Hamiltonian. It is found that the current as a function of the laser frequency exhibits characteristic peaks originating from resonant excitations of electrons to bridge levels that are unoccupied in the absence of radiation. The electric current through the molecule can exhibit a drastic enhancement by several orders of magnitude.