bluuebunny/crossref_metadata_2025_split huggingface dataset:
Metabolic factors contributing to altered Ca2+ regulation in skeletal muscle fatigue
Authors: Steele D. S. , Duke A. M. 
Published: August 2003

AbstractAim: Skeletal muscle fatigue is characterized by a failure to maintain force production or power output during intense exercise. Many recent studies on isolated fibres have used brief repetitive tetanic contractions to mimic fatigue resulting from intensive exercise and to investigate the underlying cellular mechanisms. Such studies have shown that characteristic changes in Ca2+ regulation occur during fatiguing stimulation. This includes prolongation of the ‘Ca2+‐tails’ which follow each period of tetanic stimulation and a progressive rise in resting [Ca2+]. More importantly, the final stage of fatigue is associated with a rapid decrease in tetanic [Ca2+]i and force. These fatigue‐induced changes in sarcoplasmic reticulum (SR) Ca2+ regulation are temporally associated with alterations in the intracellular levels of phosphate metabolites and a causal relationship has often been proposed. The aim of this review is to evaluate the evidence linking changes in the levels of phosphate metabolites and altered Ca2+ regulation during fatigue.Results: The following current hypotheses will be discussed: (1) the early changes in Ca2+ regulation reflect alterations in the intracellular levels of phosphate metabolites, (2) inhibition of the SR Ca2+ release mechanism (e.g. caused by ATP depletion and increased [Mg2+]) contributes to the decrease in tetanic [Ca2+]i during the final stages of fatigue and (iii) delayed entry of inorganic phosphate ions (Pi) into the SR, followed by precipitation of calcium phosphate (Ca–Pi), can explain the fatigue‐induced decrease in tetanic [Ca2+]i.Conclusion: There is strong evidence that changes in phosphate metabolite levels contribute to early changes in SR Ca2+ regulation during fatigue and that inhibition of the SR Ca2+ release mechanism can partially explain the rapid decrease in tetanic [Ca2+]i during the final stages of fatigue. While precipitation of Ca–Pi may occur within the SR during fatigue, there is currently insufficient evidence to establish whether this contributes to the late decline in tetanic [Ca2+]i.
Association between fatigue and failure to preserve cerebral energy turnover during prolonged exercise
Authors: Nybo L. , Møller K. , Pedersen B. K. , Nielsen B. , Secher N. H. 
Published: August 2003

AbstractAim: This study evaluated if the fatigue and apathy arising during exercise with hypoglycaemia could relate to a lowering of the cerebral metabolic rates of glucose and oxygen.Methods and results: Six males completed 3 h of cycling with or without glucose supplementation in random order. Cerebral blood flow, metabolism and interleukin‐6 (IL‐6) release were evaluated with the Kety–Schmidt technique. Blood glucose was maintained during the glucose trial, while it decreased from 5.2 ± 0.1 to 2.9 ± 0.3 mmol L−1 (mean ± SE) after 180 min of exercise in the placebo trial with a concomitant increase in perceived exertion (P < 0.05). During hypoglycaemia, the cerebral glucose uptake was reduced from 0.34 ± 0.05 to 0.28 ± 0.04 μmol g−1 min−1, while the cerebral uptake of β‐hydroxybutyrate increased to 5 ± 1 pmol g−1 min−1 (P < 0.05). The reduced glucose uptake was accompanied by a lowering of the cerebral metabolic rate of oxygen from 1.84 ± 0.19 mmol g−1 min−1 during exercise with glucose supplementation to 1.60 ± 0.16 mmol g−1 min−1 during hypoglycaemia (P < 0.05). In addition, the cerebral IL‐6 release was reduced from 0.4 ± 0.1 to 0.0 ± 0.1 pg g−1 min−1 (P < 0.05).Conclusions: Exercise‐induced hypoglycaemia limits the cerebral uptake of glucose, exacerbates exercise, reduces the cerebral metabolic rate of oxygen and attenuates the release of IL‐6 from the brain.
Effects of eccentric treadmill running on mouse soleus: degeneration/regeneration studied with Myf‐5 and MyoD probes
Authors: Armand A.‐S. , Launay T. , Gaspera B. Della , Charbonnier F. , Gallien C. L. , Chanoine C. 
Published: August 2003

Abstract  Aim: The aim of this report is to show that eccentric exercise under well‐controlled conditions is an alternative model, to chemical and mechanical analyses, and analyse the process of degeneration/regeneration in mouse soleus.Methods:  For this, mice were submitted to a single bout of eccentric exercise on a treadmill down a 14° decline for 150 min and the soleus muscle was analysed at different times following exercise by histology and in situ hybridization in comparison with cardiotoxin‐injured muscles.Results:  We analyse the regenerative process by detection of the accumulation of transcripts coding for the two myogenic regulatory factors, Myf‐5 and MyoD, which are good markers of the activated satellite cells. From 24 h post‐exercise (P‐E), clusters of mononucleated Myf‐5/MyoD‐positive cells were detected. Their number increased up to 96 h P‐E when young MyoD‐positive myotubes with central nuclei began to appear. From 96 to 168 h P‐E the number of myotubes increased, about 10‐fold, the new myotubes representing 58% of the muscle cells (168 h P‐E).Conclusion:  These results show that this protocol of eccentric exercise is able to induce a drastic degeneration/regeneration process in the soleus muscle. This offers the opportunity to perform biochemical and molecular analyses of a process of regeneration without muscle environment defects. The advantages of this model are discussed in the context of fundamental and therapeutical perspectives.
Physiology and biophysics of hemi‐gap‐junctional channels expressed in Xenopus oocytes
Authors: Ebihara L. 
Published: August 2003

AbstractGap junctional channels are intercellular channels that allow the passage of ions and other small molecules less than about 1 kD in size between neighbouring cells. They are composed of two oligomeric protein subunits called connexons or hemichannels which reside in the plasma membrane of closely opposed cells. Several recent studies suggest that unpaired connexons may be active on the non‐junctional plasma membrane of cells.Here I present a short overview of the properties of connexon channels expressed in Xenopus oocytes.
Gap junction hemichannels in astrocytes of the CNS
Authors: Sáez J. C. , Contreras J. E. , Bukauskas F. F. , Retamal M. A. , Bennett M. V. L. 
Published: August 2003

AbstractConnexins are protein subunits that oligomerize into hexamers called connexons, gap junction hemichannels or just hemichannels. Because some gap junction channels are permeable to negatively and/or positively charged molecules up to ∼ 1kDa in size, it was thought that hemichannels should not open to the extracellular space. A growing amount of evidence indicates that opening of hemichannels does occur under both physiological and pathological conditions in astrocytes and other cell types. Electrophysiological studies indicate that hemichannels have a low open probability under physiological conditions but may have a much higher open probability under certain pathological conditions. Some of the physiological behaviours of astrocytes that have been attributed to gap junctions may, in fact, be mediated by hemichannels. Hemichannels constituted of Cx43, the main connexin expressed by astrocytes, are permeable to small physiologically significant molecules, such as ATP, NAD+ and glutamate, and may mediate paracrine as well as autocrine signalling. Hemichannels tend to be closed by negative membrane potentials, high concentrations of extracellular Ca2+ and intracellular H+ ions, gap junction blockers and protein phosphorylation. Hemichannels tend to be opened by positive membrane potentials and low extracellular Ca2+, and possibly by as yet unidentified cytoplasmic signalling molecules. Exacerbated hemichannel opening occurs in metabolically inhibited cells, including cortical astrocytes, which contributes to the loss of chemical gradients across the plasma membrane and speeds cell death.
Gap junctional hemichannels in the heart
Authors: John S. , Cesario D. , Weiss J. N. 
Published: August 2003

AbstractUpon contacting each other, cells form gap junctions, in which each cell contributes half of the channel linking their cytoplasms, enabling them to share their metabolome up to a molecular weight of 1000. Each hemichannel (or connexon) is randomly inserted into the plasma membrane and then migrates to the site of cell‐to‐cell contact before pairing with the neighbouring cell's hemichannel to form a communicating conduit. This review summarizes the evidence for hemichannels in heart ventricular myocytes. Morphological findings are summarized describing how hemichannels are inserted into the plasma membrane. Once in the plasma membrane, hemichannels can be functionally detected electrophysiologically or by dye uptake assays. Each technique reveals specific aspects of hemichannel function. Using dye uptake studies, it is possible to investigate the biological regulation of hemichannels in vivo. Evidence is summarized which indicates that hemichannels are normally kept closed in the presence of normal extracellular Ca because they are phosphorylated at residues in the C‐terminus regulated by the MAPK signalling pathway. When hemichannels are dephosphorylated, the channels open and allow dye uptake into the cells, as well as potentially deleterious ion exchange. Biological stresses, such as hyperosmolarity and metabolic inhibition, open hemichannels by this mechanism through activating phosphatases. The resulting ion fluxes may have important roles in heart physiology and pathophysiology.
Do connexin 43 gap‐junctional hemichannels activate and cause cell damage during ATP depletion of renal‐tubule cells?
Authors: Vergara L. , Bao X. , Bello‐Reuss E. , Reuss L. 
Published: August 2003

Abstract
We review our evidence in favour of the hypothesis that gap‐junctional hemichannels (GJH) are activated by depletion of adenosine triphosphate (ATP) in human renal proximal tubule cells in primary culture (hPT cells). Undocked GJH permit fluxes of ions and hydrophilic molecules up to 1 kDa, and thus their opening can cause alterations of cell composition conducive to cell damage.We show that hPT cells express connexin 43 (Cx43) (at the mRNA and protein levels) and that the protein is expressed on the plasma membrane. Moderate levels of pharmacological depletion of ATP increased plasma‐membrane permeability, as shown by loading with the hydrophilic dye 5/6 carboxyfluorescein (CF, 376 Da) and other low‐molecular weight dyes, but not with fluorescein‐labelled dextran (>1500 Da). Roles for endocytosis and activation of purinergic‐receptor channels were experimentally ruled out. Moderate ATP depletion also caused necrosis, assessed by cell permeabilization to propidium iodide. Prolonged exposure to gadolinium reduced both the dye loading and the necrosis induced by ATP depletion, i.e. it protected the cells. Cx43 overexpressed in insect cells, purified to homogeneity and reconstituted in proteoliposomes formed hemichannels that are activated by dephosphorylation of Ser368, a residue in a protein‐kinase‐C consensus phosphorylation sequence near the end of the C‐terminal domain.Conclusions: (1) ATP depletion of hPT cells induces a Gd3+‐sensitive permeability of the plasma membrane to hydrophilic dyes with a cut‐off size consistent with Cx43 GJH. (2) ATP depletion also increases the percentage of necrotic cells, an effect also reduced by Gd3+. (3) The experiments with purified Cx43 reconstituted in liposomes suggest that dephosphorylation of Ser368 is sufficient to activate GJH, although other mechanisms may be involved in some cells.
Review article: the data supporting a role for aminosalicylates in the chemoprevention of colorectal cancer in patients with inflammatory bowel disease
Authors: Eaden J. 
Published: August 2003

SummaryThe chemoprevention of colorectal cancer (CRC) with long‐term sulfasalazine and 5‐aminosalicyclic acid (5‐ASA) treatment has been demonstrated through epidemiological and experimental studies, in patients with ulcerative colitis. In a large case‐controlled study, there was a trend for long‐term nonsteroidal anti‐inflammatory consumption to be protective against CRC in patients with inflammatory bowel disease (IBD) (OR, 0.84). Sulfasalazine treatment over a 3‐month period was shown to be protective (OR, 0.38), independently of disease activity. A longer‐term study of sulfasalazine also revealed a relationship with treatment compliance, where 3% of compliant patients developed CRC compared with 31% of the noncompliers. Treatment with 5‐ASA was associated with an increase in apoptosis, a decrease in proliferation of colorectal mucosa and has been shown to lower the rate of spontaneous mutation.In a retrospective, matched case‐control study conducted in the UK, 102 patients with ulcerative colitis and CRC were matched with ulcerative colitis patients without CRC. Incidence was correlated to treatment protocols, family history and other risk factors. Mesalazine was the only treatment to be associated with a statistically significant reduction in the risk of developing cancer. Even after adjusting for variables, mesalazine at doses > 1.2 g / day reduced the risk of cancer by 81% (P = 0.006). Frequent visits to the clinician were also associated with a protective effect.
Soil structure and pedotransfer functions
Authors: Pachepsky Y.A. , Rawls W.J. 
Published: August 2003

SummaryAccurate estimates of soil hydraulic properties from other soil characteristics using pedotransfer functions (PTFs) are in demand in many applications, and soil structural characteristics are natural candidates for improving PTFs. Soil survey provides mostly categorical data about soil structure. Many available characteristics such as bulk density, aggregate distribution, and penetration resistance reflect not only structural but also other soil properties. Our objective here is to provoke a discussion of the value of structural information in modelling water transport in soils. Two case studies are presented. Data from the US National Pedon Characterization database are used to estimate soil water retention from categorical field‐determined structural and textural classes. Regression‐tree estimates have the same accuracy as those from textural class as determined in the laboratory. Grade of structure appears to be a strong predictor of water retention at −33 kPa and −1500 kPa. Data from the UNSODA database are used to compare field and laboratory soil water retention. The field‐measured retention is significantly less than that measured in the laboratory for soils with a sand content of less than 50%. This could be explained by Rieu and Sposito's theory of scaling in soil structure. Our results suggest a close relationship between structure observed at the soil horizon scale and structure at finer scales affecting water retention of soil clods. Finally we indicate research needs, including (i) quantitative characterization of the field soil structure, (ii) an across‐scale modelling of soil structure to use fine‐scale data for coarse‐scale PTFs, (iii) the need to understand the effects of soil structure on the performance of various methods available to measure soil hydraulic properties, and (iv) further studies of ways to use soil–landscape relationships to estimate variations of soil hydraulic properties across large areas of land.
Soil crusting and infiltration on steep slopes in northern Thailand
Authors: Janeau J.L. , Bricquet J.P. , Planchon O. , Valentin C. 
Published: August 2003

SummaryPredicting the rate at which rain infiltrates on steep slopes is very uncertain. There is no consistent information in the literature. We have therefore related infiltrability to slope gradient under field conditions by experimenting on a gravelly loamy soil occupying the upper half of a cultivated convex hill in northern Thailand. Fifteen 1 m × 1 m plots with slope gradients ranging from 16 to 63% were established, and simulated rain was allowed to fall on them at controlled rates and for fixed times. We obtained the following results. The surface fell 0.4–7.2 mm due to compaction and soil loss. The proportions of crust (0–40%) and embedded gravel (10–60%), the runoff coefficient (0.05–0.78 mm mm−1), the mean sediment concentrations (0–5.6 g l−1), and soil detachment (10–313 g m−2) were more pronounced on the gentle slopes than on the steep ones. The steady final infiltration rate (1–107 mm hour−1) increased sharply with increasing slope gradient. Microaggregates tended to behave like sand and become tightly packed on gentle slopes (packing crust). These results suggest that the vertical component of kinetic energy, which is greater on gentle slopes, has a dominant role. Nevertheless, the differences in compaction and in sediment concentration could not be ascribed to the vertical component of kinetic energy alone. On steep slopes the horizontal component of the kinetic energy is transformed into shear stress, hampering the development of crusts so that water can still infiltrate. On steeper slopes, the water film was thinner, thereby limiting the role of splash. We conclude that the relationship between slope gradient and infiltrability depends on the nature of the soil and must be examined in the light of surface crusting processes.
Estimation of nitrate retention in a Ferralsol by a transient‐flow method
Authors: Duwig C. , Becquer T. , Charlet L. , Clothier B.E. 
Published: August 2003

SummaryAnion retention is important in highly weathered soils that contain large amounts of iron and aluminium oxides with surfaces of variable charge. Sorption mechanisms retard anionic solute transfer through these soils. We determined the retardation factor for nitrate in highly weathered Ferralsols from New Caledonia from dynamic experiments using a transient‐flow method, and we evaluated the effect of soil solution concentration and organic matter content. A simple method with sectionable tubes was used to determine the nitrate isotherm during non‐steady‐state water flow under unsaturated conditions. The topsoil retarded the movement of nitrate, and the sorption followed a linear isotherm. In subsoils, retardation factors were larger and increased from 1.15 to 2.05 at soil pH as the NO3–‐N concentration of the input solution decreased from 71.43 to 0.35 mm, indicative of a non‐linear isotherm. Positive surface charge sites were considered to be of two types: one with strong affinity for nitrate at small concentrations and one with weak affinity for adsorption of nitrate at larger concentrations. This type of isotherm with high‐ and low‐energy sites is similar to those found for oxyanions and heavy metals. The related anion exchange capacity was larger than that usually observed in soils of variable charge. Not all exchange sites were detected with our method, and some sites were obviously not available for nitrate retention.
Effect of the initial soil water saturation on the behaviour of a mixed LNAPL and heavy metal contaminated glaciofluvial deposit
Authors: Dubé J.‐S. , Winiarski T. , Galvez‐Cloutier R. 
Published: August 2003

SummarySoil contamination by mixtures of petroleum hydrocarbons and heavy metals is common in urban and industrial localities. Interactions between these contaminants have an impact on the mobility and the management of contamination. We have characterized the modifications to the transport of heavy metals (Cd, Cu, Pb, Zn) in soil induced by residual light non‐aqueous phase liquid (LNAPL) for two conditions of trapping. Experiments on the elution of tracers and heavy metals in columns of soil were performed with a glaciofluvial material as the soil. Tracer experiments were modelled with the mobile–immobile (MIM) system of partial differential equations. The experiments were designed to compare water flow and metal transport in LNAPL‐contaminated soil with a control set. Residual LNAPL was trapped in water‐saturated and dry soil to ensure preferential wettability of soil surfaces, namely either water‐wet or LNAPL‐wet.In water‐wet soil columns, LNAPL decreased water flow by two orders of magnitude and increased the fraction of immobile water. Solute residence times (SRTs) suggested that heavy metals resided mainly in mobile water where the reaction time was sufficient to reach steady‐state retention. The SRTs also indicated that a fraction of the heavy metal flux diffused to the immobile water where its retention was limited by diffusion. Retention of heavy metals was significantly greater than in the control columns. In LNAPL‐wet soil columns, the obstruction of small pores and surface coating by residual LNAPL significantly decreased the attenuation capacity of the soil by decreasing the diffusion of heavy metals to immobile water and surface sites. Evidently, the individual behaviour of heavy metals can be significantly modified by non‐miscible organic contaminants. These modifications can have important implications for risk evaluation, contamination management and in situ remediation of soil that is contaminated by mixtures of petroleum hydrocarbons and heavy metals.
Surface analysis of soil material by X‐ray photoelectron spectroscopy
Authors: Gerin P.A. , Genet M.J. , Herbillon A.J. , Delvaux B. 
Published: August 2003

SummaryThe surface composition of particles present in the fine earth (< 2 mm) of 50 soil horizons differing in composition and pedogenetic origin (13 soil profiles) was analysed by X‐ray photoelectron spectroscopy (XPS) to assess the capability and limitations of this technique and to gain better knowledge of the soil samples. The surfaces were systematically enriched in carbon, sometimes up to 1000 times, indicating that the soil particle surfaces are coated with organic substances, even in horizons where the bulk organic content is less than 0.1 g kg−1. The distribution of carbon in the various oxidation states was 0.569 ± 0.008 C[0], 0.275 ± 0.004 C[+1], 0.089 ± 0.003 C[+2]and 0.066 ± 0.002 C[+3]for most horizons (mean ± standard error, 69 data). Only Andosol surface horizons systematically had surface organic matter in a more oxidized state. After correcting the results for the presence of organic coatings, we found that Si was generally depleted and Al enriched at the surface of soil particles, while Fe was either depleted or enriched depending on the sample considered. However, the coating of the coarser soil particles by the finer ones and their differential composition explained this observation and limits the interest of XPS for characterizing the surface enrichment of inorganic elements in crude soil samples. These limitations should be considered when interpreting XPS results in future work. Nevertheless, XPS can analyse the adsorbed organic matter and its functional composition of carbon without the need for any chemical or physical extraction that might alter the structure and composition of the organic molecules.