X-ray characterisation of bulk stones from the patina to the depth stone

The aim of this study on monumental limestone alteration is to characterise the superficial stone called patina where transformation processes due to air and water occur. We present results on stones from the Chambord castle, so Tuffeau limestone, from the Loire Valley. Three samples has been studied and compared in relationship with their position on the monument (outside or inside). In order to describe these samples, different techniques have been used : chemical analysis, optical microscopy. The three main phases are calcite (CaCO 3), quartz and opal (SiO 2), with various granulometry. X-ray diffraction has been performed on bulk samples. A special sample holder allows to analyse very thin zones, so to describe the mineralogical composition from the epidermis to the depth stone [1]. The stones are constituted of small crystallites which differ in dimension and orientation. This conducts to a semi-quantitative description. Protecting layer of the stone is associated to the rate of dissolution of calcite in patina zone

Muscle contractile characteristics during exhaustive dynamic exercise and recovery

Our aim was to provide an in vivo assessment of human muscle twitch characteristics during and following an exhaustive dynamic exercise to explore temporal alterations of the rate of force development (RFD) and relaxation (RFR). Eleven healthy participants (mean age ± SD: 24 ± 3 years) completed a dynamic knee-extensor exercise in randomized order at three different intensities, eliciting exhaustion after ∼9 min (56 ± 10 W), ∼6 min (60 ± 10 W), and ∼4 min (63 ± 10 W), in addition to a low-intensity (28 ± 5 W) bout. In a novel setup, an electrical doublet stimulation of m. vastus lateralis was applied during exercise (every 30 s) and recovery for frequent evaluation of key contractile properties (maximal force, RFD, RFR, and electromechanical delay) in addition to M-wave characteristics. RFD and RFR remained stable throughout the low-intensity trial but declined in all exhaustive trials to reach a similar level of ∼40% of pre-exercise values at task failure but with the exponential decay augmented by intensity. Following exhaustion, there was a fast initial recovery of RFD and RFR to ∼80% of pre-exercise values within 1 min, followed by a longer suppression at this level. The M-wave characteristics remained unchanged during all trials. In conclusion, this is the first study to quantify the intensity-dependent alterations of RFD and RFR during and after exhaustive dynamic exercise in humans. A hypothesized reduction and fast reversion of RFD was confirmed, and a surprising compromised RFR is reported. The present unique experimental approach allows for novel insight to exercise-induced alterations in human muscle contractile properties which is relevant in health and disease

Oxydation lipidique et performance physique (revue de la littérature)

BREST-BU Médecine-Odontologie (290192102) / SudocPARIS-BIUM (751062103) / SudocSudocFranceF

Enhancing the behavior of virtual characters with long term planning, failure anticipation and opportunism

International audienceAutonomous virtual characters evolve in dynamic virtual environments in which changes may be unpredictable. However, they need to behave properly and adapt their behavior to perceived changes while ful lling their goals. In this article, we propose a system that combines long term action planning with failure anticipation and opportunism. The system generates plans enriched with information that enable a monitor to detect relevant changes of the environment in order to trigger plan adaptations whenever needed

Propriétés électrophysiologiques des canaux sodiques du muscle strié squelettique et contrainte mécanique

Les canaux sodiques dépendants du potentiel (Na) sont responsables du déclenchement et de la propagation du potentiel d action musculaire. Ils participent ainsi à l excitabilité de la fibre musculaire et à ses propriétés contractiles. L immobilisation musculaire induit des changements du phénotype contractile. Nous avons étudié l effet de 4 et 8 semaines d immobilisation du muscle Peroneus Longus (PL) à sa longueur optimale, sur ses propriétés contractiles et les propriétés électrophysiologiques de ses canaux sodiques. Après 4 semaines d immobilisation, les propriétés contractiles du muscle présentent une conversion vers un phénotype plus rapide avec un retour partiel vers les propriétés du muscle contrôle après 8 semaines d immobilisation. Les courants provenant du canal sodique de type 1.4 (Nav 1.4) augmentent puis diminuent, alors que les courants et l expression du Nav 1.5 diminuent continuellement au cours de l immobilisation. Ces résultats indiquent que la possibilité pour un muscle de se raccourcir ou de s allonger est indispensable pour conserver son phénotype contractile et maintenir le ratio Nav 1.4/ Nav 1.5. L expression du Na 1.4 est corrélée avec le phénotype rapide du muscle. Pour étudier l hypothèse d une participation des Na au phénotype contractile de la fibre musculaire, des fibres dissociées de muscles de la patte de rats Wistar ont été étudiées par la technique du macropatch-clamp, puis l isoforme de chaîne lourde de myosine (CLM) qu elles exprimaient a été déterminé par électrophorèse SDS-PAGE. Dans les fibres de PL, le courant sodique maximal (Imax) et la conductance sodique maximale (gNa max) augmentent selon le schéma suivant: type I->IIa->IIx->IIb de CLM. Ce résultat est cohérent avec une activation progressive des différents types de fibres (du type lent vers le type rapide) dans un muscle mixte comme le PL. En se contractant, le muscle soumet sa membrane à des variations de longueur donc de tension. Il est licite de s intéresser à l effet de ces variations de tension sur le fonctionnement des protéines membranaires comme les Nav. En configuration patch-clamp, nous avons appliqué, dans un ordre aléatoire, différents niveaux de dépression (0, -10, -20, -30 mmHg) sur la membrane. Le courant sodique maximal (Imax) et la conductance sodique maximale augmentent avec le niveau de dépression. Les courbes d activation sont décalées vers les potentiels négatifs avec la dépression. Le processus d inactivation lente des Nav est augmenté par la dépression. Sur le plan fonctionnel, ces résultats sont en faveur d une participation des Nav au phénomène de stretch-activation (augmentation de la force produite d un muscle par son étirement préalable). Toutefois la diminution du nombre de canaux activables (inactivation lente) par l étirement membranaire permet, à moyen terme, de moduler l excitabilité et donc la fatigabilité du muscle.Voltage-gated sodium channels (Nav) are involved in the triggering and the propagation of muscle action potential. The electrophysiological properties of Nav determine muscle excitability and influence the contractile properties of muscle. Muscle immobilization leads to modification in its fast/slow contractile phenotype. Therefore, we studied the effects of single immobilization on the contractile and the electrophysiological properties of Na, in rat muscle Peroneus Longus (PL). After 4 weeks of immobilization, PL shows a faster phenotype with partial recovery to control phenotype between 4 and 8 weeks of immobilization. Using the patch-clamp technique, sodium currents from Nav 1.4 displays a transitory increase alter 4 weeks of immobilization, whereas Nav 1.5 currents decrease continuously throughout immobilization. Our results indicate that a muscle immobilized at optimal functional length with the preservation of neural inputs, exhibits a transient fast phenotype conversion. Nav 1.4 expression and current are related to the contractile phenotype variation through muscle excitability. The myosin heavy chain (MHC) isoform determines the shortening velocity of muscle fibre. Whole muscle, even if selected according to its predominant mechanical properties ( slow or fast ), exhibits heterogeneous MHC composition. Since the properties of Na, are different between fast and slow muscles, we hypothesised that the electrophysiological properties of Na, could be related to MEC isoform expression in single muscle fibre. Alter patch-clamp recordings, single fibres were identified by SDS-PAGE electrophoresis according to their myosin heavy chain isoform (slow type I and the three fast types IIa, IIx, IIb). The maximal sodium current and conductance increase according to the scheme I->IIa->IIx->IIb. These data are consistent with the earlier recruitment of slow fibres in a fast-mixed muscle like PL. Slow fibres have to be activated early in order to optimize the mechanical performance of the predominant fast fibres. The contraction of skeletal muscle to produce force implies length and tension variation for its membrane. The consequences of tension variation on the properties of membrane proteins such as sodium channels remain questioning. In patch-clamp configuration, different levels of depression were applied with the pipette to stretch muscle membrane and Nav. Membrane stretch increases maximal sodium current and induces a leftward shift in activation and slow inactivation curves in a dose-dependent manner. Nav are involved in the stretch-activation process through the enhancement of its activation threshold with membrane stretch.BREST-BU Médecine-Odontologie (290192102) / SudocSudocFranceF

Effects of AMPD1 common mutation on the metabolic-chronotropic relationship: Insights from patients with myoadenylate deaminase deficiency.

Current evidence indicates that the common AMPD1 gene variant is associated with improved survival in patients with advanced heart failure. Whilst adenosine has been recognized to mediate the cardioprotective effect of C34T AMPD1, the precise pathophysiologic mechanism involved remains undefined to date. To address this issue, we used cardio-pulmonary exercise testing data (CPX) from subjects with myoadenylate deaminase (MAD) defects.From 2009 to 2013, all the patients referred in our laboratory to perform a metabolic exercise testing, i.e. a CPX with measurements of muscle metabolites in plasma during and after exercise testing, were prospectively enrolled. Subjects that also underwent an open muscle biopsy for diagnosis purpose were finally included. The metabolic-chronotropic response was assessed by calculating the slope of the linear relationship between the percent heart rate reserve and the percent metabolic reserve throughout exercise. MAD activity was measured using the Fishbein's technique in muscle biopsy sample. The common AMPD1 mutation was genotyped and the AMPD1 gene was sequenced to screen rare variants from blood DNA.Sixty-seven patients were included in the study; 5 had complete MAD deficiency, 11 had partial MAD deficiency, and 51 had normal MAD activity. Compared with normal MAD activity subjects, MAD deficient subjects appeared to have a lower-than-expected metabolic-chronotopic response during exercise. The metabolic-chronotropic relationship is more closely correlated with MAD activity in skeletal muscle (Rs = 0.57, p = 5.93E-7, Spearman correlation) than the presence of the common AMPD1 gene variant (Rs = 0.34, p = 0.005). Age-predicted O2 pulse ratio is significantly increased in MAD deficient subjects, indicating a greater efficiency of the cardiovascular system to deliver O2 (p < 0.01, Scheffé's post hoc test).The metabolic-chronotropic response is decreased in skeletal muscle MAD deficiency, suggesting a biological mechanism by which AMPD1 gene exerts cardiac effect

Exercise efficiency impairment in metabolic myopathies

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Hemodynamic effects of lipid emulsion after local anesthetic intoxication may be due to a direct effect of fatty acids on myocardial voltage-dependent calcium channels.

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