Les liens qui unissent la structure et les propriétés physiques, chimiques des matériaux sont très importants. En particulier, le degré d’ordre, les défauts cristallins, l’hétérogénéité structurale ou chimique, s’avèrent être des paramètres très pertinents dans la réactivité des matériaux. Ce travail a porté sur l’étude de la réactivité de plusieurs formes de la silice, et permet de montrer l’influence de l’ordre et de la cristallinité sur les processus de vieillissement par la réaction alcali-silice. Dans cette objectif, la réactivité de trois matériaux différents : granulats (silex), quartz et verre de silice a été suivie par différentes techniques d’investigations.Le quartz réagit très lentement, le verre très vite et le granulat de manière intermédiaire. Une analyse plus fine montre que la fraction mal cristallisée, voire amorphe, du granulat réagit préférentiellement.Le caractère désordonné des matériaux suggère l’utilisation de techniques sensibles à l’ordre local : nous avons employé, la spectroscopie d’absorption X (XANES et EXAFS) complétée par la RMN du solide.Les cartographies chimiques obtenues par microscopie électronique (en balayage et en transmission) ou au synchrotron montrent que le potassium K+ diffuse le premier et que le calcium Ca++ pénètre difficilement la structure cristalline de la silice. A l’échelle locale la RMN du silicium montre la dépolymérisation du réseau permet la diffusion des cations Ca++.Le micro-XANES révèle la présence de plusieurs environnements autour des atomes de silicium. L’un consiste en un silicium avec quatre oxygènes premiers voisins et l’autre avec moins de quatre atomes d’oxygènes. D’autre part, l’EXAFS montre l’absence du Ca et/ou K au niveau de la deuxième couche de voisins de l’atome de silicium absorbeur dans un environnement ordonné. / The relationships between the structure and the physical and chemical properties are very important in materials. In particular, the degree of order, the crystal defects and the structural heterogeneities or chemical parameters appear to play a key role in the reactivity of materials. This work is devoted to the study of the reactivity of silica-based materials, and shows of the influence of ordering and crystallinity on the sensitivity to the alkali silica reaction. In this perspective, the reactivity of three different materials: silica glass, aggregates (Flint) and quartz was followed by various techniques. Quartz reacts very slowly whereas the silica glass reacts very quickly, the aggregate exhibiting an intermediate behavior. A closer analysis shows that the amorphous or poorly crystalline fraction of the aggregate reacts preferentially. The role played by these poorly crystalline fractions suggests the use of techniques sensitive to short and medium range order such as: X-ray absorption spectroscopy (XANES and EXAFS) and solid state NMR. Chemical maps obtained by electron microscopy (scanning or in transmission) or at the synchrotron, show that the potassium K+ is the first to diffuse and that penetration of calcium Ca++ is more sluggish in crystalline silica. Locally, silicon NMR analysis shows that depolymerization of the crystalline lattice allows further penetration of calcium. The micro-XANES reveals the presence of several environments around silicon atoms. One exhibits four oxygen first neighbours and the other has less than four oxygen atoms around the silicon. On the other hand, the EXAFS shows the absence of Ca or K in the second layer of neighbouring silicon atom absorber. These results help to advance the understanding of reaction mechanisms occurring in the aggregate altered by the reaction

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Introduction: Cardiac disease is a leading cause of mortabity and morbidity in the developed countries. Cultured cardiac myocytes are widely used for exploring the underlying pathophysiology of cardiac disease. Rodents, especially mice with transgenes or gene ablation, have become popular animal models for heart disease research. However, it has been long recognized that rodent myoyctes die during long-term primary culture, which limits the use of genetically altered myocytes for signaling studies. Blebbistatin (BLB), a myosin II ATPase inhibitor, has been used to protect rodent myocytes. The mechanisms underlying the protective effects of this drug are not clear and are the topics of this study. Materials & methods: Adult rat ventricular myocytes (ARVM) were isolated and cultured with or without BLB (10 µM) for 72 hours in comparison with another protective chemical, BDM (10mM). Myocyte death was evaluated by morphology changes and trypan blue staining. The effects of these two drugs on myocyte contraction, intracellular Ca2+ transient ([Ca2+]i, indo-1,410/480), SR Ca2+ content, L-type calcium and Na+ /Ca2+exchanger currents were studied acutely. Neonatal rat ventricular myocytes (NRVM) were isolated from 1-3 days old neonatal rat hearts and cultured. The effect of BDM (10mM BDM) and BLB (10 µM) in the medium on NRVM growth and hypertrophy induced by norepinephrine (NE, 10µM) were determined. Results: 1. Both BDM and BLB promoted myocyte survival in culture at 72 hours but BLB protected more myocytes (Control: 7.0±1.8% vs. BDM: 61.5±6.4% vs. BLB: 74.0±3.2%); 2. ARVM fractional shortening was reduced by BLB to 1.7±0.4% and by BDM to 0.5±0.1% from the baseline of 6.5±0.7%; 3. Acutely, the amplitude of [Ca2+]i (∆ [Ca2+]i) evaluated with indo-1 AM (F410/F480) was depressed by both BDM (0.04±0.01) and BLB (0.07±0.01) compared to control (0.13±0.01). 4. Diastolic Ca2+ was significantly increased by BLB (0.90±0.06) but not by BDM (0.73±0.06) compared to pre-treat values (0.70±0.05); 5. BLB and BDM significantly reduced the SR Ca2+ content, as indicated by the reduced amplitudes of caffeine-induced Ca2+ transients in BLB- and BDM-treated ARVMs (∆[Ca2+]i in BLB vs. BDM vs. baseline: 0.20±0.03, 0.19±0.04, 0.30±0.03). 6. The mechanisms of the protective effects of BDM and BLB were similar but quantitatively different in that BDM reduced more Ca influx through the L-type Ca2+ channel (ICa-L) than BLB (the reduction in BDM-treated cells vs. BLB-treated cells: 70% vs. 40%) while BLB inhibited more Na+/Ca2+exchanger current (75% inhibition) than BDM (40% reduction); 7. Both BDM and BLB inhibited normal NRVM growth and NE-induced hypertrophy and NFAT translocation in NRVMs. Conclusion: These results suggest both BDM and BLB protect rodent myocytes in culture by preventing cytosolic and SR Ca2+ overload by similar mechanisms: inhibiting NCX and reducing the LTCC. The application of BLB to whole-heart studies and myocyte hypertrophy should be extremely cautioned because BLB does alter myocyte Ca2+ handling. / Physiology

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Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 194-217).

"Dissertation présentée devant la Faculté de médecine, épreuve de l'agrégation de l'enseignement supérieur." / At head of title: Université catholique de Louvain. Chaire de chirurgie orthopédique, Professeur P. Lacroix, et Institut interuniversitaire des sciences nucléaires. Includes bibliographical references.