Role of polyamines in the carotid body

Polyamines are small organic molecules which modulate many physiological processes. Here, an inhibitory effect of spermine on rat carotid body chemoreception is reported. Spermine inhibits catecholamine release, from isolated carotid bodies, induced either by high K+ or by hypoxia. This inhibitory effect could be mediated by: the activation of the Ca2+ sensing receptor (CaR) or the inhibition of the voltage-dependent Ca2+ channels. Measurements of intracellular Ca2+ in dissociated type 1 cells, demonstrated that spermine inhibits Ca2+ influx evoked by either high K+ or hypoxia, but did not affect the resting intracellular Ca2+ levels. Then, the expression of the voltage-dependent Ca2+ channels and CaR were assessed by reverse-transcription polymerase chain reaction and immunochemistry in the carotid body. Cav1.2 and Cav2.2 were found to be especially expressed in type 1 cells while Cav1.3, Cav1.4, Cav2.1, Cav2.3, Cav3.1, Cav3.2 and Cav3.3 could not be detected. CaR was detected only in the nerve ending. Having declined a role of the CaR in mediating the spermine inhibition of type 1 cell chemoreception, the effect of spermine on Cav1.2 was investigated using patch-clamp recording of HEK293 cells transiently or stably expressing human Cav1.2. Spermine inhibits Cav1.2 using 2 mM Ba2+ as a charge carrier but not with 20 mM Ba2+. The inhibition of Cav1.2 by spermine in type 1 cells was then confirmed by co-application with nifedipine using Ca2+ imaging. These experiments demonstrate an inhibitory effect of spermine on Cav1.2 and potentially Cav2.2 in rat type 1 cells. In conclusion, spermine inhibits catecholamine release by type 1 cells, via the direct inhibition of Cav1.2 and possibly Cav2.2. This mechanism could act as a negative feedback on the type 1 cells and limit neurotransmitter release.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Analyses expérimentale et numérique de l'endommagement matriciel d'un matériau composite : Cas d'un pultrudé thermoplastique renforcé de fibres de verre

The use of composite materials composed of polymeric matrix have known a growing interest in industrial structures due to the ratio between structure weight reduction and reliable mechanical properties. The pultrusion with in-situ polymerization process allows high fiber volume fraction which provides the longitudinal mechanical properties needed nevertheless, such process induces a microstructural variability. These engineering structures are often submitted to complex multiaxial stresses. Such stresses are locally amplified due to the microstructural variability and particularly due to the fact that the matrix is constrained by the fibres. It is in this context that a multi-scale top-down (global / local) experimental and numerical approach has been developped. Deformation, damage and fracture mechanisms have been experimentally studied at both global and local scales. In order to do so, experimental technics related to X ray tomography have been used and allow in-situ observation of damage in the composite material submitted to different stresses. A constitutive model of the polymeric matrix has been developped thanks to approaches from the mechanics of porous media and allows to take into account the damage behavior of the constrained matrix. A multi-scale model allowing critical zones localization on industrial structures has been set up. The resulting stresses on the critical zones are then applied to the microstructure of the composite material. This model is able to take into account the damage cinetic, as well as transverse cracks initiation and propagation through the microstructure. Such approach has been used to determine cracks initiation pressures for different plies orientation of a composite pipe.L'utilisation croissante des matériaux composites à matrice polymère dans les structures industrielles est impulsée par le besoin de contraintes environnementales tout en conservant d'excellentes propriétés mécaniques. L'évolution des procédés de fabrication et l'émergence de la pultrusion réactive permet la production de matériaux composites à matrice thermoplastique possédant des taux de fibres très importants. Ceci leur confère les propriétés longitudinales souhaitées mais ces procédés induisent une variabilité microstructurale importante. De plus, les pièces industrielles sont bien souvent sollicitées de façon complexe induisant des contraintes multiaxiales. Ces contraintes sont alors ``ressenties'' par la microstructure du matériau composite et par la matrice confinée par les fibres notamment. La variabilité microstructurale tend alors à amplifier les contraintes. C'est dans ce contexte qu'une approche multi-échelle macro-micro (globale/locale) expérimentale et numérique a été développée. Les mécanismes de déformation, d'endommagement et de rupture ont été expérimentalement analysés à l'échelle globale du matériau composite ainsi qu'à l'échelle locale de sa microstructure. Pour ce faire, de techniques expérimentales liées à la tomographie aux rayons X ont été mises en place et permettent d'observer in-situ l'évolution de la microstructure sollicitée. Il a été observé que l'endommagement se développe au sein de la matrice thermoplastique. Un modèle de comportement de la matrice endommageable a donc été mis au point à l'aide des approches issues de la mécanique des milieux poreux et permet de rendre compte des micro-mécanismes de déformation et d'endommagement de la matrice confinée par les fibres. Une approche de type ``top-down'' a été développée. Celle-ci permet de localiser les zones critiques d'une structure industrielle composite. Le chargement appliqué localement sur la pièce sert alors de conditions aux limites sur une microstructure réelle modélisée. Ainsi, il est possible de simuler la cinétique d'endommagement, permettant de comprendre l'amorçage et la propagation de fissures dans une structure industrielle. Cette approche appliquée au cas d'une canalisation composite sous pression a permis de déterminer des pressions d'amorçage de fissures en fonction de l'enroulement du composite sur la canalisation

Role of polyamines in the carotid body

Polyamines are small organic molecules which modulate many physiological processes. Here, an inhibitory effect of spermine on rat carotid body chemoreception is reported. Spermine inhibits catecholamine release, from isolated carotid bodies, induced either by high K+ or by hypoxia. This inhibitory effect could be mediated by: the activation of the Ca2+ sensing receptor (CaR) or the inhibition of the voltage-dependent Ca2+ channels. Measurements of intracellular Ca2+ in dissociated type 1 cells, demonstrated that spermine inhibits Ca2+ influx evoked by either high K+ or hypoxia, but did not affect the resting intracellular Ca2+ levels. Then, the expression of the voltage-dependent Ca2+ channels and CaR were assessed by reverse-transcription polymerase chain reaction and immunochemistry in the carotid body. Cav1.2 and Cav2.2 were found to be especially expressed in type 1 cells while Cav1.3, Cav1.4, Cav2.1, Cav2.3, Cav3.1, Cav3.2 and Cav3.3 could not be detected. CaR was detected only in the nerve ending. Having declined a role of the CaR in mediating the spermine inhibition of type 1 cell chemoreception, the effect of spermine on Cav1.2 was investigated using patch-clamp recording of HEK293 cells transiently or stably expressing human Cav1.2. Spermine inhibits Cav1.2 using 2 mM Ba2+ as a charge carrier but not with 20 mM Ba2+. The inhibition of Cav1.2 by spermine in type 1 cells was then confirmed by co-application with nifedipine using Ca2+ imaging. These experiments demonstrate an inhibitory effect of spermine on Cav1.2 and potentially Cav2.2 in rat type 1 cells. In conclusion, spermine inhibits catecholamine release by type 1 cells, via the direct inhibition of Cav1.2 and possibly Cav2.2. This mechanism could act as a negative feedback on the type 1 cells and limit neurotransmitter release

Análisis de rendimientos de los diferentes híbridos de maíz a distintas densidades y fechas de siembra en la región semiárida pampeana

Se estudió el rendimiento y sus componentes en cuatro híbridos de maíz para las fechas de siembra temprana (Octubre) y tardía (Diciembre) y seis densidades de siembra. El trabajo se realizó en la E.E.A. INTA Anguil “Ing. Agr. Guillermo Covas” durante la campaña 2014-2015 en condiciones de campo, en microparcelas experimentales. Se evaluaron cuatro híbridos de maíz, de los cuales tres eran prolíficos (DM 2771 VT3P, KM 4500 GL, KMA 4200 GL) y uno no prolífico, espiga flex (Dow 505 PW). Las densidades de siembra utilizadas fueron 15.000, 30.000, 50.000, 70.000, 90.000, 110.000 plantas.ha-1. Luego de finalizado el ciclo del cultivo, se procedió a hacer la cosecha manual sobre la que se determinó la biomasa total por planta separándose en hojas, tallos, chalas y espigas, de las últimas se registró el número y el peso de los granos, a partir de ahí el rendimiento. Los resultados indicaron que la fecha de siembra tardía tuvo mayor rendimiento, explicado por una mayor biomasa e índice de cosecha por planta por un lado, y por otro un mayor número y peso de granos en comparación con la fecha temprana. De los dos últimos componentes se vió que el número de granos es el que afectó más al rendimiento, ya que no es tan estable como el peso de los granos. El mejor híbrido en la fecha temprana fue el DM 2771 VT3P, y en la fecha tardía varió según la densidad a la cual se trabajó. Se llegó a la conclusión de que los mejores resultados se registraron para la fecha tardía dadas las condiciones climáticas de esa campaña

Experimental discrimination of ion stopping models near the Bragg peak in highly ionized matter

The energy deposition of ions in dense plasmas is a key process in inertial confinement fusion that determines the α-particle heating expected to trigger a burn wave in the hydrogen pellet and resulting in high thermonuclear gain. However, measurements of ion stopping in plasmas are scarce and mostly restricted to high ion velocities where theory agrees with the data. Here, we report experimental data at low projectile velocities near the Bragg peak, where the stopping force reaches its maximum. This parameter range features the largest theoretical uncertainties and conclusive data are missing until today. The precision of our measurements, combined with a reliable knowledge of the plasma parameters, allows to disprove several standard models for the stopping power for beam velocities typically encountered in inertial fusion. On the other hand, our data support theories that include a detailed treatment of strong ion-electron collisions

Proton stopping measurements at low velocity in warm dense carbon

: Ion stopping in warm dense matter is a process of fundamental importance for the understanding of the properties of dense plasmas, the realization and the interpretation of experiments involving ion-beam-heated warm dense matter samples, and for inertial confinement fusion research. The theoretical description of the ion stopping power in warm dense matter is difficult notably due to electron coupling and degeneracy, and measurements are still largely missing. In particular, the low-velocity stopping range, that features the largest modelling uncertainties, remains virtually unexplored. Here, we report proton energy-loss measurements in warm dense plasma at unprecedented low projectile velocities. Our energy-loss data, combined with a precise target characterization based on plasma-emission measurements using two independent spectroscopy diagnostics, demonstrate a significant deviation of the stopping power from classical models in this regime. In particular, we show that our results are in closest agreement with recent first-principles simulations based on time-dependent density functional theory