Showing papers by "University of Nice Sophia Antipolis published in 1995"

Protective effects of HOE642, a selective sodium-hydrogen exchange subtype 1 inhibitor, on cardiac ischaemia and reperfusion.

Abstract: Objective: The aim was to characterise the new compound HOE642 as a selective and cardioprotective Na+/H+ exchange inhibitor in various models. Methods: The effect of HOE642 was tested in the osmotically activated Na+/H+ exchange of rabbit erythrocytes and in propionate induced swelling of human thrombocytes. Recovery of pH after an NH4Cl prepulse and effects on other ion transport systems by patch clamp technique were investigated in rat cardiomyocytes, NHE subtype specifity of the compound was determined by 22Na+ uptake inhibition in a fibroblast cell line separately expressing subtype isoforms 1–3. Protective effects of HOE642 in cardiac ischaemia and reperfusion by ligation of coronary artery were investigated in isolated working rat hearts and in anaesthetised rats. Results: HOE642 concentration dependently inhibited the amiloride sensitive sodium influx in rabbit erythrocytes, reduced the swelling of human platelets induced by intracellular acidification, and delayed pH recovery in rat cardiomyocytes. In the isolated working rat heart subjected to ischaemia and reperfusion HOE642 dose dependently reduced the the incidence and the duration of reperfusion arrhythmias. It also reduced the the release of lactate dehydrogenase and creatine kinase, and preserved the tissue content of glycogen, ATP, and creatine phosphate. In anaesthetised rats undergoing coronary artery ligation intravenous and oral pretreatment with HOE642 caused a dose dependent reduction or a complete prevention of ventricular premature beats, ventricular tachycardia, and ventricular fibrillation. The compound was well tolerated and neutral to circulatory variables. Other cardiovascular agents tested in this model were not, or were only partly, effective at doses showing marked cardiodepressive effects. Conclusions: HOE642 is a very selective NHE subtype 1 inhibitor showing cardioprotective and antiarrhythmic effects in ischaemic and reperfused hearts. Further development of well tolerated compounds like HOE642 could lead to a new therapeutic approach in clinical indications related to cardiac ischaemia and reperfusion.

Hormonal regulation, pharmacology, and membrane sorting of vertebrate Na+/H+ exchanger isoforms

Abstract: Since the cloning of the first member of the Na+/H+ exchanger (NHE) family, termed NHE1, four NHE isoforms have been cloned (NHE2, NHE3, NHE4, and the trout beta-NHE) and expressed in exchanger-deficient cell lines. All these isoforms exhibit significant identity to NHE1 and possess a similar hydropathy profile with two highly conserved transmembrane segments presumably involved in ion transport. These isoforms are allosterically activated by intracellular H+, regulate intracellular pH in a Na(+)-dependent manner, and are inhibited by amiloride and 5-amino derivatives with distinct Ki values. NHE1 is the amiloride-sensitive, growth factor-activatable, and ubiquitously expressed NHE known to regulate intracellular pH and cellular volume. NHE2, NHE3, and NHE4 are, however, restricted in their tissue distribution, suggesting roles in specialized functions of these epithelial tissues. In this review we present and discuss the most recent advances in the molecular and biochemical features, hormonal and growth factor activation, specific expression, and membrane sorting of the members of this NHE family.

Position-dependent effective mass and Galilean invariance.

Abstract: Instantaneous Galilean invariance is used to derive from first principles the expression for the Hamiltonian of an electron with a position-dependent effective mass, as well as the adequate boundary conditions for the wave function in the case of abrupt heterojunctions. A very elementary model sustaining these results in the envelope-function approximation is also proposed.

Global Oscillations at Low Frequency from the SOHO mission (GOLF)

Abstract: The GOLF experiment on the SOHO mission aims to study the internal structure of the sun by measuring the spectrum of global oscillations in the frequency range 10−7 to 10−2 Hz. Bothp andg mode oscillations will be investigated, with the emphasis on the low order long period waves which penetrate the solar core. The instrument employs an extension to space of the proven ground-based technique for measuring the mean line-of-sight velocity of the viewed solar surface. By avoiding the atmospheric disturbances experienced from the ground, and choosing a non-eclipsing orbit, GOLF aims to improve the instrumental sensitivity limit by an order of magnitude to 1 mm s−1 over 20 days for frequencies higher than 2.10−4 Hz. A sodium vapour resonance cell is used in a longitudinal magnetic field to sample the two wings of the solar absorption line. The addition of a small modulating field component enables the slope of the wings to be measured. This provides not only an internal calibration of the instrument sensitivity, but also offers a further possibility to recognise, and correct for, the solar background signal produced by the effects of solar magnetically active regions. The use of an additional rotating polariser enables measurement of the mean solar line-of-sight magnetic field, as a secondary objective.

Multifractal scaling properties of a growing fault population

Abstract: SUMMARY A numerical rupture model, introduced in Cowie, Vanneste & Sornette (1993), is used to simulate the growth of faults in a tectonic plate driven by a constant plate boundary velocity. We find that the plate initially deforms by uncorrelated nucleation of small faults reflecting the distribution of material properties. With increasing strain, growth and coalescence of existing faults dominate over nucleation, a power-law distribution of fault sizes appears, and the fault pattern is fractal. Furthermore, the combined effect of fault clustering and the correlation between fault displacement and fault size leads to a strongly multifractal deformation pattern. We show theoretically that the multifractal spectrum depends explicitly on the exponent c, which defines the size distribution of the faults, as size and displacement are correlated. For different realizations of the numerical model, we calculate the exponent c, and fractal structure of the deformation through time as strain accumulates. We explore in detail the time evolution of the capacity (D0), information (D1), and correlation (D2) fractal dimensions. We relate these scaling parameters to the physical mechanisms of fault nucleation, growth and linkage during different phases of the deformation and discuss the factors that determine the values of the exponents. A consistently observed systematic decrease in the values of c, D1 and D2 through time indicates that the relative strain contribution of the smallest faults decreases as the total strain increases, a signature of the localization of faulting.

Oncogenic conversion of a novel orphan nuclear receptor by chromosome translocation

Abstract: A recurrent t(9;22) (q22;q12) chromosome translocation has been described in extraskeletal myxoid chondrosarcoma (EMC). Fluorescent in situ hybridization experiments performed on one EMC tumour indicated that the chromosome 22 breakpoint occurred in the EWS gene. Northern blot analysis revealed an aberrant EWS transcript which is cloned by a modified RT-PCR procedure. This transcript consists of an in-frame fusion of the 5' end of EWS to a previously unidentified gene, which was named TEC. This fusion transcript was detected in six of eight EMC studied, and three different junction types between the two genes were found. In all junction types, the putative translation product contained the amino-terminal transactivation domain of EWS linked to the entire TEC protein. Homology analysis showed that the predicted TEC protein contains a DNA-binding domain characteristic of nuclear receptors. The highest identity scores were observed with the NURR1 family of orphan nuclear receptors. These receptors are involved in the control of cell proliferation and differentiation by modulating the response to growth factors and retinoic acid. This work provides, after the PML/RAR alpha gene fusion, the second example of the oncogenic conversion of a nuclear receptor and the first example involving the orphan subfamily. Analysis of the disturbance induced by the EWS/TEc protein in the nuclear receptor network and their target genes may lead to new approaches for EMC treatment.

Higher-Order Abstract Syntax in Coq

Abstract: The terms of the simply-typed λ-calculus can be used to express the higher-order abstract syntax of objects such as logical formulas, proofs, and programs. Support for the manipulation of such objects is provided in several programming languages (e.g. λProlog, Elf). Such languages also provide embedded implication, a tool which is widely used for expressing hypothetical judgments in natural deduction. In this paper, we show how a restricted form of second-order syntax and embedded implication can be used together with induction in the Coq Proof Development system. We specify typing rules and evaluation for a simple functional language containing only function abstraction and application, and we fully formalize a proof of type soundness in the system. One difficulty we encountered is that expressing the higher-order syntax of an object-language as an inductive type in Coq generates a class of terms that contains more than just those that directly represent objects in the language. We overcome this difficulty by defining a predicate in Coq that holds only for those terms that correspond to programs. We use this predicate to express and prove the adequacy for our syntax.

Effects of salinity on the ionic balance and growth of juvenile turbot

Abstract: The effects of salinity changes (27, 19 and 10‰) on seawater-adapted juvenile turbot were studied on their plasma osmolarity and ion concentrations, on oxygen consumption, on gill Na+,K+-ATPase activity after 3 months and on growth parameters. All plasma concentrations (except chloride) were unchanged, suggesting that fish were well adapted to their environment. Oxygen consumption was significantly decreased in the 19 and 10‰ groups, where fish weighed significantly more 105 days after transfer than fish maintained in sea water. These results, and the fact that apparent food conversion rates were lower in a diluted environment, suggest that on a long term schedule growth conditions could be improved by adaptation to brackish waters (salinities between 10 and 19‰). The effects of transfer from sea water to 27, 19, 10 and 5‰ were also followed during the first 3 weeks. With salinity 10‰ a steady state was reached on day 21 with all plasma values within the same range. The significant differences observed in osmolarity, plasma ion concentrations and Na+,K+-ATPase activity 3 weeks after transfer of juveniles to 5‰ salinity, compared with transfers in higher salinities, suggest that there is a threshold of acclimation of turbot to a hypotonic environment.

Universal Log-Periodic Correction to Renormalization Group Scaling for Rupture Stress Prediction From Acoustic Emissions

Abstract: Based on the idea that the rupture of heterogenous systems is similar to a critical point, we show how to predict the failure stress with good reliability and precision (≈5%) from acoustic emission measurements at constant stress rate up to a maximum load 15-20% below the failure stress. The basis of our approach is to fit the experimental signals to a mathematical expression deduced from a new scaling theory for rupture in terms of complex fractal exponents. The method is tested successfully on an industrial application, namely high pressure spherical tanks made of various fiber-matrix composites. As a by-product, our results constitute the first observation in a natural context of the universal periodic corrections to scaling in the renormalization-group framework. Our method could be applied usefully to other similar predicting problems in the natural sciences (earthquakes, volcanic eruptions, etc.).

Optical-Flow Estimation while Preserving Its Discontinuities: A Variational Approach

Abstract: This paper describes a variational approach devised for the purpose of estimating optical flow from a sequence of images with the constraint to preserve the flow discontinuities. This problem is set as a regularization and minimization of a non quadratic functional. The Tikhonov quadratic regularization term usually used to recover smooth solution is replaced by a particular function of the gradient flow specifically derived to allow flow discontinuities formation in the solution. Conditions to be fulfilled by this specific regularizing term, to preserve discontinuities and insure stability of the regularization problem, are also derived. To minimize this non quadratic functional, two different methods have been investigated. The first one is an iterative scheme to solve the associated non-linear Euler-Lagrange equations. The second solution introduces dual variables so that the minimization problem becomes a quadratic or a convex functional minimization problem. Promising experimental results on synthetic and real image sequences will illustrate the capabilities of this approach.

Origins of G1 arrest in senescent human fibroblasts

Abstract: Human diploid fibroblasts have a finite proliferative lifespan in culture, at the end of which they are arrested with G1 phase DNA contents. Upon serum stimulation, senescent cells are deficient in carrying out a subset of early signal transduction events such as activation of protein kinase C and induction of c-fos. Later in G1, they uniformly fail to express late G1 genes whose products are required for DNA synthesis, implying that they are unable to pass the R point. Failure to pass the R point may occur because senescent cells are unable to phosphorylate the retinoblastoma protein, owing to the accumulation of inactive complexes of cyclin E/Cdk2 and possibly cyclin D/Cdk4. Senescent cells contain high amounts of p21, a potent cyclin-dependent kinase inhibitor whose levels are also elevated in cells arrested in G1 following DNA damage, suggesting that both arrests might share a common mechanism. Cell aging is accompanied by a progressive shortening of chromosomal telomeres, which could be perceived by the cells as a form of DNA damage that gives rise to the signals that inactive the cell cycle machinery.

40Ar/39Ar chronology, petrology and geodynamic setting of Mesozoic to early Cenozoic magmatism from the Benue Trough, Nigeria

Abstract: The Benue Trough is a continental-scale intraplate tectonic megastructure which is part of Mid-African Rift System. This rift, initiated in the latest Jurassic, was related to the opening of the Central and South Atlantic oceans. Mesozoic to early Cenozoic magmatism accompanied this evolution. Two principal magmatic domains are evident, the Northern and Southern Benue. In the northern domain, magmatism is characterized by transitional alkaline basalts and transitional tholeiitic basalts. Acidic magmatism of peralkaline nature is also present. In the Southern Benue, several magmatic districts exhibit alkaline or tholeiitic affinities. A detailed chronology of emplacement of this volcanism has been established using the 40 Ar/ 39 Ar radiometric method which lead to recognition of three periods of magmatic activity: (1) 147–106 Ma, well expressed in the Northern Benue represefited by transitional basaltic types; (2) 97–81 Ma, occurring only in the Southern Benue, represented exclusively by alkaline intrusive rocks; (3) 68–49 Ma, restricted also to the Southern Benue, with alkaline intrusions followed by tholeiitic subvolcanic rocks. In the light of the general geodynamic evolution, a scenario is proposed, supported by the three chronological periods. The late Jurassic to Albian magmatism occurred when the Equatorial Atlantic was still closed, contemporaneous with the NE Brazilian magmatism. Both magmatism could represent the forerunners of opening of the Equatorial Atlantic. This activity occurred under a general extensional regime during which crustal strike-slip faults gave rise to the emplacement of transitional alkaline basalts. Transitional tholeiitic basalts erupted along normal faults. The second period of activity, Cenomanian to Santonian, restricted to the Southern Benue, occurred after the opening of Atlantic Ocean during a period of decreasing extension. This period ended with a Santonian compressional episode. The last period of activity, from late Maastrichtian to Eocene, is characterized by subsidence, generated as an isostatic response to the Early Cretaceous crustal thinning and post-rift thermal relaxation of the lithosphere, expressed by Tertiary E–W extension.

Selenium and training effects on the glutathione system and aerobic performance.

Abstract: Changes in blood glutathione antioxidant system in response to exercise and training, and aerobic performance, were investigated. Selenium (Se) supplementation effects on these changes were evaluated. The study was double blind. Both groups selenium (Sel, N = 12) and placebo (Pla, N = 12), followed a 10-wk endurance training program, with a prolonged exhaustive exercise bout performed (Cap Max), before (Pre) and after (Post) training. Blood was sampled before (Bef) and after (Aft) Cap Max. The oxidation of blood glutathione after Cap Max exercise showed a reactive oxygen species production. Training developed maximal aerobic power and capacity, significantly increased (P < 0.001) plasma and erythrocyte glutathione peroxidase (GPx) activity, and decreased (P < 0.001) erythrocyte glutathione reductase activity. The Se supplementation caused an increase in the basal plasma GPx level (P < 0.05). There was also a correlation (r = 0.66, P < 0.05) between the variation in VO2max and that of erythrocyte GPx only in supplemented subjects. Our results confirm that blood glutathione remains a sensitive marker of oxidative stress induced by exhausting submaximal exercise and that the antioxidant potential of GPx can be developed by endurance training. Se supplementation at the dose used had no effect on physical performance.

Dynamics of rotating vortices in the Beeler-Reuter model of cardiac tissue

Abstract: Cardiac muscle is a highly nonlinear active medium which may undergo rotating vortices of electrical activity. We have studied vortex dynamics using a detailed mathematical model of cardiac muscle based on the Beeler-Reuter equations. Specifically, we have investigated the dependence of vortex dynamics on parameters of the excitable cardiac cell membrane in a homogeneous isotropic medium. The results demonstrate that there is a transition from the vortex with circular core that is typical of most excitable media, including the Belousov-Zhabotinsky reaction, to a vortex with linear core that has been observed in heart muscle during so-called reentrant arrhythmias. The transition is not direct but goes through the well-known sequence of nonstationary quasiperiodic rotating vortices. In the parameter space there are domains of different types of vortex dynamics. Such domains include regions where: (1) vortices can not be generated, (2) vortices occur readily, and (3) vortices arise but have a short lifetime. The results provide testable predictions about dynamics associated with initiation, maintenance and termination of cardiac arrhythmias.

An improved 45Ca protocol for investigating physiological mechanisms in coral calcification

Abstract: A sensitive experimental protocol using cloned corals (hereafter “microcolonies”) of the branching scleractinian coral Stylophora pistillata and 45Ca has been developed to enable reproducible measurements of physiological and biochemical mechanisms involved in calcium transport and compartmentalization during coral calcification. Cloned S. pistillata microcolonies were propagated in the laboratory from small fragments of parent colonies collected in 1990 in the Gulf of Aqaba, Jordan. Cloned microcolonies have several intrinsic properties that help to reduce unwanted biological variability: (1) same genotype; (2) similar sizes and shapes; and (3) absence of macroscopic boring organisms. Errors specifically associated with long-standing problems to do with isotopic exchange were further reduced by producing microcolonies with no skeletal surfaces exposed to the radioisotope-labelled incubation medium. The value of the technique resides principally in its superior ability to elucidate transportation pathways and processes and not in its ability to quantitatively estimate calcium deposition by corals in nature. We describe here a rapidly exchangeable calcium pool in which up to 90% of the radioactive label taken up during incubations is located. This pool (72.9±1.4 nmol Ca mg-1 protein) is presumably located within the coelenteric cavity as suggested by the following: (1) it has 4-min half-time saturation kinetics; (2) the accumulation of calcium is linearly correlated with the calcium concentration of sea-water; and (3) its insensitivity to metabolic and ion transport inhibitors indicate that membranes do not isolate this compartment. Washout of this large extracellular pool greatly improved estimates of calcium deposition as evidenced by 10 to 40% reduction in coefficients of variation when compared with previous 45Ca2+ methods described in the literature. Comparisons of calcification measurements simultaneously carried out using the alkalinity anomaly technique and the 45Ca protocol described here show that the correlation coefficient of both techniques is close to 1. Unlike previous reports, our 45Ca2+-derived measurements are slightly lower than those computed from the alkalinity depletion technique.

Finite time blow-up in some models of chemotaxis

Abstract: We consider a class of models of chemotactic bacterial populations, introduced by Keller-Segel. For those models, we investigate the possibility of chemotactic collapse, in other words, the possibility that in finite time the population of predators aggregates to form a delta-function. To study this phenomenon, we construct self-similar solutions, which may or may not blow-up (in finite time), depending on the relative strength of three mechanisms in competition: (i) the chemotactic attraction of bacteria towards regions of high concentration in substrate (ii) the rate of consumption of the substrate by the bacteria and (iii) (possibly) the diffusion of bacteria. The solutions we construct are radially symmetric, and therefore have no relation with the classical traveling wave solutions. Our scaling can be justified by a dimensional analysis. We give some evidence of numerical stability.

Measuring astronomical seeing: the da/iac dimm

Abstract: Accurate, absolute and reproducible measurements are the expected qualities of any instrument. A Differential Image Motion Monitor (DIMM) is presented which assesses astronomical seeing with those requirements. It has been designed also to be reliable, simple, trasportable, and to be easy to set up, operate and maintain. Its accuracy has been studied, both from theoretical and experimental points of view, mainly with respect to CCD sampling, photon noise and threshold influence on centroid determination. The DA/IAC DIMM has been cross-calibrated with the existing ESO DIMM. It monitors the seeing with a temporal resolution better than half a minute. This type of instrument is essential for testing new and already existing sites and to ascertain that the surroundings of telescopes do not generate additional turbulence. It is also indispensible to optimize astronomical instrument selection in "flexible scheduling.".

Effects of copper on gill structure and transport function in the rainbow trout, Oncorhynchus mykiss.

Abstract: Effects of copper were studied in freshwater adapted rainbow trout using the perfused head preparation. In its monovalent chemical form, copper at millimolar concentrations had no significant effects on Na+ and water transport. By contrast, the divalent form produced an increase in gill perfusion pressure, a significant reduction in Na+ influx and water fluxes and reversed Na+ net flux. Observations by light microscopy showed important cell damage (oedema, mucus production, cellular desquamation). By electron microscopy there was smoothing of apical membranes, swelling of the tubular system and destruction of mitochondria. The Na, K-ATPase activity was totally suppressed and residual ATPase activity largely inhibited by 1 mM Cu2+. There was inhibition of the Na,K-ATPase activity with an IC50 of approximately 10 microM of total copper (free and bound cupric fractions). As active sodium transport is located on the secondary lamellae, our results show that its entry mechanism is inhibited at that level by cupric ions only. Results are discussed in relation to hydromineral balance of the trout.

Pro-melanin concentrating hormone messenger ribonucleic acid and peptides expression in peripheral tissues of the rat.

Abstract: Melanin-concentrating hormone (MCH) is a cyclic peptide which is predominantly synthetized in the hypothalamus of fish and mammalian brains. In the present paper we examined the expression of MCH mRNA

Fatty acids of the scleractinian coral Galaxea fascicularis: effect of light and feeding

Abstract: In order to investigate nutritional interactions in the symbiotic scleractinian coral-zooxanthella association, fatty acids of the coral Galaxea fascicularis were analysed in two groups of cultured microcolonies. The first group was fed with Artemia sp., while the second group was starved. After an initial 1-month period during which both groups were subjected to the same “normal” light conditions (constant irradiance of 125 μE·cm-2·s-1 and 14:10 h light:dark), a light cap was used to cover the aquarium and keep all the microcolonies in permanent darkness for 20 days. During the light phase of the experiment it was shown that the nutritional status lead to large variations in the percentage of saturated, mono-unsaturated and polyunsaturated fatty acids. Palmitic acid (C16:0) was the most abundant fatty acid in both groups. Important differences between fed and starved microcolonies occurred during the dark phase of the experiment. In the fed group the dark phase was characterized by a significant increase in polyunsaturated fatty acids. Particularly arachidonic acid (C20:4 n-6) became the most important fatty acid followed by docosatrienoic acid (C22:3 n-3). A slight increase in these two fatty acids was also found in the starved group but the bulk of polyunsaturated fatty acids was significantly decreased. In this group, palmitic acid remained the most important fatty acid while an increased concentration of cis-vaccenic acid (C18:1 n-7) was found at the end of the experiment. The increased concentration of cis-vaccenic acid might indicate that bacteria serve as a source of energy. While the number of zooxanthellae per milligram of protein and the chlorophyll a to protein ratio strongly decreased in the starved microcolonies immediately after the beginning of the dark period, the decrease in fed microcolonies was delayed for about 10 days. Furthermore, after 20 days of dark incubation the chlorophyll a to protein ratio was the same as measured at the beginning of the dark period. This suggests that in the dark the metabolic requirements of the zooxanthellae are in part met from the animal host through a heterotrophic mode of nutrition.

Dual-polarization slot-coupled printed antennas fed by stripline

Abstract: This article presents recent techniques in the field of dual-polarization printed antennas for designing shielded radiating structures with high-quality performances in terms of cross-polarization level and input-port isolation. The use of gridded patches provides a natural solution to filtering surface currents and is of key importance in limiting inter-element coupling in arrays. Experimental results obtained on various designs are presented. >