Showing papers by "University of Nice Sophia Antipolis published in 1989"

A new analysis of ammonia and sodium transport through the gills of the freshwater rainbow trout (Salmo gairdneri)

Abstract: Summary The mechanism of ammonia excretion and sodium absorption was re-examined in trout using the isolated-perfused head preparation. Preliminary experiments in which ammonia concentration was increased on the blood side (internal) showed that ammonia and sodium transport was uncoupled. For ammonia excretion, our results showed that gill tissue endogenously produces ammonia. A correlation was demonstrated between ammonia excretion and the internal-external ammonia gradient. We conclude that diffusion in the form of NH3 was responsible for ammonia efflux and we were therefore able to estimate its diffusion coefficient (DNH3 = l-55xlO~ 6 cm 2 s~ 1 ) and permeability coefficient (6xlO~ 3 cms~ 1 ). This ammonia diffusion was shown to be modified according to the external proton availability. For sodium absorption, significant changes were caused by indirect modifications of intracellular pH brought about by addition of acetazolamide inside or ammonia outside or by acidification of the internal or external medium. The relationship between sodium and proton transport was further confirmed by the action of the drug amiloride and the measurement of H + excretion. A possible model representing sodium, proton and ammonia transport through the gill epithelium is proposed.

Undercrusting by serpentinite beneath rifted margins

Abstract: THE west Galicia passive margin (Spain) is bounded by a continuous belt of serpentinized peridotite. Here we present the results of petrological studies of the peridotite, 39Ar–40Ar dating of high-temperature ductile shearing of a dioritic dyke crossing the peridotite and regional seismic stratigraphy which demonstrate that the uplift, ductile shearing and pervasive serpentinization of mantle rocks occurred at early Cretaceous time, during the rifting stage of the margin. The serpentinite layer resting on fresh peridotite is probably several kilometres thick. At present seismic data and gravity data cannot distinguish serpentinite from crustal material, but our results from the Galicia margin indicate that the seismic crust beneath rifted margin may include mantle material transformed into serpentinite by syn-rift hydrothermal activity. In some cases, this undercrusting process might explain the young age and mobility of the Moho beneath stretched continental basement.

Low‐Temperature Route to Lead Magnesium Niobate

Abstract: Lead magnesium niobate, Pb(Mg/sub 1/3/Nb/sub 2/3/)O/sub 3/ (PMN), was prepared by a sol-gel technique using alkoxide precursors. The hydrolysis-condensation mechanism leads to a translucent gel which is dried under hypercritical conditions to avoid collapse of the porous texture. After drying, the aerogel exhibits a B-deficient pyrochlore structure which progressively inserts magnesium oxide when the temperature increases. Near 700{sup 0}C, this pyrochlore phase completely transforms into the PMN-perovskite phase. Above 1000{sup 0}C, the loss of lead oxide leads to the destabilization of the PMN-perovskite with formation of an A-deficient pyrochlore phase.

Neurotensin stimulates inositol trisphosphate-mediated calcium mobilization but not protein kinase C activation in HT29 cells. Involvement of a G-protein.

Abstract: It has previously been shown that neurotensin binds to high-affinity receptors in the adenocarcinoma HT29 cell line, and that receptor occupancy leads to inositol phosphate formation. The present study was designed to investigate further the effects of neurotensin on calcium mobilization and protein kinase C (PKC) activation in HT29 cells, and to assess the role of GTP-binding proteins (G-proteins) in the neurotensin response. Direct measurements of cytosolic Ca2+ variations using the fluorescent indicator quin 2 showed that neurotensin (0.1-1 microM) elicited Ca2+ transients in HT29 cells. These transients occurred after the neurotensin-stimulated formation of Ins(1,4,5)P3, as measured by means of a specific radioreceptor assay. In addition, the peptide induced a decrease in the 45Ca2+ content of cells previously equilibrated with this isotope. The peptide effect was rapid, long-lasting and concentration-dependent, with an EC50 of 2 nM. Phorbol 12-myristate 13-acetate (PMA) inhibited by 50% the neurotensin effects on both intracellular Ca2+ and inositol phosphate levels. The inhibition by PMA was abolished in PKC-depleted cells. Pertussis toxin had no effect on either the Ca2+ or inositol phosphate responses to neurotensin. Epidermal growth factor (EGF) receptors which are present in HT29 cells have been shown to be down-regulated through phosphorylation by PKC in a variety of systems. Here, PMA markedly (70-80%) inhibited EGF binding to HT29 cells. Scatchard analysis revealed that PMA abolished the high-affinity component of EGF binding, an effect that was totally reversed in PKC-depleted cells. In contrast, neurotensin slightly (10-20%) inhibited EGF binding to HT29 cells, and its effect was only partly reversed by PKC depletion. Neurotensin had no detectable effect on sn-1,2-diacylglycerol levels in HT29 cells, as measured by a specific and sensitive enzymic assay. In membranes prepared from HT29 cells, monoiodo[125I-Tyr3]neurotensin bound to a single population of receptors with a dissociation constant of 0.27 nM. Sodium and GTP inhibited neurotensin binding in a concentration-dependent manner. Maximal inhibition reached 80% with Na+ and 35% with GTP.IC50 values were 20 mM and 0.2 microM for Na+ and GTP respectively. Li+ and K+ were less effective than Na+ and the effects of GTP were shared by GDP and guanosine-5'-[beta gamma- imido]triphosphate but not by ATP. Scatchard analysis of binding data indicated that Na+ and GTP converted the high-affinity neurotensin-binding sites into lower affinity binding sites. The properties of the effects of Na+ and GTP on neurotensin-receptor interactions are characteristic of those receptors which interact with G-proteins.(ABSTRACT TRUNCATED AT 400 WORDS)

A Chebyshev collocation method for the Navier–Stokes equations with application to double‐diffusive convection

Abstract: Presentation de la methode de collocation de Tchebyshev pour resoudre les equations bidimensionnelles de Navier-Stokes en variables vorticite-fonction de courant. La discretisation en temps est obtenue a travers une classe de schemas de differences finies semi-implicites

Heteroclinic cycles involving periodic solutions in mode interactions with O(2) symmetry

Abstract: In this paper we show that in O(2) symmetric systems, structurally stable, asymptoticallystable, heteroclinic cycles can be found which connect periodic solutions with steady states and periodic solutions with periodic solutions. These cycles are found in the third-order truncated normal forms of specific codimension two steady-state/Hopf and Hopf/Hopf mode interactions.We find these cycles using group-theoretic techniques; in particular, we look for certainpatterns in the lattice of isotropy subgroups. Once the pattern has been identified, the heteroclinic cycle can be constructed by decomposing the vector field on fixed-point subspaces into phase/amplitude equations (it is here that we use the assumption of normal form). The final proof of existence (and stability) relies on explicit calculations showing that certain eigenvalue restrictions can be satisfied.

Laser oscillation of single-mode channel waveguide in Nd:MgO:LiNbO3

Abstract: Laser oscillation in an Nd:MgO:LiNbO3 single-mode channel waveguide has been demonstrated. Under IR dye laser pumping, a threshold of 1.5 mW and a slope efficiency of 14%; were achieved. Laser oscillation has also been observed with diode pumping.

Parity-breaking transitions of modulated patterns in hydrodynamic systems.

Abstract: A model for subcritical parity-breaking bifurcation of a periodic pattern is introduced. It is found that nucleated regions of the new asymmetric state propagate with a well-defined velocity in a direction determined by their parity, and leave in their wake a pattern with an altered wavelength. Successive passage of these ``parity bubbles'' enables the system to relax to a selected wavelength. The possible relevance of these findings to recent observations of ``solitary modes'' in directional solidification and hydrodynamic experiments is discussed.

Late Cretaceous deep-water agglutinated foraminiferal assemblages from the North Atlantic and its marginal seas

Abstract: The stratigraphic and biogeographic distribution of more than 170 species of deep-water agglutinated benthic foraminifers (DWAF) from the North Atlantic and adjacent marginal seas has been compared with paleoenvironmental data (e.g. paleobathymetry, oxygenation of the bottom waters, amount of terrigenous input and substrate disturbance). Six general types of assemblages, in which deep water agglutinated taxa occur, are defined from the Turonian to Maastrichtian times: 1. High latitude slope assemblages 2. Low to mid latitude slope assemblages 3. Flysch-type assemblages 4. Deep water limestone assemblages (»Scaglia«-type) 5. Abyssal mixed calcareous-agglutinated assemblages 6. Abyssal purely agglutinated assemblages Latitudinal differences in faunal composition are observed, the most important of which is the lack or extreme paucity of calcareous forms in high latitude assemblages. East-to-west differences appear to be of comparatively minor importance. Most DWAF species occur in all studied regions and are thus considered as cosmopolitan. Biostratigraphic turnovers in the taxonomic content of assemblages are observed in the lowermost Turonian, mid- Campanian and in the upper Maastrichtian to lowermost Paleocene. These datum levels correspond to inter-regional and time-constant paleooceanographic events, which probably also affected the deep-water benthic biota. This allows us to use deep-water agglutinated foraminifers for biostratigraphy in the North Atlantic sequences deposited below CCD and to geographically extend the currently used zonal schemes which have been established in the Carpathian and Alpine areas.

Cyclic Changes along Posidonia oceanica Rhizomes (Lepidochronology): Present State and Perspectives

Abstract: . Leaf sheaths in the seagrass Posidonia oceanica can persist for millcnia and they show, according to their insertion rank, cyclic variations in parameters such as thickness and tissue structure. The principal cycles are always annual, but pluriannual cycles can also be detected. Annual cycles may be changed by environmental parameters such as light, temperature, or water movement. In a fashion analogous to the study of annual tree rings (dendrochronology), the study of cyclic changes in Posidonia oceanica sheaths is thus a technique allowing the study of past yearly changes in the near-shore environment.

Synergistic stabilization of perfluorocarbon-pluronic F-68 emulsion by perfluoroalkylated polyhydroxylated surfactants

Abstract: One of the most serious limitations of the first generation of fluorocarbon emulsions destined to serve as injectable oxygen carriers (blood substitutes) is their insufficient, stability. Considerable stabilization of such emulsions has now been achieved by using a combination of Pluronic F-68, a polyoxyethylene polyoxypropylene block polymer, and of a perfluoroalkylated polyhydroxylated surfactant (PPFS) comprising a C6F13 or C8F17 fluorophilic tail and a hydrophilic head derived from maltose or xylitol. These new surfactants are either soluble in water or dispersible in an aqueous Pluronic F-68 solution. The tensions at the surface of these solutions and dispersions and at their interface with a typical fluorocarbon, F-decalin, are discussed. A strong stabilizing effect on F-decalin emulsions was obtained when small amounts of PPFS were incorporated, the total amount of surfactant used remaining constant. For 20% w/v emulsions, the maximum stabilizing effect was reached when 20–30% of PPFS were present, resulting after one year at 25°C in an up to 10 times smaller increase in particle size than for a reference emulsion prepared with Pluronic F-68 alone. The effect is even stronger with more concentrated 50% w/v emulsions, reaching a stabilizing ratio of 17 after one year for a one-to-one PPFS/Pluronic F-68 combination. None of the PPFS, when taken alone, permitted the preparation of stable emulsions. The characteristic U-shape taken after aging, by the particle size vs PPFS/Pluronic F-68 ratio curves demonstrates a strong synergistic effect of the two surfactants. They also permitted the selection of optimal formulations for the emulsions. The evolution of the particle sizes against time for such formulations was followed for 20% and 75% w/v concentrated F-decalin emulsions at 4°C, 25°C and 50°C. The best emulsion in terms of stability was obtained with the xylitol derivative C8F17CH=CHCH2OCH2(CHOH)4H; most significantly, temperature, from 4 to 50°C, had little or no effect on the aging of this emulsion over a two month period.

Coupling growth arrest and adipocyte differentiation.

Abstract: The complete differentiation program of preadipose cells can be divided into early and late events. The expression of early markers takes place at growth arrest (G1/S boundary), whereas that of late markers, leading to terminal differentiation, takes place after a limited number of mitoses of early marker-containing cells. Only terminal differentiation requires the presence of growth hormone and triiodothyronine and results in the formation of triacylglycerol-filled, nondividing cells. The events of adipose cell differentiation which take place in vitro allow a better understanding of the development of adipose tissue in vivo.

Peptidasic activities associated with acetylcholinesterase are due to contaminating enzymes.

Abstract: The esterasic and peptidasic activities of two different sources of acetylcholinesterase purified from electric eel were examined. Hydrolyses of leucine-enkephalin and neurotensin indicated that both sources exhibited exopepti-dasic and tryptic-like activities. However, the enzyme preparation which appeared 10-fold enriched with regard to the esterasic activity was found to display a 50- and 185-fold lower tryptic-like and exopeptidasic function, respectively. This lack of parallelism in the enrichment of the various activities seemed to indicate that they were not co-purified. Immunoprecipitation experiments performed with monoclonal antibodies directed towards the catalytic subunit of globular or asymmetric forms of electric eel acetylcholinesterase allowed the physical dissociation of esterasic and peptidasic functions and therefore confirmed that the ability of acetylcholinesterase to hydrolyze various neuropeptides was likely due to contaminating peptidases.

Stabilization of a stimulated Brillouin fiber ring laser by strong pump modulation

Abstract: A stable train of compressed Stokes pulses (to ~10 nsec) is obtained in a stimulated Brillouin fiber ring laser (of length L = 83 m) by periodically interrupting the argon-ion cw pump beam with an intraring cavity acousto-optic modulator. Interruption of the pump action, at each round-trip time tr ≃ Ln/c, permits damping of the excited sound waves that accumulate at the entry of the fiber owing to the inertial response of the material, well described by the coherent three-wave stimulated Brillouin scattering model (C3W-SBS equations). Amplification and compression of the backscattered Stokes pulse are limited by nonlinear optical Kerr effect, which is incorporated into the C3W-SBS equations.

Detection of late potentials by means of wavelet transform

Abstract: The wavelet transform, leading to a time-scale analysis, was used as a detection tool for ventricular late potentials. Preliminary results show that the detection is obvious from 16 beats and needs no high amplification or preliminary filtering. The experimental results are validated by averaging and comparing highly amplified filtered signals obtained from both a healthy person and a patient with a ventricular tachycardia diagnosis. >

X-ray microanalysis of calcium containing organelles in resin embedded tissue.

Abstract: The localization of calcium in cell organelles at the electron microscope level is often achieved through cytochemical techniques, and verified by X-ray microanalysis. Various methods have been used to cytochemically detect calcium or calcium-binding sites: calcium loading, calcium substitution by strontium, barium, or even lead, and calcium precipitation by oxalate, phosphate, fluoride, or pyroantimonate. Their results may have heuristic value, particularly in preliminary studies of poorly known cell types. A complementary and more physiological approach is offered by quantitative measurement of the total calcium content of organelles after cryofixation. Resin embedding is less demanding than cryomicrotomy and gives better images: it can be used after cryosubstitution in the presence of oxalic acid. This technique was tested, and applied to several cell types.

Wavelet Transform Analysis of Invariant Measures of Some Dynamical Systems

Abstract: We present the wavelet transform as a mathematical microscope which is well suited for studying the local scaling properties of fractal measures. We apply this technique, recently introduced in signal analysis, to probability measures on self-similar Cantor sets, to the 2∞ cycle of period-doubling and to the golden-mean trajectories on two-tori at the onset of chaos. We emphasize the wide range of application of the wavelet transform which turns out to be a natural tool for characterizing the structural properties of fractal objects arising in a variety of physical situations.

An easy, convenient way of describing the stability of fluorocarbon emulsions

Abstract: A simple and practical way of processing the average particle size data to describe the stability of fluorocarbon emulsions prepared with Pluronic F-68 is reported. It is based on the observation that the volume of the droplets increases linearly with time. Only a short observation period is therefore needed to assess and describe this stability. Our results are qualitatively in accordance with the theories of Lifshits and Slezov or Higuchi and Misra on Ostwald ripening. The strong influence of the molecular weight of the fluorocarbon on the stability of its emulsions also supports the view that molecular diffusion, rather than coalescence, is the main degradation process of fluorocarbon emulsions.

Tissue distribution of a novel neurotensin-degrading metallopeptidase. An immunological approach using monospecific polyclonal antibodies.

Abstract: A monospecific polyclonal antiserum was raised against a recently purified rat brain neurotensin-degrading metallopeptidase. The purified IgG fraction immunoprecipitated the peptidase and inhibited its proteolytic activity. Western blot analyses revealed that the immune fraction recognizes only one protein in rat brain homogenates, and this corresponds closely to the purified enzyme. The IgG displayed a restricted specificity towards the peptidase from murine origin. In the rat, the neurotensin-degrading enzyme was widely distributed throughout peripheral organs with the noticeable exception of the duodenum. In addition, the peptidase was detected in various cell lines or membrane preparations of neural or extraneural origin in which it had been previously characterized by means of biochemical methods. In light of this widespread distribution, the putative role of the peptidase in the metabolism of neuropeptides is discussed.