Showing papers by "University of Nice Sophia Antipolis published in 1988"

Deccan flood basalts and the Cretaceous/Tertiary boundary

Abstract: Courtillot et al.1 have presented palaeomagnetic, palaeontological and K–Ar data for the Deccan flood basalts which suggest that > 106 km3 of basalt may have been erupted in < 1 Myr, mostly in a reversed magnetic chron. This chron is argued to be 29R, the one which contains the Cretaceous/Tertiary boundary. Here we aim to test the hypothesis1–5 that the Deccan basalts could be responsible for events observed at the Cretaceous/Tertiary boundary by studying the 40Ar/39Ar ages of samples with a wide geographic distribution. Many samples have been altered too extensively to yield plateau ages, but we have made five successful determinations. Considered with earlier6 and concurrent7 results, our data confirm that the bulk of the Deccan eruptions occurred in a short time, between 65 and 69 Myr, probably coincident with the Cretaceous/Tertiary boundary.

Calcium channels: molecular pharmacology, structure and regulation.

Abstract: It is well recognized that calcium (Ca) is an important regulatory element for many cellular processes. In most eukaryotic cells a diverse array of Ca transporting systems functions to maintain the steep concentration gradient between extracellular Ca, estimated to be in the millimolar range, and intracellular Ca, which can vary between 0.1-10 /xM, depending on the state of the cell. Specific and distinct pathways exist by which Ca enters and exits cells. Several different types of Ca transport systems serve to maintain the low concentration of intracellular Ca, by transporting Ca either out of the cell or into intracellular storage sites (for review, see Carafoli, 1987). These exi t pathways have been extensively studied, and until recently our knowledge of these systems was far greater than for pathways involved in Ca entry . The major entry pathway for Ca in many cell types is via plasma membrane Ca channels. Considerable progress has now been made in elucidating the properties of certain Ca channels. The purpose of this review is to summarize our current understanding of the molecular properties of Ca channels; particular emphasis will be given to the pharmacological and biochemical characterization of Ca channels, as well as the mechanisms by which they are regulated by neurotransmitter-mediated processes.

Serotonin stimulates DNA synthesis in fibroblasts acting through 5-HT1B receptors coupled to a Gi-protein.

Abstract: Growth factors can be divided into two classes which act through distinct signal transduction pathways. One class including epidermal growth factor, platelet derived growth factor and fibroblast growth factor activates receptor tyrosine kinases, and the second class, including thrombin, bombesin, bradykinin and vasopressin activates a phosphoinositide-specific phospholipase C through GTP-binding proteins which can be inactivated by pertussis toxin. In Chinese hamster lung fibroblasts, thrombin-induced mitogenicity seems to correlate well with phospholipase C activation and both events are sensitive to pertussis toxin. Thrombin, like the other mitogens in this class, simultaneously inhibits adenylate cyclase. This involves an inhibitory G protein (Gi), a well established pertussis toxin substrate. The relative contributions of the two signalling pathways to mitogenicity has not been evaluated so far. We report here that the neurotransmitter serotonin (5-hydroxytryptamine), a contracting agent and mitogen for smooth muscle cells, activates phospholipase C, inhibits adenylate cyclase and stimulates DNA synthesis in fibroblasts. These events are sensitive to pertussis toxin. We show that the mitogenicity of 5-hydroxytryptamine can be uncoupled from phospholipase C activation that is mediated by 5-HT2 receptors, but correlates perfectly with inhibition of adenylate cyclase through 5-HT1B receptor. We propose that inhibition of adenylate cyclase or activation of an undefined effector system by Gi is important in 5-hydroxytryptamine induced DNA synthesis and contributes to the strong mitogenicity of the other members of this family of growth factors.

Dynamic simulation of hydrodynamically interacting suspensions

Abstract: A general method for computing the hydrodynamic interactions among an infinite suspension of particles, under the condition of vanishingly small particle Reynolds number, is presented. The method follows the procedure developed by O'Brien (1979) for constructing absolutely convergent expressions for particle interactions. For use in dynamic simulation, the convergence of these expressions is accelerated by application of the Ewald summation technique. The resulting hydrodynamic mobility and/or resistance matrices correctly include all far-field non-convergent interactions. Near-field lubrication interactions are incorporated into the resistance matrix using the technique developed by Durlofsky, Brady & Bossis (1987). The method is rigorous, accurate and computationally efficient, and forms the basis of the Stokesian-dynamics simulation method. The method is completely general and allows such diverse suspension problems as self-diffusion, sedimentation, rheology and flow in porous media to be treated within the same formulation for any microstructural arrangement of particles. The accuracy of the Stokesian-dynamics method is illustrated by comparing with the known exact results for spatially periodic suspensions.

Outer scale of turbulence appropriate to modeling refractive-index structure profiles.

Abstract: The outer scale of turbulence L0 has been calculated from values of the refractive-index structure coefficient CN2 obtained from spatio-angular correlation measurements of stellar scintillation. It is found that L0 ≤ 5 m for a large range of observations in France, U.S.A., and Chile and that its dependence on altitude Z follows the same general form at all these sites. The prediction of CN2(Z) profiles is shown to be feasible utilizing standard meteorological radiosonde data and this L0(Z) curve. A simple model based on dimensional analysis and a more complicated stochastic model are compared, but the latter appears to have no advantage.

Deregulation of hamster fibroblast proliferation by mutated ras oncogenes is not mediated by constitutive activation of phosphoinositide-specific phospholipase C.

Abstract: Stable expression of high levels of activated forms of Haras (T24) or v-Ki-ras by transfection of Chinese hamster lung fibroblasts (CCL39) yielded cells highly tumorigenic in nude mice. Two classes of transformed cells were distinguished, one with moderate p21 expression (10-fold increased) had retained growth factor dependency, the second with higher level of p21 (greater than 50-fold) appeared autonomous for growth. Neither class of transformants expressing Ki-ras or Ha-ras displayed a significant basal activity of polyphosphoinositide-specific phospholipase C, measured either in serum-starved cells or during exponential growth in the presence of growth factors of the tyrosine kinase family (EGF, FGF, insulin). In the growth-factor-dependent class of T24-Ha-ras-transfected cells (clone 39THaB), phospholipase C could be stimulated normally by serum, thrombin and AlF-4. In the more growth autonomous class (clones 39THaC and 39Ki9), release of inositol phosphates after stimulation with thrombin or serum was drastically reduced. This desensitization, apparently at the receptor level since the response to AlF-4 persisted, is, however, not specific to ras expression. We observed it to the same degree in polyoma virus-transformed CCL39 cells. Finally, expression of mutated forms of p21 ras did not abrogate the sensitivity of phospholipase C activation to pertussis toxin. We conclude that the transforming potential of activated forms of p21ras does not result from persistent activation of phospholipase C and that ras GTP-binding proteins cannot substitute for Gp.

TGF‐β inhibits growth factor‐induced DNA synthesis in hamster fibroblasts without affecting the early mitogenic events

Abstract: Transforming growth factor beta (TGF-beta) was found to inhibit (IC50 = 0.1 ng/ml) alpha-thrombin or FGF-induced mitogenicity in G0-arrested Chinese hamster lung fibroblasts. Growth factor-stimulated cells became rapidly insensitive to TGF-beta addition during their progression through G0/G1 suggesting that an early step of the mitogenic response was the target of TGF-beta action. Surprisingly, none of the well characterized early mitogenic events commonly triggered by growth factors was found to be affected by TGF-beta addition. These responses included: phosphoinositide breakdown, activation of protein kinase C as determined by EGF receptor down-modulation, subsequent rises in pHi, c-fos, and c-myc mRNA levels, ribosomal protein S6 phosphorylation, the increase in RNA and protein synthesis, induction of ornithine decarboxylase. Only the induction of thymidine kinase, a marker of entry in the S phase, was found to be repressed by TGF-beta, with maximal inhibition when TGF-beta was added early in G1. These results indicate that the inhibitory action of TGF-beta does not affect the growth factors signalling pathways but touches an early event different from those so far analyzed.

Thrombin exerts a dual effect on stimulated adenylate cyclase in hamster fibroblasts, an inhibition via a GTP-binding protein and a potentiation via activation of protein kinase C

Abstract: Previous studies in Chinese-hamster fibroblasts (CCL39 line) indicate that an important signalling pathway involved in thrombin9s mitogenicity is the activation of a phosphoinositide-specific phospholipase C, mediated by a pertussis-toxin-sensitive GTP-binding protein (Gp). The present studies examine the effects of thrombin on the adenylate cyclase system and the interactions between the two signal transduction pathways. We report that thrombin exerts two opposite effects on cyclic AMP accumulation stimulated by cholera toxin, forskolin or prostaglandin E1. (1) Low thrombin concentrations (below 0.1 nM) decrease cyclic AMP formation. A similar inhibition is induced by A1F4-, and both thrombin- and A1F4- –induced inhibitions are abolished by pertussis toxin. (2) Increasing thrombin concentration from 0.1 to 10 nM results in a progressive suppression of adenylate cyclase inhibition and in a marked enhancement of cyclic AMP formation in pertussis-toxin-treated cells. A similar stimulation is induced by an active phorbol ester, and thrombin-induced potentiation of adenylate cyclase is suppressed by down-regulation of protein kinase C. Therefore, we conclude that (1) the inhibitory effect of thrombin on adenylate cyclase is the direct consequence of the activation of a pertussis-toxin-sensitive inhibitory GTP-binding protein (Gi) possibly identical with Gp, and (2) the potentiating effect of thrombin on cyclic AMP formation is due to stimulation of protein kinase C, as an indirect consequence of Gp activation. Our results suggest that the target of protein kinase C is an element of the adenylate cyclase-stimulatory GTP-binding protein (Gs) complex. At low thrombin concentrations, activation of phospholipase C is greatly attenuated by increased cyclic AMP, leading to predominance of the Gi-mediated inhibition.

Experimental Characterization of Shil'nikov Chaos by Statistics of Return Times

Abstract: The dynamic behavior of a single-mode CO2 laser with feedback is characterized by global features in the phase space, related to the presence of three coexisting unstable fixed points. As a control parameter is monotonically increased, one can observe transitions from a Hopf bifurcation to a local chaos and eventually to regular spiking and Shil’nikov chaos. Furthermore, one can find evidence of competition among these different kinds of instability.1 The phase-space trajectories are affected differently by each of the three unstable points, and by adjustment of the control parameters they can be characterized by the dominant role of only one, or a pair of them.

Design, synthesis and evaluation of fluorocarbons and surfactants for in vivo applications. New perfluoroalkylated polyhydroxylated surfactants.

Abstract: The progress achieved since the advent of Fluosol-DA is summarized in this paper, with special focus on the synthesis and evaluation of more adequate, reliable, industrially feasible fluorocarbons, structure/property relationships—molecular weight being recognized as the pre-eminent determining factor of both the fluorocarbon's excretion rate and the emulsion's stability -, the preparation of significantly more concentrated, more efficacious emulsions, etc.The key to further progress and better mastery of the emulsions' characteristics, especially in relation to increased shelf-life, prolonged i.v. persistence, and versatility, now lies in the development of new surfactants, better adapted to this objective. New families of well defined, monodisperse perfluoroalkylated polyhydroxylated surfactants derived from sugars and related compounds have been synthesized and fully characterized. Preliminary evaluation of their surface-active properties, emulsion stabilizing capacity and biocompatibility are reported.

Quasi-Genericity of Bifurcations to High Dimensional Invariant Tori for Maps

Abstract: We consider a family of maps in a Banach spaceE near the situation when the derivative at the fixed point has two pairs of complex eigenvalues lying on the unit circle, the other part of the spectrum being strictly inside the unit disc. We focus our attention on the region of the parameter space where the truncated normal form of the maps shows a bifurcation of a family of invariantT 1-circles into a family of invariantT 2-tori. We show that this problem needs a 3 dimensional parameter unfolding and that, for the complete maps, bifurcation occurs at points γω,Ω, where ω is the rotation number on the non-normally hyperbolicT 1-circle, ande ±2iπΩ are the eigenvalues of the constant matrix conjugated to the non-contracting part of the linearization on the normal fiber bundle overT 1. Making some non-resonance and diophantine assumptions on (ω, Ω) leading to a positive measure Cantor set inT 2, we show that in paraboloidal regions of the 3 dim. parameter space we have “clean” bifurcations as for the truncated normal form. The complement of these regions forms a set of bubbles such as the ones obtained by Chenciner in [Chen] for a codimension 2 problem for maps in ℝ2. The main tool here is a generalization for a matrix function onT 1, close to a constant, of the quasi-conjugacy to a constant, modulo a minimum of additional parameters (“moved” quasi-conjugacy). For the infinite dimensional case we use aC ∞ decoupling result on the angular dependent linear parts into a contraction, still angular dependent, and another part quasi-conjugated to a constant matrix. This type of analysis applies for a wide range of problems, where truncated normal forms of the maps give bifurcations fromT n toT n+1 tori, and this needs a (n+1)-dimensional parameter unfolding.

Effect of mutations affecting Na+: H+ antiport activity on tumorigenic potential of hamster lung fibroblasts.

Abstract: Mutants unable to regulate intracellular pH through the Na+:H+ antiport system were found to evolve tumors less frequently than wild-type CCL39 hamster lung fibroblasts, after transplantation in athymic nude mice. When rare tumors arose, they comprised cells which were transformed in vitro, but which upon retransplantation grew at a lower rate than tumor cells originating from CCL39 cells. Both parental and mutant cells became transformed after transfection of the activated Harvey ras oncogene, but transfectants derived from the mutants had a weaker tumorigenic potential. These results suggest that transformed characteristics can be acquired independently from the Na+:H+ antiporter. However, the presence of this system provides a selective growth advantage when cells are confronted with natural environments, as it occurs during the expansion of tumors in a host.

Transmembrane Signalling Pathways Initiating Cell Growth in Fibroblasts

Abstract: The mechanisms of growth factor action were studied in a fibroblastic cell line capable of reversible growth arrest in G0-G1. This cell line, derived from Chinese hamster lung, can be stimulated to divide by a limited set of purified growth factors, including EGF, FGF, PDGF, alpha-thrombin (THR), serotonin (5-HT) and insulin. THR and 5-HT stimulate, via a G-protein (Gp), a polyphosphoinositide-specific phospholipase C (PtdIns(4,5)P2-PLC). In contrast, the mitogens EGF, FGF, PDGF, and insulin do not stimulate PtdIns(4,5)P2-PLC unless this pathway has been preactivated by THR or AlF-4. Finally, from the specific inhibitory action of pertussis toxin on THR- and 5-HT-induced DNA synthesis, and from the exploitation of the 5-HT pharmacological tools, we conclude that: (i) there are at least two distinct G-proteins involved in signalling growth: Gp, coupling receptors to PtdIns(4,5)P2-PLC, and Gi, coupling receptors negatively to adenylyl cyclase and probably to other unknown effector(s); (ii) activation of receptor-tyrosine kinases provides an alternate growth factor signalling pathway, independent of Gp- and Gi-mediated actions; and (iii) tyrosine kinases positively 'cross-communicate' with the inositol-lipid pathway (phosphorylation of Gp, PLC, PtdIns kinases...?).

Arginine vasotocin binding to isolated branchial cells of the eel: effect of salinity.

Abstract: Binding of 125I-labelled arginine vasotocin (AVT) was studied in isolated intact gill cells obtained from eels (Anguilla anguilla) adapted to fresh water (FW) or to sea water (SW). Experiments carried out at 20 degrees C showed maximum and stable binding beyond 10 min of incubation. Specific binding, determined by using labelled peptide in the presence or absence of an excess of unlabelled hormone, represented 30-50% of total and was reversible, with a half-time of less than 5 min. Scatchard plot analysis revealed the presence of a single population of saturable, high-affinity sites. Maximum binding capacity (Bmax: fmol AVT/10(6) cells) and dissociation constant (Kd: nM) were respectively 5.16 and 3.21 in FW and 24.25 and 1.05 in SW. Analysis of chloride cell number and size in gills and of binding characteristics of AVT revealed parallel changes with external salinity. These results are taken as evidence for the direct intervention of neurohypophysial peptides on the gill epithelium of teleost fishes.

Preparation and application of highly concentrated perfluoroctylbromide fluorocarbon emulsions

Abstract: The potential benefits of a stable high concentration fluorocarbon emulsion are realized in all biomedical applications. Our initial studies with 25X w/v perfluoroctylbromide (PFOB) indicated an emulsion with hi h PFOB concentration was desirable to decrease volume loading. formulation and emulsification techniques. Biocompatibility of emulsions was evaluated on the basis of several criteria; emulsion stability, animal tolerance, and tissue retention. Stability was assessed by monitoring the particle size, pH, osmolarity, and viscosity of emulsions pre and post sterilization at 121'C for 8 minutes and after accelerated shelf life studies. Animal tolerance was evaluated by LD50 studies in mice, subacute toxicity and exchange transfusion studies in rats with subsequent histopathological examination of specific organs (ie: lung, liver, spleen). ies and by tissue analysis utilizing several analytical techniques, including gas chromatography, neutron activation and computerized axial tomography (CT). a sterile, room temperature stable 100% w/v emulsion could be manufactured which had excellent biocompatibility. about 42.5gIkg and the total body Tt for 1.5g/kg is about 3.7 days. The retention studies in animals show a strong correlation between neutron activation analysis, which is invasive, and CT analysis which is non-invasive. It is, therefore, possible to measure pharmacokinetics in humans by non-invasive CT analysis. Different concentration emulsions were prepared with various

The secondary structure of the toxin ATX Ia from Anemonia sulcata in aqueous solution determined on the basis of complete sequence-specific 1H-NMR assignments.

Abstract: The toxin preparations ATX I, ATX Ia and ATX Ib from Anemonia sulcata were investigated by proton nuclear magnetic resonance (NMR). High-resolution phase-sensitive two-dimensional NMR experiments were used to monitor the separation by high-performance liquid chromatography of the two isoproteins ATX Ia and ATX Ib. For ATX Ia complete sequence-specific resonance assignments were obtained and the secondary structure was determined. To obtain the NMR assignments we used a variant of the sequential assignment technique which relied extensively on cross-peak fine-structure analysis in phase-sensitive spectra, using spectrum simulations based on density matrix calculations with the program SPHINX. These procedures, which resulted in extensive amino acid spin system identifications prior to the sequential assignments, should be generally applicable for small proteins with relatively narrow 1H-NMR lines. The secondary structure of ATX I includes a beta sheet consisting of four strands. No evidence was found for the presence of regular helical segments. The four beta strands are connected by two extended loops and a tight turn, for which further characterization has to await the complete determination of the three-dimensional structure.