Publications

2007

• Flavin-dependent thymidylate synthase ThyX activity: implications for the folate cycle in bacteria.
  
  • Leduc Damien
  • Escartin Frédéric
  • Nijhout H Frederik
  • Reed Michael C
  • Liebl Ursula
  • Skouloubris Stéphane
  • Myllykallio Hannu
  Journal of Bacteriology, American Society for Microbiology, 2007, 189 (23), pp.8537-45. Although flavin-dependent ThyX proteins show thymidylate synthase activity in vitro and functionally complement thyA defects in heterologous systems, direct proof of their cellular functions is missing. Using insertional mutagenesis of Rhodobacter capsulatus thyX, we constructed the first defined thyX inactivation mutant. Phenotypic analyses of the obtained mutant strain confirmed that R. capsulatus ThyX is required for de novo thymidylate synthesis. Full complementation of the R. capsulatus thyX::spec strain to thymidine prototrophy required not only the canonical thymidylate synthase ThyA but also the dihydrofolate reductase FolA. Strikingly, we also found that addition of exogenous methylenetetrahydrofolate transiently inhibited the growth of the different Rhodobacter strains used in this work. To rationalize these experimental results, we used a mathematical model of bacterial folate metabolism. This model suggests that a very low dihydrofolate reductase activity is enough to rescue significant thymidylate synthesis in the presence of ThyX proteins and is in agreement with the notion that intracellular accumulation of folates results in growth inhibition. In addition, our observations suggest that the presence of flavin-dependent thymidylate synthase X provides growth benefits under conditions in which the level of reduced folate derivatives is compromised. (10.1128/JB.01380-07)
  DOI : 10.1128/JB.01380-07
• Insight into the catalytic mechanism of thymidylate synthase ThyX of Campylobacter jejuni
  
  • Sodolescu S. A.
  • Graziani Sébastien
  • Boum Y.
  • Myllykallio H.
  • Liebl Ursula
  , 2007, 54 (Suppl. 1), pp.55. For de novo synthesis of the essential DNA precursor dTMP, Campylobacter jejuni uses a novel thymidylate synthase, named ThyX (1). Different from canonical dimeric thymidylate synthase ThyA, ThyX is a flavoprotein and an active tetramer that utilizes NADPH as reducing agent, methylenetetrahydrofolate as methyl donor and dUMP as methyl acceptor. Its proposed catalytic mechanism starts with the oxidation of NADPH, followed by methylation of dUMP. ThyX proteins and human ThyA are unrelated in terms of sequence and structure, and use different catalytic mechanisms, making the essential ThyX enzymes interesting antimicrobial targets .
• Detection of ultrafast infrared electric fields by chirped-pulse upconversion
  
  • Nee M.
  • Mccanne R.
  • Joffre Manuel
  • Kubarych Kevin J.
  , 2007, pp.178. Sum-frequency mixing between a chirped 800-nm pulse and an infrared pulse allows determination of the IR spectral phase and amplitude using spectral interferometry. A two-dimensional IR spectrum of a metal-carbonyl is also measured by upconversion. © 2007 Springer-Verlag. (10.1007/978-3-540-68781-8-57)
  DOI : 10.1007/978-3-540-68781-8-57
• Detection of ultrafast infrared electric fields by chirped-pulse upconversion
  
  • Kubarych Kevin J.
  • Joffre Manuel
  , 2006, pp.TuE5. Sum-frequency mixing between a chirped 800-nm pulse and a 100-fs infrared pulse allows determination of the IR spectral phase and amplitude using spectral interferometry. A dispersed vibrational echo signal is also measured by upconversion. © 2006 Optical Society of America (10.1364/UP.2006.TuE5)
  DOI : 10.1364/UP.2006.TuE5
• Imagerie de contraste ionique térahertz Physique statistique des plasmons polaritons de surface.
  
  • Masson Jean-Baptiste
  , 2007. La physiologie et le fonctionnement de cellules nerveuses ainsi que de cellules présentant une différence conséquente de molarité entre différents compartiments, restent des questions très actuelles à l'interface de la physique et de la biologie. Ainsi la possibilité d'échanges d'eau lors du fonctionnement de neurones pourrait changer de manière assez radicale la façon dont leur activité est modélisée. Afin de chercher a visualiser ces échanges une technique: la microscopie de contraste ionique térahertz a été développée. Elle est basée sur la grande sensibilité du rayonnement térahertz aux concentrations ioniques dans l'eau. Ainsi un système de génération et de mesure de rayonnement basées sur des antennes semi-conductrices fut construit. Le problème de la limite de diffraction, qui réduit les mesures par rayonnement térahertz à une résolution de l'ordre de 300 µm, fut résolu par le couplage d'imagerie de champ proche avec ouverture avec une technique d'analyse permettant de visualiser des variations spatiales avec une résolution dépassant ?/100. Cette technique d'analyse qui est aussi une configuration expérimentale fut nommée le contraste de champ proche. La microscopie de contraste ionique térahertz a permis de confirmer les échanges d'eau lors d'un ensemble d'activités biologique liés aux neurones. De plus il a permis de quantifier de manière précise les volumes d'eau déplacés. Ceci ayant pour conséquence majeure que l'eau ne peut être négligée dans l'activité biologique neuronale. De plus cette technique a pu être étendue à d'autres systèmes biologiques, comme des cellules cardiaques et a ainsi permis la mesure résolue en temps des flux d'ions à l'intérieure de celles-ci. Le positionnement énergétique du rayonnement térahertz fait de lui un outil puissant dans l'étude de processus de transformations sur de longues molécules biologiques. Cependant un rehaussement du signal parait indispensable. C'est ainsi que son couplage possible avec de la plasmonique fut envisagé. L'absence d'activité spécifique de l'immense majorité des métaux dans cette zone du spectre a poussé l'étude vers des matériaux présentant des structures de taille inférieure à la longueur d'onde. Les réseaux de trous d'Ebbesen furent le système principal étudié. L'étude se focalisa sur la modélisation des phénomènes physiques ayant lieu lors de l'interaction du rayonnement térahertz avec celle-ci. Ainsi un modèle de Fano modifié s'est montré capable de modéliser la transmission des plaques ainsi que la dépendance en taille et en forme des trous, du signal transmis. De plus il fut montré que les plasmons polaritons générés à la surface de ces plaques peuvent interagir entre eux. Enfin une modélisation inhabituelle a vu décrire un certain nombre d'expériences sur ces plaques par! des transitions de phases et de la résonance stochastique. Les travaux sur ce sujet montrent qu'il reste encore beaucoup de phénomène non compris sur la nature des interactions entre la lumière et les réseaux de trous de taille inférieure à la longueur d'onde.
• Signal epidetection in third-harmonic generation microscopy of turbid media
  
  • Débarre Delphine
  • Olivier Nicolas
  • Beaurepaire Emmanuel
  Optics Express, Optical Society of America - OSA Publishing, 2007, 15, pp.8913-8924. Third-harmonic generation (THG) imaging of thick samples or large organisms requires TH light to be epicollected through the focusing objective. In this study we first estimate the amount of backward-to-forward TH radiation created by an isolated object as a function of size and spatial frequencies in the object. Theory and model experiments indicate that no significant signal can be epidetected from a (biological) dielectric structure embedded in a transparent medium. In contrast, backward emission is observed from metal nanoparticles where THG is partly a surface effect. We then address the case of an object embedded in a turbid medium. Experiments and Monte Carlo simulations show that epidetection is possible when the absorption mean free path of harmonic light in the medium exceeds its reduced scattering length, and that epicollection efficiency critically depends on the microscope field-of-view even at shallow depths, because backscattered light is essentially diffusive. These observations provide guidelines for optimizing epidetection in third-harmonic, second-harmonic, or CARS imaging of thick tissues. (10.1364/OE.15.008913)
  DOI : 10.1364/OE.15.008913
• Extra energy coupling through subwavelength hole arrays via stochastic resonance
  
  • Masson Jean-Baptiste
  • Gallot Guilhem
  , 2007. Interaction between metal surface waves and periodic geometry of subwavelength structures is at the core of the recent but crucial renewal of interest in plasmonics. One of the most intriguing points is the observation of abnormal strong transmission through these periodic structures, which can exceed by orders of magnitude the classical transmission given by the filling factor of the plate. The actual paradigm is that this abnormal transmission arises from the periodicity, and then that such high transmission should disappear in random geometries. Here, we show that extra energy can be coupled through the subwavelength structure by adding a controlled quantity of noise to the position of the apertures. This result can be modelled in the statistical framework of stochastic resonance. The evolution of the coupled energy with respect to noise gives access to the extra energy coupled at the surface of the subwavelength array.
• A NADPH substitute for selective photo-initiation of reductive bioprocesses via two-photon induced electron transfer.
  
  • Robin Anne-Claire
  • Gmouh Saïd
  • Mongin Olivier
  • Jouikov Viatcheslav
  • Werts Martinus
  • Gautier Clément
  • Slama-Schwok Anny
  • Blanchard Desce Mireille
  Chemical Communications, Royal Society of Chemistry, 2007 (13), pp.1334-6. A NADPH substitute where the nicotinamide moiety is replaced by a chromophoric unit having much larger two-photon absorption cross-section and able to transfer electrons to flavins only upon excitation is described as an effective two-photon nanotrigger for selective photo-activation of electron transfer in bioreductive processes. (10.1039/b615628b)
  DOI : 10.1039/b615628b
• Second harmonic imaging and scoring of collagen in fibrotic tissues.
  
  • Strupler Mathias
  • Pena Ana-Maria
  • Hernest Monica
  • Tharaux Pierre-Louis
  • Martin Jean-Louis
  • Beaurepaire Emmanuel
  • Schanne-Klein Marie-Claire
  Optics Express, Optical Society of America - OSA Publishing, 2007, 15 (7), pp.4054-4065. We compare second harmonic generation (SHG) to histological and immunohistochemical techniques for the visualization and scoring of collagen in biological tissues. We show that SHG microscopy is highly specific for fibrillar collagens and that combined SHG and two-photon excited fluorescence (2PEF) imaging can provide simultaneous three-dimensional visualization of collagen synthesis and assembly sites in transgenic animal models expressing GFP constructs. Finally, we propose several scores for characterizing collagen accumulation based on SHG images and appropriate for different types of collagen distributions. We illustrate the sensitivity of these scores in a murine model of renal fibrosis using a morphological segmentation of the tissue based on endogenous 2PEF signals. © 2007 Optical Society of America (10.1364/OE.15.004054)
  DOI : 10.1364/OE.15.004054
• Coherent interferometric detection of infrared emission from bacteriorhodopsin
  
  • Martin Jean-Louis
  • Vos Marten H.
  • Joffre Manuel
  , 2007. We have developped resonance coherent emission experiments where the ensemble of charge displacements upon photon absorption is monitored and time resolved. We have recently succeeded in directly visualizing the ultrafast (~10 fs) charge separation process in bacteriorhodopsin by interferometrically monitoring the associated low-frequency emission in macroscopically ordered films. The retinal isomerization subsequently takes place in few hundreds femtoseconds and appears associated with a relaxation of the dipole moment. In addition to the instantaneous broadband infrared emission, characteristic of electronic optical rectification, long lasting modulations at positive time can be distinguished that reflect the infrared-active vibrational response of the retinal/protein system.
• Time-resolved circular dichroism in the ultraviolet: A new user-friendly technique
  
  • Hache François
  • Niezborala Claire
  , 2007.
• Synchronous photoinitiation of endothelial NO synthase activity by a nanotrigger targeted as its NADPH site
  
  • Beaumont Edward
  • Lambry Jean-Christophe
  • Gautier Clément
  • Robin Anne-Claire
  • Gmouh Saïd
  • Berka Vladimir
  • Tsai Ah-Lim
  • Blanchard Desce Mireille
  • Slama-Schwok Anny
  Journal of the American Chemical Society, American Chemical Society, 2007, 129 (7), pp.2178-2186. We designed a new nanotrigger to synchronize and monitor an enzymatic activity interacting specifically with the conserved NADPH binding site. The nanotrigger (NT) combines a docking moiety targeting the NADPH site and a chromophore moiety responsive to light excitation for efficient electron transfer to the protein. Specific binding of the nanotrigger to the reductase domain of the endothelial nitric oxide synthase (eNOSred) was demonstrated by competition between NADPH and the nanotrigger on the reduction of eNOSred flavin. A micromolar Ki was estimated. We had monitored initiation of eNOSred activity by ultrafast transient spectroscopy. The transient absorption spectrum recorded at 250 ps fits the expected sum of the reduced and oxidized species, independently obtained by other chemical methods, in agreement with a photoinduced electron transfer from the excited nanotrigger to the flavin moiety of eNOSred. The rate of electron transfer from the excited state of the nanotrigger (NT*) to the protein is estimated to be kET = (7 ± 2) × 109 s-1 using the decay of oxidized eNOSred-bound nanotrigger compared against prereduced eNOSred or glucose 6-P dehydrogenase as controls. This fast electron transfer bypasses the slow hydride transfer to initiate NOS catalysis as shown by ultrafast kinetics using the eNOSred mutated in the regulatory F1160 residue. The selective targeting of the nanotrigger to NADPH sites should allow controlled initiation of the enzymatic activity of numerous proteins containing an NADPH site. (10.1021/ja067543e)
  DOI : 10.1021/ja067543e
• Ionic contrast terahertz near-field imaging of axonal activity and water fluxes
  
  • Masson Jean-Baptiste
  • Sauviat Martin-Pierre
  • Martin Jean-Louis
  • Gallot Guilhem
  , 2007, 6441, pp.644102. We demonstrated the direct and noninvasive imaging of functional neurons,1 as well as auricular heart muscle electrical activity 2 by Ionic Contrast Terahertz (ICT) near-field microscopy. This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore, neuronal activity results from both a precise control of transient variations in ionic conductances and a much less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed ICT technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by temperature change or neurotoxin poisoning. This technique should then provide grounds for the development of advanced functional neuroimaging methods based on diffusion anisotropy of water molecules. < Previous ArticleNext Article > . .Full Content is available to subscribers Subscribe/Learn More > Proceedings Article Ionic contrast terahertz near-field imaging of axonal activity and water fluxes Jean-Baptiste Masson ; Martin-Pierre Sauviat ; Jean-Louis Martin ; Guilhem Gallot [+-] Author Affiliations Jean-Baptiste Masson, Martin-Pierre Sauviat, Jean-Louis Martin, Guilhem GallotEcole Polytechnique, CNRS, INSERM (France) Proc. SPIE 6441, Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues V, 644102 (February 19, 2007); doi:10.1117/12.698309 Text Size: A A A .From Conference Volume 6441 Imaging, Manipulation, and Analysis of Biomolecules, Cells, and Tissues V Daniel L. Farkas; Robert C. Leif; Dan V. Nicolau San Jose, CA | January 20, 2007 Abstract.abstract .We demonstrated the direct and noninvasive imaging of functional neurons,1 as well as auricular heart muscle electrical activity2 by Ionic Contrast Terahertz (ICT) near-field microscopy. This technique provides quantitative measurements of ionic concentrations in both the intracellular and extracellular compartments and opens the way to direct noninvasive imaging of neurons during electrical, toxin, or thermal stresses. Furthermore, neuronal activity results from both a precise control of transient variations in ionic conductances and a much less studied water exchange between the extracellular matrix and the intraaxonal compartment. The developed ICT technique associated with a full three-dimensional simulation of the axon-aperture near-field system allows a precise measurement of the axon geometry and therefore the direct visualization of neuron swelling induced by temperature change or neurotoxin poisoning. This technique should then provide grounds for the development of advanced functional neuroimaging methods based on diffusion anisotropy of water molecules. © (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. (10.1117/12.698309)
  DOI : 10.1117/12.698309
• Luminescent lanthanide-ion doped nanoparticles as singlebiomolecule labels and oxidant sensors
  
  • Casanova Didier
  • Giaume Domitile
  • Moreau M.
  • Gacoin Thierry
  • Boilot Jean-Pierre
  • Alexandrou Antigoni
  , 2007, 6448. We report on the single-particle properties of lanthanide-ion doped oxide nanoparticles. We have demonstrated that their size can be accurately determined from their luminosity. The optically determined size distribution is in very good agreement with the distribution obtained from transmission electron microscopy (TEM). We also showed that the photobleaching of these nanoparticles is related to a reduction process and that we can use it to sense in a concentration-dependent manner the presence of an oxidant like H 2O2. Finally, we propose a way to perform nanoparticle-protein coupling and to determine the protein-nanoparticle ratio at the single-particle level. © (2007) COPYRIGHT SPIE--The International Society for Optical Engineering. (10.1117/12.705067)
  DOI : 10.1117/12.705067
• Nonlinear microscopy of collagen fibers
  
  • Strupler Mathias
  • Pena Ana-Maria
  • Hernest Monica
  • Tharaux P.-L.
  • Fabre Aude
  • Marchal-Somme Joelle
  • Crestani Bruno
  • Débarre Delphine
  • Martin Jean-Louis
  • Beaurepaire Emmanuel
  • Schanne-Klein Marie-Claire
  , 2007, 6470. We used intrinsic Second Harmonic Generation (SHG) by fibrillar collagen to visualize the three-dimensional architecture of collagen fibrosis at the micrometer scale using laser scanning nonlinear microscopy. We showed that SHG signals are highly specific to fibrillar collagen and provide a sensitive probe of the micrometer-scale structural organization of collagen in tissues. Moreover, recording simultaneously other nonlinear optical signals in a multimodal setup, we visualized the tissue morphology using Two-Photon Excited Fluorescence (2PEF) signals from endogenous chromophores such as NADH or elastin. We then compared different methods to determine accurate indexes of collagen fibrosis using nonlinear microscopy, given that most collagen fibrils are smaller than the microscope resolution and that second harmonic generation is a coherent process. In order to define a robust method to process our three-dimensional images, we either calculated the fraction of the images occupied by a significant SHG signal, or averaged SHG signal intensities. We showed that these scores provide an estimation of the extension of renal and pulmonary fibrosis in murine models, and that they clearly sort out the fibrotic mice. (10.1117/12.713576)
  DOI : 10.1117/12.713576
• Quantitative characterization of biological liquids for third-harmonic generation microscopy.
  
  • Débarre Delphine
  • Beaurepaire Emmanuel
  Biophysical Journal, Biophysical Society, 2007, 92 (2), pp.603-12. Third-harmonic generation (THG) microscopy provides images of unstained biological samples based on spatial variations in third-order nonlinear susceptibility, refractive index, and dispersion. In this study, we establish quantitative values for the third-order nonlinear susceptibilities of several solvents (water, ethanol, glycerol), physiological aqueous (ions, amino acids, polypeptides, bovine serum albumin, glucose) and lipid (triglycerides, cholesterol) solutions as a function of solute concentration in the 1.05-1.25 microm excitation range. We use these data in conjunction with imaging experiments to show that THG imaging with approximately 1.2 microm excitation lacks specificity and sensitivity to detect physiological ion concentration changes, and that nonaqueous structures such as lipid bodies provide a more robust source of signal. Finally, we illustrate the impact of index-matching liquids in THG images. These data provide a basis for interpreting biological THG images and for developing additional applications. (10.1529/biophysj.106.094946)
  DOI : 10.1529/biophysj.106.094946
• Ligand dynamics in an electron-transfer protein: picosecond geminate recombination of carbon monoxide to heme in mutant forms of cytochrome c
  
  • Silkstone Gary
  • Jasaitis Audrius
  • Wilson M. T.
  • Vos Marten H.
  Journal of Biological Chemistry, American Society for Biochemistry and Molecular Biology, 2007, 282, pp.1638-1649. Substitution of the heme coordination residue Met-80 of the electron transport protein yeast iso-1-cytochrome c allows external ligands like CO to bind and thus increase the effective redox potential. This mutation, in principle, turns the protein into a quasi-native photoactivable electron donor. We have studied the kinetic and spectral characteristics of geminate recombination of heme and CO in a series of single M80X (X = Ala, Ser, Asp, Arg) mutants, using femtosecond transient absorption spectroscopy. In these proteins, all geminate recombination occurs on the picosecond and early nanosecond time scale, in a multiphasic manner, in which heme relaxation takes place on the same time scale. The extent of geminate recombination varies from >99% (Ala, Ser) to ∼70% (Arg), the latter value being in principle low enough for electron injection studies. The rates and extent of the CO geminate recombination phases are much higher than in functional ligand-binding proteins like myoglobin, presumably reflecting the rigid and hydrophobic properties of the heme environment, which are optimized for electron transfer. Thus, the dynamics of CO recombination in cytochrome c are a tool for studying the heme pocket, in a similar way as NO in myoglobin. We discuss the differences in the CO kinetics between the mutants in terms of the properties of the heme environment and strategies to enhance the CO escape yield. Experiments on double mutants in which Phe-82 is replaced by Asp or Gly as well as the M80D substitution indicate that such steric changes substantially increase the motional freedom-dissociated CO. (10.1074/jbc.M605760200)
  DOI : 10.1074/jbc.M605760200
• Distal Val346Ile mutation in inducible NO synthase promotes substrate-dependent NO confinement
  
  • Beaumont Edward
  • Lambry Jean-Christophe
  • Wang Z.-Q.
  • Stuehr D.J.
  • Martin Jean-Louis
  • Slama-Schwok Anny
  Biochemistry, American Chemical Society, 2007, 46 (47), pp.13533. The function of inducible NO synthase (WT iNOS) depends on the release of NO from the ferric heme before the enzyme is reduced. Key parameters controlling ligand dynamics include the distal and proximal heme pocket amino acids, as well as the inner solvent molecules. In this work, we tested how a point mutation in the distal heme side of WT iNOS affected the geminate rebinding of NO by ultrafast kinetics and molecular dynamics simulations. The mutation sequestered much of the photodissociated NO close to the heme compared to WT iNOS, with a main picosecond phase accounting for 78% of the rebinding to the arginine-bound Val346Ile protein. Consequently, the probability of NO release from Val346Ile decreased as compared to that from WT iNOS, provided the substrate binding site is filled. These data are rationalized by a steric effect of the Ile methyl group inducing events mediated by the substrate, transmitted via the propionates to the NO and the protein. This model is consistent with the role of the H-bonding network involving the heme, the substrate, and the BH4 cofactor in controlling NO release, with a key role of the heme propionates [Gautier et al. (2006) Nitric Oxide 15, 312]. These data support the effect of Val346Ile mutation in decreasing NO release and slowing down NO synthesis compared to WT iNOS determined by single turnover catalysis [Wang et al. (2004) J. Biol. Chem. 279, 19018]. Cop. 2007 American Chemical Society. (10.1021/bi701567h)
  DOI : 10.1021/bi701567h
• Sinuosities in vascular structures
  
  • Masson Jean-Baptiste
  • Martin Jean-Louis
  European Physical Journal: Applied Physics, EDP Sciences, 2007, 40 (3), pp.351. In most organs, depending on the scale, the nature of the heart pump, the geometry and topology of the organ, some of the blood vessels tend to exhibit sinuous trajectories. We describe a part of this sinuous behavior, including partial biological and strong physical effects in a global physical framework. We will voluntarily focus on physical and topological effects. This study is performed on the vitelline membrane of the chicken embryo. Crossing angles, sinuosity, and the oscillation amplitude of the vascular system are analyzed. Surprisingly, the equation of river meandering dynamics is found to model the sinuosities in the vascular system, and an extension of this equation to non planar case is able to explain the effect of tissue global curvature on the vascular system. Results of this study could lead to a new understanding of the interplay between biological signaling and physical effects in determining the vascular pattern in different tissues. (10.1051/epjap:2007161)
  DOI : 10.1051/epjap:2007161
• Nanosecond T-jump experiment in poly(glutamic acid): A circular dichroism study
  
  • Mendonça Lucille
  • Hache François
  International Journal of Molecular Sciences, MDPI, 2007, 13 (2), pp.2239-2248. Poly(glutamic acid) has been studied with a nanosecond T-jump experiment. A new experimental set-up based on the frequency-quadrupling of an 82 MHz Titanium-Sapphire laser allows rapid CD measurements to be performed. Combining time-resolved absorption and circular dichroism at 204 and 220 nm, we are able to measure precisely the unfolding relaxation time as well as the helical fraction evolution. We show that only CD at 220 nm is relevant to observe the unfolding of an alpha helix whereas no change is observed for CD at 204 nm. Conversely, both absorptions yield information on the dynamics of the process. (10.3390/ijms13022239)
  DOI : 10.3390/ijms13022239
• Hypericin activates L-type Ca2+ channels in cardiac myocytes
  
  • Sauviat Martin-Pierre
  • Colas Anthony
  • J. Chauveau M.
  • C. Drapier J.
  • Négrerie Michel
  Journal of Natural Products, American Chemical Society, 2007, 70 (4), pp.510-514. (10.1021/np060309h)
  DOI : 10.1021/np060309h
• Effects of lindane (gamma-hexachlorocyclohexane) on rat heart muscle contraction.
  
  • Sauviat Martin-Pierre
  • Pagès Nicole
  General Physiology and Biophysics, Rand d Print, 2007, 26 (4), pp.275. The effects of micromolar concentrations of lindane on the mechanical activity of cardiac left ventricular papillary muscles were studied in adult female rats. Lindane decreased the amplitude and duration of the contraction, and slowed down the time course of its ascending phase (i.e. decreased the maximum rate of rise of the initial phase (dC/ dtmax)). Both amplitude and duration of the contraction, but not dC/dtmax, were restored by subsequent application of the rapid delayed outward K+ current (IKr) blocker E-4031 (10 nmol/l). Increasing the stimulation frequency from 1 to 3.3 Hz in the control solution produced a decrease in the amplitude of the first beat peak contraction while a slow recovery phase (srp) developed, as the result of the Na+-Ca2+ exchanger activity. When the frequency was restored to 1 Hz, a post rest potentiation (prp) with a negative staircase (ns) developed due to the sarcoplasmic reticulum (SR) Ca2+ refilling. Lindane increased the amplitude of both srp and prp, but did not affect ns, which indicates that SR Ca2+ refilling was not altered by the pesticide. In conclusion, the results strongly suggest that some of the lindane-induced negative inotropic and chronotropic-like effects on the contraction are due to an increased IKr while the decrease in dC/dtmax (i.e. the rate of cross-bridge formation) results from lindane oxidative properties.
• Chirped molecular vibration in a stilbene derivative in solution
  
  • Colonna Anne
  • Yabushita A.
  • Iwakura I.
  • Kobayashi T.
  Chemical Physics, Elsevier, 2007, 341 (40969), pp.336. The wave packet dynamics of 4-methoxy-4'-nitrostilbene in solution was studied by femtosecond pump-probe spectroscopy. Transient changes in absorbance exhibit oscillations, which reflect vibrational motions on the ground-state potential surface. Modification of this oscillatory feature in three different solvents (benzene, methanol, and acetonitrile) can be explained in term of the strength of hydrogen bonding and the stabilization of charge-transfer state, confirmed by steady-state absorption and fluorescence spectra. Cop. 2007 Elsevier B.V. All rights reserved. (10.1016/j.chemphys.2007.08.028)
  DOI : 10.1016/j.chemphys.2007.08.028
• Subpicosecond UV spectroscopy of carbonmonoxy-myoglobin: Absorption and circular dichroism studies
  
  • Dartigalongue Thibault
  • Niezborala Claire
  • Hache François
  Physical Chemistry Chemical Physics, Royal Society of Chemistry, 2007, 9 (13), pp.1611. A thorough absorption and circular dichroism study is performed in carbonmonoxy-myoglobin with a sub-picosecond visible pump, ultraviolet probe experiment. Differential absorption in the 220-360 nm range shows that the time-resolved response mainly comes from the heme and that aromatic amino acids do not contribute significantly. Time-resolved CD at 260 nm shows no dynamics and confirms this result. On the contrary, a strong CD dynamics is observed at 230 nm. This signal could originate from transient deformation of the a-helices in the protein. Cop. the Owner Societies. (10.1039/b616173a)
  DOI : 10.1039/b616173a
• Alterations of offspring heart muscle electrical activity transferred by rat male genitors chronically treated with lindane (7-hexachlorocyclohexane) trace concentrations
  
  • Sauviat Martin-Pierre
  • Godeau Gaston
  • Pages Nicole
  Pesticide Biochemistry and Physiology, Elsevier, 2007, 87 (2), pp.131. Using intracellular microelectrodes, we Studied transmembrane resting and action potentials (AP) of left ventricle papillary muscles isolated from the heart of adult lindane-treated (TMG) and untreated (UMG) male genitor rat offspring, obtained by mating untreated female with males chronically treated and untreated with lindane (2 ppb) trace concentrations through beverage. The AP magnitude and duration (APD) were similar in both groups and their response to low temperature (22 degrees C) unchanged. Lowering the external Ca2+ concentration from 2.5 to 0.625 mM prolonged APD in the TMG group but not in the UMG group. In the TMG group, (i) cumulative addition of Sr2+ (1 mM) to the physiological Solution prolonged APD; (ii) apamin (4 mu M) and charybdotoxin (4 mu M) prolonged the APD. In conclusion, our data revealed that an altered sensitivity of the Ca2+-induced Ca2+ inactivation of L-type Ca2+ channels and of Ca2+-activated K+ channels to Ca2+ has been transferred to TMG offspring. (cop) 2006 Elsevier Inc. All rights reserved. (10.1016/j.pestbp.2006.07.002)
  DOI : 10.1016/j.pestbp.2006.07.002