Pierre Vacher

Seismic tomography beneath stable tectonic regions and the origin and composition of the continental lithospheric mantle

Abstract On a large scale, seismic waves travel faster through old continental shields than through Paleozoic platforms. On a smaller scale, the continental lithosphere appears to be composed of blocks with different velocities. Sharp vertical contacts between different blocks of lithosphere are revealed by short-wavelength offsets in P-vertical travel times; some contacts have been preserved for more than one billion years. These observations cannot be explained by temperature differences alone and imply persistent mineralogical differences within the lithosphere. To reconcile global and local seismological observations, a bimodal model is required: the continental lithosphere appears to consist of cores of depleted, refractory lithosphere surrounded by and/or superposed on younger, more fertile lithosphere. The seismic characteristics and mineralogical compositions correlate on a large scale with the age of the lithosphere and reflect episodic growth of the continents. Temperatures in the lithosphere of stable continental regions vary less than commonly assumed and may be close to the geotherms proposed by Jaupart and Mareschal [Lithos 48 (1999) 93–114].

Imaging of Ca(2)+ intracellular dynamics with a third-harmonic generation microscope.

We describe the promising development of third-harmonic generation (THG) in laser scanning microscopy for study of the functional imaging of live biological cells. The dynamics of Ca(2+) in biological cells is shown. The Ca(2+) signal consists of a transient increase in the intracellular concentration. THG microscopy allows one to temporally visualize the release of Ca(2+) from internal stores and (or) calcium influx.

Arachidonic Acid-Induced Hormone Release in Somatotropes: Involvement of Calcium

Arachidonic acid (AA) has been implicated in signaling actions in several cell types including endocrine cells. In the present study, we investigated the effect of exogenous AA on GH release from dispersed pituitary cells and tried to elucidate the mechanism involved in this process. We show that AA stimulates GH release in a dose- and extracellular calcium-dependent manner. The effects of AA on cytosolic calcium concentration ([Ca2+]i) were studied using dual-emission microspectrofluorimetry in identified somatotropes. AA (1 microM) induced an increase in intracellular calcium concentration ([Ca2+]i) by stimulating Ca2+ influx through dihydropyridine-sensitive, voltage-dependent calcium channels. In these cells, the effects of AA were only reduced by the inhibition of protein kinase C (PKC) activity, suggesting that the fatty acid may act by both PKC-dependent and PKC-independent pathways. In order to determine whether AA metabolites were involved in the effects attributed to AA, and, if so, which ones, we inhibited the three arachidonate metabolic pathways: cyclo-oxygenase by indomethacin (50 microM), lipoxygenase by nordihydroguaiaretic acid (NGDA, 50 microM), and epoxygenase by 5,8,11, 14-eicosatetraynoic acid (ETYA, 10 microM). NGDA and ETYA reduced the effects of AA on GH release (50 and 74%, respectively) and inhibited the [Ca2+]i response, whereas indomethacin slightly potentiated both AA-induced GH release and [Ca2+]i increase. As these results suggested that lipoxygenase metabolites may be responsible for AA-induced Ca2+ influx and GH release, we tested the effects of 5-, 12- and 15-hydroperoxyeicosatetraenoic acids (5-, 12- and 15-HpETE) on [Ca2+]i and GH release. They all stimulated calcium influx and GH release in a dose-dependent manner, 12-HpETE being more potent than 5- and 15-HpETE. We conclude that lipoxygenase metabolites of arachidonic acid, particularly 12-HpETE, may be involved in the GH secretion mechanism, probably by facilitating Ca2+ influx via L-type Ca2+ channels.

Visualization of intracellular Ca2+ dynamics with simultaneous two-photon-excited fluorescence and third-harmonic generation microscopes

We present a promising development of third-harmonic generation (THG) coupled with two-photon excited fluorescence (TPEF) in laser scanning microscopy to study in vivo glial human cells. In this letter, intracellular Ca2+ dynamics in biological cells are shown. The THG microscopy allows visualizing precisely the localization of the Ca2+ release whereas TPEF microscopy only gives functional mechanisms.

PROLACTIN RECEPTOR AND SIGNAL TRANSDUCTION TO MILK PROTEIN GENES

Abstract After cloning of the mammary gland prolactin (PRL) receptor cDNA, a functional assay was established using co-transfection of PRL receptor cDNA together with a milk protein promoter/chloramphenicol acetyl transferase (CAT) construct in Chinese hamster ovary (CHO) cells. Different mutants of the PRL receptor were tested in this CAT assay to delimit the domains in the receptor necessary for signal transduction to milk protein genes. In CHO cells stably transfected with PRL receptor cDNA, high numbers of PRL receptor are expressed. By metabolic labeling and immunoprecipitation, expressed PRL receptor was identified as a single species of 100 kDa. Using these cells, we analyzed the effects of PRL on intracellular free Ca++ concentration. PRL stimulates Ca++ entry and induces secondary Ca++ mobilization. The entry of Ca++ is a result of an increase in K+ conductance that hyperpolarizes the membranes. We have also analyzed tyrosine phosphorylation induced by PRL. In CHO cells stably transfected with PRL receptor cDNA, PRL induced a very rapid and transient tyrosine phosphorylation of a 100-kDa protein which is most probably the PRL receptor. The same finding was obtained in mammary membranes after PRL injection to lactating rabbits. Whereas tyrosine kinase inhibitors genistein and lavendustin were without effect, PRL stimulation of milk protein gene promoters was partially inhibited by 2 μM herbimycin in CHO cells co-transfected with PRL receptor cDNA and the β lactoglobulin CAT construct. Taken together these observations indicate that the cytoplasmic domain of the PRL receptor interacts with one or several tyrosine kinases, which may represent early postreceptor events necessary for PRL signal transduction to milk protein genes.

Inhibitors of 1,2-diacylglycerol kinase potentiate the TRH-induced stimulation of Ca2+-activated K+ current

Transient activation of the outward K+ current caused by a rise in the cytosolic free Ca2+ concentration, [Ca2+]i was the predominant change in plasma membrane ion flux during the first phase of thyrotropin-releasing hormone (TRH) action on pituitary cells. Following the intracellular application of inhibitors of 1,2-diacylglycerol (DG) kinase, R59022 and 1-oleyl-2-acetyl glycerol (OAG) the outward K+ current response to TRH in cells of the pituitary line GH3B6 was potentiated. This potentiation was analyzed further with the combination of microfluorimetric and electrophysiological recording techniques. Receptor-induced changes in [Ca2+]i and ion channel activation were monitored simultaneously in the same cell. It was found that R59022 and OAG altered in parallel the TRH-induced transient rise in [Ca2+]i and outward K+ current. This resulted in a significant correlation between the kinetic parameters (speed of onset, duration) of the [Ca2+]i and the K+ current responses to TRH. Intracellular application of vanadate abolished the rapid start of the TRH response presumably by its block of Ca2+ uptake into the endoplasmic reticulum, leading to depletion of a Ca2+ pool mobilizable by inositol 1,4,5-trisphosphate (Ins(1,4,5)P3). The use of vanadate unmasked a slowly developing response to TRH, which was still potentiated by OAG and R59022. Together, these observations suggest that Ca2+ mobilization during the first phase of TRH action is mediated by two distinct processes, one of which is linked to receptor stimulation of DG production.

STUDY OF PSEUDOELASTIC BEHAVIOUR OF POLYCRISTALLIN SHAPE MEMORY ALLOYS BY RESISTIVITY MEASUREMENTS AND ACOUSTIC EMISSION

ABSTRACT The determination of the hyperelastic behavior of polycristalline Cu Zn Al shape memory alloys is performed using loading-unloading tension and tension-compression tests with resistivity and acoustic emission measurements. In the case of uniaxial mechanical loading, these measurements show, on the one hand, that the hyperplastic strain is proportional to the volume fraction x of martensite, and on the other hand, that the obtained acoustic emission data allows the evolution of x during the mechanical test, to be followed.

Visualization of intracellular Ca2+ dynamics with third-harmonic generation microscopy

Measurements by Laser scanning Third Harmonic Generation microscopy of Ca2+ dynamic release from internal stores and/or calcium influx in biological cells is presented. The Ca2+ signal consists of a transient increase in the intracellular concentration. A good correlation is found between these measurements and measurements done with microspectrofluorometry.

Imaging intracellular Ca/sup 2+/ dynamic with third harmonic generation microscope

Summary form only given. The validity of the third harmonic generation (THG) microscopy for imaging has been shown and its potential use in material science and more precisely in biology. All these studies have demonstrated that THG microscopy is a method which has the advantage that no labeling is necessary. In order to develop further imaging instruments, biological dynamic events has to be measured and especially Ca/sup 2+/ dynamics which is a special importance in cellular biology. For the biological experiments, we have used a human astrocytome cell line: U-87 MG.

Modeling of the Pseudo-Elastic Behavior of Polycrystalline Shape Memory Alloys CU-ZN-AL

Pseudoelastic behaviour of Cu Zn Al shape memory alloys is studied by means of tensile and tensile compressive test. Electrical resistance measurements performed “in situ” allow the martensitic fraction present in the alloy to be known. So, the formulation of the pseudoelastic deformation rate is established.