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Ariel Provost - One of the best experts on this subject based on the ideXlab platform.

  • Electron microProbe dating of monazite
    Chemical Geology, 1996
    Co-Authors: Jean-marc Montel, Christian Nicollet, Suzanne Foret, Michèle Veschambre, Ariel Provost
    Abstract:

    Because monazite is extremely rich in U and Th, radiogenic Pb ( * Pb) accumulates very quickly, and reaches, in about 100 Ma, a level where it is possible to analyse it with the Electron Probe. Assuming that common Pb is negligible, and that partial loss of Pb has not occurred, the simultaneous measurement of U, Th, and Pb allows to obtain a geologically meaningful age from a single Electron Probe Analysis. Here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method. A specific statistical method to deal with the large number of data which can be obtained on a single sample is described, and several guidelines, illustrated by examples, are suggested to optimize the method. Electron Probe measurements carried out on samples of known age, from 200 Ma to 3.1 Ga, yield ages that always fall inside the confidence interval of the isotopically determined age, demonstrating that this method is reliable. The younger age limit is approximately 100 Ma, although it can be younger in some favourable cases. In old monazites, extremely high *Pb contents have been found (up to 5 wt%) indicating that monazite can tolerate high radiation doses without experiencing lead loss. The final precision on the age, for a 'normal' monazite, is + 30-50 Ma, for a total counting time of 600 s. A complete dating procedure can be completed in less than 1 h. First results indicate that old ages can be preserved in monazite, either in small relict cores in crystals, or by the coexistence of several generations of monazites in a sample. This method has all the advantages of the Electron Probe: it is non-destructive, has an excellent spatial resolution (monazites as small as 5 I~m can be dated), and because it is possible to work on normal polished thin-sections, the petrographical position of the dated crystal is known. This method offers a large number of geologists access to an in-situ dating technique at moderate cost.

M Wittner - One of the best experts on this subject based on the ideXlab platform.

  • Evidence supporting a role for KCl cotransporter in the thick ascending limb of Henle's loop
    Kidney international, 2001
    Co-Authors: Antonio Di Stefano, Sylvie Jounier, M Wittner
    Abstract:

    Evidence supporting a role for KCl cotransporter in the thick ascending limb of Henle's loop. Background A basolateral Ba 2+ -sensitive KCl cotransporter has previously been proposed as participating in basolateral K + recycling and transepithelial NaCl reabsorption in the thick ascending limb of Henle's loop (TAL). The aim of the present study was to answer the question as to whether this cotransporter plays a role in transepithelial K + reabsorption and whether dietary Mg 2+ deficiency, known to regulate the KCl cotransporter in erythrocytes, also regulates KCl transport in the TAL. Methods The effects of a low-Mg 2+ diet were investigated on urinary and plasma K + concentration in control mice and Mg 2+ -deficient mice. Transepithelial Na + , Cl - and K + net fluxes (J Na , J Cl , J K ), determined in isolated perfused TALs with Electron Probe Analysis or cation-exchange high-performance liquid chromatography (HPLC) and electrophysiological parameters (V te , R te ), were measured in both animal groups. Expression of transcripts for the KCl cotransporter and its possible regulation by low-Mg 2+ were studied by RT-PCR in microdissected mouse cortical TAL (CTAL) and medullary TAL (MTAL) segments. Results In isolated perfused CTALs, basolateral Ba 2+ and amiloride induced a large K + net secretion towards the tubular lumen, paralleled by a 50% decrease in transepithelial NaCl reabsorption. KCC1 transcripts were found in the mouse CTAL and MTAL. A low-Mg 2+ diet led to diminished urinary K + excretion, lowered plasma K + concentration and up-regulation of KCC1 transcripts in the TAL. For low-Mg 2+ diet, this upregulation was associated with increased transepithelial K + reabsorption in the in vitro-perfused CTAL. Conclusions: Our study provides evidence that the KCl cotransporter, which is functionally expressed in the TAL, plays an important role in transepithelial K + reabsorption. Direct inhibition of this transporter by Ba 2+ and its indirect inhibition by amiloride lead to a strong transepithelial K + secretion and diminished NaCl reabsorption in the TAL. Up-regulation of KCC1 mRNA by dietary Mg 2+ restriction is associated with an increased K + reabsorption in the in vitro perfused CTAL.

Jean-marc Montel - One of the best experts on this subject based on the ideXlab platform.

  • Electron microProbe dating of monazite
    Chemical Geology, 1996
    Co-Authors: Jean-marc Montel, Christian Nicollet, Suzanne Foret, Michèle Veschambre, Ariel Provost
    Abstract:

    Because monazite is extremely rich in U and Th, radiogenic Pb ( * Pb) accumulates very quickly, and reaches, in about 100 Ma, a level where it is possible to analyse it with the Electron Probe. Assuming that common Pb is negligible, and that partial loss of Pb has not occurred, the simultaneous measurement of U, Th, and Pb allows to obtain a geologically meaningful age from a single Electron Probe Analysis. Here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method. A specific statistical method to deal with the large number of data which can be obtained on a single sample is described, and several guidelines, illustrated by examples, are suggested to optimize the method. Electron Probe measurements carried out on samples of known age, from 200 Ma to 3.1 Ga, yield ages that always fall inside the confidence interval of the isotopically determined age, demonstrating that this method is reliable. The younger age limit is approximately 100 Ma, although it can be younger in some favourable cases. In old monazites, extremely high *Pb contents have been found (up to 5 wt%) indicating that monazite can tolerate high radiation doses without experiencing lead loss. The final precision on the age, for a 'normal' monazite, is + 30-50 Ma, for a total counting time of 600 s. A complete dating procedure can be completed in less than 1 h. First results indicate that old ages can be preserved in monazite, either in small relict cores in crystals, or by the coexistence of several generations of monazites in a sample. This method has all the advantages of the Electron Probe: it is non-destructive, has an excellent spatial resolution (monazites as small as 5 I~m can be dated), and because it is possible to work on normal polished thin-sections, the petrographical position of the dated crystal is known. This method offers a large number of geologists access to an in-situ dating technique at moderate cost.

Antonio Di Stefano - One of the best experts on this subject based on the ideXlab platform.

  • Evidence supporting a role for KCl cotransporter in the thick ascending limb of Henle's loop
    Kidney international, 2001
    Co-Authors: Antonio Di Stefano, Sylvie Jounier, M Wittner
    Abstract:

    Evidence supporting a role for KCl cotransporter in the thick ascending limb of Henle's loop. Background A basolateral Ba 2+ -sensitive KCl cotransporter has previously been proposed as participating in basolateral K + recycling and transepithelial NaCl reabsorption in the thick ascending limb of Henle's loop (TAL). The aim of the present study was to answer the question as to whether this cotransporter plays a role in transepithelial K + reabsorption and whether dietary Mg 2+ deficiency, known to regulate the KCl cotransporter in erythrocytes, also regulates KCl transport in the TAL. Methods The effects of a low-Mg 2+ diet were investigated on urinary and plasma K + concentration in control mice and Mg 2+ -deficient mice. Transepithelial Na + , Cl - and K + net fluxes (J Na , J Cl , J K ), determined in isolated perfused TALs with Electron Probe Analysis or cation-exchange high-performance liquid chromatography (HPLC) and electrophysiological parameters (V te , R te ), were measured in both animal groups. Expression of transcripts for the KCl cotransporter and its possible regulation by low-Mg 2+ were studied by RT-PCR in microdissected mouse cortical TAL (CTAL) and medullary TAL (MTAL) segments. Results In isolated perfused CTALs, basolateral Ba 2+ and amiloride induced a large K + net secretion towards the tubular lumen, paralleled by a 50% decrease in transepithelial NaCl reabsorption. KCC1 transcripts were found in the mouse CTAL and MTAL. A low-Mg 2+ diet led to diminished urinary K + excretion, lowered plasma K + concentration and up-regulation of KCC1 transcripts in the TAL. For low-Mg 2+ diet, this upregulation was associated with increased transepithelial K + reabsorption in the in vitro-perfused CTAL. Conclusions: Our study provides evidence that the KCl cotransporter, which is functionally expressed in the TAL, plays an important role in transepithelial K + reabsorption. Direct inhibition of this transporter by Ba 2+ and its indirect inhibition by amiloride lead to a strong transepithelial K + secretion and diminished NaCl reabsorption in the TAL. Up-regulation of KCC1 mRNA by dietary Mg 2+ restriction is associated with an increased K + reabsorption in the in vitro perfused CTAL.

Christian Nicollet - One of the best experts on this subject based on the ideXlab platform.

  • Electron microProbe dating of monazite
    Chemical Geology, 1996
    Co-Authors: Jean-marc Montel, Christian Nicollet, Suzanne Foret, Michèle Veschambre, Ariel Provost
    Abstract:

    Because monazite is extremely rich in U and Th, radiogenic Pb ( * Pb) accumulates very quickly, and reaches, in about 100 Ma, a level where it is possible to analyse it with the Electron Probe. Assuming that common Pb is negligible, and that partial loss of Pb has not occurred, the simultaneous measurement of U, Th, and Pb allows to obtain a geologically meaningful age from a single Electron Probe Analysis. Here we present the results of two years of systematical investigations aiming to define both the limits and potential of this method. A specific statistical method to deal with the large number of data which can be obtained on a single sample is described, and several guidelines, illustrated by examples, are suggested to optimize the method. Electron Probe measurements carried out on samples of known age, from 200 Ma to 3.1 Ga, yield ages that always fall inside the confidence interval of the isotopically determined age, demonstrating that this method is reliable. The younger age limit is approximately 100 Ma, although it can be younger in some favourable cases. In old monazites, extremely high *Pb contents have been found (up to 5 wt%) indicating that monazite can tolerate high radiation doses without experiencing lead loss. The final precision on the age, for a 'normal' monazite, is + 30-50 Ma, for a total counting time of 600 s. A complete dating procedure can be completed in less than 1 h. First results indicate that old ages can be preserved in monazite, either in small relict cores in crystals, or by the coexistence of several generations of monazites in a sample. This method has all the advantages of the Electron Probe: it is non-destructive, has an excellent spatial resolution (monazites as small as 5 I~m can be dated), and because it is possible to work on normal polished thin-sections, the petrographical position of the dated crystal is known. This method offers a large number of geologists access to an in-situ dating technique at moderate cost.