C. Gauthier - Academia.edu (original) (raw)

Papers by C. Gauthier

IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 2000

Page 1. IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION (VLSI) SYSTEMS, VOL. 6, NO. 1, MARCH 19... more Page 1. IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION (VLSI) SYSTEMS, VOL. 6, NO. 1, MARCH 1998 47 Overview of Complementary GaAs Technology for High-Speed VLSI Circuits Richard B. Brown, Bruce ...

Polymer, 2001

Effects of irradiation on the viscoelastic properties of peroxide-crosslinked PDMS elastomers (EV... more Effects of irradiation on the viscoelastic properties of peroxide-crosslinked PDMS elastomers (EVC) without ®ller (1), ®lled with 30% untreated nanoscopic SiO 2 (2) and with 30% surface modi®ed silica (3) were investigated. Electron irradiation in air using a high dose rate allowing homogeneous irradiation at different doses ranging from 25 to 500 kGy have led to additional crosslinking of these three types of silicone rubbers making them become more rigid and brittle. The apparent crosslink density is higher for ®lled elastomers since links at the polymer±silica interfaces have been created as a result of irradiation. A further crosslink density enhancement is obtained for the surfacetreated silica ®llers. High resolution low frequency dynamic mechanical spectroscopy shows that the magnitude of the crystallisation peak located at approximately 2408C decreases with the irradiation dose. As a result, the amplitude of the relaxation process associated with the glass transition near 21258C increases, since a larger amount of amorphous phase is present due to the hindrance of the crystallisation behaviour. DSC measurements con®rm that crystallisation is limited by the formation of a higher number of crosslinks, and that this effect is ampli®ed for ®lled PDMS samples. A study of mechanical hysteresis at high strains (Mullins effect) shows an increase of the associated dissipative phenomena due to the induced polymer/silica bonds. q

Synthesis, Properties, and Applications, 2014

MRS Proceedings, 2002

This work reports the dynamic mechanical characterization of nanocomposites based on a poly(butyl... more This work reports the dynamic mechanical characterization of nanocomposites based on a poly(butyl acrylate) matrix filled with spherical particles of either polystyrene or silica both of diameter around 100 nm. A discrete numerical simulation, taking into account the microstructure and the nature of contact between reinforcing particles has been developed. This simulation enables to quantify the effect of interactions between filler particles on the elastic modulus, and in a more general sense, to clarify the concept of mechanical percolation. It gives results in very good agreement with experimental data.

Polymer Nanotube …, 2010

Page 1. 3 New Microscopy Techniques for a Better Understanding of the Polymer/ Nanotube Composite... more Page 1. 3 New Microscopy Techniques for a Better Understanding of the Polymer/ Nanotube Composite Properties K. Masenelli-Varlot, A. Bogner, C. Gauthier, L. Chazeau and JY Cavaillé Université de Lyon, INSA-Lyon, MATÉIS ...

Polymer Composites, 1996

Cellulose whiskers have been used as reinforcement in a copolymer matrix prepared from a latex ph... more Cellulose whiskers have been used as reinforcement in a copolymer matrix prepared from a latex phase. If a water suspension-mixing procedure is adopted, the fibril breakage that usually occurs during the mixing with a molten polymer can be avoided, and an enhanced filler dispersion can be expected. In this study, different processing methods have been used to prepare composite films, either by film casting (water evaporation) or by freeze drying, followed by classical compression or extrusion processes. The thermomechanical properties of these nanocomposites have been investigated, and the influence of processing conditions and the effect of whisker content have been considered. Processing conditions have a large influence on the mechanical behavior and can be classified in ascending order of their reinforcement efficiency: It can be attributed to a decrease of the apparent whisker aspect ratio, due to gradual breakage and/or orientation of the whiskers when hot pressing or extrusion is used. Below Tg, good agreement is found between experimental moduli and the theoretical predictions of the Halpin-Kardos equation. On the other hand, above Tgr a spectacular reinforcing effect is observed, which is widely underestimated by this short fiber composite model. This is related to the presence of a rigid cellulose network, linked by hydrogen bonds, when the whisker content is above its percolation threshold. The quality of this network (i.e., density and homogeneity) and thus, the magnitude of the reinforcing effect, depend on processing conditions.

Polymer, 2001

... Influence of the crystalline phase on the mechanical properties of unfilled and CaCO3 filled ... more ... Influence of the crystalline phase on the mechanical properties of unfilled and CaCO3 filled polypropylene . Part I :Structural and mechanical characterization. Thomas Labour 1 , CatherineGauthier 1 , Roland Seguela 1 , Gérard Vigier 1 , Y. Bomal, G. Orange. (2001). ...

Nature Materials, 2009

Colloidal particles are often seen as big atoms that can be directly observed in real space. They... more Colloidal particles are often seen as big atoms that can be directly observed in real space. They are therefore becoming increasingly important as model systems to study processes of interest in condensed-matter physics such as melting, freezing and glass transitions. The solidification of colloidal suspensions has long been a puzzling phenomenon with many unexplained features. Here, we demonstrate and rationalize the existence of instability and metastability domains in cellular solidification of colloidal suspensions, by direct in situ high-resolution X-ray radiography and tomography observations. We explain such interface instabilities by a partial Brownian diffusion of the particles leading to constitutional supercooling situations. Processing under unstable conditions leads to localized and global kinetic instabilities of the solid/liquid interface, affecting the crystal morphology and particle redistribution behaviour.

Journal of the American Ceramic Society, 2009

This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior ... more This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior of colloidal suspensions of alumina partic les during directional solidification by freezing. The combination of these techniques provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particle redistribution between the crystals and a particle-enriched phase, and the three-dimensional organization of the ice crystals. In this first part of two companion papers, the precursor phenomena leading to directional crystallization during the first instants of solidification are studied. Mullins-Sekerka instabilities are not necessary to explain the dynamic evolution of the interface pattern. Particle redistribution during these first instants is dependent on the type of crystals growing into the suspension. The insights gained into the mechanisms of solidification of colloidal suspensions may be valuable for the materials processing routes derived for this type of directional solidification (freeze-casting), and of general interest for those interested in the interactions between solidification fronts and inert particles.

Journal of Polymer Science Part B: Polymer Physics, 2007

The nonlinear effect at small strains (Payne effect) has been investigated in the case of silica-... more The nonlinear effect at small strains (Payne effect) has been investigated in the case of silica-filled styrene-butadiene rubber. The originality of this study lies in the careful preparation of samples in order to fix all parameters except one, that is, the modification of the silica ...

The Journal of Immunology, 2014

European Polymer Journal, 2013

Solid polymer electrolytes (SPEs) were prepared by incorporating either aqueous LiClO 4 or 1-ethy... more Solid polymer electrolytes (SPEs) were prepared by incorporating either aqueous LiClO 4 or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) ionic liquid into Poly(ethylene oxide) (PEO)/polybutadiene (PB) Interpenetrating Polymer Networks (IPNs). With a given PEO/PB ratio, either transparent or translucent films depending on the synthesis route of these IPNs, have been investigated. TEM observations confirm that the morphology of these IPN films depends also on the PEO weight proportion whereas mechanical properties measured by DMA are only slightly modified. Measurements of ionic conductivity of SPEs are also very dependent on the IPNs morphology. For instance, EMITFSI ionic conductivity increases over four orders of magnitude from 2.2 Â 10 À7 to 2.5 Â 10 À3 S cm À1 at 30°C.

Comptes Rendus Chimie, 2003

We describe in this work the copolymerization reaction of 3-trimethoxysilyl propyl methacrylate (... more We describe in this work the copolymerization reaction of 3-trimethoxysilyl propyl methacrylate (MPS) with styrene (Styr.) and n-butyl acrylate (BuA) monomers through emulsion polymerization. The so-produced hybrid copolymer (P(BuA-co-MPS)) and terpolymer (P(Styr-co-BuA-co-MPS)) latexes were cast into films that displayed a good optical transparency. The copolymers microstructure in the films was characterized by FTIR, 13 C and 29 Si solid state NMR spectroscopies, and was found to be highly dependent on parameters such as the monomer feed composition, the suspension pH and the silane addition profile. The films obtained from the hybrid latexes showed improved dynamic mechanical properties indicating that a reinforcing organo-mineral network had formed in the composite materials. The dynamic modulus of the hybrids increased with increasing silane contents while, concurrently, the tan d peak shifted to higher temperatures, broadened and decreased in intensity. To cite this article: S. Vitry et al., C. R. Chimie 6 (2003).

Composites Science and Technology, 2006

Fibrous arrays and composites are among the strongest structures created by man or found in natur... more Fibrous arrays and composites are among the strongest structures created by man or found in nature. Such materials often fail in a slow, cumulative fashion, suppressing the sudden occurrence of rapid structural collapse. Our classical understanding of the statistical tensile strength and failure of unidirectional composites is usually based on a stochastic model where the key predictor is the size (N*) of a critical cluster of adjacent broken fibres, which inevitably leads to final composite failure. Here we show, via direct measurements using high-resolution synchrotron X-ray tomography, that in a quartz-epoxy composite the classical stochastic theory underpredicts -by a factor 3-5 -the size N* of the critical Ôfailed-fibreÕ cluster. A simple fracture mechanics argument which relates the critical fibre cluster size to the material strength is proposed to account for our data.

Composites Science and Technology, 2005

The reinforcement of rubbery matrices by vapour grown carbon nanofibres (VGCFs) is studied in the... more The reinforcement of rubbery matrices by vapour grown carbon nanofibres (VGCFs) is studied in the case of a rubbery epoxy and a styrene butadiene rubber (SBR). In the case of epoxy, the VGCF were introduced in the hardener and blended with the prepolymer. Nanocomposites were produced by subsequent polymerization. For the second matrix, samples were prepared by casting of a mixture of SBR latex and a water suspension of VGCF. Evaluation of mechanical performances revealed a linear increase of the modulus measured above and below the glass transition temperature for nanofibre content up to 10 wt%. This increase is low, but in good agreement with the estimation based on mechanical coupling models. In the case of epoxy matrix, the ultimate stress and strain are largely increased, even for very low fibre content (i.e. 1 wt%). However, this improvement is not observed in the case of nanocomposites based on SBR matrix, due to the non-optimized dispersion of the fibres.

Biochimie, 2003

Using precise examples, this paper shows that carbon 13 NMR spectroscopy in conjunction with radi... more Using precise examples, this paper shows that carbon 13 NMR spectroscopy in conjunction with radioactive and enzymatic methods as well as with adequate mathematical modeling of metabolic pathways allows not only to identify but also to quantify fluxes through enzymes involved in substrate and drug metabolism. Carbon 13 NMR spectroscopy is a tool of unprecedented power to unravel the complexity of renal metabolism. Currently it plays a major role in what is nowadays called metabolomics.

Biochemical Journal, 2005

The metabolism of glutamine, a physiological substrate of the human kidney, plays a major role in... more The metabolism of glutamine, a physiological substrate of the human kidney, plays a major role in systemic acid-base homoeostasis. Not only because of the limited availability of human renal tissue but also in part due to the lack of adequate cellular models, the mechanisms regulating the renal metabolism of this amino acid in humans have been poorly characterized. Therefore given the renewed interest in their use, human precision-cut renal cortical slices were incubated in Krebs-Henseleit medium (118 mM NaCl, 4.7 mM KCl, 1.18 mM KH2PO4, 1.18 mM MgSO4*7H2O, 24.9 mM NaHCO3 and 2.5 mM CaCl2*2H2O) with 2 mM unlabelled or 13C-labelled glutamine residues. After incubation, substrate utilization and product formation were measured by enzymatic and NMR spectroscopic methods. Glutamate accumulation tended to plateau but glutamine removal and ammonia, alanine and lactate production as well as flux through GLDH (glutamate dehydrogenase) increased to various extents with time for up to 4 h of incubation indicating the metabolic viability of the slices. Valproate, a stimulator of renal glutamine metabolism, markedly and in a dose-dependent fashion increased ammonia production. With [3-13C]glutamine as a substrate, and in the absence and presence of valproate, [13C]glutamate, [13C]alanine and [13C]lactate accounted for 81 and 96%, 34 and 63%, 30 and 46% of the glutamate, alanine and lactate accumulations measured enzymatically respectively. The slices also metabolized glutamine and retained their reactivity to valproate during incubations lasting for up to 48 h. These results demonstrate that, although endogenous metabolism substantially operates in the presence of glutamine, human precision-cut renal cortical slices are metabolically viable and strongly respond to the ammoniagenic effect of valproate. Thus, this experimental model is suitable for metabolic and pharmaco-toxicological studies.

Biochimica et Biophysica Acta (BBA) - Biomembranes, 1988

In the kidney, filtered proteins are rapidly reabsorbed so that the final excretion is less than ... more In the kidney, filtered proteins are rapidly reabsorbed so that the final excretion is less than 0.1% of the filtered amount for low molecular weight proteins such as fl2-microgiobulin and a few percent for albumin. In order to investigate the affinity of proteins for luminal membranes, rat renal brush-border membranes were incubated with les l-labelled human/~2-microgiobulin and the initial binding rate determined by the filtration method. Scatchard plot analysis of binding rate revealed two types of binding sites: one with K m = 0.25 • 10 -6 M and Vm~ , --0.1 nmol/min per mg protein and another with K m = 1" 10-s M and Vma x = 1.3 nmul/min per mg protein. The lower affinity type is likely to represent non-specific binding the physiological role of which is to be discussed. The higher affinity sites seem to play the major role in binding rate. fl2-Microglobulin initial binding is reversible, and inhibited by bovine serum albumin. Comparison of the time course of bound fl2-microglobulin removal by unlabelled/~2-microglobulin and by albumin suggests that these two proteins have a different internalization mechanism.

IEEE Transactions on Very Large Scale Integration (VLSI) Systems, 2000

Page 1. IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION (VLSI) SYSTEMS, VOL. 6, NO. 1, MARCH 19... more Page 1. IEEE TRANSACTIONS ON VERY LARGE SCALE INTEGRATION (VLSI) SYSTEMS, VOL. 6, NO. 1, MARCH 1998 47 Overview of Complementary GaAs Technology for High-Speed VLSI Circuits Richard B. Brown, Bruce ...

Polymer, 2001

Effects of irradiation on the viscoelastic properties of peroxide-crosslinked PDMS elastomers (EV... more Effects of irradiation on the viscoelastic properties of peroxide-crosslinked PDMS elastomers (EVC) without ®ller (1), ®lled with 30% untreated nanoscopic SiO 2 (2) and with 30% surface modi®ed silica (3) were investigated. Electron irradiation in air using a high dose rate allowing homogeneous irradiation at different doses ranging from 25 to 500 kGy have led to additional crosslinking of these three types of silicone rubbers making them become more rigid and brittle. The apparent crosslink density is higher for ®lled elastomers since links at the polymer±silica interfaces have been created as a result of irradiation. A further crosslink density enhancement is obtained for the surfacetreated silica ®llers. High resolution low frequency dynamic mechanical spectroscopy shows that the magnitude of the crystallisation peak located at approximately 2408C decreases with the irradiation dose. As a result, the amplitude of the relaxation process associated with the glass transition near 21258C increases, since a larger amount of amorphous phase is present due to the hindrance of the crystallisation behaviour. DSC measurements con®rm that crystallisation is limited by the formation of a higher number of crosslinks, and that this effect is ampli®ed for ®lled PDMS samples. A study of mechanical hysteresis at high strains (Mullins effect) shows an increase of the associated dissipative phenomena due to the induced polymer/silica bonds. q

Synthesis, Properties, and Applications, 2014

MRS Proceedings, 2002

This work reports the dynamic mechanical characterization of nanocomposites based on a poly(butyl... more This work reports the dynamic mechanical characterization of nanocomposites based on a poly(butyl acrylate) matrix filled with spherical particles of either polystyrene or silica both of diameter around 100 nm. A discrete numerical simulation, taking into account the microstructure and the nature of contact between reinforcing particles has been developed. This simulation enables to quantify the effect of interactions between filler particles on the elastic modulus, and in a more general sense, to clarify the concept of mechanical percolation. It gives results in very good agreement with experimental data.

Polymer Nanotube …, 2010

Page 1. 3 New Microscopy Techniques for a Better Understanding of the Polymer/ Nanotube Composite... more Page 1. 3 New Microscopy Techniques for a Better Understanding of the Polymer/ Nanotube Composite Properties K. Masenelli-Varlot, A. Bogner, C. Gauthier, L. Chazeau and JY Cavaillé Université de Lyon, INSA-Lyon, MATÉIS ...

Polymer Composites, 1996

Cellulose whiskers have been used as reinforcement in a copolymer matrix prepared from a latex ph... more Cellulose whiskers have been used as reinforcement in a copolymer matrix prepared from a latex phase. If a water suspension-mixing procedure is adopted, the fibril breakage that usually occurs during the mixing with a molten polymer can be avoided, and an enhanced filler dispersion can be expected. In this study, different processing methods have been used to prepare composite films, either by film casting (water evaporation) or by freeze drying, followed by classical compression or extrusion processes. The thermomechanical properties of these nanocomposites have been investigated, and the influence of processing conditions and the effect of whisker content have been considered. Processing conditions have a large influence on the mechanical behavior and can be classified in ascending order of their reinforcement efficiency: It can be attributed to a decrease of the apparent whisker aspect ratio, due to gradual breakage and/or orientation of the whiskers when hot pressing or extrusion is used. Below Tg, good agreement is found between experimental moduli and the theoretical predictions of the Halpin-Kardos equation. On the other hand, above Tgr a spectacular reinforcing effect is observed, which is widely underestimated by this short fiber composite model. This is related to the presence of a rigid cellulose network, linked by hydrogen bonds, when the whisker content is above its percolation threshold. The quality of this network (i.e., density and homogeneity) and thus, the magnitude of the reinforcing effect, depend on processing conditions.

Polymer, 2001

... Influence of the crystalline phase on the mechanical properties of unfilled and CaCO3 filled ... more ... Influence of the crystalline phase on the mechanical properties of unfilled and CaCO3 filled polypropylene . Part I :Structural and mechanical characterization. Thomas Labour 1 , CatherineGauthier 1 , Roland Seguela 1 , Gérard Vigier 1 , Y. Bomal, G. Orange. (2001). ...

Nature Materials, 2009

Colloidal particles are often seen as big atoms that can be directly observed in real space. They... more Colloidal particles are often seen as big atoms that can be directly observed in real space. They are therefore becoming increasingly important as model systems to study processes of interest in condensed-matter physics such as melting, freezing and glass transitions. The solidification of colloidal suspensions has long been a puzzling phenomenon with many unexplained features. Here, we demonstrate and rationalize the existence of instability and metastability domains in cellular solidification of colloidal suspensions, by direct in situ high-resolution X-ray radiography and tomography observations. We explain such interface instabilities by a partial Brownian diffusion of the particles leading to constitutional supercooling situations. Processing under unstable conditions leads to localized and global kinetic instabilities of the solid/liquid interface, affecting the crystal morphology and particle redistribution behaviour.

Journal of the American Ceramic Society, 2009

This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior ... more This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior of colloidal suspensions of alumina partic les during directional solidification by freezing. The combination of these techniques provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particle redistribution between the crystals and a particle-enriched phase, and the three-dimensional organization of the ice crystals. In this first part of two companion papers, the precursor phenomena leading to directional crystallization during the first instants of solidification are studied. Mullins-Sekerka instabilities are not necessary to explain the dynamic evolution of the interface pattern. Particle redistribution during these first instants is dependent on the type of crystals growing into the suspension. The insights gained into the mechanisms of solidification of colloidal suspensions may be valuable for the materials processing routes derived for this type of directional solidification (freeze-casting), and of general interest for those interested in the interactions between solidification fronts and inert particles.

Journal of Polymer Science Part B: Polymer Physics, 2007

The nonlinear effect at small strains (Payne effect) has been investigated in the case of silica-... more The nonlinear effect at small strains (Payne effect) has been investigated in the case of silica-filled styrene-butadiene rubber. The originality of this study lies in the careful preparation of samples in order to fix all parameters except one, that is, the modification of the silica ...

The Journal of Immunology, 2014

European Polymer Journal, 2013

Solid polymer electrolytes (SPEs) were prepared by incorporating either aqueous LiClO 4 or 1-ethy... more Solid polymer electrolytes (SPEs) were prepared by incorporating either aqueous LiClO 4 or 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI) ionic liquid into Poly(ethylene oxide) (PEO)/polybutadiene (PB) Interpenetrating Polymer Networks (IPNs). With a given PEO/PB ratio, either transparent or translucent films depending on the synthesis route of these IPNs, have been investigated. TEM observations confirm that the morphology of these IPN films depends also on the PEO weight proportion whereas mechanical properties measured by DMA are only slightly modified. Measurements of ionic conductivity of SPEs are also very dependent on the IPNs morphology. For instance, EMITFSI ionic conductivity increases over four orders of magnitude from 2.2 Â 10 À7 to 2.5 Â 10 À3 S cm À1 at 30°C.

Comptes Rendus Chimie, 2003

We describe in this work the copolymerization reaction of 3-trimethoxysilyl propyl methacrylate (... more We describe in this work the copolymerization reaction of 3-trimethoxysilyl propyl methacrylate (MPS) with styrene (Styr.) and n-butyl acrylate (BuA) monomers through emulsion polymerization. The so-produced hybrid copolymer (P(BuA-co-MPS)) and terpolymer (P(Styr-co-BuA-co-MPS)) latexes were cast into films that displayed a good optical transparency. The copolymers microstructure in the films was characterized by FTIR, 13 C and 29 Si solid state NMR spectroscopies, and was found to be highly dependent on parameters such as the monomer feed composition, the suspension pH and the silane addition profile. The films obtained from the hybrid latexes showed improved dynamic mechanical properties indicating that a reinforcing organo-mineral network had formed in the composite materials. The dynamic modulus of the hybrids increased with increasing silane contents while, concurrently, the tan d peak shifted to higher temperatures, broadened and decreased in intensity. To cite this article: S. Vitry et al., C. R. Chimie 6 (2003).

Composites Science and Technology, 2006

Fibrous arrays and composites are among the strongest structures created by man or found in natur... more Fibrous arrays and composites are among the strongest structures created by man or found in nature. Such materials often fail in a slow, cumulative fashion, suppressing the sudden occurrence of rapid structural collapse. Our classical understanding of the statistical tensile strength and failure of unidirectional composites is usually based on a stochastic model where the key predictor is the size (N*) of a critical cluster of adjacent broken fibres, which inevitably leads to final composite failure. Here we show, via direct measurements using high-resolution synchrotron X-ray tomography, that in a quartz-epoxy composite the classical stochastic theory underpredicts -by a factor 3-5 -the size N* of the critical Ôfailed-fibreÕ cluster. A simple fracture mechanics argument which relates the critical fibre cluster size to the material strength is proposed to account for our data.

Composites Science and Technology, 2005

The reinforcement of rubbery matrices by vapour grown carbon nanofibres (VGCFs) is studied in the... more The reinforcement of rubbery matrices by vapour grown carbon nanofibres (VGCFs) is studied in the case of a rubbery epoxy and a styrene butadiene rubber (SBR). In the case of epoxy, the VGCF were introduced in the hardener and blended with the prepolymer. Nanocomposites were produced by subsequent polymerization. For the second matrix, samples were prepared by casting of a mixture of SBR latex and a water suspension of VGCF. Evaluation of mechanical performances revealed a linear increase of the modulus measured above and below the glass transition temperature for nanofibre content up to 10 wt%. This increase is low, but in good agreement with the estimation based on mechanical coupling models. In the case of epoxy matrix, the ultimate stress and strain are largely increased, even for very low fibre content (i.e. 1 wt%). However, this improvement is not observed in the case of nanocomposites based on SBR matrix, due to the non-optimized dispersion of the fibres.

Biochimie, 2003

Using precise examples, this paper shows that carbon 13 NMR spectroscopy in conjunction with radi... more Using precise examples, this paper shows that carbon 13 NMR spectroscopy in conjunction with radioactive and enzymatic methods as well as with adequate mathematical modeling of metabolic pathways allows not only to identify but also to quantify fluxes through enzymes involved in substrate and drug metabolism. Carbon 13 NMR spectroscopy is a tool of unprecedented power to unravel the complexity of renal metabolism. Currently it plays a major role in what is nowadays called metabolomics.

Biochemical Journal, 2005

The metabolism of glutamine, a physiological substrate of the human kidney, plays a major role in... more The metabolism of glutamine, a physiological substrate of the human kidney, plays a major role in systemic acid-base homoeostasis. Not only because of the limited availability of human renal tissue but also in part due to the lack of adequate cellular models, the mechanisms regulating the renal metabolism of this amino acid in humans have been poorly characterized. Therefore given the renewed interest in their use, human precision-cut renal cortical slices were incubated in Krebs-Henseleit medium (118 mM NaCl, 4.7 mM KCl, 1.18 mM KH2PO4, 1.18 mM MgSO4*7H2O, 24.9 mM NaHCO3 and 2.5 mM CaCl2*2H2O) with 2 mM unlabelled or 13C-labelled glutamine residues. After incubation, substrate utilization and product formation were measured by enzymatic and NMR spectroscopic methods. Glutamate accumulation tended to plateau but glutamine removal and ammonia, alanine and lactate production as well as flux through GLDH (glutamate dehydrogenase) increased to various extents with time for up to 4 h of incubation indicating the metabolic viability of the slices. Valproate, a stimulator of renal glutamine metabolism, markedly and in a dose-dependent fashion increased ammonia production. With [3-13C]glutamine as a substrate, and in the absence and presence of valproate, [13C]glutamate, [13C]alanine and [13C]lactate accounted for 81 and 96%, 34 and 63%, 30 and 46% of the glutamate, alanine and lactate accumulations measured enzymatically respectively. The slices also metabolized glutamine and retained their reactivity to valproate during incubations lasting for up to 48 h. These results demonstrate that, although endogenous metabolism substantially operates in the presence of glutamine, human precision-cut renal cortical slices are metabolically viable and strongly respond to the ammoniagenic effect of valproate. Thus, this experimental model is suitable for metabolic and pharmaco-toxicological studies.

Biochimica et Biophysica Acta (BBA) - Biomembranes, 1988

In the kidney, filtered proteins are rapidly reabsorbed so that the final excretion is less than ... more In the kidney, filtered proteins are rapidly reabsorbed so that the final excretion is less than 0.1% of the filtered amount for low molecular weight proteins such as fl2-microgiobulin and a few percent for albumin. In order to investigate the affinity of proteins for luminal membranes, rat renal brush-border membranes were incubated with les l-labelled human/~2-microgiobulin and the initial binding rate determined by the filtration method. Scatchard plot analysis of binding rate revealed two types of binding sites: one with K m = 0.25 • 10 -6 M and Vm~ , --0.1 nmol/min per mg protein and another with K m = 1" 10-s M and Vma x = 1.3 nmul/min per mg protein. The lower affinity type is likely to represent non-specific binding the physiological role of which is to be discussed. The higher affinity sites seem to play the major role in binding rate. fl2-Microglobulin initial binding is reversible, and inhibited by bovine serum albumin. Comparison of the time course of bound fl2-microglobulin removal by unlabelled/~2-microglobulin and by albumin suggests that these two proteins have a different internalization mechanism.