Biomedical subjects

E Thiaudiere

Publications and source records attributed to E Thiaudiere.

6 recordsLinked to original sources

PubMed2000

Aminomethylphosphonate and 2-aminoethylphosphonate as (31)P-NMR pH markers for extracellular and cytosolic spaces in the isolated perfused rat liver.

Aminomethylphosphonate (NMePo) and 2-aminoethylphosphonate (NEthPo) were evaluated as alternative pH indicators in the isolated perfused rat liver using (31)P-nuclear magnetic resonance (NMR). NMePo did not distribute within cells and remained in the extracellular space. It exhibited pH titration with a low pK(a) value (5.35). This behaviour makes NMePo useful for extracellular volume or acidic pH determination. In contrast, NEthPo accumulated within cells without altering liver energetic steady state, evaluated from nucleosides triphosphates resonances, even for prolonged (100 min) experiments. Withdrawal of NEthPo from perfusate revealed a residual resonance corresponding to the internalized amount of this phosphonate. This fraction was almost stable vs time and allowed determination of spin-lattice relaxation time constant T(1) within the liver (2.2 +/- 0.3 s; n = 6). Comparison of the titration curves for NEthPo and inorganic phosphate revealed that the accuracy of pH determination within physiologic or acidic range in both cases was comparable. Finally, when extracellular pH was decreased, the NEthPo resonance frequency was found to undergo the same chemical shift variations as observed for cytosolic P(i) signal, which was in good agreement with a cytosolic accumulation of this phosphonate. Therefore, NEthPo could be considered as an interesting cytosolic pH probe suitable for (31)P-NMR measurements, especially when experimental conditions prevent reliable observation of cytosolic Pi resonance.

Aminoethylphosphonic Acid↗

PubMed2000

Single-coil surface imaging using a radiofrequency field gradient

A method for in-plane imaging of large objects as compared to the RF coil is proposed based on the use of a single specially designed surface coil, without using B(0) gradients. A constant B(1) gradient was generated along the main axis of a ladder-shaped coil, and RF-encoding along the direction of the gradient made it possible to obtain spin-density profiles. Successive acquisitions of profiles obtained by translation of the NMR coil resulted in distorted images-due to the presence of non-zero gradients perpendicular to the constant gradient-that were successfully processed using a mathematical treatment based on linear combinations of calculated altered images from single-pixel objects. Copyright 2000 Academic Press.

Journal Article↗

PubMed2000

The metabolism of [3-(13)C]lactate in the rat brain is specific of a pyruvate carboxylase-deprived compartment.

Lactate metabolism in the adult rat brain was investigated in relation with the concept of lactate trafficking between astrocytes and neurons. Wistar rats were infused intravenously with a solution containing either [3-(13)C]lactate (534 mM) or both glucose (750 mM) and [3-(13)C]lactate (534 mM). The time courses of both the concentration and (13)C enrichment of blood glucose and lactate were determined. The data indicated the occurrence of [3-(13)C]lactate recycling through liver gluconeogenesis. The yield of glucose labeling was, however, reduced when using the glucose-containing infusate. After a 20-min or 1-h infusion, perchloric acid extracts of the brain tissue were prepared and subsequently analyzed by (13)C- and (1)H-observed/(13)C-edited NMR spectroscopy. The (13)C labeling of amino acids indicated that [3-(13)C]lactate was metabolized in the brain. Based on the alanine C3 enrichment, lactate contribution to brain metabolism amounted to 35% under the most favorable conditions used. By contrast with what happens with [1-(13)C]glucose metabolism, no difference in glutamine C2 and C3 labeling was evidenced, indicating that lactate was metabolized in a compartment deprived of pyruvate carboxylase activity. This result confirms, for the first time from an in vivo study, that lactate is more specifically a neuronal substrate.

Animals↗

PubMed1993

Compartmentation of inorganic phosphate in perfused rat liver. Can cytosol be distinguished from mitochondria by 31P NMR?

Compartmentation of inorganic phosphate was studied in intact perfused rat liver at 4 degrees C by 31P NMR. It was shown that decreases in cytosolic pH or cytosolic Pi concentration induced the appearance of an additional Pi resonance at low field which was assigned to Pi from an alkaline compartment. Valinomycin (K+ ionophore) induced a further splitting of the lines whereas nigericin (K+/H+ antiport) or potassium cyanide (inhibitor of cytochrome oxidase) had opposite effects. As valinomycin acts mainly on the cytosolic/mitochondrial K+ gradient and KCN on the mitochondrial respiratory chain, it was deduced that the alkaline compartment as revealed by the second Pi resonance was probably mitochondria. Single Pi lines observed on perchloric extracts of livers exhibiting two resonances during cold perfusion confirmed that the split peaks in the intact liver indeed arose from the same molecular species.

Animals↗

PubMed1989

Interaction of staphylococcal delta-toxin and synthetic analogues with erythrocytes and phospholipid vesicles. Biological and physical properties of the amphipathic peptides.

Staphylococcal delta-toxin, a 26-residue amphiphilic peptide is lytic for cells and phospholipid vesicles and is assumed to insert as an amphipathic helix and oligomerize in membranes. For the first time, the relationship between these properties and toxin structure is investigated by means of eight synthetic peptides, one identical in sequence to the natural toxin, five 26-residue analogues and two shorter peptides corresponding to residues 1-11 and 11-26. These peptides were designed by the Edmundson wheel axial projection in order to maintain: (a) the hydrophilic/hydrophobic balance while rationalizing the sequence, (b) the alpha-helical configuration and (c) the common epitopic structure. The fluorescence of the single Trp residue was used to monitor the behaviour of the natural toxin and analogues. All 26-residue analogues were hemolytically active although to a lesser extent than natural toxin. The peptide of residues 11-26 bound lipids weakly and was hemolytic at high concentration. The peptide of residues 1-11 did not bind lipids and was hemolytically inactive. All peptides except the latter cross-reacted in immunoprecipitation tests with the natural toxin. The study of a 26-residue analogue by circular dichroism revealed an alpha-helical configuration in both the free and lipid-bound state. Changes in the fluorescence of the peptides in the presence of lipid micelles and bilayers varied according to the position of the reporter group. When bound to lipids, Trp5, Trp16 and the Fmoc-1 positions of the analogues became buried while Trp15 of the natural toxin and its synthetic replicate remained more exposed. All changes are rationalized by the proposal of an amphipathic helix whose hydrophobic face is embedded within the apolar core of bilayers while the hydrophilic and charged face remains more exposed to solvent.

Animals↗

PubMedDate not supplied

Magnetization transfer fast imaging of implanted glioma in the rat brain at 4.7 T: interpretation using a binary spin-bath model.

C6 glioma cells were implanted in the left caudate nucleus of the rat brain. Histologic studies confirmed the presence of neoplastic tissue surrounded by a thin edematous region. Proton magnetization transfer contrast (MTC) fast imaging, using continuous wave off-resonance irradiation, was performed in vivo at 4.7 T with the rapid acquisition with relaxation enhancement (RARE) sequence. The observed MTC allowed very clear distinction of the tumoral region, in which magnetization transfer (MT) ratios were lower than in healthy tissues. Contrasts were analyzed as a function of the offset frequency and the amplitude of the radiofrequency (RF) irradiation. The contrast was higher between the contralateral basal ganglia and the tumor and lower between the tumor and the temporal lobe. Modeling of MT in the three brain regions was performed using a system including free water and a pool of protons with restricted motions. The rate of exchange between the two pools exhibited a decreasing hierarchy from the basal ganglia to the tumor. T2B values for the immobile protons ranged from 9.3 microsec in the basal ganglia to 7.5 microsec for the glioma. The acquisition conditions leading to the highest contrasts between the tumor and the healthy tissues correspond to 3,000 Hz offset frequency and 300 to 700 Hz RF irradiation amplitude.

Animals↗