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  • 1
    Electronic Resource
    Electronic Resource
    Transport of glutamine inXenopus laevis oocytes: Relationship with transport of other amino acids (1989)
    Springer
    The journal of membrane biology 112 (1989), S. 149-157 
    Details
    ISSN: 1432-1424
    Keywords: Xenopus oocyte ; amino acid ; Na+-dependent transport ; glutamine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have investigated transport of the amino acid glutamine across the surface membranes of prophase-arrestedXenopus laevis oocytes. Glutamine accumulation was linear with time for 30 min; it was stereospecific with aK m of 0.12±0.02mm andV max of 0.92±0.17 pmol/oocyte · min forl-glutamine. Transport ofl-glutamine was Na+-dependent, the cation not being replaceable with Li+, K+, choline, tris(hydroxymethyl)-aminomethane (Tris), tetramethylammonium (TMA) or N-methyld-glucamine NMDG); external Cl− appeared to be necessary for full activation of Na+-dependent glutamine transport. Two external Na+ may be required for the transport of one glutamine molecule.l-glutamine transport (at 50 μm glutamine) was inhibited by the presence of other amino acids:l-alanine,d-alanine,l-leucine,l-asparagine andl-arginine (about 60% inhibition at 1mm);l-histidine,l-valine and glycine (25 to 40% inhibition at 1mm);l-serine,l-lysine,l-phenylalanine andl-glutamate (45 to 55% inhibition at 10mm). N-methylaminoisobutyric acid (meAIB) had no effect at 10mm, but 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid (BCH) inhibited Na+/glutamine transport by about 50% at 10mm.l-glutamine was a competitive inhibitor of the Na+-dependent transport ofl-alanine,d-alanine andl-arginine; this evidence is consistent with the existence of a single system transporting all four amino acids. Glutamine uptake in oocytes appears to be catalyzed by a transport system distinct from the cotransport Systems A, ASC, N and Gly, although it resembles System B0,+.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01871276
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  • 2
    Electronic Resource
    Electronic Resource
    Transport and membrane binding of the glutamine analogue 6-diazo-5-oxo-L-norleucine (DON) in Xenopus laevis oocytes (1992)
    Springer
    The journal of membrane biology 128 (1992), S. 181-191 
    Details
    ISSN: 1432-1424
    Keywords: Xenopus oocyte ; amino acid ; Na+-dependent transport ; membrane binding
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Summary We have examined transport and membrane binding of 6-diazo-5-oxo-l-norleucine (DON, a photoactive diazo-analogue of glutamine) and their relationships to glutamine transport in Xenopus laevis oocytes. DON uptake was stereospecific and saturable (V max of 0.44 pmol/oocyte · min and a K m of 0.065 mm). DON uptake was largely Nau+ dependent (80% at 50 μ m DON) and inhibited (〉75%) by glutamine and arginine (substrates of the System B0,+ transporter) at 1 mm. Glutamine and DON show mutual competitive inhibition of Na+-dependent transport. Preincubation of oocytes in medium containing 0.1 mm DON for 24 or 48 hr depressed the V max for System B0,+ transport (as measured by Na+-dependent glutamine uptake), this effect was highly specific (neither d-DON nor the System B0,+ substrates glutamine and d-alanine showed any independent effect) and required Na+ ions. Glutamine (1 mm in preincubation medium) protected transport from inhibition by DON. The possibility that specific inactivation of System B0,+ by DON reflects attachment of DON to the transporter was tested by examining the binding of [14C]DON to Xenopus oocyte membranes. Oocytes incubated in 100 mm NaCl in the presence of [14C]DON for up to 48 hr showed 2.4-fold higher 14C-binding to membranes than oocytes incubated in choline chloride. Na+-dependent DON binding (31 ± 11 fmol/μg membrane protein) was suppressed by external glutamine, arginine or alanine and was largely confined to a membrane protein fraction of 48–65 kDa (as assessed by SDS-polyacrylamide gel electrophoresis). The present studies indicate that DON and glutamine uptake in oocytes are both mediated by System B0,+ and demonstrate that DON binding to a particular membrane protein fraction is associated with inactivation of the transporter, offering the prospect of using [14C]DON as a covalent label for the transport protein in order to facilitate its isolation and subsequent biochemical characterization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00231811
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  • 3
    Electronic Resource
    Electronic Resource
    Application of ultrasonic transit time flowmetry to the measurement of umbilical vein blood flow at caesarean section (1996)
    Oxford, UK : Blackwell Publishing Ltd
    BJOG 103 (1996), S. 0 
    Details
    ISSN: 1471-0528
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Objective To determine the applicability of ultrasonic transit time flowmetry to the measurement at caesarean section of umbilical vein blood flow rate and to examine the relationship between flow rates and birthweight for gestational age.Design Umbilical vein blood flow was measured at caesarean section using a transonic time flow probe on a loop of the umbilical cord in 33 appropriate and 21 small for gestational age fetuses.Results The mean (SD) umbilical vein blood flow in the 54 fetuses was 78.4 (23.1) ml kg−1 min−1. There was a linear relation between umbilical vein blood flow measured by ultrasonic transit time flowmetry and birthweight (r= 0.63, P 〈 0.0001). The mean umbilical vein blood flow in appropriate for gestational age fetuses [90 (18) ml kg−1 min−1] was greater than that in the small for gestational age group [66 (23) ml kg−1 min−1]; P 〈 0.04).Conclusions Umbilical vein blood flow measurements obtained by the ultrasonic transit time flowmetry technique are simple to perform and compare well with reported values obtained by the Doppler ultrasound technique (when vessel diameter is greater than 4 mm). Umbilical venous blood flow rate is significantly lower in small for gestational age fetuses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-0528.1996.tb09551.x
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  • 4
    Electronic Resource
    Electronic Resource
    Control of the Size of the Human Muscle Mass (2004)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 66 (2004), S. 799-828 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: This review is divided into two parts, the first dealing with the cell and molecular biology of muscle in terms of growth and wasting and the second being an account of current knowledge of physiological mechanisms involved in the alteration of size of the human muscle mass. Wherever possible, attempts have been made to interrelate the information in each part and to provide the most likely explanation for phenomena that are currently only partially understood. The review should be of interest to cell and molecular biologists who know little of human muscle physiology and to physicians, physiotherapists, and kinesiologists who may be familiar with the gross behavior of human muscle but wish to understand more about the underlying mechanisms of change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physiol.66.052102.134444
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  • 5
    Electronic Resource
    Electronic Resource
    Control of the Size of the Human Muscle Mass (2004)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 66 (2004), S. 799-828 
    Details
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: This review is divided into two parts, the first dealing with the cell and molecular biology of muscle in terms of growth and wasting and the second being an account of current knowledge of physiological mechanisms involved in the alteration of size of the human muscle mass. Wherever possible, attempts have been made to interrelate the information in each part and to provide the most likely explanation for phenomena that are currently only partially understood. The review should be of interest to cell and molecular biologists who know little of human muscle physiology and to physicians, physiotherapists, and kinesiologists who may be familiar with the gross behavior of human muscle but wish to understand more about the underlying mechanisms of change.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.physiol.66.052102.134444
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  • 6
    Electronic Resource
    Electronic Resource
    PROTEIN AND AMINO ACID METABOLISM DURING AND AFTER EXERCISE AND THE EFFECTS OF NUTRITION (2000)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Nutrition 20 (2000), S. 457-483 
    Details
    ISSN: 0199-9885
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Sustained dynamic exercise stimulates amino acid oxidation, chiefly of the branched-chain amino acids, and ammonia production in proportion to exercise intensity; if the exercise is intense enough, there is a net loss of muscle protein (as a result of decreased protein synthesis, increased breakdown, or both); some of the amino acids are oxidized as fuel, whereas the rest provide substrates for gluconeogenesis and possibly for acid-based regulation. Protein balance is restored after exercise, but no hypertrophy occurs with habitual dynamic exercise. Resistance exercise causes little change in amino acid oxidation but probably depresses protein synthesis and elevates breakdown acutely. After exercise, protein synthesis rebounds for 〈=48 h, but breakdown remains elevated, and net positive balance is achieved only if amino acid availability is increased. There is no evidence that habitual exercise increases protein requirements; indeed protein metabolism may become more efficient as a result of training.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.nutr.20.1.457
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  • 7
    Electronic Resource
    Electronic Resource
    Na+/amino acid coupling stoichiometry of rheogenic system B0,+ transport in Xenopus oocytes is variable (1994)
    Springer
    Pflügers Archiv 426 (1994), S. 121-128 
    Details
    ISSN: 1432-2013
    Keywords: Glutamine ; Alanine ; Arginine ; Membrane carriers ; Evoked currents
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract Using electrophysiological and radiotracer studies in parallel, we have investigated the characteristics of the endogenous Na+-dependent amino acid transporter (system B0,+) in Xenopus oocytes with regard to ion dependence, voltage dependence and transport stoichiometry. In voltage-clamped oocytes (−60 mV) superfusion with saturating concentrations of amino acids (1 mM) in 100 mM NaCl resulted in reversible, inward currents (mean±SEM): alanine, 1.83±0.09 nA (n=21); arginine, 2.54±0.18 nA (n=17); glutamine, 1.73±0.10 nA (n=19). Only arginine evoked a current in choline medium (0.50±0.13 nA, n=10), whereas Cl− replacement had no effect on evoked currents. The glutamine-evoked current was saturable (I max=1.73 nA, glutamine K m=0.12 mM) and linearly dependent upon voltage between −90 and −30 mV. Using direct and indirect (activation) methods, we found that transport can proceed with Na+/amino acid coupling stoichiometry of either 1∶1 or 2∶1, but coupling was the same for each amino acid tested (alanine, arginine and glutamine) within a batch of oocytes (i.e. from a single toad). Despite the net single positive charge on arginine, the magnitude of the net transmembrane charge movement during Na+-coupled arginine transport was identical to that for the zwitterionic neutral amino acids glutamine and alanine; this may be explained by a concomitant stimulation of K+ efflux during arginine transport with a putative coupling of 1 K+∶1 arginine.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00374679
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  • 8
    Electronic Resource
    Electronic Resource
    Different patterns of protein turnover in skeletal and gastrointestinal smooth muscle and the production of Nτ-methylhistidine during fasting in the rat (1986)
    Springer
    Bioscience reports 6 (1986), S. 143-153 
    Details
    ISSN: 1573-4935
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract During four days of fasting in rats skeletal muscle protein synthesis fell pro-gressively, whereas skeletal muscle protein breakdown was unchanged until the third and fourth days when it rose dramatically. In contrast, the synthetic rate of smooth muscle protein was unchanged during three days of fasting despite a loss of protein content, indicating an abrupt rise in protein breakdown in this tissue on the first day of fasting which was sustained thereafter. Urinary excretion of Nτ-methylhistidine was significantly increased throughout fasting. The concentration of free Nτ-methylhistidine in plasma and in muscle tissue was elevated throughout the period of fasting. This elevation was not caused by reduced renal clearance, but appears to have been mainly the result of increased breakdown of Nτ-methylhistidine-containing proteins in tissues other than skeletal muscle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01115000
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  • 9
    Electronic Resource
    Electronic Resource
    Exercise and the oxidation and storage of glucose, maize-syrup solids and sucrose determined from breath13CO2 (1996)
    Springer
    European journal of applied physiology 72 (1996), S. 349-356 
    Details
    ISSN: 1439-6327
    Keywords: Exercise ; Carbohydrate ; Oxidation ; Carbon stable isotope
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Abstract In order to determine which of maize syrup solids, glucose and sucrose were more readily oxidised during exercise and least readily oxidised afterwards, the rates of oxidation of three almost identical isoenergetic solutions of carbohydrates (330 ml of 18.5% w/v solutions of glucose, maize syrup solids and sucrose, 989–1050 kJ total energy) naturally enriched with13C were examined at rest and during and after 1 h uphill walking at 75% maximum oxygen uptake ( $$\dot VO_{2max}$$ ) in nine subjects [mean (SEM) $$\dot VO_{2max}$$ , 45.4 (0.9) ml·kg−1-min−1]. Rates of production of expired13CO2 were used to estimate rates of oxidation of each exogenous substrate. Energy expenditure and the contributions from total carbohydrate and fat oxidation were calculated from whole-body gas exchange. At rest, aize syrup solids were oxidised less than sucrose during the 1st h [glucose 2.7 (0.2) g · h−1, maize syrup solids 1.9 (0.3) g · h−1, sucrose 3.7 (0.2) g · h−1; maize syrup solids vs sucroseP 〈 0.01], but this difference disappeared after a further 3 h at rest [glucose 8.3 (0.5) g · h−1, maize syrup solids 7.7 (0.5) g · h−1, sucrose 8.1 (0.4) g · h-1]. During exercise, all the carbohydrates were oxidised to the same extent [glucose 23.0 (2.8) g · h−1, maize syrup solids 23.9 (3.4) g · h−1, sucrose 27.5 (2.6) g · h−1) but during 4 h of recovery after exercise, maize syrup solids were oxidised least [glucose 4.6 (0.1) g · h−1, maize syrup solids 3.7 (0.1) g · h−1, sucrose 6.4 (0.1) g · h−1;P 〈 0.05] suggesting that it may be stored to a greater extent. The results suggest that 18.5% glucose, maize syrup solids and sucrose solutions were equally well oxidised during exercise. During recovery from exercise maize syrup solids were oxidised less than glucose, which in turn was oxidised less than sucrose.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00599696
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  • 10
    Electronic Resource
    Electronic Resource
    Preparation of CO2 from blood and protein-bound amino acid carboxyl groups for quantification and 13C-isotope measurements (1984)
    Chichester : Wiley-Blackwell
    Biological Mass Spectrometry 11 (1984), S. 348-352 
    Details
    ISSN: 0306-042X
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Measurements of protein and amino acid metabolism in man using stable isotopes and selected ion monitoring gas chromatographic/mass spectrometric techniques are limited by the requirement of relatively high levels of labelling for adequate precision ( 〉 0.05 at % excess). We describe here a means of extending the scope of such studies by measurement of lower levels of enrichment achieved in gaseous CO2 derived from whole blood or protein-bound amino acids following the administration of tracer amounts of appropriately labelled substrates. Construction and operation of a novel glass vacuum line required for this work are described in detail and specific applications relevant to clinical investigations are outlined. Measurements of both the total amount of CO2 and its 13C enrichment are performed in an isotope-ratio mass spectrometer which provides acceptable levels of accuracy and reproducibility for both measurements ( ±0.1% and ±0.0001 at% excess respectively).
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bms.1200110706
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