Transport of glutamine across blood-facing membranes of perfused rat jejunum

1989 ◽  
Vol 256 (4) ◽  
pp. E550-E558 ◽  
Author(s):  
P. M. Taylor ◽  
C. J. Egan ◽  
M. J. Rennie
Keyword(s):  
Rat Jejunum ◽  
Portal Circulation ◽  
Dilution Technique ◽  
Mutual Inhibition ◽  
System A ◽  
Glutamine Transporter ◽  
System L ◽  
Dependent Component ◽  
Glutamine Transport ◽  
Tracer Isotope

Transport of glutamine and other neutral amino acids across the blood-facing membranes of isolated, dually perfused rat jejunum was measured using a paired-tracer isotope-dilution technique. Glutamine, asparagine, histidine, alanine, and leucine showed mutual inhibition of transport. The major component of physiological glutamine transport was saturable (Km = 0.88 +/- 0.15 mM, Vmax = 454 +/- 49 nmol.g-1.min-1; mean +/- SE), stereospecific and Na-independent and appeared to exhibit symmetry of glutamine transport; it most resembled system L. The minor Na-dependent component of glutamine transport resembled system A, i.e., it transported N-methylaminoisobutyric acid (Km approximately equal to 10 microM, Vmax approximately equal to 1.2 nmol.g-1.min-1). At 0.5 mM glutamine transport was insensitive to insulin and glucagon and was unaffected by perfusate pH (7.0-7.8). Glutamine extracted by the jejunum is rapidly utilized; at physiological blood glutamine concentrations the basolateral glutamine-transporter flux may thus not only restrict intestinal glutamine catabolism but also the consequent release of glutamine-derived ammonia (a substrate and stimulant of ureogenesis) into the portal circulation.

Characteristics of L-glutamine transport by lactating mammary tissue

1998 ◽  
Vol 65 (2) ◽  
pp. 199-208 ◽  
Author(s):  
DAVID T. CALVERT ◽  
TAE-GYU KIM ◽  
JAI-JUN CHOUNG ◽  
CAROLYNN BURNS ◽  
DAVID B. SHENNAN
Keyword(s):  
Mammary Gland ◽  
Isobutyric Acid ◽  
Mammary Tissue ◽  
System A ◽  
System L ◽  
Dependent Component ◽  
Glutamine Transport ◽  
Rat Mammary Gland ◽  
Glutamine Uptake

The transport of L-glutamine by the lactating rat mammary gland has been investigated using rat mammary tissue explants and the in situ perfused rat mammary gland. L-glutamine uptake by both explants and the perfused mammary gland was via both Na+-dependent and Na+-independent pathways. It appeared that these pathways are situated on the blood-facing aspect of the mammary gland. L-glutamine uptake by both mammary preparations was markedly inhibited by 2-aminobicyclo[2,2,1]heptane-2-carboxylic acid in the absence of external Na+. This is consistent with L-glutamine uptake via system L. The Na+-dependent component(s) of L-glutamine uptake remains to be precisely identified. However, system A can be ruled out on the basis that L-glutamine was not inhibited by (methylamino)isobutyric acid. Mammary tissue concentrates L-glutamine with respect to both milk and plasma: we suggest that the Na+-dependent component(s) of L-glutamine uptake is responsible for generating the intracellular to extracellular concentration gradient.

Characteristics of glutamine transport in dog jejunal brush-border membrane vesicles

1989 ◽  
Vol 257 (1) ◽  
pp. G80-G85 ◽  
Author(s):  
N. M. Bulus ◽  
N. N. Abumrad ◽  
F. K. Ghishan
Keyword(s):  
Brush Border ◽  
Brush Border Membrane ◽  
Ph Dependence ◽  
Membrane Vesicles ◽  
Brush Border Membrane Vesicles ◽  
Transport Systems ◽  
System A ◽  
System L ◽  
Glutamine Transport ◽  
Glutamine Uptake

The present study characterizes glutamine transport across brush-border membrane vesicles (BBMV) prepared from dog jejunum. The purity of these vesicles was demonstrated by a 20-fold enrichment of leucine aminopeptidase, a marker for BBM. Glutamine uptake was found to occur into an osmotically active space with no membrane binding and to exhibit temperature and pH dependence (optimal uptake at pH 7-7.5). Glutamine uptake was driven by an inwardly directed Na+ gradient with a distinct overshoot not observed under K+ gradient. Lithium could not substitute for Na+ as a stimulator of glutamine uptake. Na+-dependent glutamine uptake was not inhibited by methylaminoisobutyric acid, a typical substrate for system A, and was found to be electrogenic and saturable with a Km of 0.97 +/- 0.58 mM and a Vmax of 3.93 +/- 0.99 nmol.mg protein-1.10 s-1. A Na+-glutamine coupling ratio of 1:1 could be demonstrated by a plot of Hill transformation. Na+-independent glutamine uptake was found to be electroneutral and saturable with a Km of 3.70 +/- 0.66 mM and a Vmax of 2.70 +/- 1.55 nmol.mg protein-1.10 s-1. Inhibition studies confirmed the presence of a Na+-dependent as well as a Na+-independent carrier for glutamine uptake. We conclude that glutamine uptake across dog BBMV occurs via two transport systems: a Na+-dependent high-affinity system similar to the neutral brush-border system and a Na+-independent lower-affinity system similar to system L.

scholarly journals A rapid method for the functional reconstitution of amino acid transport systems from rat liver plasma membranes. Partial purification of System A

1988 ◽  
Vol 255 (3) ◽  
pp. 963-969 ◽  
Author(s):  
A R Quesada ◽  
J D McGivan
Keyword(s):  
Amino Acid ◽  
Rapid Method ◽  
Amino Acid Transport ◽  
Plasma Membranes ◽  
Transport Systems ◽  
Partial Purification ◽  
Acid Transport ◽  
Transport Activity ◽  
System A ◽  
System L

A rapid method for the functional reconstruction of amino acid transport from liver plasma-membrane vesicles using the neutral detergent decanoyl-N-glucamide (‘MEGA-10’) is described. The method is a modification of that previously employed in this laboratory for reconstitution of amino acid transport systems from kidney brush-border membranes [Lynch & McGivan (1987) Biochem. J. 244, 503-508]. The transport activities termed ‘System A’, ‘System N’, and ‘System L’ are all reconstituted. The reconstitution procedure is rapid and efficient and is suitable as an assay for transport activity in studies involving membrane fractionation. By using this reconstitution procedure, System A transport activity was partially purified by lectin-affinity chromatography.

Characterization of amino acid transport in human endothelial cells

1993 ◽  
Vol 265 (4) ◽  
pp. C1006-C1014 ◽  
Author(s):  
O. Bussolati ◽  
R. Sala ◽  
A. Astorri ◽  
B. M. Rotoli ◽  
V. Dall'Asta ◽  
...  
Keyword(s):  
Amino Acids ◽  
Endothelial Cells ◽  
Amino Acid ◽  
Umbilical Vein ◽  
Specific System ◽  
Human Umbilical Vein ◽  
System A ◽  
System L ◽  
Intracellular Amino Acids ◽  
Umbilical Vein Endothelial Cells

The transport of amino acids has been studied in human umbilical vein endothelial cells. Neutral amino acids enter human umbilical vein endothelial cells through three distinct agencies endowed with the characteristics of systems A, ASC, and L. Each system has been studied by evaluating the influx of preferential substrates. The influx of L-proline and 2-methylaminoisobutyric acid occurs through an Na(+)-dependent adaptively regulated trans-inhibited agency identifiable with system A. L-Threonine influx occurs mainly through a distinct Na(+)-dependent trans-stimulated pathway corresponding to system ASC. System L accounts for Na(+)-independent influx of L-leucine. These systems cooperate for the transport of L-glutamine, which is due mainly to system ASC, whereas the component due to the operation of system A increases upon amino acid starvation. No clear evidence was found for a glutamine-specific system ("system N"). Two systems, one Na+ dependent (system XAG-) and the other Na+ independent (system xc-), transport anionic amino acids. L-Arginine influx exhibits a poor dependence on extracellular Na+, whereas it is sensitive to conditions known to change membrane potential and to trans-stimulation by intracellular amino acids. These features are consistent with a process mediated by system y+ and may be of significance for the regulation of the intracellular concentration of L-arginine.

Quantitation of renal uric acid synthesis in the chicken

1978 ◽  
Vol 234 (5) ◽  
pp. F446-F451 ◽  
Author(s):  
Theodore Y. Chin ◽  
A. J. Quebbemann
Keyword(s):  
Uric Acid ◽  
Isotope Dilution ◽  
Activity Ratio ◽  
Specific Activity ◽  
Acid Synthesis ◽  
Systemic Circulation ◽  
Portal Circulation ◽  
Dilution Technique ◽  
Renal Metabolism ◽  
Isotope Dilution Technique

The contribution of uric acid synthesized in the kidney (nephrogenic uric acid) to the total uric acid excreted in the urine was studied in the chicken by use of the isotope-dilution technique. In the nonfasted chicken the urine-to-plasma specific activity ratio (SAR) of [14C]uric acid was 0.83, suggesting that a minimum of 17% of the uric acid excreted in the urine is synthesized in the kidney. During allopurinol infusion into the renal portal circulation of one kidney the SAR increased to 0.99, indicating that the renal synthesis of uric acid was almost completely inhibited and that the SAR is a valid indicator of the contribution of nephrogenic uric acid excreted into the urine without first entering the circulation. Chickens fasted for 18 h showed a lower rate of renal synthesis of uric acid. Hypoxanthine infusion into the systemic circulation increased the rate of renal synthesis of uric acid in both fasted and nonfasted chickens, suggesting that circulating precursor levels may in part regulate the renal synthesis of uric acid. kidney; specific activity ratio; allopurinol; renal metabolism Submitted on July 14, 1977

Amino acid transporters: éminences grises of nutrient signalling mechanisms?

2009 ◽  
Vol 37 (1) ◽  
pp. 237-241 ◽  
Author(s):  
Peter M. Taylor
Keyword(s):  
Amino Acid ◽  
Binding Sites ◽  
Mammalian Target Of Rapamycin ◽  
Amino Acid Transporters ◽  
System A ◽  
System L ◽  
Underlying Mechanisms ◽  
Substrate Binding Sites ◽  
Amino Acid Concentrations ◽  
Mtor Signalling

Nutrient signalling by the mTOR (mammalian target of rapamycin) pathway involves upstream sensing of free AA (amino acid) concentrations. Several AA-regulated kinases have recently been identified as putative intracellular AA sensors. Their activity will reflect the balance between AA flows through underlying mechanisms which together determine the size of the intracellular free AA pool. For indispensable AAs, these mechanisms are primarily (i) AA transport across the cell membrane, and (ii) protein synthesis/breakdown. The System L AA transporter is the primary conduit for cellular entry of indispensable neutral AAs (including leucine and phenylalanine) and potentially a key modulator of AA-sensitive mTOR signalling. Coupling of substrate flows through System L and other AA transporters (e.g. System A) may extend the scope for sensing nutrient abundance. Factors influencing AA transporter activity (e.g. hormones) may affect intracellular AA concentrations and hence indirectly mTOR pathway activity. Several AA transporters are themselves regulated by AA availability through ‘adaptive regulation’, which may help to adjust the gain of AA sensing. The substrate-binding sites of AA transporters are potentially direct sensors of AA availability at both faces of the cell surface, and there is growing evidence that AA transporters of the SNAT (sodium-coupled neutral AA transporter) and PAT (proton-assisted AA transporter) families may operate, at least under some circumstances, as transporter-like sensors (or ‘transceptors’) upstream of mTOR.

scholarly journals Substrate-specificity of glutamine transporters in membrane vesicles from rat liver and skeletal muscle investigated using amino acid analogues

1991 ◽  
Vol 278 (1) ◽  
pp. 105-111 ◽  
Author(s):  
S Y Low ◽  
P M Taylor ◽  
A Ahmed ◽  
C I Pogson ◽  
M J Rennie
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Rat Liver ◽  
Membrane Vesicles ◽  
Transport Processes ◽  
System A ◽  
Liver Membrane ◽  
Glutamine Transport ◽  
Fold Excess ◽  
Glutamine Uptake

We investigated the effects of glutamine and histidine analogues on glutamine transport processes in membrane vesicles prepared from rat liver (sinusoidal membrane) and skeletal muscle (sarcolemma). L-[14C]Glutamine is transported in these membranes predominantly by Systems N/Nm (liver and muscle respectively), and to a lesser extent by Systems A and L (e.g. about 60, 20 and 20% of total flux respectively via Systems N, A and L at 0.05 mM-glutamine in liver membrane vesicles). The glutamine anti-metabolites 6-diazo-5-oxo-L-norleucine and acivicin were relatively poor inhibitors of glutamine uptake into liver membrane vesicles (less than 25% inhibition at 20-fold excess) and appeared primarily to inhibit System A activity (i.e. N-methylaminoisobutyric acid-inhibitable glutamine uptake). In similar experiments azaserine (also a glutamine anti-metabolite) inhibited approx. 50% of glutamine uptake, apparently by inhibition of System A and also of System L (i.e. 2-amino-2-carboxybicyclo[2,2,1]heptane-inhibitable glutamine uptake). Glutamate gamma-hydroxamate, aspartate beta-hydroxamate, histidine and N'-methylhistidine were all strong inhibitors of glutamine uptake into liver membrane vesicles (greater than 65% inhibition at 20-fold excess), but neither homoglutamine nor N'-methylhistidine produced inhibition. L-Glutamate-gamma-hydroxamate was shown to be a competitive inhibitor of glutamine transport via System N (Ki approximately 0.6 mM). Glutamine uptake in sarcolemmal vesicles showed a similar general pattern of inhibition as in liver membrane vesicles. The results highlight limits on the substrate tolerance of System N; we suggest that the presence of both an L-alpha-amino acid group and a nitrogen group with a delocalized lone-pair of electrons (amide or pyrrole type), separated by a specific intramolecular distance (C2-C4 chain equivalent), is important for substrate recognition by this transporter.

scholarly journals Reduction of In Vivo Placental Amino Acid Transport Precedes the Development of Intrauterine Growth Restriction in the Non-Human Primate

Nutrients ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 2892
Author(s):  
Fredrick J. Rosario ◽  
Anita Kramer ◽  
Cun Li ◽  
Henry L. Galan ◽  
Theresa L. Powell ◽  
...  
Keyword(s):  
Amino Acid ◽  
Amino Acid Transport ◽  
Intrauterine Growth Restriction ◽  
Growth Restriction ◽  
Acid Transport ◽  
Mole Percent ◽  
System A ◽  
System L ◽  
Human Primate

Intrauterine growth restriction (IUGR) is associated with reduced placental amino acid transport (AAT). However, it remains to be established if changes in AAT contribute to restricted fetal growth. We hypothesized that reduced in vivo placental AAT precedes the development of IUGR in baboons with maternal nutrient restriction (MNR). Baboons were fed either a control (ad libitum) or MNR diet (70% of control diet) from gestational day (GD) 30. At GD 140, in vivo transplacental AA transport was measured by infusing nine (13)C- or (2)H-labeled essential amino acids (EAAs) as a bolus into the maternal circulation at cesarean section. A fetal vein-to-maternal artery mole percent excess ratio for each EAA was measured. Microvillous plasma membrane (MVM) system A and system L transport activity were determined. Fetal and placental weights were not significantly different between MNR and control. In vivo, the fetal vein-to-maternal artery mole percent excess ratio was significantly decreased for tryptophan in MNR. MVM system A and system L activity was markedly reduced in MNR. Reduction of in vivo placental amino acid transport precedes fetal growth restriction in the non-human primate, suggesting that reduced placental amino acid transfer may contribute to IUGR.

Effects of inhibition of myo-inositol transport on MDCK cells under hypertonic environment

1997 ◽  
Vol 272 (2) ◽  
pp. F267-F272 ◽  
Author(s):  
H. Kitamura ◽  
A. Yamauchi ◽  
T. Nakanishi ◽  
Y. Takamitsu ◽  
T. Sugiura ◽  
...  
Keyword(s):  
Mdck Cells ◽  
Competitive Inhibitor ◽  
Maximal Velocity ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
System A ◽  
Neutral Amino Acid Transporter ◽  
Colony Forming Efficiency ◽  
Dependent Component ◽  
Forming Efficiency

To investigate the role of myo-inositol under hypertonic conditions, we examined the effects of inhibition of myo-inositol transport in Madin-Darby canine kidney (MDCK) cells using an analog of myo-inositol, 2-O,C-methylene-myo-inositol (MMI). We first characterized the inhibitory effects of MMI on myo-inositol transport in MDCK cells. The Na+-dependent component of [3H] myo-inositol uptake was inhibited by MMI in a concentration-dependent manner, although MMI did not inhibit the activities of the betaine transporter and system A neutral amino acid transporter. We found decreased affinity for myo-inositol in the presence of MMI, whereas the maximal velocity (Vmax) of the transporter did not change. Thus MMI behaves as a competitive inhibitor of myo-inositol transport with a relatively high inhibition constant (K(i)) value (1.6 mM). Myo-inositol content in hypertonic MDCK cells was markedly reduced in the presence of 5 mM MMI, but MMI itself did not accumulate in these cells. The hypertonic cells began to detach in the presence of MMI 3 days after increasing medium osmolality, whereas MMI did not affect the cells in isotonic medium. We also examined the effects of MMI on colony-forming efficiency of MDCK cells. MMI decreased colony-forming efficiency in a concentration-dependent manner, and addition of myo-inositol returned the efficiency to the value without MMI. Addition of betaine also increased colony-forming efficiency in the presence of MMI. These results indicate that myo-inositol plays an important role in survival and growth under hypertonic environment.

Tertiary active transport of amino acids reconstituted by coexpression of System A and L transporters in Xenopus oocytes

2009 ◽  
Vol 297 (3) ◽  
pp. E822-E829 ◽  
Author(s):  
Fiona E. Baird ◽  
Kevin J. Bett ◽  
Catherine MacLean ◽  
Andrew R. Tee ◽  
Harinder S. Hundal ◽  
...  
Keyword(s):  
Amino Acids ◽  
Active Transport ◽  
Xenopus Oocytes ◽  
Plasma Concentrations ◽  
Transport Systems ◽  
Functional Coupling ◽  
Specific System ◽  
Tor Pathway ◽  
System A ◽  
System L

The System L transporter facilitates cellular import of large neutral amino acids (AAs) such as Leu, a potent activator of the intracellular target of rapamycin (TOR) pathway, which signals for cell growth. System L is an AA exchanger, proposed to accumulate certain AAs by coupling to dissipation of concentration gradient(s) of exchange substrates generated by secondary active AA transporters such as System A (SNAT2). We addressed the hypothesis that this type of coupling (termed tertiary active transport) acts as an indirect mechanism to extend the range of AA stimulating TOR to those transported by both Systems A and L (e.g., Gln) through downstream enhancement of Leu accumulation. System A overexpression enabled Xenopus oocytes to accumulate substrate AAs (notably Ser, Gln, Ala, Pro, Met; totaling 2.6 nmol/oocyte) from medium containing a physiological AA mixture at plasma concentrations. Net accumulation of System L (4F2hc-xLAT1) substrates from this medium by System L-overexpressing oocytes was increased by 90% (from 0.7 to 1.35 nmol/oocyte; mainly Leu, Ile) when Systems A and L were coexpressed, coincident with a decline in accumulation of specific System A substrates (Gln, Ser, Met), as expected if the latter were also System L substrates and functional coupling of the transport Systems occurred. AA flux coupling was confirmed as trans-stimulation of Leu influx in System L-expressing oocytes by Gln injection (0.5 nmol/oocyte). The observed changes in Leu accumulation are sufficient to activate the TOR pathway in oocytes, although intracellular AA metabolism limits the potential for AA accumulation by tertiary active transport in this system.

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