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 Transport of l-glutamine and l-glutamate across sinusoidal membranes of rat liver. Effects of starvation, diabetes and corticosteroid treatment

1992 ◽  
Vol 284 (2) ◽  
pp. 333-340 ◽  
Author(s):  
S Y Low ◽  
P M Taylor ◽  
H S Hundal ◽  
C I Pogson ◽  
M J Rennie
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Glutamate Uptake ◽  
Membrane Vesicles ◽  
Corticosteroid Treatment ◽  
Functional Expression ◽  
Liver Membrane ◽  
Health And Disease ◽  
Dependent Transport ◽  
Glutamine Uptake

There is increasing evidence that membrane transporters for glutamine and glutamate are involved in control of liver metabolism in health and disease. We therefore investigated the effects of three catabolic states [starvation (60 h), diabetes (4 days after streptozotocin treatment) and corticosteroid (8-day dexamethasone) treatment] associated with altered hepatic amino acid metabolism on the activity of glutamine and glutamate transporters in sinusoidal membrane vesicles from livers of treated rats. In control preparations, L-[14C]glutamine uptake was largely Na(+)-dependent, but L-[14C]glutamate uptake was largely Na(+)-independent. Vmax. values for Na(+)-dependent uptake of glutamine and/or glutamate exceeded control values (by about 2- and 12-fold respectively) in liver membrane vesicles from starved (glutamine), diabetic (glutamate) or steroid-treated (glutamine and glutamate) rats. The Km values for Na(+)-dependent transport of glutamine or glutamate and the rates of their Na(+)-independent uptake were not significantly altered by any treatment. Na(+)-independent glutamate uptake appeared to include a dicarboxylate-exchange component. The patterns of inhibition of glutamine and glutamate uptake by other amino acids indicated that the apparent induction of Na(+)-dependent amino acid transport in catabolic states included increased functional expression of systems A, N (both for glutamine) and X-ag (for glutamate). The results demonstrate that conditions resulting in increased secretion of catabolic hormones (e.g. corticosteroid, glucagon) are associated with increased capacity for Na(+)-dependent transport of amino acids into liver cells from the blood. The modulation of hepatic permeability to glutamine and glutamate in these situations may control the availability of amino acids for intrahepatic metabolic processes such as ureagenesis, ammonia detoxification and gluconeogenesis.

Effects of insulin and exercise on amino acid transport in rat skeletal muscle

1994 ◽  
Vol 266 (2) ◽  
pp. C524-C530 ◽  
Author(s):  
P. A. King
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Acute Exercise ◽  
Acid Transport ◽  
Rat Skeletal Muscle ◽  
Plasma Membrane Vesicles ◽  
System A ◽  
Alanine Transport ◽  
Glutamine Transport

In the present study, the initial rates of amino acid transport by isolated rat skeletal muscle plasma membrane vesicles were investigated. This approach facilitates the study of the transport of naturally occurring amino acids independent of the effects of cellular metabolism. Alanine and glutamine influxes were measured using a rapid filtration technique. Transport was examined in the presence and absence of Na and the properties of membranes from control, insulin-treated, or acutely exercised rats were studied. Both alanine and glutamine were transported by Na-dependent processes. The values for maximum rate of transport (Vmax) for Na-dependent alanine and glutamine transport were 203 and 224 pmol.mg-1.s-1, respectively. The K1/2 values were 2.9 mM alanine and 1.9 mM glutamine. The Vmax for Na-dependent alanine transport was increased by insulin treatment of the animal and by acute exercise. 2-(Methylamino)-isobutyric acid (MeAIB) partially inhibited the control Na-dependent alanine influx and completely inhibited the increase due to insulin or exercise treatment, indicating the importance of both system A and a non-system A, Na-dependent carrier for alanine transport. The Vmax for Na-dependent MeAIB uptake was also increased by insulin or exercise treatments of the rats. Unlike alanine, Na-dependent glutamine transport was not affected by insulin.

Characterization of Na(+)-independent glutamine transport in rat liver

1993 ◽  
Vol 265 (1) ◽  
pp. G90-G98 ◽  
Author(s):  
A. J. Pacitti ◽  
Y. Inoue ◽  
W. W. Souba
Keyword(s):  
Amino Acids ◽  
Rat Liver ◽  
Ph Dependence ◽  
Membrane Vesicles ◽  
Plasma Membrane Vesicles ◽  
Charged Amino Acids ◽  
Amino Acids Transport ◽  
System L ◽  
Glutamine Transport ◽  
Glutamine Uptake

In hepatic plasma membrane vesicles (HPMVs) from rat liver, we observed that approximately 40-45% of Na(+)-independent glutamine uptake occurs by a saturable carrier-mediated process. This component of glutamine uptake is mediated by a transport agency distinct from that of previously described systems for the Na(+)-independent transport of amino acids. Transport of glutamine was electroneutral and occurred into an osmotically active space with negligible membrane binding. The model system L substrate 2-amino-2-norbornane-carboxylic acid (BCH) showed no appreciable inhibition of Na(+)-independent glutamine uptake by HPMVs but effectively inhibited the uptake of leucine, a classic system L substrate, in identical vesicle preparations. Further evidence against system L-mediated glutamine transport was provided by the pH dependence and the lack of trans-stimulation of saturable uptake. Competition experiments with selected amino acids revealed a pattern of inhibition of glutamine transport that was inconsistent with assignment of glutamine entry to systems asc, T, or systems for the Na(+)-independent transport of the charged amino acids. This BCH-noninhibitable transport system in HPMVs was highly selective for glutamine, histidine, and, to a lesser extent, asparagine. Inhibition of Na(+)-independent glutamine transport by leucine was noncompetitive in nature. On the basis of Na+ independence, pH sensitivity, absence of trans-stimulation, and an amino acid selectivity similar to that of the previously described hepatic Na(+)-dependent system N, we have provisionally designated the glutamine transport agency described in this article as system "n."

scholarly journals Sensitivity of system A and ASC transport activities to thiol-group-modifying reagents in rat liver plasma-membrane vesicles. Evidence for a direct binding of N-ethylmaleimide and iodoacetamide on A and ASC carriers

1990 ◽  
Vol 271 (2) ◽  
pp. 297-303 ◽  
Author(s):  
E Pola ◽  
J Bertran ◽  
A Roca ◽  
M Palacín ◽  
A Zorzano ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Amino Acid ◽  
Rat Liver ◽  
Membrane Vesicles ◽  
Thiol Group ◽  
Transport Activity ◽  
Plasma Membrane Vesicles ◽  
Liver Plasma Membrane ◽  
System A ◽  
Alanine Transport

1. In the present study we have examined the sensitivity of A and ASC amino-acid-carrier activities in rat liver plasma-membrane vesicles to the thiol-group modifying reagents N-ethylmaleimide (NEM) and iodoacetamide (IA). To this end, the different Na(+)-dependent entities involved in alanine transport were assessed. 2. NEM inactivated Na(+)-dependent alanine transport as a result of the inhibition of both system A and ASC transport activities. The functional sensitivity of system A to NEM was greater than that of system ASC. 3. The presence of L-alanine (10 mM) during the exposure of vesicles to NEM afforded partial protection to system A, but not to the ASC, carrier. This effect was specific, since the presence of L-phenylalanine (10 mM) did not cause any protection. 4. Na+ did not protect A or ASC carriers against NEM inactivation; however, the presence of Na+ (100 mM-NaCl) and L-alanine (10 mM) during the exposure of the vesicles to NEM protected against inactivation of system A and ASC transport activities. The extent of protection was greater in the case of the system ASC transport activity than in the case of the A carrier. 5. IA also diminished Na(+)-dependent alanine transport by inhibition of A and ASC transport activities. Sodium and L-alanine afforded protection to both A and ASC transport activities from the inhibitory action of IA. The extent of protection induced by substrates was similar for both carriers. 6. It is concluded that there is one, or several, free thiol groups in A and ASC carriers, the integrity of which is essential for transport activity. Sensitivity to thiol-group-specific reagents and the pattern of protection with substrates against inactivation is different in A and ASC carriers. That suggests the existence of topological dissimilarities regarding the thiol-group containing site(s) in A and ASC amino acid carriers.

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.

Ceramide down‐regulates System A amino acid transport and protein synthesis in rat skeletal muscle cells

2004 ◽  
Vol 19 (3) ◽  
pp. 1-24 ◽  
Author(s):  
Russell Hyde ◽  
Eric Hajduch ◽  
Darren J. Powell ◽  
Peter M. Taylor ◽  
Harinder S. Hundal
Keyword(s):  
Skeletal Muscle ◽  
Protein Synthesis ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Muscle Cells ◽  
Skeletal Muscle Cells ◽  
Acid Transport ◽  
Rat Skeletal Muscle ◽  
System A

Glutamine transport by the blood-brain barrier: a possible mechanism for nitrogen removal

1998 ◽  
Vol 274 (4) ◽  
pp. C1101-C1107 ◽  
Author(s):  
Wha-Joon Lee ◽  
Richard A. Hawkins ◽  
Juan R. Viña ◽  
Darryl R. Peterson
Keyword(s):  
Endothelial Cells ◽  
Amino Acid ◽  
Membrane Vesicles ◽  
Bovine Brain ◽  
Glutamate Transport ◽  
Plasma Membrane Vesicles ◽  
Amino Acid Transport System ◽  
Luminal Membrane ◽  
Glutamine Transport ◽  
Glutamine Transporters

Glutamine and glutamate transport activities were measured in isolated luminal and abluminal plasma membrane vesicles derived from bovine brain endothelial cells. Facilitative systems for glutamine and glutamate were almost exclusively located in luminal-enriched membranes. The facilitative glutamine carrier was neither sensitive to 2-aminobicyclo(2,2,1)heptane-2-carboxylic acid inhibition nor did it participate in accelerated amino acid exchange; it therefore appeared to be distinct from the neutral amino acid transport system L1. Two Na-dependent glutamine transporters were found in abluminal-enriched membranes: systems A and N. System N accounted for ∼80% of Na-dependent glutamine transport at 100 μM. Abluminal-enriched membranes showed Na-dependent glutamate transport activity. The presence of 1) Na-dependent carriers capable of pumping glutamine and glutamate from brain into endothelial cells, 2) glutaminase within endothelial cells to hydrolyze glutamine to glutamate and ammonia, and 3) facilitative carriers for glutamine and glutamate at the luminal membrane may provide a mechanism for removing nitrogen and nitrogen-rich amino acids from brain.

Effects of prior exercise on the action of insulin-like growth factor I in skeletal muscle

1992 ◽  
Vol 263 (2) ◽  
pp. E340-E344 ◽  
Author(s):  
E. J. Henriksen ◽  
L. L. Louters ◽  
C. S. Stump ◽  
C. M. Tipton
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Growth Factor ◽  
Glucose Transport ◽  
Amino Acid Transport ◽  
Acid Transport ◽  
Factor I ◽  
System A ◽  
Prior Exercise ◽  
Igf I

Prior exercise increases insulin sensitivity for glucose and system A neutral amino acid transport activities in skeletal muscle. Insulin-like growth factor I (IGF-I) also activates these transport processes in resting muscle. It is not known, however, whether prior exercise increases IGF-I action in muscle. Therefore we determined the effect of a single exhausting bout of swim exercise on IGF-I-stimulated glucose transport activity [assessed by 2-deoxy-D-glucose (2-DG) uptake] and system A activity [assessed by alpha-(methylamino)isobutyric acid (MeAIB) uptake] in the isolated rat epitrochlearis muscle. When measured 3.5 h after exercise, the responses to a submaximal concentration (0.2 nM), but not a maximal concentration (13.3 nM), of insulin for activation of 2-DG uptake and MeAIB uptake were enhanced. In contrast, prior exercise increased markedly both the submaximal (5 nM) and maximal (20 nM) responses to IGF-I for activation of 2-DG uptake, whereas only the submaximal response to IGF-I (3 nM) for MeAIB uptake was enhanced after exercise. We conclude that 1) prior exercise significantly enhances the response to a submaximal concentration of IGF-I for activation of the glucose transport and system A neutral amino acid transport systems in skeletal muscle and 2) the enhanced maximal response for IGF-I action after exercise is restricted to the signaling pathway for activation of the glucose transport system.

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