Placental amino acid uptake. VI. Regulation by intracellular substrate

1982 ◽  
Vol 243 (1) ◽  
pp. C46-C51 ◽  
Author(s):  
R. B. Steel ◽  
C. H. Smith ◽  
L. K. Kelley
Keyword(s):  
Amino Acid ◽  
Placental Tissue ◽  
Membrane Vesicles ◽  
Amino Acid Uptake ◽  
Maternal Plasma ◽  
Acid Uptake ◽  
L System ◽  
Intracellular Amino Acids ◽  
Human Placental Tissue

Amino acid uptake by human placental tissue is regulated by intracellular amino acids. alpha-Aminoisobutyric acid (AIB) uptake was reduced at intracellular AIB concentrations of 0.8 mM. The magnitude of reduction increased sharply between 1 and 3 mM and reached a maximum of 45% at 5 mM. Suppression was specific to the "A" system. It occurred only when both the amino acid used for preloading and that used as an uptake substrate were active with that system. In the "L" system, facilitation apparently occurs, and in the "ASC" system there is no apparent effect. The system specificity as well as other evidence indicated that suppression is caused by substrate present intracellularly rather than by dilution of extracellular substrate. Suppression was independent of inhibitors of protein synthesis and was not seen in membrane vesicles prepared from preloaded tissue, indicating that intracellular substrate interacts directly with the carrier (transinhibition) rather than altering its synthesis or degradation. The A system transinhibition has the potential to regulate syncytial uptake in vivo and limit variation due to changes in maternal plasma amino acid concentration.

scholarly journals Amino acid uptake by liver of genetically obese Zucker rats

1991 ◽  
Vol 280 (2) ◽  
pp. 367-372 ◽  
Author(s):  
B Ruiz ◽  
A Felipe ◽  
J Casado ◽  
M Pastor-Anglada
Keyword(s):  
Plasma Membrane ◽  
Amino Acid ◽  
Membrane Vesicles ◽  
Amino Acid Uptake ◽  
Zucker Rats ◽  
Acid Uptake ◽  
Plasma Membrane Vesicles ◽  
Net Uptake ◽  
Obese Zucker Rats

Alanine and glutamine uptake by the liver of 50-52-day-old genetically obese Zucker rats and their lean littermates has been studied. The net uptake in vivo of L-alanine is 2-fold higher in the obese animals. No significant change in L-glutamine net balance was found. We also studied the Na(+)-dependent uptake of L-alanine and L-glutamine into plasma-membrane vesicles isolated from either obese- or lean-rat livers. Vmax. values of both L-alanine and L-glutamine transport were 2-fold higher in those preparations from obese rats. No change in Km was observed. As suggested by inhibition studies, this seemed to be mediated by an enhancement of the activities of systems A, ASC and N. We conclude that the liver of the obese Zucker rat is extremely efficient in taking up neutral amino acids from the afferent blood, which results in an enhanced net uptake of L-alanine in vivo. The changes in transport activities at the plasma-membrane level might contribute to increase amino acid disposal by liver, probably for lipogenic purposes, as recently reported by Terrettaz & Jeanrenaud [Biochem. J. (1990) 270, 803-807].

scholarly journals Studies on Aromatic Amino Acid Uptake by Rat Brain in Vivo

1962 ◽  
Vol 237 (3) ◽  
pp. 803-806
Author(s):  
Gordon Guroff ◽  
Sidney Udenfriend
Keyword(s):  
Amino Acid ◽  
Rat Brain ◽  
Aromatic Amino Acid ◽  
Amino Acid Uptake ◽  
Acid Uptake

Somatostatin inhibits insulin-stimulated amino acid uptake into cultured rat myoblasts

1987 ◽  
Vol 114 (4) ◽  
pp. 470-474 ◽  
Author(s):  
G. S. G. Spencer ◽  
D. J. Hill ◽  
G. J. Garssen ◽  
J. P. G. Williams
Keyword(s):  
Amino Acid ◽  
Nutrient Uptake ◽  
Monolayer Culture ◽  
Amino Acid Uptake ◽  
Inhibitory Effect ◽  
Isobutyric Acid ◽  
Acid Uptake ◽  
Newborn Rat ◽  
Amino Isobutyric Acid

Abstract. The effects of somatostatin on the acute metabolic actions of insulin on newborn rat myoblasts in culture has been examined during monolayer culture. Somatostatin significantly inhibited the insulin-stimulated uptake of [3H]leucine and [3H]amino-isobutyric acid into myoblasts but had no effect on basal (unstimulated) uptake of these two substances. The lowest concentration of somatostatin to have a significant effect was 10 μg/l, and this was apparent in all the experiments undertaken. The inhibitory effect of somatostatin was seen at all effective concentrations of insulin used (0.3–1 U/l). These findings lend support to the concept of an endocrine role for somatostatin in vivo and suggest that a peripheral antagonism may exist between circulating insulin and somatostatin on anabolic processes such as nutrient uptake into cells.

Hepatic Amino Acid Uptake Is Decreased in Lactating Rats. In Vivo and In Vitro Studies

1994 ◽  
Vol 124 (11) ◽  
pp. 2163-2171 ◽  
Author(s):  
José García de la Asunción ◽  
Amparo Devesa ◽  
Juan R. Viña ◽  
Teresa Barber
Keyword(s):  
Amino Acid ◽  
Amino Acid Uptake ◽  
In Vitro Studies ◽  
Acid Uptake

Myocardial amino acid transport by canine sarcolemma vesicles

1987 ◽  
Vol 252 (6) ◽  
pp. H1070-H1076
Author(s):  
L. H. Young ◽  
B. L. Zaret ◽  
E. J. Barrett
Keyword(s):  
Amino Acid ◽  
Sarcoplasmic Reticulum ◽  
Membrane Vesicles ◽  
Amino Acid Uptake ◽  
Ventricular Myocardium ◽  
Transport Systems ◽  
Acid Uptake ◽  
Leucine Uptake ◽  
Alanine Transport ◽  
Canine Ventricular Myocardium

The transport of L-alanine and L-leucine into membrane vesicles isolated from mature canine ventricular myocardium was studied. Transport was assessed in purified sarcolemma and in vesicles differentially enriched either for sarcolemma or sarcoplasmic reticulum to further localize these transport systems. An imposed inward gradient of a NaNO3 stimulated uptake of L-alanine but not L-leucine by these vesicles. Amino acid uptake by these vesicles occurred into an osmotically active space. The stimulatory effect of Na+ on alanine transport was most striking in the purified sarcolemma vesicles, where Na+-stimulated alanine flux was 45 +/- 14 pmol X mg-1 X min-1. Furthermore, Na+-dependent alanine transport activity appeared to copurify with Na+-K+-ATPase activity, which served as a marker for sarcolemma membrane when these activities were compared in the three different membrane preparations. Leucine transport by sarcolemma was not altered by an imposed Na+ gradient. However, leucine uptake was a saturable function of extravesicular leucine and was inhibited by valine. In contrast, in sarcoplasmic reticulum membrane vesicles leucine uptake increased proportionately with increasing media leucine and was unaffected by valine. Our results demonstrate the feasibility of directly studying the transport of naturally occurring amino acids in membrane vesicles from mammalian heart, and the presence of Na+-dependent alanine transport system and a Na+-independent leucine transporter in the sarcolemma but not in sarcoplasmic reticulum of canine ventricular myocardium.

Lack of effects of hypothermia on cerebral amino acid uptake in vivo

1977 ◽  
Vol 125 (1) ◽  
pp. 187-191 ◽  
Author(s):  
Emirbek Z. Emirbekov ◽  
Henry Sershen ◽  
Abel Lajtha
Keyword(s):  
Amino Acid ◽  
Amino Acid Uptake ◽  
Acid Uptake

Anionic amino acid uptake by microvillous membrane vesicles from human placenta

1989 ◽  
Vol 257 (5) ◽  
pp. C1005-C1011 ◽  
Author(s):  
A. J. Moe ◽  
C. H. Smith
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Glutamate Uptake ◽  
Membrane Vesicles ◽  
Amino Acid Uptake ◽  
Maternal Blood ◽  
Acid Uptake ◽  
Dependent Manner ◽  
Concentration Dependent Manner

The transport mechanisms for anionic amino acids in trophoblast microvillous (maternal facing) membrane were investigated by characterization of L-[3H]aspartate and L-[3H]glutamate uptake in membrane vesicles. Uptake of the anionic amino acids was by a single high-affinity Na+-dependent K+-stimulated cotransporter that is pH sensitive and electrogenic. A second Na+-dependent transporter could not be discriminated, and there was no observable Na+-independent uptake. An outwardly directed K+ gradient (100 mM KCl inside) resulted in a 5- to 10-fold stimulation in glutamate uptake in the presence of Na+. Intravesicular KCl had no effect on transporter affinity but increased transporter velocity in a concentration-dependent manner. Inhibition of Na+-K+-dependent uptake of L-aspartate and L-glutamate (20 mM, 30 s) by 2 mM unlabeled amino acids demonstrated stereoselectivity for L-glutamate but not for L-aspartate. The neutral amino acids (L-alanine, L-threonine, L-serine, L-cysteine, L-phenylalanine) were not effective inhibitors. These data are consistent with an anionic amino acid transporter in the microvillous membrane of the trophoblast, which has characteristics qualitatively similar to the X-AG system found in other epithelia. This system may mediate the concentrative placental uptake of anionic amino acids from maternal blood in utero.

scholarly journals Alanine uptake activates hepatocellular chloride channels

1997 ◽  
Vol 273 (4) ◽  
pp. G849-G853 ◽  
Author(s):  
Steven D. Lidofsky ◽  
Richard M. Roman
Keyword(s):  
Amino Acid ◽  
Mammalian Cells ◽  
Chloride Channels ◽  
Amino Acid Uptake ◽  
Experimental Models ◽  
Cell Swelling ◽  
Acid Uptake ◽  
Adaptive Responses ◽  
Anion Channels

Cells involved in the retrieval and metabolic conversion of amino acids undergo significant increases in size in response to amino acid uptake. The resultant adaptive responses to cell swelling are thought to include increases in membrane K+ and Cl− permeability through activation of volume-sensitive ion channels. This viewpoint is largely based on experimental models of hypotonic swelling, but few mammalian cells experience hypotonic challenge in vivo. Here we have examined volume regulatory responses in a physiological model of cell-swelling alanine uptake in immortalized hepatocytes. Alanine-induced cell swelling was followed by a decrease in cell volume that was temporally associated with an increase in membrane Cl− currents. These currents were dependent both on alanine concentration and Na+, suggesting that currents were stimulated by Na+-coupled alanine uptake. Cl− currents were outwardly rectifying, exhibited an anion permeability sequence of I− > Br− > Cl−, and were inhibited by the Cl− channel blocker 5-nitro-2-(3-phenylpropylamino)benzoic acid, features similar to those reported for a widely distributed class of volume-sensitive anion channels evoked by experimental hypotonic stress. These findings suggest that volume-sensitive anion channels participate in adaptive responses to amino acid uptake and provide such channels with a new physiological context.

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