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].

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.

Effect of exercise and obesity on skeletal muscle amino acid uptake

1990 ◽  
Vol 69 (4) ◽  
pp. 1347-1352 ◽  
Author(s):  
J. E. Friedman ◽  
P. W. Lemon ◽  
J. A. Finkelstein
Keyword(s):  
Skeletal Muscle ◽  
Amino Acid ◽  
Extracellular Fluid ◽  
Amino Acid Uptake ◽  
Zucker Rats ◽  
Acid Uptake ◽  
Bicarbonate Buffer ◽  
Obese Rats ◽  
Obese Zucker Rats

The genetically obese Zucker rat has a reduced capacity to deposit dietary protein in skeletal muscle. To determine whether amino acid uptake by muscle of obese Zucker rats is impaired, soleus strip (SOL) and epitrochlearis (EPI) muscles from 10-wk-old lean and obese Zucker rats were studied in vitro by use of [14C]alpha-aminoisobutyric acid (AIB). Muscles from fasted rats were incubated under basal conditions at rest or after a 1-h treadmill run at 8% grade. To equate total work completed, lean and obese rats ran at 27 and 20 m/min, respectively. Muscles were pinned at resting length, preincubated for 30 min at 37 degrees C in Krebs-Ringer bicarbonate buffer containing 5 mM glucose under 95% O2-5% CO2, and then incubated up to 3 h in Krebs-Ringer bicarbonate with 0.5 mM AIB, [14C]AIB, and [3H]inulin as a marker of extracellular fluid. Basal AIB uptake in EPI and SOL from obese rats was significantly reduced by 40 and 30% (P less than 0.01), respectively, compared with lean rats. For both lean and obese rats, exercise increased (P less than 0.05) basal AIB uptake in EPI and SOL, but the relative increases were greater in the obese rats (EPI 54% and SOL 71% vs. EPI 32% and SOL 37%). These results demonstrate that genetically obese Zucker rats have reduced basal skeletal muscle amino acid uptake and suggest that physical inactivity may partially contribute to this defect.

Kinetic and energetic aspects of the inhibition of taurocholate uptake by Na+-dependent amino acids: studies in rat liver plasma membrane vesicles

1985 ◽  
Vol 249 (1) ◽  
pp. G120-G124
Author(s):  
B. L. Blitzer ◽  
R. L. Bueler
Keyword(s):  
Amino Acids ◽  
Plasma Membrane ◽  
Bile Acid ◽  
Amino Acid ◽  
Initial Velocity ◽  
Membrane Vesicles ◽  
Acid Uptake ◽  
Plasma Membrane Vesicles ◽  
Liver Plasma Membrane ◽  
Bile Acid Uptake

The kinetic and energetic aspects of the inhibition of taurocholate uptake by the Na+-dependent amino acid L-alanine were studied in rat basolateral liver plasma membrane vesicles. In the presence of an inwardly directed Na+ gradient, alanine (5 mM) reduced the initial velocity of taurocholate uptake to 60% of control and virtually abolished the overshoot. In the presence of a K+ gradient, the slow rate of Na+-independent taurocholate uptake was similar in the presence or absence of the amino acid. Inhibition of Na+-dependent taurocholate uptake increased nonlinearly with alanine concentration (half-maximal inhibition at approximately 1 mM) and plateaued at 5–10 mM. Kinetic studies showed that alanine significantly reduced the Vmax for taurocholate uptake from 6.32 +/- 0.22 to 3.68 +/- 0.21 nmol X mg prot-1 X min-1 but did not significantly affect taurocholate Km (38.4 +/- 3.6 vs. 29.0 +/- 4.9 microM). In contrast, the Na+-independent amino acid 2-aminobicyclo[2.2.1]heptane-2-carboxylic acid did not affect either the initial velocity or peak uptake of taurocholate. The effects of alanine on the driving forces for bile acid uptake were directly assessed by measuring vesicle uptake of 22Na. At early time points, 22Na uptake was faster in the presence of alanine than under control conditions. These findings provide further evidence that Na+-dependent amino acids noncompetitively inhibit Na+-dependent bile acid uptake in association with accelerated dissipation of the transmembrane Na+ gradient and extend previous observations of this phenomenon made in isolated rat hepatocytes [Am. J. Physiol. 245 (Gastrointest. Liver Physiol. 8): G399-G403, 1983].

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.

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