Uptake and asymmetric efflux of amino acids at maternal and fetal sides of placenta

1981 ◽  
Vol 241 (3) ◽  
pp. C106-C112 ◽  
Author(s):  
B. M. Eaton ◽  
D. L. Yudilevich
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Guinea Pig ◽  
Cellular Uptake ◽  
Transport Systems ◽  
Acid Transport ◽  
Dilution Technique ◽  
Acidic Amino Acids ◽  
Tracer Dilution ◽  
Paired Tracer Dilution

Unidirectional uptake of eighteen amino acids into the syncytiotrophoblast was measured from both the maternal and fetal circulations of isolated dually perfused guinea pig placentas using a single-circulation, paired-tracer dilution technique. A bolus containing a tritiated amino acid and L-[14C]glucose (extracellular marker) was injected intra-arterially into one circulation, and both venous outflows were sequentially sampled. The maximal cellular uptake (Umax) on the injection side was determined from (1-[3H]/[14C]) values and used to calculate the unidirectional influx. Umax values for neutral and basic amino acids ranged between 15 and 58% and were similar on both sides of the trophoblast. Uptake of the acidic amino acids and taurine was minimal. Amino acid influx from either circulation was followed by rapid tracer backflux and transplacental transfer. Tracer efflux was asymmetric and preferentially directed towards the fetal side. It is suggested that amino acid transport systems are present on both surfaces of the placenta and that net transfer from mother to fetus is the result of asymmetric efflux from the trophoblast.

Amino Acid Transport in a Water-mould: The Possible Regulatory Roles of Calcium and N6-(Δ2-isopentenyl)adenine

1975 ◽  
Vol 53 (9) ◽  
pp. 975-988 ◽  
Author(s):  
Danny P. Singh ◽  
Hérb. B. LéJohn
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Osmotic Shock ◽  
Inhibitory Effect ◽  
Transport Systems ◽  
Acid Transport ◽  
Isopentenyl Adenine ◽  
Energy Dependent ◽  
Water Mould

Transport of amino acids in the water-mould Achlya is an energy-dependent process. Based on competition kinetics and studies involving the influence of pH and temperature on the initial transport rates, it was concluded that the 20 amino acids (L-isomers) commonly found in proteins were transported by more than one, possibly nine, uptake systems. This is similar to the pattern elucidated for some bacteria but unlike those uncovered for all fungi studied to date. The nine different transport systems elucidated are: (i) methionine, (ii) cysteine, (iii) proline, (iv) serine–threonine, (v) aspartic and glutamic acids, (vi) glutamine and asparagine, (vii) glycine and alanine, (viii) histidine, lysine, and arginine, and (ix) phenylalanine–tyrosine–tryptophan and leucine–isoleucine–valine as two overlapping groups. Transport of all of these amino acids was inhibited by azide, cyanide, and its derivatives and 2,4-dinitrophenol. These agents normally interfere with metabolism at the level of the electron transport chain and oxidative phosphorylation. Osmotic shock treatment of the cells released, into the shock fluid, a glycopeptide that binds calcium as well as tryptophan but no other amino acid. The shocked cells are incapable of concentrating amino acids, but remain viable and reacquire this capacity when the glycopeptide is resynthesized.Calcium played more than a secondary role in the transport of the amino acids. When bound to the membrane-localized glycopeptide, it permits concentrative transport to take place. However, excess calcium can inhibit transport which can be overcome by chelating with citrate. Calculations show that the concentration of free citrate is most important. At low citrate concentrations (less than 1 mM) in the absence of exogenously supplied calcium, enhancement of amino acid transport occurs. At high concentrations (greater than 5 mM), citrate inhibits but this effect can be reversed by titrating with calcium. Evidently, the glycopeptide acts as a calcium sink to regulate the concentration of calcium made available to the cell for its membrane activities.N6-(Δ2-isopentenyl) adenine (a plant growth 'hormone') and analogues mimic the inhibitory effect of citrate and bind to the glycopeptide as well. Replot data for citrate and N6-(Δ2-isopentyl) adenine inhibition indicate that both agents have no more than one binding constant. These results implicate calcium, glycopeptide, and energy-dependent transport of solutes in some, as yet undefinable, way.

Placental amino acid transport

1995 ◽  
Vol 268 (6) ◽  
pp. C1321-C1331 ◽  
Author(s):  
A. J. Moe
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Human Placenta ◽  
Amino Acid Transport ◽  
Single Layer ◽  
Maternal Blood ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Principal Mechanism

Normal fetal growth and development depend on a continuous supply of amino acids from the mother to the fetus. The placenta is responsible for the transfer of amino acids between the two circulations. The human placenta is hemomonochorial, meaning that the maternal and fetal circulations are separated by a single layer of polarized epithelium called the syncytiotrophoblast, which is in direct contact with maternal blood. Transport proteins located in the microvillous and basal membranes of the syncytiotrophoblast are the principal mechanism for transfer from maternal blood to fetal blood. Knowledge of the function and regulation of syncytiotrophoblast amino acid transporters is of great importance in understanding the mechanism of placental transport and potentially improving fetal and newborn outcomes. The development of methods for the isolation of microvillous and basal membrane vesicles from human placenta over the past two decades has contributed greatly to this understanding. Now a primary cultured trophoblast model is available to study amino acid transport and regulation as the cells differentiate. The types of amino acid transporters and their distribution between the syncytiotrophoblast microvillous and basal membranes are somewhat unique compared with other polarized epithelia. These differences may reflect the unusual circumstance of this epithelium that is exposed to blood on both sides. The current state of knowledge as to the types of transport systems present in syncytiotrophoblast, their regulation, and the effects of maternal consumption of drugs on transport are discussed.

Multiple pathways for cationic amino acid transport in rat thyroid epithelial cell line PC Cl3

2005 ◽  
Vol 288 (2) ◽  
pp. C290-C303 ◽  
Author(s):  
Tiziano Verri ◽  
Cinzia Dimitri ◽  
Sonia Treglia ◽  
Fabio Storelli ◽  
Stefania De Micheli ◽  
...  
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Cell Line ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Residual Fraction ◽  
Acid Transport ◽  
Thyroid Cells ◽  
Cationic Amino Acid ◽  
Rat Thyroid

Information regarding cationic amino acid transport systems in thyroid is limited to Northern blot detection of y+LAT1 mRNA in the mouse. This study investigated cationic amino acid transport in PC cell line clone 3 (PC Cl3 cells), a thyroid follicular cell line derived from a normal Fisher rat retaining many features of normal differentiated follicular thyroid cells. We provide evidence that in PC Cl3 cells plasmalemmal transport of cationic amino acids is Na+ independent and occurs, besides diffusion, with the contribution of high-affinity, carrier-mediated processes. Carrier-mediated transport is via y+, y+L, and b0,+ systems, as assessed by l-arginine uptake and kinetics, inhibition of l-arginine transport by N-ethylmaleimide and neutral amino acids, and l-cystine transport studies. y+L and y+ systems account for the highest transport rate (with y+L > y+) and b0,+ for a residual fraction of the transport. Uptake data correlate to expression of the genes encoding for CAT-1, CAT-2B, 4F2hc, y+LAT1, y+LAT2, rBAT, and b0,+AT, an expression profile that is also shown by the rat thyroid gland. In PC Cl3 cells cationic amino acid uptake is under TSH and/or cAMP control (with transport increasing with increasing TSH concentration), and upregulation of CAT-1, CAT-2B, 4F2hc/y+LAT1, and rBAT/b0,+AT occurs at the mRNA level under TSH stimulation. Our results provide the first description of an expression pattern of cationic amino acid transport systems in thyroid cells. Furthermore, we provide evidence that extracellular l-arginine is a crucial requirement for normal PC Cl3 cell growth and that long-term l-arginine deprivation negatively influences CAT-2B expression, as it correlates to reduction of CAT-2B mRNA levels.

Amino acid transport by juxtamedullary nephrons: distal reabsorption and recycling

1988 ◽  
Vol 255 (3) ◽  
pp. F397-F407 ◽  
Author(s):  
W. H. Dantzler ◽  
S. Silbernagl
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Acid Transport ◽  
Acidic Amino Acids ◽  
Vasa Recta ◽  
Collecting Ducts ◽  
Distal Site

Amino acid transport by juxtamedullary (JM) nephrons and its relationship to transport by superficial cortical (SC) nephrons and to function of vasa recta and collecting ducts were examined in vivo and in situ by free-flow micropuncture of Henle's loops, collecting ducts, and vasa recta and by continuous microinfusion of Henle's loops in exposed rat papillae. Fractional deliveries (FDs) of six neutral amino acids, two acidic amino acids, and taurine to tips of Henle's loops of JM nephrons could be substantially below those to early distal loops of SC nephrons, indicating that reabsorption before loop tips could be greater in JM than in SC nephrons. FDs to collecting ducts lower than to JM loop tips suggested reabsorption distal to loop tips. This was confirmed by continuous microinfusion of ascending limbs of Henle's loops. Distal site of reabsorption is unknown, but amino acids may move passively out of the thin ascending limb and be recycled into vasa recta and descending limb. Recycling of amino acids was supported by high FDs to tips of Henle's loops (sometimes greater than 1.0), higher concentrations in ascending than in descending vasa recta at same papilla level, and high mean concentrations in vasa recta.

Amino acid transport systems in intestinal brush-border membranes from lepidopteran larvae

1989 ◽  
Vol 257 (3) ◽  
pp. R494-R500 ◽  
Author(s):  
B. Giordana ◽  
V. F. Sacchi ◽  
P. Parenti ◽  
G. M. Hanozet
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Brush Border ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Acid Transport ◽  
Specific System ◽  
Neutral Amino Acids ◽  
Intestinal Brush Border ◽  
Lepidopteran Larvae

Experiments with intestinal brush-border membrane vesicles from lepidopteran larvae disclosed the occurrence of unique cotransporter proteins that use K+ as the driver cation for the transmembrane transfer of amino acids across the luminal border of midgut enterocytes. Six apical membrane amino acid transport systems have been identified. These systems are 1) a neutral amino acid transporter with a broad spectrum of interactions with most neutral amino acids, which is highly concentrative, strongly K+- and electrical potential-dependent, poorly stereospecific, and recognizes histidine, but not proline, glycine, or alpha-(methylamino)isobutyric acid (MeAIB); 2) a specific system for L-proline; 3) a specific system for glycine with a higher affinity for Na+ than for K+; 4) a specific system for L-lysine, which is dependent on membrane potential, is highly sensitive to external K+, and does not interact with L-arginine or neutral amino acids; 5) a specific K+-dependent process for glutamic acid, which does not recognize aspartic acid; and last, 6) an apparently unique K+- driven mechanism for D-alanine, which is potential-dependent and strongly stereospecific.

AMINO ACID TRANSPORT IN BRAIN CORTEX SLICES: II. COMPETITION BETWEEN AMINO ACIDS

1962 ◽  
Vol 40 (11) ◽  
pp. 1591-1602 ◽  
Author(s):  
P. N. Abadom ◽  
P. G. Scholefield
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Rat Brain ◽  
Amino Acid Transport ◽  
Brain Cortex ◽  
Transport Systems ◽  
Acid Transport ◽  
Inhibitory Effects ◽  
Brain Cortex Slices ◽  
Cortex Slices

Evidence is presented which indicates that several amino acid transport systems are present in rat brain cortex slices, each with its own specificity with regard to substrate and with regard to amino acids which produce inhibitory effects. The nature of these inhibitory effects may be either direct (competition for a limiting number of sites) or indirect (as they are when glutamate or aspartate cause a decrease in the ATP content).Comparison of the specificities of the glycine transport systems present in rat brain cortex slices and in Ehrlich ascites carcinoma cells indicates that these two systems have little in common and the relation of this finding to the structural requirements necessary for chemotherapeutic activity is discussed.

Glucose carriers at maternal and fetal sides of the trophoblast in guinea pig placenta

1979 ◽  
Vol 237 (5) ◽  
pp. C205-C212 ◽  
Author(s):  
D. L. Yudilevich ◽  
B. M. Eaton ◽  
A. H. Short ◽  
H. P. Leichtweiss
Keyword(s):  
Guinea Pig ◽  
Intact Animal ◽  
Sugar Uptake ◽  
Dilution Technique ◽  
Nondestructive Technique ◽  
Guinea Pig Placenta ◽  
The Mean ◽  
Pig Placenta ◽  
Tracer Dilution ◽  
Paired Tracer Dilution

Trophoblast uptake and unidirectional influx of 3H-labeled hexoses were measured relative to L-[14C]glucose (extracellular marker) using a single-circulation, paired-tracer dilution technique. Successive runs were performed in the fetal and maternal circulations of isolated dually perfused guinea pig placentas, obtained from anesthetized dams and perfused for 60--140 min. The leakiness, estimated from the percentage of the L-glucose dose that crossed the trophoblast, varied (25 +/- 3% (SE), n = 28). On the injection side the maximal sugar uptake (Umax) was measured from early venous concentration ratios, since rapid tracer backflux occurred: Umax = (1 -- 3H/14C) x 100. Umax was independent of the leakiness. In all 14 placentas studied, stereospecific saturable transport of D-glucose was demonstrated at fetal (Umax = 56 +/- 4% (SE), n = 14) and maternal (62 +/- 1% (SE), n = 14) surfaces. The mean unidirectional influxes were 3.3 and 3.5 mumol.min-1.g-1, respectively. Uptakes were inhibited by phloretin and less effectively by phlorizin. D-glucose, 3-O-methylglucose, D-mannose and D-galactose had similar Umax values, about four times that of D-fructose. Tracer backflux and transplacental flux were also equal from both sides. It is concluded that similar hexose carriers, which resemble the human erythrocyte carrier, exist at the membrane on both sides of the trophoblast. The nondestructive technique employed characterizes carriers and receptors at the blood side of cells and could be applied to the placenta or other organs in the intact animal.

In vivo muscle amino acid transport involves two distinct processes

2004 ◽  
Vol 287 (1) ◽  
pp. E136-E141 ◽  
Author(s):  
Sharon Miller ◽  
David Chinkes ◽  
David A. MacLean ◽  
Dennis Gore ◽  
Robert R. Wolfe
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Amino Acid Transport ◽  
Interstitial Fluid ◽  
Muscle Blood Flow ◽  
Amino Acid Uptake ◽  
Transport Systems ◽  
Acid Uptake ◽  
Acid Transport ◽  
Rate Limiting

We have tested the hypothesis that transit through the interstitial fluid, rather than across cell membranes, is rate limiting for amino acid uptake from blood into muscle in human subjects. To quantify muscle transmembrane transport of naturally occurring amino acids, we developed a novel 4-pool model that distinguishes between the interstitial and intracellular fluid compartments. Transport kinetics of phenylalanine, leucine, lysine, and alanine were quantified using tracers labeled with stable isotopes. The results indicate that interstitial fluid is a functional compartment insofar as amino acid kinetics are concerned. In the case of leucine and alanine, transit between blood and interstitial fluid was potentially rate limiting for muscle amino acid uptake and release in the postabsorptive state. For example, in the case of leucine, the rate of transport between blood and interstitial fluid compared with the corresponding rate between interstitial fluid and muscle was 247 ± 36 vs. 610 ± 95 nmol·min−1·100 ml leg−1, respectively ( P < 0.05). Our results are consistent with the process of diffusion governing transit from blood to interstitial fluid without selectivity, and of specific amino acid transport systems with varying degrees of efficiency governing transit from interstitial fluid to muscle. These results imply that changes in factors that affect the transit of amino acids from blood through interstitial fluid, such as muscle blood flow or edema, could play a major role in controlling the rate of muscle amino acid uptake.

scholarly journals Amino Acid Transport into Cultured McCoy Cells Infected with Chlamydia trachomatis

2000 ◽  
Vol 68 (9) ◽  
pp. 5439-5442 ◽  
Author(s):  
Angela Harper ◽  
Christopher I. Pogson ◽  
John H. Pearce
Keyword(s):  
Amino Acids ◽  
Amino Acid ◽  
Chlamydia Trachomatis ◽  
Amino Acid Transport ◽  
Equilibrium Concentration ◽  
Transport Systems ◽  
Acid Transport ◽  
Entry Rate ◽  
Great Capacity ◽  
Cationic Amino Acids

ABSTRACT Amino acid transport into McCoy cells infected with strains representative of the two major biovars of Chlamydia trachomatis has been studied to determine if uptake is increased during infection. Preliminary work suggested that the transport systems L, A/ASC (for neutral amino acid transport), N (for transport of Asn, Gln, and His) and y+ (for cationic amino acids) were present in McCoy cells. With lymphogranuloma venereum biovar strain 434, little difference in the influx of representative amino acids Trp, His, and Lys or the analogue 2-aminoisobutyric acid (AIB) was observed during infection. With trachoma biovar strain DK20, a small increase in the initial entry rate and equilibrium concentration of each amino acid was found. McCoy cells appear to have great capacity for concentrating amino acids, which might obviate the need for transport induction by chlamydiae under conditions favoring the growth of infectious organisms.

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