System β and System A amino acid transporters in the feline endotheliochorial placenta

2004 ◽  
Vol 287 (6) ◽  
pp. R1369-R1379 ◽  
Author(s):  
E. E. Champion ◽  
S. J. Mann ◽  
J. D. Glazier ◽  
C. J. P. Jones ◽  
J. M. Rawlings ◽  
...  
Keyword(s):  
Amino Acid ◽  
Human Placenta ◽  
Amino Acid Transport ◽  
Time Course ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Transport Mechanisms ◽  
Acid Transport ◽  
System A ◽  
Taurine Uptake

There is no knowledge of the transport mechanisms by which solutes cross the cat placenta or any other endotheliochorial placenta. Here, we investigated whether the amino acid transport systems β and A are present in the cat placenta using a placental fragment uptake technique. Data were compared with studies in the human placenta, in which the presence of these two transport systems has been well established. A time course of [3H]taurine (substrate for system β) and [14C]MeAIB (nonmetabolizable substrate for system A) uptake was determined in the term cat and human placental fragments in the presence and absence (choline substituted) of Na+, and further studies were carried out over 15 min. Taurine uptake into both cat and human placenta fragments was found to be Na+ and Cl− dependent, and Na+-dependent taurine uptake was blocked by excess β-alanine. MeAIB uptake was found to be Na+ dependent, and Na+-dependent MeAIB uptake was blocked by excess MeAIB or glycine. Western blotting and immunohistochemistry performed on cat and human placenta showed expression of TAUT and ATA2 (SNAT2), proteins associated with system β and system A activity, respectively. This study therefore provides the first evidence of the presence of amino acid transport systems β and A in the cat placenta.

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.

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.

Heteromeric amino acid transporters: biochemistry, genetics, and physiology

2001 ◽  
Vol 281 (6) ◽  
pp. F995-F1018 ◽  
Author(s):  
Josep Chillarón ◽  
Ramón Roca ◽  
Alfonso Valencia ◽  
Antonio Zorzano ◽  
Manuel Palacín
Keyword(s):  
Amino Acid ◽  
Amino Acid Transport ◽  
Human Genetics ◽  
Disulfide Bridge ◽  
Transport Systems ◽  
Cell Physiology ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Membrane Glycoproteins ◽  
Cell Functions

The heteromeric amino acid transporters (HATs) are composed of two polypeptides: a heavy subunit (HSHAT) and a light subunit (LSHAT) linked by a disulfide bridge. HSHATs are N-glycosylated type II membrane glycoproteins, whereas LSHATs are nonglycosylated polytopic membrane proteins. The HSHATs have been known since 1992, and the LSHATs have been described in the last three years. HATs represent several of the classic mammalian amino acid transport systems (e.g., L isoforms, y+L isoforms, asc, x[Formula: see text], and b0,+). Members of the HAT family are the molecular bases of inherited primary aminoacidurias cystinuria and lysinuric protein intolerance. In addition to the role in amino acid transport, one HSHAT [the heavy subunit of the cell-surface antigen 4F2 (also named CD98)] is involved in other cell functions that might be related to integrin activation. This review covers the biochemistry, human genetics, and cell physiology of HATs, including the multifunctional character of CD98.

scholarly journals Leptin Affects System A Amino Acid Transport Activity in the Human Placenta: Evidence for STAT3 Dependent Mechanisms

Placenta ◽  
2009 ◽  
Vol 30 (4) ◽  
pp. 361-367 ◽  
Author(s):  
F. von Versen-Höynck ◽  
A. Rajakumar ◽  
M.S. Parrott ◽  
R.W. Powers
Keyword(s):  
Amino Acid ◽  
Human Placenta ◽  
Amino Acid Transport ◽  
Acid Transport ◽  
Transport Activity ◽  
System A

scholarly journals Gene-product designations for amino acid transporters.

1994 ◽  
Vol 196 (1) ◽  
pp. 51-57 ◽  
Author(s):  
H N Christensen ◽  
L M Albritton ◽  
D K Kakuda ◽  
C L MacLeod
Keyword(s):  
Amino Acid ◽  
Gene Product ◽  
Amino Acid Transport ◽  
Full Range ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Gene Products ◽  
Acid Transport ◽  
Good Set ◽  
Cloned Gene

The molecular cloning of genes that encode amino acid transporters presents the scientific community with the opportunity to name their gene products using a scheme that could usefully recall the well-defined transport system most similar in properties to the newly identified cloned gene product. To avoid the problem of rising confusion, we propose to take advantage of established designation methods that indicate the types of amino acids transported and the co-substrate ion requirement of their transport. The economy obligated by the necessity to keep the number of symbols in a gene name to a minimum will rarely permit a listing of the full range of substrates, since amino acid transport systems have broad substrate specificities with co-substrate requirements that can differ in a substrate-specific manner. Hence, the use of established systems to codify groups of amino acid transport systems, which allow identification of the substrate range by using 1-3 letters, e.g. A, L or even ASC, could be integrated with a system used to indicate the ion-dependence of transport. The discoverers of transporters are mainly proceeding with commendable reserve and are inviting discussion, a desire which this essay urges be facilitated by more formal arrangements for further planning. These discoverers have also shown, along with an expressed desire for guidance, well-advised spontaneity in making reference to the substrate range, two trends that together suggest that a good set of designations can evolve that will be highly descriptive.(ABSTRACT TRUNCATED AT 250 WORDS)

Molecular Biology of Mammalian Plasma Membrane Amino Acid Transporters

1998 ◽  
Vol 78 (4) ◽  
pp. 969-1054 ◽  
Author(s):  
MANUEL PALACÍN ◽  
RAÚL ESTÉVEZ ◽  
JOAN BERTRAN ◽  
ANTONIO ZORZANO
Keyword(s):  
Plasma Membrane ◽  
Amino Acid ◽  
Molecular Biology ◽  
Structure Function ◽  
Amino Acid Transport ◽  
Transport Systems ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
Cationic Amino Acid ◽  
Function Relationship

Palacı́n, Manuel, Raúl Estévez, Joan Bertran, and Antonio Zorzano. Molecular Biology of Mammalian Plasma Membrane Amino Acid Transporters. Physiol. Rev. 78: 969–1054, 1998. — Molecular biology entered the field of mammalian amino acid transporters in 1990–1991 with the cloning of the first GABA and cationic amino acid transporters. Since then, cDNA have been isolated for more than 20 mammalian amino acid transporters. All of them belong to four protein families. Here we describe the tissue expression, transport characteristics, structure-function relationship, and the putative physiological roles of these transporters. Wherever possible, the ascription of these transporters to known amino acid transport systems is suggested. Significant contributions have been made to the molecular biology of amino acid transport in mammals in the last 3 years, such as the construction of knockouts for the CAT-1 cationic amino acid transporter and the EAAT2 and EAAT3 glutamate transporters, as well as a growing number of studies aimed to elucidate the structure-function relationship of the amino acid transporter. In addition, the first gene ( rBAT) responsible for an inherited disease of amino acid transport (cystinuria) has been identified. Identifying the molecular structure of amino acid transport systems of high physiological relevance (e.g., system A, L, N, and x−c) and of the genes responsible for other aminoacidurias as well as revealing the key molecular mechanisms of the amino acid transporters are the main challenges of the future in this field.

Hypoxia reduces expression and function of system A amino acid transporters in cultured term human trophoblasts

2003 ◽  
Vol 284 (2) ◽  
pp. C310-C315 ◽  
Author(s):  
D. M. Nelson ◽  
S. D. Smith ◽  
T. C. Furesz ◽  
Y. Sadovsky ◽  
V. Ganapathy ◽  
...  
Keyword(s):  
Amino Acid ◽  
Amino Acid Transport ◽  
Northern Analysis ◽  
Total Amino Acid ◽  
Amino Acid Transporters ◽  
Acid Transport ◽  
System A ◽  
Normal Human ◽  
And Function ◽  
Transporter Expression

We tested the hypothesis that hypoxia diminishes the expression and transport of neutral amino acids by system A in full-term human trophoblasts. Cytotrophoblasts from normal human placentas were cultured in standard conditions of 20% O2 or in 1% and 3% O2 for 24 h before assay. Neutral amino acid transport for systems A, ASC, and L was assayed at 24 and 72 h by the cluster-tray technique. Hypoxia during the initial 24 h of culture reduced system A transport by 82% in 1% O2 and by 37% in 3% O2 ( P < 0.01) compared with standard conditions. Hypoxia during the latter 24 h of the 72 h in culture reduced system A transport by 55% in 1% O2 and by 20% in 3% O2 ( P < 0.05) compared with standard conditions at 72 h. Hypoxia (1% O2) also reduced total amino acid transport by 40% in the more differentiated syncytiotrophoblasts present at 72 h. Northern analysis of trophoblasts in standard conditions showed that subtypes of human amino acid transporter A (hATA1 and hATA2) were each expressed in cytotrophoblasts and syncytiotrophoblasts. Hypoxia decreased expression of hATA1 and hATA2 in both trophoblast phenotypes. We conclude that hypoxia downregulates system A transporter expression and activity in cultured human trophoblasts.

Okadaic acid, insulin, and denervation effects on glucose and amino acid transport and glycogen synthesis in muscle

1993 ◽  
Vol 265 (1) ◽  
pp. E36-E43 ◽  
Author(s):  
K. A. Robinson ◽  
K. P. Boggs ◽  
M. G. Buse
Keyword(s):  
Insulin Resistance ◽  
Amino Acid ◽  
Glucose Transport ◽  
Okadaic Acid ◽  
Amino Acid Transport ◽  
Glycogen Synthesis ◽  
Transport Systems ◽  
Calyculin A ◽  
Acid Transport ◽  
System A

Effects of okadaic acid (OKA) and calyculin A, cell-permeating specific inhibitors of phosphoprotein phosphatases-1 and -2A, were studied in isolated rat hemidiaphragms. OKA stimulated glucose transport (half-maximum = approximately 0.1 microM; maximum = approximately 1 microM) but was less effective than 6 nM insulin. Insulin and OKA effects were not additive. OKA diminished or abolished glucose transport-stimulation by insulin. System A amino acid transport was also stimulated by OKA, insulin was more effective, and preexposure to OKA inhibited insulin stimulation. Calyculin A affected both transport systems similarly to OKA. OKA did not affect basal glycogen synthesis but abolished its stimulation by insulin. Denervated muscles develop post-receptor insulin resistance. Glucose transport and glycogen synthesis were essentially unresponsive to insulin 3 days postdenervation; however, glucose transport was stimulated by OKA similarly to controls. OKA did not affect glycogen synthesis in denervated muscle except for abolishing a small insulin effect. The data suggest similar acute regulation of glucose and system A amino acid transport in muscle. Enhanced Ser/Thr phosphorylation of unidentified protein(s) stimulates both processes but inhibits their full stimulation by insulin. Postdenervation insulin resistance likely reflects impaired signal transduction.

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