共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
3.
Using immunochemical techniques, we identified forms of erythrocyte membrane proteins in apical and basal plasma membranes of human placental trophoblast. A wheat germ agglutinin-binding intrinsic protein was present in the microvillous (maternal facing) but not the basal (fetal facing) membrane of the syncytiotrophoblast epithelium. Conversely, erythrocyte-related proteins of the basal membrane included two intrinsic membrane proteins, a 95,000 Mr band 3 isoform and a form of spectrin. These four proteins were all absent from the microvillous membrane. The basal membrane spectrin isoform was also present in basal membrane skeletons. A 70,000 Mr polypeptide which reacted with antibodies to band 3 was present in both microvillous and basal plasma membranes. Therefore, certain isoforms of red cell membrane proteins are polarized between the two surfaces of the human placental syncytiotrophoblast. We propose that the localization of spectrin to the basal membrane is related to the less bundled organization of microfilaments at this membrane compared with that of the microvillous membrane. The band 3 isoforms are candidates for participation in maternofetal anion transport. 相似文献
4.
Marc U. Baumann Henning Schneider Antoine Malek Vidya Palta Daniel V. Surbek Ruth Sager Stacy Zamudio Nicholas P. Illsley 《PloS one》2014,9(8)
Glucose transport to the fetus across the placenta takes place via glucose transporters in the opposing faces of the barrier layer, the microvillous and basal membranes of the syncytiotrophoblast. While basal membrane content of the GLUT1 glucose transporter appears to be the rate-limiting step in transplacental transport, the factors regulating transporter expression and activity are largely unknown. In view of the many studies showing an association between IGF-I and fetal growth, we investigated the effects of IGF-I on placental glucose transport and GLUT1 transporter expression. Treatment of BeWo choriocarcinoma cells with IGF-I increased cellular GLUT1 protein. There was increased basolateral (but not microvillous) uptake of glucose and increased transepithelial transport of glucose across the BeWo monolayer. Primary syncytial cells treated with IGF-I also demonstrated an increase in GLUT1 protein. Term placental explants treated with IGF-I showed an increase in syncytial basal membrane GLUT1 but microvillous membrane GLUT1 was not affected. The placental dual perfusion model was used to assess the effects of fetally perfused IGF-I on transplacental glucose transport and syncytial GLUT1 content. In control perfusions there was a decrease in transplacental glucose transport over the course of the perfusion, whereas in tissues perfused with IGF-I through the fetal circulation there was no change. Syncytial basal membranes from IGF-I perfused tissues showed an increase in GLUT1 content. These results demonstrate that IGF-I, whether acting via microvillous or basal membrane receptors, increases the basal membrane content of GLUT1 and up-regulates basal membrane transport of glucose, leading to increased transepithelial glucose transport. These observations provide a partial explanation for the mechanism by which IGF-I controls nutrient supply in the regulation of fetal growth. 相似文献
5.
J C Challier 《Reproduction, nutrition, development》1989,29(6):703-716
The concept of placental barrier has been evaluated using recent advances in ultrastructure and in transport physiology. On a structural basis, the barrier effect is grounded by the syncytiotrophoblast continuity, and by basal and plasma membrane's electrical charges and by basement membrane porosity. The aqueous phase continuity for diffusion operates through intercellular gap, fenestrations (rat, rabbit) and transcellular channels (guinea pig). However, these connections are not apparent in the human syncytiotrophobast. For the molecular size selectivity, the hemochorial placentas with a pore radius of 10 nm appear much less selective than the epitheliochorial ones. The metabolic capacity of the placental cells (trophoblast, macrophages) participates to the barrier effect by metabolizing or by converting some substrates. Similarly, trophoblast asymmetry in the location of enzymes, carriers and receptors on outer (maternal side) and on basal (fetal side) plasma membranes, and in the release of secretory products, contributes to maintain separate fetal and maternal compartments. The functional polarity of trophoblast is expressed in metabolism (corticostéroids), nutrients (amino acids) and ions (iron) transport, and most of its secretions (hPL, hCG, SP1). 相似文献
6.
Cationic amino acid transporters play an important role in the intracellular supply of L-Arg and the generation of nitric oxide. Since the transport of L-Arg is voltage-dependent, we aimed at determining the intracellular L-Arg concentration and describing the transport of L-Arg in terms of Michaelis-Menten kinetics, taking into account membrane voltage. The human isoforms of the cationic amino acid transporters, hCAT-1, hCAT-2A, and hCAT-2B, were expressed in oocytes from Xenopus laevis and studied with the voltage clamp technique and in tracer experiments. We found that L-Arg was concentrated intracellularly by all hCAT isoforms and that influx and efflux, in the steady state of exchange, were nearly mirror images. Conductance measurements at symmetric concentrations of L-Arg (inside/outside) allowed us to determine KM and Vmax. The empty transporter of hCAT-2B featured an unexpected potassium conductance, which was inhibited by L-Arg. 相似文献
7.
Localization of erythrocyte/HepG2-type glucose transporter (GLUT1) in human placental villi 总被引:5,自引:0,他引:5
Kuniaki Takata Toshiko Kasahara Michihiro Kasahara Osamu Ezaki Hiroshi Hirano 《Cell and tissue research》1992,267(3):407-412
Summary The syncytiotrophoblast covering the surface of the placental villi contains the machinery for the transfer of specific substances between maternal and fetal blood, and also serves as a barrier. Existence of a facilitated-diffusion transporter for glucose in the syncytiotrophoblast has been suggested. Using antibodies to erythrocyte/HepG2-type glucose transporter (GLUT1), one isoform of the facilitated-diffusion glucose transporters, we detected a 50 kD protein in human placenta at term. By use of immunohistochemistry, GLUT1 was found to be abundant in both the syncytiotrophoblast and cytotrophoblast. Endothelial cells of the fetal capillaries also showed positive staining for GLUT1. Electron-microscopic examination revealed that GLUT1 was concentrated at both the microvillous apical plasma membrane and the infolded basal plasma membrane of the syncytiotrophoblast. Plasma membrane of the cytotrophoblast was also positive for GLUT1. GLUT1 at the apical plasma membrane of the syncytiotrophoblast may function for the entry of glucose into its cytoplasm, while GLUT1 at the basal plasma membrane may be essential for the exit of glucose from the cytoplasm into the stroma of the placental villi. Thus, GLUT1 at the plasma membranes of syncytiotrophoblast and endothelial cells may play an important role in the transport of glucose across the placental barrier. 相似文献
8.
Sequential Amino Acid Exchange across b0,+-like System in Chicken Brush Border Jejunum 总被引:2,自引:0,他引:2
Torras-Llort M Torrents D Soriano-García JF Gelpí JL Estévez R Ferrer R Palacín M Moretó M 《The Journal of membrane biology》2001,180(3):213-220
In the small intestine, cationic amino acids are transported by y+-like and b0,+-like systems present in the luminal side of the epithelium. Here, we report the characterization of a b0,+-like system in the apical membrane of the chicken jejunum, and its properties as an amino acid exchanger. Analysis of the
brush border membrane by Western blot points out the presence of rBAT (protein related to b0,+ amino acid transport system) in these membranes. A functional mechanism for amino acid exchange across this system was established
by kinetic analysis measuring fluxes at varying substrate concentrations both in internal (in) and external (out) vesicle
compartments. This intestinal b0,+-like system functions for l-arginine as an obligatory exchanger since its transport capacity increases 100–200 fold in exchange conditions, thus suggesting
an important role in the intestinal absorption of cationic amino acids. The kinetic analysis of Argin efflux velocities is compatible with the formation of a ternary complex and excludes a model involving a ping-pong mechanism. The binding affinity of Argout is higher than that of Argin, suggesting a possible order of binding (Argout first) for the formation of the ternary complex during the exchange cycle. A model of double translocation pathways with
alternating access is discussed.
Received: 23 March 2000/Revised: 29 December 2000 相似文献
9.
Role of MDR1 and MRP1 in trophoblast cells,elucidated using retroviral gene transfer 总被引:9,自引:0,他引:9
Atkinson DE Greenwood SL Sibley CP Glazier JD Fairbairn LJ 《American journal of physiology. Cell physiology》2003,285(3):C584-C591
Natural differences in expression and retroviral transduction techniques were used to test the hypothesis that MDR1 P-glycoprotein (P-gp) and MRP1 (multidrug resistance-related protein) contribute to xenobiotic handling by placental trophoblast. RT-PCR and Western blotting in placenta, primary cytotrophoblast cell cultures, and BeWo, JAr, and JEG choriocarcinoma cell lines showed that MRP1 was ubiquitously expressed, whereas MDR1 was absent or minimally expressed in BeWo and JEG cell lines. In syncytiotrophoblast, P-gp was localized predominantly to the microvillous, maternal facing plasma membrane, and MRP1 to the basal, fetal facing plasma membrane. Functional studies showed that cyclosporin A-sensitive accumulation of [3H]vinblastine by cells containing both transport proteins was significantly different from those expressing predominantly MRP1. Retroviral gene transfer of MDR1 to BeWo cells confirmed that this difference was due to the relative expression of MDR1. Therefore, both P-gp and MRP1 contribute to xenobiotic handling by the trophoblast. Localization of P-gp to the microvillous membrane suggests an essential role in preventing xenobiotic accumulation by the syncytiotrophoblast and, therefore, in protecting the fetus. placenta; multidrug resistance; xenobiotic 相似文献
10.
We have studied binding and membrane transfer rates of unsaturated long-chain fatty acids in sheep red cells, as previously
done for human red cells, in order to elucidate the transport mechanism. Observed differences must be assigned to the different
composition of the membrane in the two species.
Equal surface areas of the membranes of the two species have similar binding capacities and affinities for palmitic-, linoleic-,
oleic- and arachidonic acid at 37°C. The competitive bindings of linoleic- and arachidonic acid as well as the distribution
of bound arachidonic acid on the two sides of the membrane are not different in the two species. However, the rate constants
for membrane transfer in sheep are less than half of those measured previously for human ghosts. This finding is confirmed
by the exchange efflux kinetics of ghosts containing albumin-bound fatty acid. Studies of sheep ghost membranes with oleic-,
arachidonic- and linoleic acid reveal a proportionality between the membrane transfer rate constants and the number of fatty
acid double bonds, as found previously for human ghost membrane, and the effect of double bonds is in harmony with a large
negative activation entropy for diffusion through the membrane. The established replacement of lecithin by sphingomyelin with
a low unsaturation fatty acid index in sheep membranes probably causes a lower transversal lipid phase fluidity. Double bonds
diminish the flexibility of hydrocarbon chains and thus the large negative activation entropy of diffusion across the membrane.
The smaller transfer rate constants of the three unsaturated fatty acids in sheep membranes support the hypothesis that the
transfer is diffusion in protein defined annular lipid domains and not carrier mediated.
Received: 24 February 1999/Revised: 10 June 1999 相似文献
11.
The rBAT protein, when expressed in Xenopus oocytes, was previously shown to reproduce the selectivity of the Na+-independent neutral and basic amino acid transport system called bo,+. More recently, the capacity of rBAT to generate a transmembrane current was demonstrated when addition of neutral amino
acids stimulated the efflux of cations (presumably basic amino acids) in rBAT-injected oocytes. In the present paper, aminoisobutyric
acid (AIB), a neutral amino acid analogue, was shown to induce outward currents (efflux of basic amino acids) through rBAT
similar to those caused by alanine in terms of affinity, maximal currents and I-V curves. Despite generating similar currents, the AIB transport rate was more than 30 times lower than that of alanine, thus
challenging the assumption that rBAT functions as a classical exchanger. Experiments using a cut-open oocyte voltage clamp
demonstrated that AIB was capable of stimulating rBAT-mediated currents from either side of the membrane. AIB, like alanine,
was able to stimulate the efflux of radiolabeled alanine and arginine while no rBAT-mediated efflux was measurable in the
absence of external rBAT substrates. These results demonstrate that (i) the presence of amino acids is required on both sides
of the membrane for rBAT to mediate amino acid flux and thus rBAT must be some type of exchanger but (ii) rBAT-mediated amino
acid influx is not stoichiometrically related to the efflux. A model of a ``double gated pore' is proposed to account for
these properties of rBAT, which contravene standard models of exchangers and other transporters.
Received: 15 June 1995/Revised: 21 September 1995 相似文献
12.
New Glycoprotein-Associated Amino Acid Transporters 总被引:2,自引:0,他引:2
Verrey F Jack DL Paulsen IT Saier MH Pfeiffer R 《The Journal of membrane biology》1999,172(3):181-192
The L-type amino acid transporter LAT1 has recently been identified as being a disulfide-linked ``light chain' of the ubiquitously
expressed glycoprotein 4F2hc/CD98. Several LAT1-related transporters have been identified, which share the same putative 12-transmembrane
segment topology and also associate with the single transmembrane domain 4F2hc protein. They display differing amino acid
substrate specificities, transport kinetics and localizations such as, for instance, y+LAT1 which is localized at the basolateral membrane of transporting epithelia, and the defect of which causes lysinuric protein
intolerance. The b0,+AT transporter which associates with the 4F2hc-related rBAT protein to form the luminal high-affinity diamino acid transporter
defective in cystinuria, belongs to the same family of glycoprotein-associated amino acid transporters (gpaATs). These glycoprotein-associated
transporters function as amino acid exchangers. They extend the specificity range of vectorial amino acid transport when located
in the same membrane as carriers that unidirectionally transport one of the exchanged substrates. gpaATs belong to a phylogenetic
cluster within the amino acid/polyamine/choline (APC) superfamily of transporters. This cluster, which we designate the LAT
family (named after its first vertebrate member), includes some members from nematodes, yeast and bacteria. The latter of
these proteins presumably lack association with a second subunit. In this review, we focus on the animal members of the LAT
cluster that form, together with some of the nematode members, the family of glycoprotein-associated amino acid transporters
(gpaAT family).
Received: 20 July 1999/Revised: 7 September 1999 相似文献
13.
《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2019,1864(3):394-402
The mechanisms of placental transfer of long chain polyunsaturated fatty acids are poorly understood, however fatty acid transporters in the syncytiotrophoblast microvillous (MVM) and basal plasma membrane (BM) are believed to be involved. Using LC-MS/MS and samples from normal term pregnant women, we found that the concentration of lysophosphatidylcholine-docosahexaenoyl (DHA-LPC) was 4-fold higher in umbilical vein plasma compared to maternal venous concentrations while conversely phosphatidylcholine (PC) containing DHA or arachidonic acid were higher in maternal circulation. Using primary human trophoblast cells incubated with DHA we show that DHA was highly incorporated into PC and LPC species in the placenta. Protein expression of Phosphatidylcholine Transfer Protein (PCTP) was 14-fold higher in MVM and the expression of MFSD2a, an LPC transporter, was 5-fold higher in BM than in MVM. Interestingly, BM MFSD2a expression was positively correlated with DHA-LPC in the umbilical vein. These findings suggest that syncytiotrophoblast takes up PC from the maternal circulation, as well as preferentially incorporating DHA into PC. Placental PC are converted to LPC forms, which are transported across the BM mediated by MFSD2a, with a strong selectivity for DHA. 相似文献
14.
Theresa L. Powell Kelsey Barner Lana Madi Michael Armstrong Jonathan Manke Charis Uhlson Thomas Jansson Véronique Ferchaud-Roucher 《Biochimica et Biophysica Acta (BBA)/Molecular and Cell Biology of Lipids》2021,1866(3):158861
Fatty acid metabolism and oxidation capacity in the placenta, which likely affects the rate and composition of lipid delivered to the fetus remains poorly understood. Long chain polyunsaturated fatty acids, such as docosahexaenoic acid (DHA), are critical for fetal growth and brain development. We determined the impact of maternal obesity on placental fatty acid oxidation, esterification and transport capacity by measuring PhosphatidylCholine (PC) and LysoPhosphatidylCholine (LPC) containing DHA by mass spectrometry in mother-placenta-baby triads as well as placental free carnitine and acylcarnitine metabolites in women with normal and obese pre-pregnancy BMI. Placental protein expression of enzymes involved in beta-oxidation and esterification pathways, MFSD2a (lysophosphatidylcholine transporter) and OCTN2 (carnitine transporter) expression in syncytiotrophoblast microvillous (MVM) and basal (BM) membranes were determined by Western Blot. Maternal obesity was associated with decreased umbilical cord plasma DHA in LPC and PC fractions in male, but not female, fetuses. Basal membrane MFSD2a protein expression was increased in placenta of males of obese mothers. In female placentas, despite an increased MVM OCTN2 expression, maternal obesity was associated with a reduced MUFA-carnitine levels and increased esterification enzymes. We speculate that lower DHA-PL in fetal circulation of male offspring of obese mothers, despite a significant increase in transporter expression for LPC-DHA, may lead to low DHA needed for brain development contributing to neurological consequences that are more prevalent in male children. Female placentas likely have reduced beta-oxidation capacity and appear to store FA through greater placental esterification, suggesting impaired placenta function and lipid transfer in female placentas of obese mothers. 相似文献
15.
Summary. In the kidney the proximal tubule is responsible for the uptake of amino acids. This occurs via a variety of functionally
and structurally different amino acid transporters located in the luminal and basolateral membrane. Some of these transporters
show an ion-dependence (e.g. Na+, Cl− and K+) or use an H+-gradient to drive transport. Only a few amino acid transporters have been cloned or functionally characterized in detail
so far and their structure is known, while little is known about a majority of amino acid transporters. Only few attempts
have been untertaken looking at the regulation of amino acid transport. We summarized more recent information on amino acid
transport in the renal proximal tubule emphasizing functional and regulatory aspects.
Received August 8, 1999; Accepted April 20, 2000 相似文献
16.
Improving amino acid nutrition to prevent intrauterine growth restriction in mammals 总被引:1,自引:0,他引:1
Gang Lin Xiaoqiu Wang Guoyao Wu Cuiping Feng Huaijun Zhou Defa Li Junjun Wang 《Amino acids》2014,46(7):1605-1623
Intrauterine growth restriction (IUGR) is one of the most common concerns in human obstetrics and domestic animal production. It is usually caused by placental insufficiency, which decreases fetal uptake of nutrients (especially amino acids) from the placenta. Amino acids are not only building blocks for protein but also key regulators of metabolic pathways in fetoplacental development. The enhanced demands of amino acids by the developing conceptus must be met via active transport systems across the placenta as normal pregnancy advances. Growing evidence indicates that IUGR is associated with a reduction in placental amino acid transport capacity and metabolic pathways within the embryonic/fetal development. The positive relationships between amino acid concentrations in circulating maternal blood and placental amino acid transport into fetus encourage designing new therapies to prevent or treat IUGR by enhancing amino acid availability in maternal diets or maternal circulation. Despite the positive effects of available dietary interventions, nutritional therapy for IUGR is still in its infancy. Based on understanding of the underlying mechanisms whereby amino acids promote fetal growth and of their dietary requirements by IUGR, supplementation with functional amino acids (e.g., arginine and glutamine) hold great promise for preventing fetal growth restriction and improving health and growth of IUGR offspring. 相似文献
17.
D.T. Thwaites D. Markovich H. Murer N.L. Simmons 《The Journal of membrane biology》1996,151(3):215-224
The nature of transepithelial and cellular transport of the dibasic amino acid lysine in human intestinal epithelial Caco-2
cells has been characterized. Intracellular accumulation of lysine across both the apical and basolateral membranes consists
of a Na+-independent, membrane potential-sensitive uptake. Na+-independent lysine uptake at the basolateral membrane exceeds that at the apical membrane. Lysine uptake consists of both
saturable and nonsaturable components. Na+-independent lysine uptake at both membranes is inhibited by lysine, arginine, alanine, histidine, methionine, leucine, cystine,
cysteine and homoserine. In contrast, proline and taurine are without inhibitory effects at both membranes. Fractional Na+-independent lysine efflux from preloaded epithelial layers is greater at the basolateral membrane and shows trans-stimulation
across both epithelial borders by lysine, arginine, alanine, histidine, methionine, and leucine but not proline and taurine.
Na+-independent lysine influx (10 μm) in the presence of 10 mm homoserine shows further concentration dependent inhibition by lysine. Taken together, these data are consistent with lysine
transport being mediated by systems bo,+, y+ and a component of very low affinity (nonsaturable) at both membranes. The relative contribution to lysine uptake at each
membrane surface (at 10 μm lysine), normalized to total apical uptake (100%), is apical bo,+ (47%), y+ (27%) and the nonsaturable component (26%), and basal bo,+ (446%), y+ (276%) and the nonsaturable component (20%). Northern analysis shows hybridization of Caco-2 poly(A)+RNA with a human rBAT cDNA probe.
Received: 3 July 1995/Revised: 6 February 1996 相似文献
18.
O G Belokurov S B Golumb I I Nikitina 《Biulleten' eksperimental'no? biologii i meditsiny》1976,81(4):394-397
A method of bilateral perfusion of the isolated human placenta was used to study the urea transport from the fetal placental stream into the maternal one, and of amino acid transport in the opposite direction. Experiments demonstrated that the method provided a sufficiently full perfusion of the intervillous space and offered possibilities for studying the placental transport. With equal amino nitrogen concentration in both circulations, its content in the fetal stream increased during the experiment. This elevation was more expressed when amino acid was added to the maternal circulation. The idea of amino acid "secretion" by the trophoblast cell elements into the fetal circulation was confirmed by the above experiments. 相似文献
19.
Human cationic amino acid transporter hCAT-3 is preferentially expressed in peripheral tissues 总被引:7,自引:0,他引:7
At least five distinct carrier proteins form the family of mammalian cationic amino acid transporters (CATs). We have cloned a cDNA containing the complete coding region of human CAT-3. hCAT-3 is glycosylated and localized to the plasma membrane. Transport studies in Xenopus laevis oocytes revealed that hCAT-3 is selective for cationic L-amino acids and exhibits a maximal transport activity similar to other CAT proteins. The apparent substrate affinity and sensitivity to trans-stimulation of hCAT-3 resembles most closely hCAT-2B. This is in contrast to rat and murine CAT-3 proteins that have been reported to display a very low activity and to be inhibited by neutral and anionic L-amino acids as well as D-arginine (Hosokawa, H., et al. (1997) J. Biol. Chem. 272, 8717-8722; Ito, K., and Groudine, M. (1997) J. Biol. Chem. 272, 26780-26786). Also, in adult rat and mouse, CAT-3 has been found exclusively in central neurons. Human CAT-3 expression is not restricted to the brain, in fact, by far the highest expression was found in thymus. Also in other peripheral tissues, hCAT-3 expression was equal to or higher than in most brain regions, suggesting that hCAT-3 is not a neuron-specific transporter. 相似文献
20.
Amino acid transport of y+L-type by heterodimers of 4F2hc/CD98 and members of the glycoprotein-associated amino acid transporter family. 总被引:10,自引:1,他引:9
下载免费PDF全文
![点击此处可从《The EMBO journal》网站下载免费的PDF全文](/ch/ext_images/free.gif)
Amino acid transport across cellular membranes is mediated by multiple transporters with overlapping specificities. We recently have identified the vertebrate proteins which mediate Na+-independent exchange of large neutral amino acids corresponding to transport system L. This transporter consists of a novel amino acid permease-related protein (LAT1 or AmAT-L-lc) which for surface expression and function requires formation of disulfide-linked heterodimers with the glycosylated heavy chain of the h4F2/CD98 surface antigen. We show that h4F2hc also associates with other mammalian light chains, e.g. y+LAT1 from mouse and human which are approximately 48% identical with LAT1 and thus belong to the same family of glycoprotein-associated amino acid transporters. The novel heterodimers form exchangers which mediate the cellular efflux of cationic amino acids and the Na+-dependent uptake of large neutral amino acids. These transport characteristics and kinetic and pharmacological fingerprints identify them as y+L-type transport systems. The mRNA encoding my+LAT1 is detectable in most adult tissues and expressed at high levels in kidney cortex and intestine. This suggests that the y+LAT1-4F2hc heterodimer, besides participating in amino acid uptake/secretion in many cell types, is the basolateral amino acid exchanger involved in transepithelial reabsorption of cationic amino acids; hence, its defect might be the cause of the human genetic disease lysinuric protein intolerance. 相似文献