Microvillous Plasma Membrane Research Articles

Neutral Amino Acid Uptake by the Microvillous Plasma Membrane of the Human Placenta Is Inversely Related to Fetal Size at Birth in Normal Pregnancy

Neutral Amino Acid Uptake by the Microvillous Plasma Membrane of the Human Placenta Is Inversely Related to Fetal Size at Birth in Normal Pregnancy

Differential Distribution of Binding Sites for 125I-Insulin-Like Growth Factor II on Trophoblast Membranes of Human Term Placenta

The syncytiotrophoblast, which is delineated by two polar membranes (the microvillous and the basal plasma membranes), is the main placental structural element controlling maternal-fetal exchanges. These studies of the full-term placenta were undertaken in order to determine whether the microvillous membranes, which are bathed by the maternal intervillous circulation, and basal plasma membrane, which lines the fetal blood capillaries, have binding sites for insulin-like growth factor (IGF)-II. The microvillous and basal plasma membranes were purified and found to bind 125I-IGF-II with significantly different (p < 0.0001) Kd (0.51 and 1.02 nM, respectively). There were more available binding sites in the microvillous (4.4+/-0.3 pmol/mg protein) than in the basal (2.7+/-0.4 pmol/mg protein) plasma membranes (p < 0.0001). Both membranes contained three major (250, 135, and 130 kDa) 125I-IGF-II/binding-site protein complexes as determined by affinity cross-linking and PAGE. The 250-kDa band (type 2 IGF receptor) was the main band in the basal plasma membranes (46% total bound 125I-IGF-II). The 135-kDa band (insulin-receptor alpha subunit) was the main one in the microvillous membranes (48% total bound 125I-IGF-II). The amounts of 130-kDa band (type 1 IGF-receptor alpha subunit) in the two types of membranes were similar (30% total bound 125I-IGF-II). Only IGF-II displaced 125I-IGF-II from the 250-kDa band, while 125I-IGF-II bound to the 135-kDa band was displaced by insulin, and ligand bound to the 130-kDa band was displaced by IGF-I. Thus there are IGF receptors in both types of membranes of syncytiotrophoblast in the human full-term placenta, and the distributions of the IGF and insulin receptors are asymmetrical. This may reflect the fact that they face and interact with two independent, different media. Maternal IGF may influence the syncytiotrophoblast by binding to receptors on the microvillous membranes, while fetal IGF may also influence syncytiotrophoblast functions by activating receptors in the basal plasma membranes.

Suppressive effect on lymphoproliferation in vitro by soluble annexin II released from isolated placental membranes.

Syncytiotrophoblast microvillous plasma membranes (StMPM) are potent suppressors of lymphoproliferation in vitro. We have previously shown that soluble annexin II (AII) is present at higher levels in retroplacental serum (RPS) than in peripheral serum, and that soluble AII has an immunosuppressive effect. The aims of this study were to determine whether AII can be released from StMPM and whether soluble AII from StMPM exerts any immunosuppressive effect. Isolated StMPM were incubated in growth medium for 18 hr and supernatants were prepared by ultracentrifugation. Soluble AII was detected by immunoblotting. StMPM, StMPM supernatant, and affinity-purified AII were analysed in a lymphoproliferation assay for immunomodulating activity. AII heavy chain and its p11 light chain were detected both in StMPM supernatant and in RPS after removal of StMPM particles by ultracentrifugation. StMPM, StMPM supernatant, and purified AII suppressed lymphoproliferation in a dose-dependent manner. Absorption of AII from StMPM supernatant reduced the suppressive activity. The suppressive effect of StMPM supernatant and purified AII was completely reversed by heating at 100 degrees C for 30 min or by adding recombinant interleukin-2 at 100 units/ml. Although StMPM and affinity-purified AII suppressed the proliferation of lymphocytes from all donors tested, StMPM supernatant suppressed the proliferation of lymphocytes from 12 of 23 donors. Six of eight female non-suppressed donors were multiparae, whereas five of five female suppressed donors were nulliparae. Annexin II is released by isolated placental membranes in vitro and is present in RPS, indicating in vivo release of AII at the fetomaternal interface, probably as AII heterotetramer. AII has immunosuppressive activity and may be important in fetal allograft survival.

Localization of IL-4 and IL-4 receptors in the human term placenta, decidua and amniochorionic membranes.

There has been much recent interest in cytokine expression at the materno-fetal interface. Although T-helper 2 (Th2)-type cytokines have been described in the murine feto-placental unit, few studies have as yet been performed in human pregnancy. We have examined the production of interleukin-4 (IL-4) and expression of IL-4 receptors in the human term placenta, decidua and amniochorionic membranes. Immunohistochemical analyses revealed that cytotrophoblast, decidual macrophages and both maternal and fetal endothelial cells consistently expressed IL-4, whereas syncytiotrophoblast and placental macrophages showed an inconsistent pattern between specimens. High- and low-affinity IL-4 receptors were demonstrated by immunohistochemistry at the same cellular sites as stained for IL-4, and detection of IL-4 receptors was also variable in syncytiotrophoblast. Reverse-transcribed-polymerase chain reaction (RT-PCR) analysis showed that both IL-4 and its alternative splice variant, IL-482, are produced both in placental villi and in amniochorionic and decidual tissue. Ligand-binding assays identified the presence, on isolated term syncytiotrophoblast microvillous plasma membrane vesicle preparations, of functional high-affinity binding sites for IL-4 with a Kd in the range 102-112 pM and an apparent receptor density in the range 99-102 x 10(8) sites/mg protein. Three human choriocarcinoma (BeWo, JEG-3 and Jar) and one amnion-derived (AV3) cell lines expressed IL-4 and both high- and low-affinity IL-4 receptors. The constitutive expression of both IL-4 and IL-4 receptors, together with the novel finding of the alternative splice variant IL-482 in the immediate tissues at the materno fetal interface suggest an immunobiological role for IL-4 in human pregnancy.

Placental membrane transport

Brush border (microvillous) plasma membranes (BBM) and the basal surfaces (BCM) from the syncytiotrophoblast of human term placenta were prepared by a method of sonication, dialysis and differential centrifugation in specific buffer systems. Such plasma membranes formed closed, osmotically active, right-side-out vesicles in which amino acid transport could be studied unidirectionally by a carefully designed membrane filtration assay under reduced pressure. In such vesicles, L-leucine (1 mM) was found to be transported in a time-dependent manner, peak accumulation being attained at 45 s in both BBM and BCM. The accumulation of L-leucine in the vesicles was dependent on an inward NaC1 gradient, as replacing the Na+ with K+, Li+ and choline, or replacing the C1- with S0(2-4) failed to influence the amino acid movement. Leucine transport in the vesicles also appeared to be dependent on the substrate concentration, indicating saturation at a higher concentration. The transport process showed a k(t) (affinity constant) of 3.85 and 6.67 mM, while the values recorded for the J max (maximum apparent initial velocity) were 270.27 and 384.62 nmol/mg protein-1 per min in the BBM and BCM respectively. Leucine transport was inhibited by a number of amino acids, among which amino isobutyric acid (AIB) produced the maximum inhibition. The k(i) inhibition constant) for different amino acids has also been listed. Lysine showed the least k(i) value, thus showing it to be the most inhibitory compound. These findings are discussed in relation to the mechanism and regulation of transplacental amino acid transfer.

Surface annexin II on placental membranes of the fetomaternal interface.

The phospholipidbinding membrane protein annexin II has been demonstrated to possess FcR activity for IgG and has been localized to the outer part of the syncytiotrophoblast cell layer. The question has arisen whether annexin II is exposed on the surface of syncytiotrophoblast cells thus enabling it to take part in the transport of IgG across the maternal barrier. Syncytiotrophoblast microvillous plasma membranes were analyzed by flow cytometry for annexin II as well as established surface molecules. Fresh, fixed placental tissue was preincubated with antibodies to annexin II or known trophoblast surface molecules, and analyzed by confocal laser scanning microscopy. Annexin II and its subunit p11 were expressed on the surface of the syncytiotrophoblast microvillous plasma membranes as were other established surface proteins (CD46, CD59, placental alkaline phosphatase), using both flow cytometry and confocal microscopy. Annexin was not detected on the surface of viable cultured trophoblast cells. Annexin II is exposed on the surface of syncytiotrophoblast cells as a heterotetramer together with its light chain p11. It is exposed to maternal blood and may be instrumental in IgG transport across the placental barrier by binding.

Na+ transport, H+ concentration gradient dissipation, and system A amino acid transporter activity in purified microvillous plasma membrane isolated from first-trimester human placenta: Comparison with the term microvillous membrane

Our purpose was to isolate microvillous plasma membrane from first-trimester placenta and to measure its transport properties with regard to Na+, H+, and a neutral amino acid. Microvillous membrane was isolated from first-trimester (10 to 13 weeks) and term (38 to 42 weeks) placenta and the purity determined. Uptake of 22Na+ was measured in the presence of an outwardly directly H+ gradient in the presence or absence of amiloride (0.5 mmol/L). The rate of dissipation of an H+ concentration gradient was determined with the H(+)-sensitive fluorescent probe 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein. 14C-methylaminoisobutyric acid uptake was measured in the presence and absence of an inwardly directed Na+ gradient. Purity, vesicle volume, vesicle orientation, and electron micrographic appearance of the first-trimester membranes were similar to those obtained from term placenta, but vesicle protein recovery was lower. Amiloride-sensitive Na+ uptake and Na(+)-dependent 14C-methylaminoisobutyric acid uptake was threefold to fourfold lower by first-trimester than by term membranes. The rate of H+ concentration gradient dissipation was greater in the former. The first-trimester microvillous membrane has similar general characteristics to that from term placenta, but its transport activity is quite different.

GTP-binding proteins associated with the human placental syncytiotrophoblast plasma membrane

International Journal of Gynecology & ObstetricsVolume 47, Issue 2 p. 194-194 Citations from the literature placenta GTP-binding proteins associated with the human placental syncytiotrophoblast plasma membrane P. Kenton, P. KentonSearch for more papers by this authorP.M. Johnson, P.M. JohnsonSearch for more papers by this author P. Kenton, P. KentonSearch for more papers by this authorP.M. Johnson, P.M. JohnsonSearch for more papers by this author First published: November 1994 https://doi.org/10.1016/0020-7292(94)90374-3AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume47, Issue2November 1994Pages 194-194 RelatedInformation

Neutral Amino Acid Uptake by Microvillous and Basal Plasma Membrane Vesicles from Appropriate- and Small-for-Gestational Age Human Pregnancies

Fetal growth depends upon nutrient availabilty in the maternal circulation as well as appropriate transfer across the placenta via known transport mechanisms in the maternal- and fetal-facing plasma membranes of the syncytiotrophoblast. In this study, microvillous (maternal-facing) and basal (fetal-facing) plasma membrane vesicles were isolated from the placentas of appropriate-for-gestational age (AGA) and small-for-gestational age (SGA) human pregnancies and the uptakes of tritiated leucine, alanine, and glycine were determined. There was no significant difference in the uptakes of either alanine or leucine by the microvillous and basal vesicles from AGA and SGA pregnancies. In contrast, glycine uptake by both microvillous and basal membrane vesicles from SGA pregnancies was significantly less than vesicles from AGA pregnancies. Glycine is delivered to the umbilical circulation in amounts only minimally in excess of its accretion into protein resulting in a narrow margin of safety for fetal growth. The ...

GTP-Binding proteins associated with the human placental syncytiotrophoblast plasma membrane

The nature of GTP-binding components associated with isolated human term placental syncytiotrophoblast microvillous plasma membrane vesicles (SPMV) was determined; these are relevant to elucidation of intracellular signal transduction mechanisms. Four proteins were identified, with molecular weights of 29, 27, 23 and 21 kDa, which specifically bound [alpha-32P]GTP in the presence of Mg2+. Studies employing anti-p21c-ras monoclonal antibodies indicated these four GTP-binding components were ras-related and one, the 21 kDa component, may be p21c-ras. In addition, SPMV were also found to express the alpha subunits of three separate G proteins. A 45 kDa SPMV GTP-binding protein was identified as a substrate for Vibrio cholera toxin and was recognized by a rabbit antibody to the alpha subunit of the adenylate cyclase stimulating G protein, Gs. A 41 kDa SPMV GTP-binding protein substrate of Bordetella pertussis toxin was also recognized by rabbit antibodies to the alpha subunits of the adenylate cyclase inhibiting G proteins, Gi-1 and Gi-3. No evidence was found to support the presence of the 21 kDa Gp, a G protein previously associated with membranes prepared from whole placental tissue homogenates.

Cyanide-resistant reduction of nitroblue tetrazolium and hydrogen peroxide production by the rabbit blastocyst.

The ability of the rabbit blastocyst to reduce nitroblue tetrazolium (NBT) to formazan in the presence of cyanide was assayed as an indicator of extramitochondrial oxidase activity capable of generating the superoxide radical. A cytochemical method initially developed for the detection and localization of hydrogen peroxide production at the ultrastructural level in phagocytosing leukocytes (Briggs et al.: J Cell Biol 67:566, 1975) was also applied to the blastocyst. The results demonstrate that the rabbit blastocyst acquires the ability to reduce NBT by a cyanide-insensitive process and to generate hydrogen peroxide between the fourth and fifth days postcoitum. The enzymatic activity responsible is apparently an NAD(P)H-dependent oxidase in the outer, microvillous plasma membrane of the trophoblast.

Localization of Na(+)-dependent active type and erythrocyte/HepG2-type glucose transporters in rat kidney: immunofluorescence and immunogold study.

Glucose is actively taken up from the glomerular filtrate into the tubule cells by the Na(+)-dependent active glucose transporter (GT), and passively crosses the basolateral membrane via facilitated diffusion GT. With the use of antibodies directed against two types of GTs, we show the immunocytochemical localization of the Na(+)-dependent active GT (SGLT1) and the erythrocyte/HepG2-type facilitated diffusion GT (GLUT1). For light microscopic observation, frozen sections were stained by the rhodamine labeling method. Counterstaining with fluorescein-phalloidin and 4,6-diamidino-2-phenylindole dihydrochloride (DAPI) was employed to facilitate cell type identification. Immunogold staining was carried out on ultra-thin frozen sections for electron microscopy. The antibody to SGLT1 reacted with a 77 KD protein in immunoblotting of a kidney lysate. By immunocytochemistry, SGLT1 was localized in the microvillous plasma membrane in the apical brush borders of the cells of all three proximal tubule segments (S1, S2, and S3). The antibodies to GLUT1, a member of the facilitated diffusion GT family, were raised against human erythrocyte GT or synthetic oligopeptides derived from HepG2 GT, which reacted with a 48 KD protein in immunoblotting of the kidney lysate. GLUT1 was found at the basolateral plasma membranes of S3 proximal tubule cells, cells of the thick limb of Henle's loop, and collecting duct cells. Combined with known physiological data, our findings suggest that SGLT1 in the apical plasma membrane of the proximal tubule cells is responsible for the Na(+)-dependent active reabsorption of glucose from the glomerular filtrate. GLUT1 in the basolateral plasma membrane of S3 cells may transport reabsorbed glucose to the blood vessels. GLUT1 in the basolateral plasma membranes of cells of the thick limb of Henle's loop and of the collecting duct, on the other hand, may nourish these metabolically active cells by facilitating the diffusion of extracellular glucose provided from blood through the basolateral side of the cells.

Anionic amino acid transport systems in isolated basal plasma membrane of human placenta

The placenta absorbs anionic amino acids from the maternal and fetal circulations but does not significantly transfer these amino acids from mother to fetus. Uptake of L-aspartate and L-glutamate by basal (fetal-facing) plasma membrane vesicles from placental syncytiotrophoblast was stimulated by an inward sodium and an outward potassium gradient. Measurable saturable uptake was entirely sodium dependent and electrogenic. Studies of concentration dependence resolved a high-affinity (microM) system that has characteristics of the X-AG system found in other tissues including the placental microvillous plasma membrane. Uptake of 0.2 microM L-glutamate was inhibited by 2 mM L-glutamate, L-aspartate, D-aspartate, L-cysteate, and L-cysteinesulfinic acid and was uninhibited by 2 mM D-glutamate, L-glutamine, L-alanine, L-serine, L-asparagine, and taurine or by 1 mM methylaminoisobutyric acid. The X-AG system in the two membranes of the placental syncytiotrophoblast may mediate the concentrative uptake of anionic amino acids from the maternal and fetal circulations into the placenta.

Proteins associated with activity of Fc receptors on isolated human placental syncytiotrophoblast microvillous plasma membranes.

To identify Fc receptors from human placental microvilli, proteins that were liberated by detergents from human placental synctiotrophoblast microvillous membranes (StMPM) were characterized by their abilities to bind human IgG in immune complexes with sheep or goat anti-human IgG and to monomeric rabbit anti-dinitrophenol (DNP) IgG bound to DNP-lysine Sepharose. Three placental IgG-binding proteins coprecipitated with immune complexes (Mr = 68,000, 52,000-56,000, 40,000) and were designated pIBP68, pIBP56 and pIBP40, respectively. Of the three proteins only pIBP56 bound to immobilized monomeric rabbit IgG. It was isolated from detergent lysates of StMPM and LDS/phenol glycoprotein extracts of placental plasma membranes suggesting that pIBP56 was a glycoprotein FcR previously reported (Mikulska et al, 1982). The binding specificities of pIBP56 and pIBP40 appeared to be detergent dependent. Photoaffinity crosslinking of StMPM surface proteins in situ to monomeric rabbit derivatized with N-succinimidyl(4-azidophenyl)-I, 3-dithiopropionate identified IgG-binding proteins identical in size to pIBP56 and pIBP40. Crosslinking further suggested that monomeric IgG covalently bound to a complex of StMPM proteins with a total size of 110,000-120,000 Mr. The findings suggest that pIBP68, pIBP56 and pIBP68 are responsible for IgG binding activity of placental StMPM.

Carrier-mediated transport system for cephalexin in human placental brush-border membrane vesicles

The uptake of cephalosporin antibiotics, cephalexin, was studied with brush-border microvillous plasma membrane vesicles prepared and purified from human full-term placental syncytiotrophoblasts. The uptake of cephalexin by the membrane vesicles was not stimulated in the presence of an Na + gradient from the outside to the inside of the vesicles, whereas α-(methylamino)isobutyrate uptake into the vesicles of the same preparation was stimulated by an Na + gradient. The equilibrium level of cephalexin uptake decreased with increasing osmolarity of the medium, which indicates that cephalexin is transported into the membrane vesicles. When cephalexin concentrations were varied, the initial rate of uptake obeyed Michaelis-Menten kinetics with K m and V max values of 2.29 mM and 2.98 nmol/mg of protein per 60 s, respectively. The uptake of cephalexin was inhibited by structural analogues and sulfhydryl modifying reagents. These results indicate the existence of a carrier-mediated transport system for cephalexin in the human placental brush-border membranes.

Human placental sterylsulfatase: immunocytochemical and biochemical localization.

Human placental sterylsulfatase was localised in situ by light and electron microscope immunocytochemical techniques as well as in homogenate and tissue extract fractions by enzyme assays. Light microscope observations on frozen sections of term and preterm placenta revealed sterylsulfatase immunoactivity primarily in the syncytiotrophoblast. Electron microscope observations confirmed the light microscope findings; in addition, they showed that the sulfatase is present in the endoplasmic reticulum of endothelial cells, too. In the syncytiotrophoblast, the enzyme was detectable in the cytoplasmic membrane of the nuclear evelope, in the membranes of the rough endoplasmic reticulum, in the plasma membrane with predominant localisation in coated pits, and in the membranes of endosomes and multivesicular bodies; little or no reactivity was detectable over the membranes of the Golgi complex and of lysosomes. Sterylsulfatase immunoactivity was absent in placentas with hereditary sterylsulfatase deficiency. The observations indicate that human placental sterylsulfatase is normally present in the membranes of compartments along the secretory pathway and the endocytic route of cells lining the fetal and maternal blood. Homogenates of normal term placenta as well as membrane vesicle preparations obtained by extraction of trophoblast tissue with isotonic saline were fractionated by differential centrifugation; the fractions were assayed for specific activities of sterylsulfatase and several marker enzymes of cellular topography. In agreement with our immunocytochemical findings, the results of these biochemical localisation experiments indicate the repeatedly described association of the placental sterylsulfatase with microsomal membranes but also point to the presence of the enzyme's activity in the microvillous plasma membrane of the syncytiotrophoblast. This localisation of sterylsulfatase may have functional implications in the placental uptake of circulating steroid sulfates.

Neutral amino acid transport systems of microvillous membrane of human placenta.

Placental transport produces concentrations of amino acids in fetal blood greater than those of maternal blood. Competitive inhibition studies of zwitterionic amino acid transport in isolated vesicles from the microvillous (maternal facing) plasma membranes of syncytiotrophoblast defined three transport systems: 1) a sodium-dependent system that supports methylaminoisobutyric acid (MeAIB) transport and has the characteristics of an A system; 2) a sodium-independent system with a high affinity for leucine and other amino acids with branched or aromatic side chains; and 3) a sodium-independent system with a preference for alanine as a substrate. The two sodium-independent systems could be further discriminated by marked specificity for trans stimulation with alanine or with leucine. System ASC, known to be present in whole placenta, and the neutral brush-border or imino systems of other polarized epithelia were apparently absent. Kinetic characteristics of the A system make it the probable primary driving force for concentrative transfer of its substrate amino acids to the fetus. Characteristics of the high-affinity leucine system demonstrated that it is saturated by normal serum leucine concentrations. Regulation of either system has the potential to alter placental amino acid uptake and transfer to the fetus.

Human Trophoblast Glycoproteins Defined by Monoclonal Antibody 1D2

A cell surface antigen has been defined by a monoclonal antibody 1D2, raised following immunisation with lectin-purified syncytiotrophoblast glycoproteins. 1D2 was nonreactive with any one of 8 common trophoblast proteins in immunodot. Analysis of nonreduced western blots of syncytiotrophoblast microvillous plasma membrane (StMPM) protein indicated that mAb 1D2 was reactive with a series of sialylated proteins with molecular weights of 16-22 kilodaltons. Immunoprecipitates of radiolabelled StMPM protein contained molecules that co-migrated with placental alkaline phosphatase in addition to those identified by western blotting. This set of human trophoblast molecules has not been previously identified by monoclonal antibodies; the antigenicity is widely distributed in human tissues.

Calcium-dependant binding proteins associated with human placental syncytiotrophoblast microvillous cytoskeleton

Isolated human placental syncytiotrophoblast microvillous plasma membrane vesicles were extracted with Triton X-100 to yield a detergent-insoluble residue. The residue contained approx. 50% of the total membrane protein and was qualitatively different from untreated trophoblast on SDS-polyacrylamide gel electrophoresis, Western blots and dot-immunobinding assay. Three major proteins, with molecular weights of 68, 36 and 34 kDa, dissociated from this non-ionic detergent-insoluble submembranous cytoskeletal fraction in the presence of calcium chelators. They were immunologically related to human lymphocyte cytoskeletal calcium-binding proteins, and the 36 kDa component reacted with antisera to the phospholipase A 2 inhibitor, lipocortin II. Anti-lipocortin I sera did not recognise the 34 kDa protein, but did react with a series of trophoblast cytoskeletal proteins in the 34–37 kDa region. Incubation of epidermal growth factor with isolated trophoblast membrane vesicles stimulated the phosphorylation of a 36 kDa protein on tyrosine residues. Immunoprecipitation studies further showed there was no phosphorylation of the 34 kDa protein, but the 68 kDa protein was a major phosphorylated component of isolated syncytiotrophoblast membranes. p68 was principally phosphorylated on serine with slight tyrosine phosphorylation which showed an apparent increase after epidermal growth factor treatment. These results indicate a family of calcium-dependant binding proteins, some of which are phosphorylated, associated with the submembranous cytoskeleton of syncytiotrophoblast microvilli.

A Study of Taurine Transport and Absorption in Placenta and Neonatal Intestine and Kidney

AbstractSerum taurine concentration in the human fetus (umbilical blood) and neonate was measured from the 24th to 40th week of pregnancy. The concentration was considerably higher than in maternal serum with a peak at the 24th week of pregnancy and then a gradual decrease until it approached the adult level on the 9th day after birth.To clarify the underlying mechanism of the human findings, the distribution of 14C‐taurine was investigated after intravenous injection to maternal rats on the 20th day of pregnancy. The taurine administered to the maternal side became concentrated in the placenta and reached the fetus. It was confirmed that taurine accumulated in the human placenta was present in a higher concentration than any other free animo acid.Placental transport of taurine was studied in isolated brush border microvillous plasma membrane vesicles by a rapid filtration technique. The membrane vesicles exhibited uptake of H3‐labeled traurine into an osmotically reactive intravesicular space. Taurine uptake by vesicles was stimulated specifically by an inward sodium gradient, and replacement of NaCl in the transport medium by KCl, LiCl or choline chloride had no effect on the transport activity of the vesicles. Taurine transport was inhibited competivively by the presence of β‐alanine and GABA. The initial rate of transport followed saturation kinetics with respect to taurine concentration: an apparent Km of 0.22 mM and Vmax of 67 pmol/mg protein were calculated in 20 seconds. These results indicate that transport of taurine across the placental brush border membrane is sodium‐dependent and carrier‐mediated.The taurine transport system in human fetal small intestine, especially in the jejunum, is a passive transport system quite unlike that of other amino acids.Reabsorption of taurine through the proximal convoluted tubule is by active transport which depends on sodium. This transport system is developed from the 24th to the 32nd gestational week.