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C P Sibley

Publications and source records attributed to C P Sibley.

At least 19 recordsLinked to original sources
PubMed2006

Taurine transporter in fetal T lymphocytes and platelets: differential expression and functional activity.

Transplacental transfer of taurine, a beta-amino acid essential for fetal and neonatal development, constitutes the primary source of taurine for the fetus. Placental transport of taurine is compromised in pregnancies complicated by intrauterine growth restriction, resulting in a reduced concentration of taurine in cord plasma. This could impact on fetal cellular metabolism as taurine represents the most abundant intracellular amino acid in many fetal cell types. In the present study, we have used pure isolates of fetal platelets and T lymphocytes from cord blood of placentas, from normal, term pregnancies, as fetal cell types to examine the cellular uptake mechanisms for taurine by the system beta transporter and have compared gene and protein expression for the taurine transporter protein (TAUT) in these two cell types. System beta activity in fetal platelets was 15-fold higher compared with fetal T lymphocytes (P < 0.005), mirroring greater TAUT mRNA expression in platelets than T lymphocytes (P < 0.005). Cell-specific differences in TAUT protein moieties were detected with a doublet of 75 and 80 kDa in fetal platelets compared with 114 and 120 kDa in fetal T lymphocytes, with relatively higher expression in platelets. We conclude that greater system beta activity in fetal platelets compared with T lymphocytes is the result of relatively greater TAUT mRNA and protein expression. This study represents the first characterization of amino acid transporters in fetal T lymphocytes.

Blood Platelets↗
PubMed2006

L-serine uptake by human placental microvillous membrane vesicles.

The human fetus requires more glycine than any other amino acid but placental glycine transfer to the fetus is insufficient to meet fetal demand. L-Serine could represent a major metabolic source of glycine for the human fetus but little is known about the kinetics and physiology of L-serine uptake by the human placenta. We have characterised the amino acid transport systems involved in the uptake of L-serine by the microvillous membrane of the human placental syncytiotrophoblast and compared the uptake rates to those of glycine. L-Serine uptake into microvillous membrane (MVM) vesicles was primarily mediated by system A (MeAIB inhibitable) and system L (BCH inhibitable). Further characterisation using specific substrates of LAT1 and LAT2 found the pattern of L-serine uptake was consistent with that expected for uptake mediated by LAT2. Uptakes were performed with tracer levels of (14)C-L-serine, physiological levels of L-serine, or with physiological levels of amino acids. As amino acid concentrations rose, the proportion of uptake by System L decreased while uptake by uncharacterised Na(+)-independent systems increased. Uptake of Lserine into MVM vesicles had a V(max) of 2.1+/-0.4 nmol/mg protein/min, which was significantly higher than for glycine (V(max) 1.0+/-0.2 nmol/mg protein/min). This indicates that MVM vesicles have a higher uptake capacity for L-serine than glycine, despite a greater demand for glycine over serine for fetal protein synthesis. Further studies are now required to define the fate of L-serine taken up by the placenta and its importance for the fetus.

Amino Acid Transport System A↗
PubMed2006

Artificial perfusion of the fetal circulation of the in situ mouse placenta: methodology and validation.

Here we present methodology and validation (including measurement of unidirectional maternofetal clearance (Kmf) of (45)Ca and (14)C-mannitol) for in situ perfusion of the mouse placenta. On day 18 of gestation (term=19 days) mice were anaesthetised and the uterus delivered into a saline bath (40 degrees C). A fetus was selected, the umbilical artery and vein catheterised and perfused with Krebs Ringer (pH 7.4) at 60 microl/min. (45)Ca/(14)C-mannitol (2 microCi/5 microCi in 50 microl saline) was injected via maternal tail vein. Perfusate samples were collected every 5 min for 45 min. Maternal carotid artery pressure was monitored throughout perfusion. A terminal maternal cardiac blood sample was taken and analysed. Placentas were immersion fixed and processed for electron microscopy. Kmf for (45)Ca and (14)C-mannitol was calculated as perfusate [(45)Ca or (14)C-mannitol] x perfusion rate/maternal plasma [(45)Ca or (14)C-mannitol]xplacental weight. Maternal cardiac blood chemistry at termination (n=8-15, mean+/-SEM) was as follows: pH 7.153+/-0.016, PCO(2) 45.48+/-2.06 mmHg, PO(2) 66.47+/-7.10 mmHg, Na(+) 151.4+/-1.2 mmol/l, K(+) 5.54+/-0.17 mmol/l, Ca(2+) 1.15+/-0.03 mmol/l, glucose 7.2+/-0.5 mmol/l, and lactate 1.76+/-0.77 mmol/l. A successful 45 min perfusion in which perfusate recovery was >95% occurred in >50% of animals. Perfusion did not alter placental morphology or carotid pressure. Kmf (microl/min/g placenta) for (45)Ca (66.0+/-8.4 (n=7)) was significantly higher than Kmf for (14)C-mannitol (20.0+/-2.4 (n=5)) (p<0.01). These data demonstrate physiological perfusion of the mouse placenta in situ and its usefulness for measurement of solute transfer.

Animals↗
PubMed2006

Placental transport and metabolism in fetal overgrowth -- a workshop report.

Fetal overgrowth in pregnancies complicated by diabetes is the result of an increased substrate availability which stimulates fetal insulin secretion and fetal growth. However, despite strict glycemic control in modern clinical management of the pregnant woman with diabetes, fetal overgrowth remains an important clinical problem. Recent studies in vivo provide evidence for increased delivery of amino acids to the fetus in gestational diabetes (GDM) even when metabolic control is strict. This could be due to that truly normal maternal substrate levels cannot be achieved in diabetic pregnancies and/or caused by altered placental nutrient transport and metabolism. Studies in vitro demonstrate an up-regulation of placental transport systems for certain amino acids in GDM associated with fetal overgrowth. GDM is also characterized by changes in placental gene expression, including up-regulation of inflammatory mediators and Leptin. In type-I diabetes with fetal overgrowth the in vitro activity of placental transporters for both glucose and certain amino acids as well as placental lipoprotein lipase is increased. Furthermore, both clinical observations in type-I diabetic pregnancies and preliminary animal experimental studies suggest that even brief periods of metabolic perturbation early in pregnancy may affect placental growth and transport function for the remainder of pregnancy, thereby contributing to fetal overgrowth. Ultrasound measurements of fetal fat deposits and abdominal circumference as well as 3D ultrasound assessment of placental volume represent non-invasive techniques for in utero diagnosis of fetal and placental overgrowth. It is proposed that these methods represent valuable additions to the clinical management of the diabetic pregnancy. In conclusion, altered placental function may be a mechanism contributing to fetal overgrowth in diabetic pregnancies with apparent optimal metabolic control. It is proposed that detailed information on placental metabolism and transport functions obtained in vitro and in vivo represent a placental phenotype that provides important information and may facilitate diagnosis and improve clinical management of fetal overgrowth.

Amino Acid Transport Systems↗
PubMed2005

Purinergic receptors in human placenta: evidence for functionally active P2X4, P2X7, P2Y2, and P2Y6.

Appropriate regulation of ion transport by the human placental syncytiotrophoblast is important for fetal growth throughout pregnancy. In nonplacental tissues, ion transport can be modulated by extracellular nucleotides that raise intracellular calcium ([Ca2+]i) via activation of purinergic receptors. We tested the hypothesis that purinergic receptors are expressed by human placental cytotrophoblast cells and that their activation by extracellular nucleotides modulates ion (K+) efflux and [Ca2+]i. P2X/P2Y receptor agonists 5-bromouridine 5'-triphosphate (5-BrUTP), ADP, ATP, 2',3'-O-(4-benzoyl-benzoyl)adenosine 5'-triphosphate (BzATP), and UTP stimulated 86Rb (K+ tracer) efflux from cultured cytotrophoblast cells at early (mononuclear) or later (multinucleate syncytiotrophoblast-like) stages of differentiation, with ATP and UTP particularly potent. 2-Methylthioadenosine 5'-triphosphate (2-MeS-ATP), and UDP elevated 86Rb efflux only from multinucleated cells. All agonists caused a significant peak and plateau increase in [Ca2+]i, although the magnitude of responses was variable. The effect of BzATP, UTP, and UDP in multinucleated cells was unaffected, and that of ATP partially inhibited, by removal of extracellular Ca2+, implicating P2Y receptor activation. mRNA encoding P2X1, P2X2, P2X4, and P2X7 and P2Y1, P2Y2, P2Y4, P2Y6, and P2Y11 were identified in mono- and multinucleated cells, whereas P2X3 and P2X5 mRNA were absent from all samples. Western blot analysis revealed P2X4, P2X7, P2Y2, and P2Y6 protein in cytotrophoblast cells, but P2Y4 was not detected. On the basis of published agonist selectivity, the data indicate the presence of functionally active P2X4, P2X7, P2Y2, and P2Y6 receptors in cytotrophoblast cells. We propose that activation of these receptors, and subsequent elevation of [Ca2+]i, modulates syncytiotrophoblast homeostasis and/or maternofetal ion exchange in response to extracellular nucleotides.

Adenosine Diphosphate↗
PubMed2005

Regulation of transplacental water transfer: the role of fetoplacental venous tone.

We used the in vitro dually perfused human placental lobule to test the hypothesis that known vasoconstrictors of the fetal placental circulation, angiotensin II and the thromboxane mimetic U46619 could induce fetomaternal water transfer. Secondly, we used a combination of vasoconstrictor and mechanically induced increases in fetal placental circulatory pressure to examine the role of the venous system in this context. Fetal-side administration of angiotensin II (A-II) and U46619 (n=6 and n=9, for A-II and U46619, respectively) induced dose dependent, recoverable elevations in fetal inflow hydrostatic pressure (HP; A-II: maximum contractility=83 mmHg, EC50=22.0 nM; U46619: maximum contractility was not achieved, but exceeded the A-II effect) and loss of perfusate from the fetal side (A-II: EC50=70.2 nM, maximum fetal-side solvent loss=1906 microl/min; U46619: maximum fetal-side solvent loss was not achieved, but exceeded the A-II effect). Fetal-side solvent loss, for both agonists, was correlated linearly with fetomaternal inflow HP (FMIHP) in a biphasic manner (between 0 and 30 mmHg the slopes (+/-S.E.) were 6.4+/-2.2 and 17.1+/-5.8 microl/(min mmHg) for A-II and U46619, respectively; between 30 and 70 mmHg the slopes (+/-S.E.) were 35.6+/-6.5 and 43.7+/-15.9 microl/(min mmHg) for A-II and U46619, respectively). Increasing fetal-side lumenal pressure (n=3) by raising the fetal outflow catheter caused a loss of perfusate from the fetal side which was reduced in the presence of U46619 (fetal solvent loss per unit increase in fetal-side inflow HP: slopes were 1.198+/-0.123 and 0.783+/-0.085 microl/(min mmHg mmHg), respectively). Notwithstanding the possibility of fetoplacental arterial constriction, we conclude that vasoconstrictive agonists in the fetoplacental circulation affect venous resistance, causing fetomaternal fluid loss. These observations could be relevant to the oligohydramnios associated with intrauterine growth restriction, a condition associated with increased resistance in the umbilical circulation.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed2005

SNAT4 isoform of system A amino acid transporter is expressed in human placenta.

The system A amino acid transporter is encoded by three members of the Slc38 gene family, giving rise to three subtypes: Na+-coupled neutral amino acid transporter (SNAT)1, SNAT2, and SNAT4. SNAT2 is expressed ubiquitously in mammalian tissues; SNAT1 is predominantly expressed in heart, brain, and placenta; and SNAT4 is reported to be expressed solely by the liver. In the placenta, system A has an essential role in the supply of neutral amino acids needed for fetal growth. In the present study, we examined expression and localization of SNAT1, SNAT2, and SNAT4 in human placenta during gestation. Real-time quantitative PCR was used to examine steady-state levels of system A subtype mRNA in early (6-10 wk) and late (10-13 wk) first-trimester and full-term (38-40 wk) placentas. We detected mRNA for all three isoforms from early gestation onward. There were no differences in SNAT1 and SNAT2 mRNA expression with gestation. However, SNAT4 mRNA expression was significantly higher early in the first trimester compared with the full-term placenta (P < 0.01). We next investigated SNAT4 protein expression in human placenta. In contrast to the observation for gene expression, Western blot analysis revealed that SNAT4 protein expression was significantly higher at term compared with the first trimester (P < 0.05). Immunohistochemistry and Western blot analysis showed that SNAT4 is localized to the microvillous and basal plasma membranes of the syncytiotrophoblast, suggesting a role for this isoform of system A in amino acid transport across the placenta. This study therefore provides the first evidence of SNAT4 mRNA and protein expression in the human placenta, both at the first trimester and at full term.

Amino Acid Transport System A↗
PubMed2005

MDR1 P-gp expression and activity in intact human placental tissue; upregulation by retroviral transduction.

This study investigates P-gp activity in placental villous fragments and the possibility of upregulating its expression and function by retroviral transduction. In fresh fragments, cyclosporin A caused a significant increase in 3H-vinblastine accumulation (187+/-48% at 180 min n=4), consistent with multi-drug resistance activity. After 7 days in culture, villous fragments showed a similar increase in 3H-vinblastine accumulation (143+/-10% at 180 min n=4), which was not significantly different from that in fresh tissue. Following transduction, immunohistochemistry revealed increased P-gp expression. However, the distribution of the protein differed from that in controls, with P-gp being located throughout the tissue as opposed to the normal specific location on the maternal facing plasma membrane. Transduced explants showed a significantly larger increase in 3H-vinblastine accumulation in the presence of cyclosporin A than control explants (245+/-15.5% at 180 min, n=4), suggesting reduced capacity to efflux vinblastine. This study demonstrates P-gp activity in intact placental tissue which is maintained in explant culture. Retroviral transduction of P-gp to such tissue leads to increased but undirected expression of the protein. The consequent increased activity at sites such as the basal, fetal facing, plasma membrane probably explains the increased substrate accumulation within the tissue.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed2005

Diabetes in rat pregnancy alters renal calcium and magnesium reabsorption and bone formation in adult offspring.

AIMS/HYPOTHESIS: We tested the hypothesis that diabetes in pregnancy can result in the in-utero reprogramming of renal calcium and magnesium handling and of bone formation in the offspring, which persists into adulthood. METHODS: Male offspring of streptozotocin-treated diabetic rats (OD rats) and of control non-diabetic animals (OC rats) were investigated as neonates and at 8, 12 and 16 weeks of age. RESULTS: Compared with OC rats, urinary calcium and magnesium output was significantly reduced in OD rats at every age studied; Na+ and K+ outputs were unaffected. The renal expression of proteins involved in the tubular reabsorption of calcium (calcium ATPase, calbindin-D28k and epithelial calcium channel) was increased in OD animals compared with that in OC animals. Additionally, we observed that adult OD rats had lower trabecular and higher cortical femoral bone volumes, explained by deposition of bone on the endosteal surface. CONCLUSIONS/INTERPRETATION: These data show that diabetes in pregnancy has profound effects on male offspring in terms of renal tubular calcium and magnesium reabsorption and the normal pattern of bone formation. These effects persist into adulthood. Such long-lasting effects of diabetes on kidney and the skeleton were not suspected and could have important implications for the health of children born to diabetic women.

Aging↗
PubMed2005

Activity and expression of Na+/H+ exchanger isoforms in the syncytiotrophoblast of the human placenta.

The purpose of this study was to compare Na+/H+ exchanger (NHE) activity in the microvillous (MVM) and basal (BM) plasma membrane of the human placental syncytiotrophoblast and to determine the relative contribution of various NHE isoforms to this activity. Uptake of 22Na into isolated MVM vesicles in the presence of a H+ gradient, at initial rate, was four- to fivefold higher than that by BM vesicles (214+/-28 vs. 49+/-9 pmol/mg protein per 30 s, respectively, means+/-SEM, n=8, 6, P<0.001). The 22Na uptake by MVM, but not by BM, was reduced in the absence of a H+ gradient and in the presence of 500 microM amiloride. To determine the contribution of NHE1, NHE2 and NHE3 isoforms to NHE activity in MVM, we investigated the effect of amiloride analogues which show isoform selectivity. HOE 694, an analogue selective for NHE1 at low concentrations, inhibited 22Na uptake with an EC50 of 0.13+/-0.05 microM (n=6), whereas S3226, an analogue selective for NHE3 at low concentrations had an EC50 of 3.01+/-0.85 microM (n=5). To investigate this further, we measured recovery of syncytiotrophoblast intracellular pH (pHi) from an acid load using a H+-selective, fluorescent dye (BCECF) loaded into isolated intact placental fragments. This recovery was blocked in the absence of Na+ and the presence of amiloride (500 microM) and concentrations of HOE 694 and S3226 were comparable to those used in vesicle experiments. Overall these data show that under the conditions used NHE activity in the term placental syncytiotrophoblast is absent from BM. NHE activity in the MVM is attributable predominantly to NHE1.

Cation Transport Proteins↗
PubMed2005

Gestational profile of Na+/H+ exchanger and Cl-/HCO3- anion exchanger mRNA expression in placenta using real-time QPCR.

The onset of maternal blood flow (10-12 weeks gestation) results in increased oxygenation of the placenta. We investigated whether the expressions of Na+/H+ exchanger (NHE) and Cl-/HCO3- anion exchanger (AE), thought to have an important role in maintaining intracellular pH of the syncytiotrophoblast and fetal pH homeostasis, are altered at the same time as this increase in blood flow. Real-time quantitative PCR was used to examine steady state levels of NHE (NHE1, 2, 3) and AE (AE1, 2) mRNA expression in early (6-9 weeks) and late (10-13 weeks) first trimester and full-term (38-40 weeks) placentas. beta-Actin, IF2B and GAPDH mRNA was also measured. None of the genes showed a significant difference in expression between the early and late first trimester groups. However, NHE2 (p < 0.001) and GAPDH (p < 0.05) mRNA expression significantly increased 18- and 3.7-fold between early first trimester and term. In conclusion, this study provides additional evidence that GAPDH is an unsuitable housekeeping gene for normalization of transcript levels in placenta. The expression of NHE and AE in the villous placenta is not altered concomitant with the onset of maternal blood flow. However, NHE2 transcripts appear to be gestationally regulated, which may contribute to changes in NHE activity.

Adult↗
PubMed2005

Electrical potential difference between mother and conceptus in the mouse.

This study aimed to determine whether there is a maternofetal potential difference (PD) in the mouse. The mean (+/- SEM) in vivo electrical potential difference (PD(sa)) between saline filled catheters in the maternal subcutaneous space (s) and the fetal amniotic sac (a) measured, according to strict criteria, in anaesthetised MF1 mice at a gestational age of 18-20 (term 20) days was 3.9+/-0.5 mV (significantly different from zero P<0.0001) in 16 conceptuses from 11 mice with the amniotic sac positive with respect to the maternal catheter. The PD(sv) between maternal tail vein (v) and maternal subcutaneous space was -0.8+/-0.4 mV (n=3: not significantly different from zero). Measurement of PD between two different maternal subcutaneous catheters (n=4) was < or =0.5 mV. This study shows that there is a maternofetal PD in the mouse and provides the foundation for studies addressing its mechanism of generation in this species.

Amniotic Fluid↗
PubMed2005

Multiple anti-apoptotic pathways stimulated by EGF in cytotrophoblasts.

Epidermal growth factor (EGF) reduces apoptosis in primary cytotrophoblast (CT) in culture through two separate pathways: the extracellular signal related kinase (ERK) 1/2 and phosphatidyl inositol 3-kinase (PI-3 kinase) paths. Whether other pathways are involved in survival signalling is unknown. We here show that the c-Jun NH2 terminal kinase (JNK) and the mitogen activated kinase (MAPK) p38 are also activated by EGF as seen by increases in JNK and p38 phosphorylation. However, inhibition of JNK phosphorylation with the specific inhibitor SP600125 increases apoptosis in a manner refractory to the addition of EGF but inhibition of p38 phosphorylation with its specific inhibitor SB 203580 does not increase apoptosis. EGF also activates sphingosine kinase-1 (SPHK-1), which converts sphingosine to sphingosine-1-phosphate, and its inhibition with dimethyl sphingosine (DMS) increased trophoblast death. Inhibition of SPHK-1 also did not affect EGF stimulated phosphorylation of PI-3 kinase, Akt, ERK1/2 or p38 but inhibition of PI-3 kinase with a specific inhibitor LY294002 partly (40%) inhibited the EGF-stimulated increase in SPHK-1 activity. We conclude that, in addition to the PI-3 kinase and ERK1/2 pathways, EGF acts through its receptor to stimulate JNK, p38 and SPHK-1 pathways, but that the JNK and SPHK-1, and not the p38, pathways are involved in suppressing apoptosis. This information provides evidence that EGF stimulates survival along multiple pathways that differ in trophoblast and other cell types.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Intrauterine programming of urinary calcium and magnesium excretion in children born to mothers with insulin dependent diabetes mellitus.

BACKGROUND: Offspring of diabetic rats have reduced urinary calcium and magnesium excretion compared with offspring of controls; these differences persist up to 16 weeks after birth, a time equivalent to young adulthood in humans. OBJECTIVES: To test the hypothesis that urinary calcium and magnesium excretion would be lower in children born to mothers with insulin dependent diabetes mellitus (ChMIDDM) than those born to non-diabetic mothers. METHODS: Concentrations of calcium, magnesium, sodium, and creatinine were measured in first void spot urine samples collected from 45 (28 male; median age 9.6 years) ChMIDDM and 127 (58 male; median age 11.3 years) controls. Analysis of covariance was used to test for differences in urinary calcium to creatinine ratios (UCa/Cr), magnesium to creatinine ratios (UMg/Cr), and log sodium to creatinine ratios (logUNa/Cr) between controls and ChMIDDM after allowing for the effects of sex and age. RESULTS: UCa/Cr (difference -0.10, 95% confidence interval (CI) -0.19 to -0.01; p = 0.03) and UMg/Cr (difference -0.15, 95% CI -0.22 to -0.08; p<0.0001) were lower in ChMIDDM than controls. However, logUNa/Cr did not differ between ChMIDDM and controls (difference -0.14, 95% CI -0.33 to 0.05; p = 0.1). The daily estimated intake of magnesium, sodium, and protein were significantly higher and that of calcium non-significantly higher in ChMIDDM than controls. In ChMIDDM, UCa/Cr and UMg/Cr were not related to diabetic control of mothers. CONCLUSIONS: Results of this study provide the first evidence that in humans, as in rats, there is modification of renal Ca and Mg handling in ChMIDDM, which persists well into childhood.

Adolescent↗
PubMed2004

Ultrastructural aspects of long-term cat placental explant culture.

Changes in tissue architecture and ultrastructure in the cat placenta during long-term explant culture have been examined over an 11-day period. Pieces of cat placenta, dissected from the lamellar region, were cultured in CMRL-1066 medium and tissue was fixed for electron microscopy at 2, 5, 7, and 11 days' culture, as well as before culture was initiated (day 0). Four samples were examined at each time point. After two days, the trophoblast basal lamina and attached cytotrophoblast cells had begun to separate from the syncytium and the cytotrophoblasts were spreading over the surface of the exposed fetal stromal compartment, and by five days were showing signs of growth. At seven days' culture, cytotrophoblast multilayering was common, and vascular and stromal components were also well preserved with collagen biosynthesis evident. By 11 days, the centre of the culture was compacted and degenerate with loss of tissue architecture, but on the outside polyp-like growths could be seen, with a well-developed covering of trophoblast containing fat and secretory droplets, lining a connective tissue matrix and stromal components. The cat placenta, therefore, like the human, has the capacity for regrowth in explant culture, including both trophoblast and stromal components.

Animals↗
PubMed2004

Characterisation of long term cat placental explant cultures: uptake of taurine by system beta.

Dietary taurine is essential for cats and deficiency during pregnancy may lead to abortion, growth restriction or impaired neurological function of kittens. We previously described Na(+)- and Cl(-)-dependent taurine transport by system beta in fragments of freshly isolated cat placenta [Champion EE, Bailey SJ, Glazier JD, Jones CJP, Mann SJ, Rawlings JM, et al. Taurine uptake into cat placental tissue fragments. Placenta 2001;22:A.42]. Here we evaluate long term culture of cat placental explants as a model for the future study of chronic nutrient regulation of amino acid transport in this species. The cat placental explants displayed (i) Na(+)-dependent [(3)H]taurine uptake and (ii) taurine transporter protein on day 7 of culture, as observed in fresh cat placental fragments. The explants had preserved the ability to secrete PGF(2alpha) hormone until day 11 of culture and remained morphologically largely intact until day 7 of culture. This model of placental explant culture will provide an important in vitro method for the study of chronic regulation of amino acid transport in the cat.

Amino Acid Transport Systems↗
PubMed2004

System beta and system A amino acid transporters in the feline endotheliochorial placenta.

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 beta 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 [(3)H]taurine (substrate for system beta) and [(14)C]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 beta-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 beta and system A activity, respectively. This study therefore provides the first evidence of the presence of amino acid transport systems beta and A in the cat placenta.

Amino Acid Transport Systems↗