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J Dancis

Publications and source records attributed to J Dancis.

150 records · Page 9Linked to original sources
PubMedDate not supplied

Asymmetrical transfer of alpha-aminoisobutyric acid (AIB), leucine and lysine across the in vitro perfused human placenta.

The mechanism for establishing transplacental gradients for leucine, lysine and alpha-aminoisobutyric acid (AIB) has been investigated in the perfused human placenta. Experiments were done with either the maternal or the fetal circulation closed and the donor circulation open. Transfer of the amino acids towards the fetal side was more rapid than it was in the reverse direction. When the maternal perfusate was recirculated, the amino acid concentrations were maintained at a considerably lower level in the maternal circulation than in the open fetal circuit. When the fetal circuit was closed, the concentrations approached or slightly exceeded those in the maternal perfusate over a period of three hours. Within the placenta, higher concentrations were established during the experiments with transfer towards the fetal side than in the reverse direction. Of the three amino acids, leucine was transferred most rapidly across the placenta while AIB reached the highest concentrations in the placental tissue. The asymmetry of the transplacental amino acid flux is favoured by rapid uptake from the maternal circulation and transfer towards the fetus. Both rates exceed those observed in the reverse direction. The transfer rate of D-leucine was 1.7 times that of L-glucose. For in vitro studies of the transfer rate of physiological compounds a correction for diffusion is required. The results may differ considerably depending on which marker is used as the basis.

Aminoisobutyric Acids↗
PubMedDate not supplied

Synthesis and secretion of apolipoprotein E by human placenta and choriocarcinoma cell lines.

The synthesis and secretion of apolipoproteins (apos) by cells from a human choriocarcinoma cell line, JAR, were examined by [35S]-methionine labeling followed by immunoprecipitation and SDS/PAGE. Apo E, but not apos A-I, A-IV, or B, was synthesized and secreted. Apo E was also synthesized by fragments of chorionic villi from human placenta and by another choriocarcinoma line, BeWo. Pulse-chase experiments with JAR cells revealed that apoE was initially synthesized as a 33 kDa protein followed by a 34 KDa protein, probably the result of glycosylation. The latter was secreted into the medium where it was detected coincident with a 21/22 kDa doublet, possibly proteolytic fragments of apo E. Approximately 50 per cent of the apo E in the medium was complexed with lipid as indicated by ultracentrifugation at a density of 1.21 g/ml. The amount of apo E produced by JAR was not affected by preincubation with dibutyryl cAMP and theophylline, or by the cholesterol content of the cells. Following perfusion of an isolated lobule of human placenta with [14C]-amino acids, [14C]-apo E was detected by immunoprecipitation of the maternal and fetal perfusates with 88 per cent in the maternal perfusate. These studies suggest that apo E, which promotes receptor-mediated lipoprotein uptake, is secreted by the trophoblast to facilitate uptake of maternal lipoproteins.

Apolipoproteins E↗
PubMedDate not supplied

Nucleoside transport by perfused human placenta.

Nucleoside transport and metabolism by human placenta was studied using the dual perfusion technique. With [3H] thymidine added to the maternal perfusate and neither perfusate recirculated (steady-state studies) around 40 per cent of the thymidine in the maternal outflow and 50 per cent of the transferred thymidine was degraded. In similar studies with adenosine, over 95 per cent of the nucleoside was degraded. Even with the bolus technique which sharply limits the duration of contact with the placenta, degradation of adenosine was over 95 per cent. Uptake as calculated by the dual-tracer method ([3H] adenosine/[14C] L-glucose) was equally rapid from the maternal and fetal perfusates, was saturable and inhibited by nitrosobenzylthioinosine, consistent with the facilitated diffusion system for nucleosides. Thymidine was taken up at one-third the rate of adenosine. Thymidine in large excess (500 microM) reduced adenosine uptake suggesting a common transporter. Zidovudine, a thymidine analogue used for the treatment of AIDS in which the ribose is modified at the 2' 3' position, did not compete with adenosine for uptake consistent with previous reports that zidovudine is transferred across the placenta by simple diffusion.

Adenosine↗
PubMedDate not supplied

The effect of ouabain on placental transport of 86Rb.

Human placental fragments concentrate 86Rb 10--20-fold during a two-hour incubation period. Inhibition of ouabain is dose-dependent, reaching 90 + per cent at a concentration of 5 x 10(-5) M. The clearance index of 86Rb across the perfused human placenta is 0.34 +/- 0.08, comparing to previously reported indices for Na22 and Cl36 of 0.28 and 0.41, respectively. Ouabain in concentrations up to 5 x 10(-5) M had no detectable effect on transfer across the placenta. The clearance index of ouabain is low, averaging 0.07 in 3 experiments. 3H-ouabain is not detectably bound to albumin or placental homogenate.

Chlorine↗
PubMedDate not supplied

The effect of hypoxia on human trophoblast in culture: morphology, glucose transport and metabolism.

The response to hypoxia of trophoblast isolated from term placenta and maintained in culture was studied. Trophoblast exposed to normoxic (PO2 120-130 mmHg) or hypoxic (PO2 12-14 mmHg) conditions were examined by electron microscopy. After 48 h, the cytoplasm of the hypoxic cells was more electron-dense with increased numbers of mitochondria, lysosomes and vacuoles. Compared to normoxic cells, the surface microvilli of the hypoxic cells were sparse, short and unevenly distributed. [3H]thymidine incorporation by both hypoxic and normoxic trophoblast fell rapidly and equivalently after 2 days in culture. The percentage of cells with the proliferation-associated nuclear antigen, Ki 67, also decreased, but remained higher in hypoxic cells suggesting that hypoxia retarded completion of the cell cycle (normoxia, 10.80 +/- 2.51 s.e.; hypoxia, 19.87 +/- 2.73, P < 0.01). Glucose consumption was elevated in hypoxia (3.73 +/- 1.07 s.e. mumol/10(6) cells/24 h) as compared to normoxia (1.46 +/- 0.83, P = 0.01). Although lactate production was consistently higher in hypoxia, the difference was not statistically significant (hypoxia 5.38 +/- 1.54 mumol/10(6) cells/24 h versus normoxia, 1.52 +/- 0.29, P = 0.07). After 48 h, uptake of [3H]2-deoxglucose ([3H]2DG) by hypoxic cells was reduced to 12 per cent +/- 4.3 s.e. of that in normoxic cells; return to normoxia resulted in recovery within 10 min. Lineweaver-Burk plots of [3H]2DG uptake indicated high affinity (KM 2.2 +/- 0.4 x 10(-4) M) and low affinity transporters (KM 4.5 +/- 1.6 x 10(-3) M). Northern blot analysis identified mRNA for GLUT1 and GLUT3. In hypoxia, steady-state GLUT1 and GLUT3 mRNA were approximately three- and 10-fold higher than in normoxia respectively. Inhibitors of oxidative metabolism of glucose increased the uptake of [3H]2DG within 2 h, whereas hypoxia reduced uptake. Hence, trophoblast in culture survives in extreme hypoxia, but manifests striking changes in morphology and in glucose metabolism and transport. Completion of cell cycle appears to be retarded.

Biological Transport↗