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Anionic amino acid uptake by microvillous membrane vesicles from human placenta
1Edward Mallinckrodt Department of Pediatrics, Washington University School of Medicine, Children's Hospital, St. Louis, Missouri 63110.
The American Journal of Physiology
|November 1, 1989
Summary
Researchers identified a specific transporter for anionic amino acids in the placenta. This transporter, dependent on sodium and potassium, is crucial for nutrient uptake from maternal blood.
Area of Science:
- Biochemistry
- Cell Biology
- Physiology
Background:
- The placenta facilitates nutrient transfer from mother to fetus.
- Understanding amino acid transport mechanisms is vital for fetal development.
Purpose of the Study:
- To investigate the transport mechanisms of anionic amino acids in the trophoblast microvillous membrane.
- To characterize the properties of the identified transporter.
Main Methods:
- Utilized L-[3H]aspartate and L-[3H]glutamate uptake assays in membrane vesicles.
- Investigated the effects of ion gradients (Na+, K+), pH, and competing amino acids on uptake.
- Analyzed transporter kinetics, including affinity and velocity.
Main Results:
- Identified a single, high-affinity, Na+-dependent, K+-stimulated, pH-sensitive, and electrogenic cotransporter for anionic amino acids.
- Demonstrated that K+ gradients stimulate transporter velocity but not affinity.
- Observed stereoselectivity for L-glutamate but not L-aspartate, with no inhibition by neutral amino acids.
Conclusions:
- The findings suggest the presence of an anionic amino acid transporter in the trophoblast microvillous membrane.
- This transporter shares characteristics with the X-AG system found in other epithelia.
- The identified system likely mediates the placental uptake of anionic amino acids from maternal circulation.