Transport of glycine in the brush border and basal cell membrane vesicles of the human term placenta.
Active glycine transport was demonstrated in microvillous (maternal-facing, BBM) and basal (fetal-facing, BCM) plasma membranes of the human term placental syncytiotrophoblast. The kinetic studies showed that the amino acid had a distinct overshoot at 1 min in BBM and 3 min in BCM vesicles while a steady state rate was achieved in approx 5 min in both the vesicles. Glycine transport is highly ion-specific and its dependency on Na+ can not be satisfied by replacing with other monovalent cation. Cl- is also implicated in the generation of the electrochemical gradient and replacement of Cl- with SO4(2-) anions failed to stimulate the transport process. The transport process was saturable with external glycine which exhibited rectangular hyperbolic kinetics typical of a mediated movement. The calculated kt and Jmax from the linear transformation of the data were 6.67 & 4 mM and 294 & 263 nmoles glycine. mg protein-1.min-1 in the BBM and BCM vesicles, respectively. The glycine transport was inhibited by a number of other amino acids which are known to be transported through the A and ASC systems. The glycine transport system may be dependent on multiple pathways such as the A, ASC or Gly which is a variant of pathway A. Glycine transport was inhibited by ouabain, a known Na+/K+ -ATPase inhibitor, in the BCM vesicles but not in the BBM system. Nicotine, insulin, sodium fluoride and sodium arsenate were inhibitors for both the vesicles.
Anand
R J
RJ
Department of Zoology and Biophysics, Panjab University, Chandigarh, India.
Kanwar
U
U
Sanyal
S N
SN
D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism; D005260:Female; D005998:Glycine / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008565:Membrane Proteins / Q000378:metabolism; D008871:Microvilli / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D012965:Sodium Chloride / Q000494:pharmacology; D013431:Sulfates / Q000494:pharmacology
D002352:Carrier Proteins; D008565:Membrane Proteins; D013431:Sulfates; D012965:Sodium Chloride; D010042:Ouabain; D005998:Glycine