L-arginine transport at the fetal side of human placenta: effect of aspirin in pregnancy.
L-Arginine transport by the fetal side of human placenta was investigated through the characterization of L-[3H]arginine uptake in isolated perfused cotyledon. Competitive inhibition experiments suggest the presence of at least two transport systems: a Na+-independent, pH-insensitive system inhibitable by cationic amino acids, similar to system y+, and a Na+-dependent system which recognizes both cationic and neutral amino acids only in the presence of Na+, i.e. a Bo,+-like system. The kinetic analysis of L-arginine uptake in the presence of Na+ revealed that the process is mediated by saturable components: a high-affinity system (Km = 167 +/- 18.0 microM; Vmax = 0.174 +/- 0.012 micromol min-1) and a low-affinity carrier (Km = 980 +/- 112 microM; Vmax = 1.60 +/- 0.12 micromol min-1). In the absence of Na+, L-arginine uptake was fitted by one model with a Michaelis-Menten constant of 200 +/- 24.8 microM. These results suggest that the high-affinity component corresponds to the Na+-independent system y+, whilst the low-affinity system may represent the activity of the Na+-dependent Bo,+ transporter. Kinetic studies in placentae taken from aspirin-treated pregnancies showed that L-arginine is transported with a significantly higher affinity (Km = 42.5 +/- 5.7 microM), but with a lower capacity (Vmax = 0.064 +/- 0.003 micromol min-1) than in the non-treated group. The latter finding suggests that aspirin would facilitate the uptake of the NO precursor only at very low arginine concentrations.
Acevedo
C G
CG
Department of Physiology Faculty of Biological Sciences, University of Concepcion, PO Box 160-C, Concepcion, Chile. cacevedo@udec.cl
Rojas
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S
Bravo
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D000328:Adult; D000596:Amino Acids / Q000494:pharmacology; D001120:Arginine / Q000378:metabolism*; D001241:Aspirin / Q000494:pharmacology*; D001692:Biological Transport / Q000187:drug effects; D002677:Chile; D005260:Female; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D010920:Placenta / Q000187:drug effects / Q000378:metabolism*; D011225:Pre-Eclampsia / Q000188:drug therapy; D011247:Pregnancy; D012964:Sodium / Q000494:pharmacology
D000596:Amino Acids; D001120:Arginine; D012964:Sodium; D001241:Aspirin