Taurine transport by microvillous membrane vesicles and the perfused cotyledon of the human placenta.
Human placental uptake and maternal-to-fetal (M-to-F) net transfer of taurine were evaluated in purified microvillous membrane vesicles (MMV) and the isolated perfused cotyledon. Taurine uptake by MMV was specifically stimulated by an inward Na+ gradient [maximum velocity (Vmax), 24.5 +/- 0.6 pmol.mg-1.30 s-1; Michaelis constant (Km), 6.2 +/- 0.7 microM], with uptake stoichiometry showing approximately 2 Na+/taurine molecule. In the presence or absence of Na+, Cl- did not stimulate uptake. Na(+)-stimulated uptake was enhanced by an outward K+ gradient. beta-Alanine and hypotaurine competitively inhibited uptake of taurine in MMV. Two-way uptake inhibition studies showed no interaction between taurine and non-beta-amino acids. When MMV were preloaded with taurine there was enhancement of Na(+)-stimulated uptake. In the perfused placentas, saturable M-to-F net transfer of taurine was not observed, despite saturation of tissue uptake from the maternal circulation. During 3 h of perfusion, no fetal-to-maternal (F-to-M) gradient formed for taurine; yet, a 2:1 gradient simultaneously occurred for histidine. This study demonstrates that taurine uptake by the microvillous membrane of the human placenta is highly specific, of high affinity, and Na+ coupled.
Karl
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PI
Department of Pediatrics, North Shore University Hospital-Cornell University Medical College, Manhasset, New York 11030.
Fisher
S E
SE
D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D005260:Female; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008431:Maternal-Fetal Exchange; D008871:Microvilli / Q000378:metabolism*; D010920:Placenta / Q000378:metabolism*; D011189:Potassium Chloride / Q000494:pharmacology; D011247:Pregnancy; D012965:Sodium Chloride / Q000494:pharmacology; D013654:Taurine / Q000378:metabolism*; D013861:Thiocyanates / Q000494:pharmacology; D014316:Tritium
D002250:Carbon Radioisotopes; D013861:Thiocyanates; D014316:Tritium; D013654:Taurine; D012965:Sodium Chloride; D011189:Potassium Chloride; D005947:Glucose; C009941:potassium thiocyanate