[The study on human placental DHA-S transport mechanism (using placental microvillous membrane vesicles)]

To investigate the placental DHA-S (dehydroepiandrosterone sulfate) transport mechanism, the uptake of DHA-S into microvillous membrane vesicles prepared from human term placenta was studied using the rapid filtration technique. 1. The uptake of DHA-S into microvillous membrane vesicles was not dependent on both Na+ electrochemical gradient and membrane potential difference. 2. The uptake of DHA-S into microvillous membrane vesicles was dependent on temperature. The initial uptake rate of DHA-S at 37 degrees C was three times as great as at 4 degrees C. 3. The initial rate of DHA-S transport exhibited saturation kinetics with respect to the DHA-S concentration; an apparent Km of 0.067 mM and Vmax of 1.01 nmol/mg protein/20 sec were calculated. 4. The uptake of DHA-S into microvillous membrane vesicles was inhibited by DHA, but not by estriol. These results indicated that placental DHA-S transport was carrier mediated and a passive one.