[The study on the human placental L-lactate transport mechanism (using placental microvillous membrane vesicles)]

To elucidate the human placental L-lactate transport mechanism, we investigated L-lactate uptake by microvillous membrane vesicles (MMV) prepared from full termed human placenta using the rapid filtration technique. 1. The transport of L-lactate into the MMV was not dependent on the Na+ electrochemical gradient (extravesicular greater than intravesicular). 2. The transport of L-lactate into the MMV was dependent on the H+ gradient (extravesicular greater than intravesicular) and this H+ dependent L-lactate uptake showed a tendency to overshoot. This overshoot disappeared with the addition of H+ ionophore (FCCP). 3. The initial rate of this H+ dependent L-lactate transport into the MMV exhibited saturation kinetics with respect to the L-lactate concentration: An apparent Km of 4.35mM and Vmax of 2.78n mol/mg protein/20sec were calculated. These results indicated that there existed a H+ and L-lactate transport system in human placental MMV.