[Study on Na+ and L-alanine cotransport of the human placenta using microvillous membrane vesicles]

Using microvillous membrane vesicles prepared from human normal term placenta, placental cotransport system of Na+ and L-alanine was studied using rapid filtration technique. The uptake of L-alanine into microvillous membrane vesicles was Na+ ion electrochemical gradient (extravesicular greater than intravesicular) dependent and showed typical overshoot phenomenon. Both Na+ dependent L-alanine uptake and Na+ ion uptake into microvillous membrane were membrane potential dependent and were markedly increased when the intravesicular space was rendered electrically more negative by membrane diffusion potentials, induced by the use of highly permeant anions. L-alanine gradient (extravesicular greater than intravesicular) induced a temporary accumulation of Na+ ions. These results indicated that L-alanine and Na+ ions were cotransported across microvillous membrane and this cotransport was dependent on the electrical potential difference in the membrane.