[Absorption of L-alanine in small intestine of human fetus (by using brush border membrane vesicles of jejunum)].

By using brush border membrane vesicles prepared from human mid gestational fetal intestine (jejunum), the intestinal L-alanine transport mechanism was studied using a rapid filtration technique. The uptake of L-alanine by the vesicles was osmotically sensitive. This finding indicated that the uptake of L-alanine by the vesicles represented transport into the vesicles. A Na+ electrochemical gradient (extravesicular greater than intravesicular) stimulated the initial rate of L-alanine uptake, and Na+ dependent uptake of L-alanine into vesicles showed a typical overshoot phenomenon. This overshoot and the initial rate of uptake markedly increased when the intravesicular space was rendered electrically more negative by membrane diffusion potentials induced by with highly permeant anions. A similar stimulation of L-alanine uptake was observed, when membrane potential (inside negative) was imposed by K+ diffusion potentials via valinomycin. These results indicated that an Na+ dependent uptake of L-alanine into the brush border membrane vesicles was dependent on the electrical potential difference of the membrane. The initial rate of L-alanine transport exhibited saturation kinetics with respect to the L-alanine concentration; an apparent Km of Km1; 1.6mM, Km2; 14.1mM, and Vmax of Vmax1; 4.0n mol/mg protein/20sec, Vmax2; 8.2n mol/mg protein/20 sec were calculated. From these results mid gestational fetal intestine (jejunum) already has an L-alanine absorption system which is comparable to the adult one's.