Proline, Leucine, and Alanine Transport in Placental Microvillous Membrane Vesicles Prepared from Late Gestational Rats

Abstract

To characterize the active transport of amino acids across the placenta, uptakes of proline, leucine, and alanine were kinetically examined in placental microvillous membrane vesicles (PMV) prepared from rats in the late gestational period. Uptake rates of these amino acids in PMV showed saturable hyperbolic curves that obeyed Michaelis-Menten kinetics. Proline, leucine, and alanine transport were demonstrated to be carrier mediated systems with sodium-dependent, -independent, and both manner, respectively. In addition, sodium-dependent l-alanine transport showed two different systems, and new sodium-independent alanine transport system (K _m of 1.12 mM) was observed in rat placenta. From these results, rat placenta has carrier mediated amino acid transport systems, and posseses at least three different transport systems for alanine.