L-alanine carriers at maternal and fetal surfaces of the guinea pig placenta trophoblast.

An active transport for amino acids exists in maternofetal direction through the hemochorial placenta of man and guinea pig. With respect to the trophoblastic barrier some properties of the transplacental transport at both sides of this tissue are investigated. The results are compared to the methods of the transport of amino acids at intestine and kidney. The maternal and the fetal (basic) membrane can be investigated separately and one after another at one placenta by the technique of the bolus injections. The results were as follows: The 3H-L-alanine uptake is significantly higher by maternal injection than by fetal injection. Opposite to this the backflux is higher out of the trophoblast into the perfusion medium of the donor side at fetal injections. Out of this transplacental transport is higher in materno-fetal direction than in the opposite direction (p less than or equal to 0.05). A sodium dependence of the 3H-L-alanine transport is found at the maternal and fetal side. Nevertheless, the withdrawal of sodium ions inhibits more strongly at the maternal than at the fetal side. The sodium-dependent transport system predominates at the maternal membrane of the trophoblasts. Phloretin only inhibits significantly the uptake (maximal) and the transport of 3H-L-alanine at the fetal side (at the basic membrane). That means that the sodium independent by phloretin inhibited transport system exists mostly, if not totally, at the fetal membrane. Ouabain reduces uptake (maximal and total) and transport of 3H-L-alanine only significantly at the maternal side (p less than or equal to 0.05). Therefore the active sodium transport must be mostly localized at the maternal membrane. The flux of L-alanine diminishes with increasing L-alanine concentrations at the fetal and maternal side. The determinations of the transport capacity (Jmax) and the transport affinity (Km) show that Jmax is significantly higher at the maternal side and Km at the fetal side (p less than or equal to 0.05). By means of these results a model can be described to characterise the transport of amino acid through the placenta.