ISOLATION OF SYNCYTIAL MICROVILLOUS MEMBRANE-VESICLES FROM HUMAN TERMPLACENTA AND THEIR APPLICATION IN DRUG NUTRIENT INTERACTION STUDIES

The initial step in placental uptake of nutrients occurs across the sy ncytial microvillous membrane of the trophoblast. This study was desig ned to isolate syncytial microvillous membrane vesicles (SMMV) of huma n term placenta, to validate their purity and viability, and to invest igate the interaction of several commonly used drugs with the transpor t of two essential nutrients: alanine and choline. SMMV were isolated according to an established procedure, but instead of homogenization t he initial preparation step was replaced by mincing of placental tissu e followed by gently stirring to loosen the microvilli. These modifica tions doubled the protein recovery and increased the enrichment in alk aline phosphatase, whereas no substantial contamination with basal mem branes nor interfering subcellular organelles was found. The functiona l viability of the vesicles was evaluated through the transport of ala nine. In accordance with literature, uptake was sodium-dependent, inhi bitable by structural analogues, and saturable. A number of cationic d rugs were able to inhibit choline uptake, whereas no effect on alanine transport was observed. Anionic drugs, drugs of abuse, and catecholam ines did not interfere with alanine transport either. In conclusion, o ur isolated SMMV provide a suitable tool for screening drug-nutrient i nteractions at the level of membrane transport. In view of the very lo w susceptibility of the alanine transporter to drug inhibition and the relatively high drug concentrations necessary to inhibit choline tran sport, it seems unlikely that clinically important drug interactions m ay occur with these nutrients.