UPTAKE OF CHOLINE INTO SYNCYTIAL MICROVILLUS MEMBRANE-VESICLES OF HUMAN TERM PLACENTA

The uptake of the quaternary ammonium compound choline was studied in syncytial microvillus membrane vesicles of human term placenta. Uptake was stimulated by an inside negative membrane potential and by loadin g the vesicles with unlabeled choline. Imposition of an inwardly direc ted Na+ or outwardly directed H+ gradient did not stimulate choline up take. Several organic cations were able to inhibit choline transport i n the following order: hemicholinium-3 greater than or equal to cholin e greater than or equal to mepiperphenidol > cimetidine greater than o r equal to famotidine. The kinetics of uptake involved a saturable pro cess for choline with high affinity (K-m = 550 mu M). Our results conf irm the presence of a carrier mediated transport system in human place ntal syncytial microvillus membranes. The system appears to be electro genic, and able to transport choline efficiently from the maternal cir culation into the placenta.