Em. Vanderaa et al., UPTAKE OF CHOLINE INTO SYNCYTIAL MICROVILLUS MEMBRANE-VESICLES OF HUMAN TERM PLACENTA, Biochemical pharmacology, 47(3), 1994, pp. 453-456
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.