Endogenous transmembrane electrical gradients associated with human placental microvillous membrane vesicles

Experiments were designed to test for the presence of an endogenous (i.e. Donnan) electrical potential in human placental microvillous membrane vesicles. Vesicles were capable of passively accumulating K+ (86Rb+) above unity in a manner which was influenced by both pH and ionic strength of the medium. It appears that the transmembrane electrical potential is generated by the presence of fixed negative charges associated with the vesicle interior.