Electrogenic nature of rat sodium-dependent multivitamin transport

We report on the electrogenic nature of the transport process mediated by t he rat sodium-dependent multivitamin transporter. In Cos-7 cells, the relat ionship of Na+ concentration versus biotin and pantothenate uptake rate was sigmoidal with a Na+:substrate stoichiometry of 2:1. In Cos-7 cells expres sing rat SMVT biotin transport was significantly higher when the membrane w as hyperpolarized and considerably reduced when the membrane was depolarize d Similarly, biotin uptake in X. laevis oocytes expressing rat SMVT was inh ibited with depolarized oocyte membrane by altering the K+ permeability acr oss the membrane. It is concluded that the transport of biotin and pantothe nate mediated by rat SMVT is electrogenic with a Na+:substrate coupling rat io of 2:1 and that the transport process is associated with the transfer of one net positive charge across the membrane per transport cycle. (C) 2000 Academic Press.