title: Active transport of dopamine in human placental brush-border membrane vesicles.
abstract: Brush-border membrane vesicles isolated from normal human term placentas were found to accumulate dopamine against a concentration gradient when an inwardly directed NaCl gradient was imposed across the membrane. The activity of the transport system was obligatorily dependent on Na+ as well as Cl-. Intravesicular H+ and intravesicular K+ stimulated the transport activity. The system possessed high affinity for dopamine and norepinephrine, with considerably lower affinity for serotonin. The stoichiometry of Na(+)-Cl(-)- dopamine was 1:1:1. The system was electrogenic because the NaCl-dependent dopamine uptake was stimulated by an inside-negative membrane potential, and this characteristic was observed in the presence and in the absence of intravesicular K+. Kinetic analysis revealed that the uptake was due to a carrier-mediated component plus a diffusion/binding component. The apparent Michaelis-Menten constant for dopamine for the carrier-mediated component was 19 +/- 7 nM. The transport system was clearly distinct from the serotonin transporter. Analysis of the inhibition of dopamine uptake by various monoamine uptake inhibitors showed that the uptake occurred via a transport system that is similar to the neuronal norepinephrine transporter.
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912-2100.
authors.forename: S
authors.initials: S
authors.lastname: Ramamoorthy
authors.forename: F H
authors.initials: FH
authors.lastname: Leibach
authors.forename: V B
authors.initials: VB
authors.lastname: Mahesh
authors.forename: V
authors.initials: V
authors.lastname: Ganapathy
mesh_terms: D000838:Anions / Q000494:pharmacology; D001693:Biological Transport, Active; D002412:Cations / Q000494:pharmacology; D002712:Chlorides / Q000378:metabolism; D004298:Dopamine / Q000493:pharmacokinetics*; D004563:Electrochemistry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008871:Microvilli / Q000378:metabolism; D010920:Placenta / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D012701:Serotonin / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism; D012965:Sodium Chloride / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D000838:Anions; D002412:Cations; D002712:Chlorides; D012701:Serotonin; D012965:Sodium Chloride; D012964:Sodium; D011188:Potassium; D004298:Dopamine