title: Anomalous dopamine release associated with a human dopamine transporter coding variant.
abstract: Dopamine (DA) signaling at synapses is tightly coordinated through opposing mechanisms of vesicular fusion-mediated DA release and transporter-mediated DA clearance. Altered brain DA signaling is suspected to underlie multiple brain disorders, including schizophrenia, Parkinson's disease, bipolar disorder, and attention-deficit hyperactivity disorder (ADHD). We identified a pedigree containing two male children diagnosed with ADHD who share a rare human DA transporter (DAT; SLC6A3) coding variant, Ala559Val. Among >1000 control and affected subjects, the Val559 variant has only been isolated once previously, in a female subject with bipolar disorder. Although hDAT Ala559Val supports normal DAT protein and cell surface expression, as well as normal DA uptake, the variant exhibits anomalous DA efflux from DA-loaded cells. We also demonstrate that hDAT Ala599Val exhibits increased sensitivity to intracellular Na(+), but not intracellular DA, and displays exaggerated DA efflux at depolarized potentials. Remarkably, the two most common ADHD medications, amphetamine and methylphenidate, both block hDAT Ala559Val-mediated DA efflux, whereas these drugs have opposite actions at wild-type hDAT. Our findings reveal that DA efflux, typically associated with amphetamine-like psychostimulants, can be produced through a heritable change in hDAT structure. Because multiple gene products are known to coordinate to support amphetamine-mediated DA efflux, the properties of hDAT Ala559Val may have broader significance in identifying a new mechanism through which DA signaling disorders arise. Additionally, they suggest that block of inappropriate neurotransmitter efflux may be an unsuspected mechanism supporting the therapeutic actions of existing transporter-directed medications.
authors.affiliation: Department of Pharmacology, Vanderbilt University Medical Center, Nashville, Tennessee 37232-8548, USA.
authors.forename: Michelle S
authors.initials: MS
authors.lastname: Mazei-Robison
authors.forename: Erica
authors.initials: E
authors.lastname: Bowton
authors.forename: Marion
authors.initials: M
authors.lastname: Holy
authors.forename: Martin
authors.initials: M
authors.lastname: Schmudermaier
authors.forename: Michael
authors.initials: M
authors.lastname: Freissmuth
authors.forename: Harald H
authors.initials: HH
authors.lastname: Sitte
authors.forename: Aurelio
authors.initials: A
authors.lastname: Galli
authors.forename: Randy D
authors.initials: RD
authors.lastname: Blakely
mesh_terms: D000409:Alanine / Q000235:genetics; D000661:Amphetamine / Q000494:pharmacology; D000704:Analysis of Variance; D019921:Biotinylation / Q000379:methods; D002461:Cell Line, Transformed; D004298:Dopamine / Q000378:metabolism*; D050483:Dopamine Plasma Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D018765:Dopamine Uptake Inhibitors / Q000494:pharmacology; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008774:Methylphenidate / Q000494:pharmacology; D009154:Mutation / Q000235:genetics*; D018408:Patch-Clamp Techniques; D021381:Protein Transport / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D014162:Transfection; D014633:Valine / Q000235:genetics
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D018765:Dopamine Uptake Inhibitors; C493214:SLC6A3 protein, human; D008774:Methylphenidate; D012964:Sodium; D000661:Amphetamine; D014633:Valine; D000409:Alanine; D004298:Dopamine