Abstract
This study reveals a novel receptor mechanism for methamphetamine action in dopamine transporter (DAT) regulation. Trace amine-associated receptor 1 (TAAR1) is expressed in brain dopaminergic nuclei and is activated by methamphetamine in vitro. Here, we show that methamphetamine interaction with TAAR1 inhibits [(3)H]dopamine uptake, enhances or induces [(3)H]dopamine efflux, and triggers DAT internalization. In time course assays in which methamphetamine and [(3)H]dopamine were concurrently loaded into cells or synaptosomes or in pretreatment assays in which methamphetamine was washed away before [(3)H]dopamine loading, methamphetamine caused a distinct inhibition in [(3)H]dopamine uptake in TAAR1 + DAT-cotransfected cells and in wild-type mouse and rhesus monkey striatal synaptosomes. This distinct uptake inhibition was not observed in DAT-only transfected cells or in TAAR1 knockout mouse striatal synaptosomes. In [(3)H]dopamine efflux assays using the same cell and synaptosome preparations, methamphetamine enhanced [(3)H]dopamine efflux at a high loading concentration of [(3)H]dopamine (1 muM) or induced [(3)H]dopamine efflux at a low loading concentration of [(3)H]dopamine (10 nM) in a TAAR1-dependent manner. In DAT biotinylation assays using the same cell and synaptosome preparations, we observed that 1 muM methamphetamine induced DAT internalization in a TAAR1-dependent manner. All these TAAR1-mediated effects of methamphetamine were blocked by the protein kinase inhibitors H89 [N-[2-(4-bromocinnamylamino)ethyl]-5-isoquinoline] and/or 2-{8-[(dimethylamino) methyl]-6,7,8,9-tetrahydropyrido[1,2-a]indol-3-yl}-3-(1-methylindol-3-yl)maleimide (Ro32-0432), suggesting that methamphetamine interaction with TAAR1 triggers cellular phosphorylation cascades and leads to the observed effects of methamphetamine on DAT. These findings demonstrate a mediatory role of TAAR1 in methamphetamine action in DAT regulation and implicate this receptor as a potential target of therapeutics drugs for methamphetamine addiction.