Amphetamine activates calcium channels through dopamine transporter-mediated depolarization

Amphetamine (AMPH) and its more potent enantiomer S(+)AMPH are psychostimulants used therapeutically to treat attention deficit hyperactivity disorder and have significant abuse liability. AMPH is a dopamine transporter (DAT) substrate that inhibits dopamine (DA) uptake and is implicated in DA release. Furthermore, AMPH activates ionic currents through DAT that modify cell excitability presumably by modulating voltage-gated channel activity. Indeed, several studies suggest that monoamine transporter-induced depolarization opens voltage-gated Ca2+ channels (Ca-v), which would constitute an additional AMPH mechanism of action. In this study we co-express human DAT (hDAT) with Ca2+ channels that have decreasing sensitivity to membrane depolarization (Ca(v)1.3, Ca(v)1.2 or Ca(v)2.2). Although S(+)AMPH is more potent than DA in transport-competition assays and inward-current generation, at saturating concentrations both substrates indirectly activate voltage-gated L-type Ca2+ channels (Ca(v)1.3 and Ca(v)1.2) but not the N-type Ca2+ channel (Ca(v)2.2). Furthermore, the potency to achieve hDAT-Cav electrical coupling is dominated by the substrate affinity on hDAT, with negligible influence of L-type channel voltage sensitivity. In contrast, the maximal coupling-strength (defined as Ca2+ signal change per unit hDAT current) is influenced by Ca-v voltage sensitivity, which is greater in Ca(v)1.3- than in Ca(v)1.2-expressing cells. Moreover, relative to DA, S(+)AMPH showed greater coupling-strength at concentrations that induced relatively small hDAT-mediated currents. Therefore S(+)AMPH is not only more potent than DA at inducing hDAT-mediated L-type Ca2+ channel currents but is a better depolarizing agent since it produces tighter electrical coupling between hDAT-mediated depolarization and L-type Ca2+ channel activation. (C) 2015 Elsevier Ltd. All rights reserved.