Calmodulin kinase II regulates amphetamine-induced reverse transport in the dopamine transporter: implications for the importance of the dopamine transporter in Angelman syndrome

Background The dopamine transporter (DAT) mediates dopamine (DA) reuptake once DA gets released into the synaptic cleft; thereby, the DAT regulates DA content available for synaptic transmission. Psychostimulants like amphetamines can induce the reverse operation and induce outward transport, thereby increasing extracellular dopamine concentrations. Increases of DA in the synaptic cleft are associated with psychosis and drug addiction. Influx and efflux of substrate via the DAT are thought to be asymmetrical and were shown to possess consensus sites for the regulation by intracellular kinases. It was demonstrated that the loss of Nterminal serines ablates amphetamine-induced reverse transport in the DAT and that Ca/calmodulin-dependent protein kinase IIa (CaMKIIa) can physically bind the DAT C-terminus and phosphorylate N-terminal serines. Pharmacological inhibition of CaMKIIa with KN93 dramatically reduces amphetamine-induced efflux in both cells stably transfected with the human DAT and in rat striatal slices. Here we show that amphetamine-induced DAT-mediated efflux is reduced in CamKIIa mutants and in a mouse model of Angelman syndrome (AS). Methods Mouse striatal synaptosomes preloaded with [H]MPP, a substrate for the DAT, were superfused using a superfusion system. [H]MPP release was induced by the addition of 3 μM D-amphetamine. Superfusates were collected and quantified using a szintillation counter. Immunoblots and [H]CFT binding experiments were used to assess DAT protein expression levels. Uptake assays were performed in striatal synaptosomes using [H]MPP as substrate. For non-specific uptake we used the DAT-inhibitor mazindol.