Amphetamine Action at the Cocaine- and Antidepressant-Sensitive Serotonin Transporter Is Modulated by αCaMKII

Serotonergic neurotransmission is terminated by reuptake of extracellular serotonin (5-HT) by the high-affinity serotonin transporter (SERT). Selective 5-HT reuptake inhibitors (SSRIs) such as fluoxetine or escitalopram inhibit SERT and are currently the principal treatment for depression and anxiety disorders. In addition, SERT is a major molecular target for psychostimulants such as cocaine and amphetamines. Amphetamine-induced transport reversal at the closely related dopamine transporter (DAT) has been shown previously to be contingent upon modulation by calmodulin kinase II alpha (alpha CaMKII). Here, we show that not only DAT, but also SERT, is regulated by alpha CaMKII. Inhibition of alpha CaMKII activity markedly decreased amphetamine-triggered SERT-mediated substrate efflux in both cells coexpressing SERT and alpha CaMKII and brain tissue preparations. The interaction between SERT and alpha CaMKII was verified using biochemical assays and FRET analysis and colocalization of the two molecules was confirmed in primary serotonergic neurons in culture. Moreover, we found that genetic deletion of alpha CaMKII impaired the locomotor response of mice to 3,4-methylenedioxymethamphetamine (also known as "ecstasy") and blunted D-fenfluramine-induced prolactin release, substantiating the importance of alpha CaMKII modulation for amphetamine action at SERT in vivo as well. SERT-mediated substrate uptake was neither affected by inhibition of nor genetic deficiency in alpha CaMKII. This finding supports the concept that uptake and efflux at monoamine transporters are asymmetric processes that can be targeted separately. Ultimately, this may provide a molecular mechanism for putative drug developments to treat amphetamine addiction.