Biogenic amine transporters: regulation in flux.

Following vesicular release, the biogenic amine neurotransmitters dopamine, norepinephrine and serotonin are actively cleared from extracellular spaces by presynaptic transporters. These transporters interact with multiple psychoactive agents including cocaine, amphetamines and antidepressants. Recent findings indicate that amine reuptake is likely to be a tightly regulated component of synaptic plasticity rather than a constitutive determinant of transmitter clearance. Protein kinase C activation and transporter phosphorylation have been linked to regulatory protein trafficking, and both phosphorylation and trafficking may be influenced by transporter ligands. Recognition that transmitters, antagonists and second messengers can modify the intrinsic activity, surface expression or protein levels of amine transporters raises new questions about the fundamental nature of drug actions in vivo. The theory that dysregulation of transporters may contribute to disease states is supported by the recent discovery that a coding mutation in the human norepinephrine transporter contributes to orthostatic intolerance.