Abstract
The antidepressant-sensitive norepinephrine (NE) transporter (NET) inactivates NE released during central and peripheral neuronal activity by transport into presynaptic cells. Altered NE clearance due to dysfunction of NET has been associated with the development of mental illness and cardiovascular diseases. NET activity in vivo is influenced by stress, neuronal activity, hormones and drugs. We investigated the mechanisms of Ca(2+) regulation of NET and found that Ca(2+) influenced both V(max) and K(m) for NE transport into cortical synaptosomes. Changes in extracellular Ca(2+) triggered rapid and bidirectional surface trafficking of NET expressed in cultured cells. Deletion of residues 28-47 in the NET NH(2)-terminus abolished the Ca(2+) effect on surface trafficking. Mutagenesis studies identified Thr30 in this region as the essential residue for both Ca(2+)- dependent phosphorylation and trafficking of NET. Depolarization of excitable cells increased surface NET in a Thr30 dependent manner. A proteomic analysis, RNA interference, and pharmacological inhibition supported roles of CaMKI and CaMKII in Ca(2+)-modulated NE transport and NET trafficking. Depolarization of primary noradrenergic neurons in culture with elevated K(+) increased NET surface expression in a process that required external Ca(2+) and depended on CaMK activity. Hippocampal NE clearance in vivo was also stimulated by depolarization, and inhibitors of CaMK signaling prevented this stimulation. In summary, Ca(2+) signaling influenced surface trafficking of NET through a CaMK-dependent mechanism requiring Thr30.