The norepinephrine transporter or NET is a monoamine transporter that transports the neurotransmitter norepinephrine (noradrenaline) from the synapse back to its vesicles for storage until later use. It also appears to transport the neurotransmitter dopamine in the same way, but to a lesser degree.
"The norepinephrine transporter (NET) protein consists of 617 amino acids and has 12 transmembrane domains" and is encoded by the SLC6A2 gene. Certain antidepressant medications act to raise noradrenaline, such as the SNRIs and the tricyclic antidepressants (TCAs). In other words, these medications prevent the noradrenaline transporter from doing its job. Noradrenaline therefore remains in the synapse longer, allowing it to reach more normal levels.