Dopamine cell surface expression

Daws L., Callaghan P., Morom J. et al. Cocaine increases dopamine uptake and cell surface expression of dopamine transporters. Biochem. Biophys. Res. Commun. 290 1545, 2002. 

C-termini and a large glycosylated extracellular loop between transmembrane domains 3 and 4. The proteins show the most homology in their transmembrane spanning domains, particularly domains 1, 2, and 4-8, which may be involved in moving the transmitter across the membrane. The transporters are substrates for PKC-dependent phosphorylation, which reduces their activity. The dopamine transporter is phosphorylated on the extreme end of the N-terminal tail, and consensus phosphorylation sites for various other kinases are present in the intracellular loops and domains [20-22] (Fig. 12-4). The dopamine and norepinephrine transporters form functional homo-oligomers, although it is not known if this is required for transport activity, and the transporters also interact with many other membrane proteins that may control their cell-surface expression or other properties. 

The transporters for 5HT, noradrenaline and dopamine, biogenic monoamines, are genetically related, exist as single isoforms and are expressed on the surface of nerve cells, which use monoamines as (or convert them into) their cognate neurotransmitter. The single-isoform monoamine transporters fulfil all three fundamental functions (reuptake, limiting synaptic transmission, and control of the extracellular neurotransmitter concentration). Inactivation of DAT, NET, or SERT results in an increased extracellular lifetime and level of monoamine neurotransmitter, but decreased intracellular storage and evoked release (Fig. 3). 

Amphetamine acts on both transmitter transporters - the plasmalemmal one, which is the site of action of cocaine, and the vesicular transporter, which is targeted by reserpine. It is imported into the cell by the plasmalemmal transporter. This will result in inhibited reuptake of the physiological transmitter, not so much apparently by direct competition (as is the case with cocaine) but by subsequent endocytosis of the receptor. This is clearly shown in Figure 10.16. In the experiment shown, the dopamine reuptake transporter was recombinantly expressed in cultured cells and visualized by immimofluorescence . Initially, the fluorescence is confined to the surface of the cells expressing the transporter (Figure 10.16b, left panel). After exposure of the cells to amphetamine, the stain gradually disappears from the surface and is translocated into the cell interior, indicating endocytosis of the transporter". Simultaneously, the... 

---