Excitatory amino acid transporters (EAATs) are the primary regulators of 
extracellular glutamate concentrations in the central nervous system. Their 
dysfunction may contribute to several neurological diseases. To date, five 
distinct mammalian glutamate transporters have been cloned. In brain, EAAC1 
(excitatory amino acid carrier 1) is the primary neuronal glutamate transporter, 
localized on the perisynaptic membranes that are near release sites. Despite its 
potential importance in synaptic actions, little is known concerning the 
regulation of EAAC1 trafficking from the endoplasmic reticulum (ER) to the cell 
surface. Previously, we identified an EAAC1-associated protein, GTRAP3-18, an ER 
protein that prevents ER exit of EAAC1 when induced. Here we show that RTN2B, a 
member of the reticulon protein family that mainly localizes in the ER and ER 
exit sites interacts with EAAC1 and GTRAP3-18. EAAC1 and GTRAP3-18 bind to 
different regions of RTN2B. Each protein can separately and independently form 
complexes with EAAC1. RTN2B enhances ER exit and the cell surface composition of 
EAAC1 in heterologous cells. Expression of short interfering RNA-mediated 
knockdown of RTN2B decreases the EAAC1 protein level in neurons. Overall, our 
results suggest that RTN2B functions as a positive regulator in the delivery of 
EAAC1 from the ER to the cell surface. These studies indicate that transporter 
exit from the ER controlled by the interaction with its ER binding partner 
represents a critical regulatory step in glutamate transporter trafficking to 
the cell surface.