A distinct step in inter-cellular communication involves termination of synaptic tranmission via the removal of neurotramsitters by specialized transporters. The regulated exocytotoxic release of neurotransmitters in reponse to neural activity requires storage within extracellular vesicles. In the nervous sytem, these vesicles are the synaptic vesicles that are derived from the endosomal compartment, whereas in endocrine cells larger secratory granules, such as the chromaffin granules of adrenal medulla, are derived from the trans golgi networks. Glutamate is the main excitatory neurotransmitter in the brain. To date five glutamate transporters have been cloned: GLAST (EAAT1), GLT1 (EAAT2), EAAC1 (EAAT3), EAAT4, and EAAT5. These transporters are believed to be critical in reducing potentially toxic extracellular concentration of glutamate by rapid uptake into nerve terminals and glial cells.