IDENTIFICATION AND CHARACTERIZATION OF A CDNA-ENCODING A NEURONAL GLUTAMATE TRANSPORTER FROM DROSOPHILA-MELANOGASTER

Sodium-dependent glutamate transporters influence neurotransmission in the central nervous system by removing synaptically released glutamat e from the extracellular space and by maintaining extracellular glutam ate concentrations below neurotoxic levels. In insects, glutamate also serves as the neurotransmitter at the neuromuscular junction, but the mechanism for neurotransmitter clearance at this synapse has not been well-established. Here we report the cloning and characterization of a sodium-dependent glutamate transporter, dEAAT, from Drosophila melan ogaster. The 479 amino acid dEAAT gene product is 40-50% homologous to mammalian members of this carrier family. A 3.3 kilobase (kb) transcr ipt for dEAAT was detected in adult fly heads and to a lesser extent i n bodies by Northern-blot analysis and was also localized to neurons i n the central nervous system by in situ hybridization. The transport a ctivity observed following expression of dEAAT in Xenopus oocytes or C OS-7 cells shows a high affinity for L-glutamate, L-aspartate and D-as partate, an absolute dependence on external sodium ions, and considera ble stereoselectivity for the transport of L-glutamate over D-glutamat e. As has been observed for the human carriers, EAAT 4 and EAAT 5, a s ignificant component of the current activated by L-glutamate applicati on to dEAAT-expressing oocytes appears to arise from the activation of a chloride channel associated with the carrier.