Cloning and expression of a neuronal rat brain glutamate transporter.

Glutamate is the major excitatory transmitter in the mammalian central nervous system. Glutamate transporters, which keep the extracellular glutamate concentration low, are required both for normal brain function and for protecting neurons against harmful glutamatergic overstimulation. We have isolated the cDNA for a rat brain glutamate transporter (REAAC1) which has 90% amino acid and 86% nucleotide identity to the rabbit EAAC1. When REAAC1 was expressed in HeLa cells using a recombinant vaccinia-T7 virus expression system, a sodium dependent glutamate uptake was observed. The affinity of the carrier to various substrates was typical of brain "high affinity' glutamate uptake: threo-3-hydroxyaspartate, (R)-aspartate, (S)-glutamate and (S)-trans-pyrrolidine-2,4-dicarboxylic acid were strong inhibitors, but not (R)-glutamate or gamma-aminobutyrate. High resolution, non-radioactive in situ hybridization histochemistry in rat brain revealed the mRNA in several types of glutamatergic as well as non-glutamatergic neurons, but not in glial cells.