AN EXCITATORY AMINO-ACID TRANSPORTER WITH PROPERTIES OF A LIGAND-GATED CHLORIDE CHANNEL

EXCITATORY amino-acid transporters (EAATs) in the central nervous syst em maintain extracellular glutamate concentrations below excitotoxic l evels and may limit the activation of glutamate receptors. Here we rep ort the cloning of a novel human aspartate/glutamate transporter, EAAT 4, which is expressed predominantly in the cerebellum. The transport a ctivity encoded by EAAT4 has high apparent affinity for L-aspartate an d L-glutamate, and has a pharmacological profile consistent with previ ously described cerebellar transport activities. In Xenopus oocytes ex pressing EAAT4, L-aspartate and L-glutamate elicited a current predomi nantly carried by chloride ions. This chloride conductance was not blo cked by components that block endogenous oocyte chloride channels. Thu s EAAT4 combines the re-uptake of neurotransmitter with a mechanism fo r increasing chloride permeability, both of which could regulate excit atory neurotransmission.