An excitatory amino-acid transporter with properties of a ligand-gated chloride channel

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Abstract
Excitatory amino-acid transporters (EAATs) in the central nervous system maintain extracellular glutamate concentrations below excitotoxic levels and may limit the activation of glutamate receptors. Here we report the cloning of a novel human aspartate/glutamate transporter, EAAT4, which is expressed predominantly in the cerebellum. The transport activity encoded by EAAT4 has high apparent affinity for L-aspartate and L-glutamate, and has a pharmacological profile consistent with previously described cerebellar transport activities. In Xenopus oocytes expressing EAAT4, L-aspartate and L-glutamate elicited a current predominantly carried by chloride ions. This chloride conductance was not blocked by components that block endogenous oocyte chloride channels. Thus EAAT4 combines the re-uptake of neurotransmitter with a mechanism for increasing chloride permeability, both of which could regulate excitatory neurotransmission.