Download Does the brain contain the glutamate transporter and inhibitory

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Does the brain contain the glutamate transporter and
inhibitory glutamate receptor EAAT5?
David Pow1 and Aven Lee2
1
RMIT University, Melbourne, Australia
2
University of Queensland, Brisbane, Australia
Excitatory amino acid transporter 5 (EAAT5 ) is a member of
the glutamate transporter family. It was first described in the
retina, where it is expressed by glutamatergic neurons including
photoreceptors. In the rest of the nervous system EAAT5 is
generally considered to be absent, and the majority of glutamate
transport is mediated by EAAT1 and EAAT2, which are mainly
expressed by astrocytes. We have re-evaluated whether EAAT5
is expressed in the brain. We have performed PCR and
demonstrate that with primers that amplify between exons 6
and 11 of EAAT5, we generate an amplicon that is identical to
retinal EAAT5. Surprisingly antibodies to the amino-or carboxylterminal regions of EAAT5 do not normally detect EAAT5 in the
brain, plausibly because these epitopes are modified by events
including cleavage (as has been suggested for EAATs1 and 2).
We have generated an antibody against an internal epitope of
EAAT5 that would not be subject to N- or C-terminal cleavage.
We demonstrate by immunocytochemistry that in mixed cultures
from rat brains, neurons are strongly labeled. Preliminary data
also suggest labeling of neurons in vivo. We conclude that
EAAT5, which is both a (relatively poor) glutamate transporter and
an inhibitory glutamate receptor, is expressed at significant levels
in brain tissues. Accordingly the role of this protein and the
contributions to glutamate homeostasis, relative to astrocytic
glutamate transporters, requires future evaluation.