Developmental expression of excitatory amino acid transporter 5: a photoreceptor and bipolar cell glutamate transporter in rat retina

Excitatory amino acid transporter 5 (EAAT5) is a retina-specific glutamate transporter which has an associated chloride conductance. Thus it is compar able in its functional properties to the glutamate transport systems previo usly described in photoreceptors and some bipolar cells. We have raised ant ibodies to the carboxyl- and amino-terminal regions of EAAT5. Labeling for both of these antisera was developmentally regulated: weak labeling appeare d in photoreceptors around P7; by P10 strong labeling was present in photor eceptors and by P21 a population of bipolar elements were also weakly label ed. In adult retinae both antisera heavily immunolabeled all photoreceptors as well as a heterogeneous population of bipolar cell somata and their pro ximal axonal processes: synaptic terminals of these cells were also labeled after partial proteolytic digestion of the tissues. The positions and morp hology of these terminals suggests ;that they a re the terminals of both ro d and cone rod bi polar cells. We conclude that in rat retina, EAAT5 is a p hoto receptor and bipolar cell glutamate transporter. (C) 2000 Published by Elsevier Science Ireland Ltd. All rights reserved.