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 comparable in its functional properties to the glutamate transport systems previously described in photoreceptors and some bipolar cells. We have raised antibodies to the carboxyl- and amino-terminal regions of EAAT5. Labeling for both of these antisera was developmentally regulated: weak labeling appeared in photoreceptors around P7; by P10 strong labeling was present in photoreceptors and by P21 a population of bipolar elements were also weakly labeled. In adult retinae both antisera heavily immunolabeled all photoreceptors as well as a heterogeneous population of bipolar cell somata and their proximal axonal processes: synaptic terminals of these cells were also labeled after partial proteolytic digestion of the tissues. The positions and morphology of these terminals suggests that they are the terminals of both rod and cone rod bipolar cells. We conclude that in rat retina, EAAT5 is a photoreceptor and bipolar cell glutamate transporter.