Differential expression of three glutamate transporter subtypes in the rat retina

The immunocytochemical distribution of the three excitatory amino acid transporter subtypes GLT-1, GLAST-1 and EAAC-1 was studied in the rat retina using antibodies raised against synthetic peptides corresponding to the C-terminus of each transporter subtype. A comparative immunoblot analysis of rat cortex, cerebellum and retina membrane proteins suggested the following rank order of glutamate transporter subtype expression in retina: GLAST-1 ≤ EAAC-1 > GLT-1. GLAST-1 immunoreactivity was seen in Muller cells and astrocytes. EAAC-1 was found in horizontal cells, in amacrine and displaced amacrine cells, and in ganglion cells. A minority of bipolar cells also expressed EAAC-1. GLT-1 was preferentially expressed by different types of bipolar cells; however, it was also found in some amacrine cells. The functional role of this differential distribution of glutamate transporters in the retina is discussed.