Immunocytochemical localization of 5 glutamate transporters cloned from salamander retina

Purpose. Glutamate is the predominant neuroiransmitier of the vertébrale retina and glutamatergic transmission is terminated by the uptake of glutamate into neurons and glia. Five unique glutamate transporter subtypes have been cloned trom the salamander retina: sEAATl, SEAAT2.1. SEAAT2.2. sEAATS.l. sEAAT5.2. We have examined the cellular and suhccllutar locali/alion of these live transporters using immunocytochemical techniques. Methods. Affinity purified polyclonal antihodics directed against a portion of the C-terminus for each of ihe five transporters were used on 10-15 μM thick slices from the salamander retina. The antibody localization was studied by fluorescently (CY5 ) tagged secondary antibodies viewed with a confocal microscope and by the avidin-biotin complex method viewed with a light microscope. Results. sEAATl staining is largely glial in origin: it is present in both plexiform layers, the glial endt'eet. in glial membranes spanning the INL. and completely surrounding the photoreceptor cell bodies ,sEAAT2.1 is both glial and neuronal: it is localized primarily in the 1PL. bm is also present in the OPL and photoreceptor terminals, and in dissociated glial cells. sEAAT2.2 appears to be localized primarily in hyperpolarizing bipolar cells: it is present in the OPL. in and around cell bodies in ihc outer hall of the INL. and bright punclale staining is seen in the outer half of the IPL. Some weak staining is also seen in photorecepior cell bodies. sEAAT5.1 is expressed throughout the retina, and appears to be present in both neurons and glia. sEAAT5 2 is localized in bright punctate staining in ihe OPL near photoreceptor terminals, and in punctate staining throughout the IPL. Conclusions. Glutamate transporters are abundantly present throughout the synaptic layers of the salamander retina, thereby allowing rapid removal of glutamate following vesicular release. Unlike studies performed in the rat brain, there does not appear to be a sharp dichotomy between neuronal and glial glutamate transporter subtypes. The five glutamate transporters have unique staining patterns supcestinc that they serve different roles.