Immunocytochemical localization of three subtypes of GABA transporter in rat retina

Cellular distributions of three subtypes of GABA transporter (GAT1, GAT2, GAT3) in the eye were examined using polyclonal antisera for each subtype. GAT1 was present in the inner plexiform layer and proximal part of the inner nuclear layer, while GAT3 was distributed throughout the entire sensory retina, being predominant in the distal part of the inner plexiform layer and in the outer plexiform layer. GAT2 immunoreactivity was seen in the retina, including the retinal pigment epithelium layer and nerve fiber layer, also in the ciliary body epithelium. Confocal scanning laser fluorescence microscopy disclosed that the GAT1 immunoreactivity consisted of a number of small deposits in the inner plexiform layer and that GAT1-immunoreactive dots encircle immunonegative neurons in the inner nuclear layer. GAT2 immunoreactivity was present in the fiber bundle of the optic nerve and in the retinal pigment epithelium within the retina. GAT3 immunoreactive cells had long processes running vertically throughout the sensory retina. GAT1 is suggested to be present mainly in the processes of amacrine cells and GAT3 to be distributed in Müller cells. We conclude that GAT1, GAT2 and GAT3 are expressed in different cells, that they are involved in distinct GABAergic transmission in the retina, and that GAT2 may be involved in non-neuronal functions in the eye.