title: Localization and expression of the glutamate transporter, excitatory amino acid transporter 4, within astrocytes of the rat retina.
abstract: Mechanisms for the removal of glutamate are vital for maintaining normal function of the retina. Five excitatory amino acid transporters have been characterized to date from neuronal tissue, all of which are expressed within the retina except excitatory amino acid transporter 4 (EAAT4). In this study we examined the expression and localization of the glutamate transporter EAAT4 in the rat retina using RT-PCR and immunocytochemistry. RT-PCR using rat EAAT4 specific primers revealed a prominent 296-bp product in the retina, cortex and cerebellum. The identity of the EAAT4 fragment was confirmed by DNA sequencing. We examined the tissue expression levels of EAAT4 in cortex, retina and cerebellum using real-time PCR. The highest expression level was found in the cerebellum. Expression in the cortex was approximately 3.1% that of the cerebellum and the retina was found to have approximately 0.8% the total cerebellar EAAT4 content. In order to examine the specific cell types within the retina that express EAAT4, we performed immunocytochemistry using a rat EAAT4 specific antiserum. Cellular processes within the nerve fibre layer of the retina were intensely labelled for EAAT4. Double labelling EAAT4 with glial fibrillary acidic protein (GFAP) revealed extensive colocalization indicating that EAAT4 is localized within astrocytes within the retina. Double labelling of EAAT4 and the glutamate transporter EAAT1 (GLAST) revealed extensive colocalization suggesting that astrocytes in the retina express at least two types of glutamate transporters. These results suggest that astrocytes within the retina are well placed to provide mechanisms for glutamate removal as well as controlling cellular excitability.
authors.affiliation: Department of Anatomy and Cell Biology, The University of Melbourne, Grattan St., 3010 Parkville, Victoria, Australia.
authors.forename: Michelle M
authors.initials: MM
authors.lastname: Ward
authors.forename: Andrew I
authors.initials: AI
authors.lastname: Jobling
authors.forename: Theresa
authors.initials: T
authors.lastname: Puthussery
authors.forename: Lisa E
authors.initials: LE
authors.lastname: Foster
authors.forename: Erica L
authors.initials: EL
authors.lastname: Fletcher
mesh_terms: D027322:Amino Acid Transport System X-AG / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D001253:Astrocytes / Q000166:cytology / Q000378:metabolism*; D027341:Excitatory Amino Acid Transporter 1 / Q000378:metabolism; D050581:Excitatory Amino Acid Transporter 4; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D050491:Glutamate Plasma Membrane Transport Proteins; D018613:Microscopy, Confocal; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D012160:Retina / Q000166:cytology / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D027981:Symporters
chemical_list: D027322:Amino Acid Transport System X-AG; D027341:Excitatory Amino Acid Transporter 1; D050581:Excitatory Amino Acid Transporter 4; D005904:Glial Fibrillary Acidic Protein; D050491:Glutamate Plasma Membrane Transport Proteins; D012333:RNA, Messenger; C493392:Slc1a3 protein, rat; C493389:Slc1a6 protein, rat; D027981:Symporters