Localization and possible function of the glutamate transporter, EAAC1, in the rat retina.
We investigated the localization and possible function of EAAC1 in the rat retina. Immunocytochemical localization of EAAC1 at the light-microscopic level revealed a fine dust-like labelling pattern across the two synaptic layers. Horizontal cell and subpopulations of amacrine cell somata were labelled, as were some somata within the ganglion cell layer. Some immunoreactive puncta were observed within the cytoplasm of amacrine cells, in regions well away from synaptic sites. At the ultrastructural level, EAAC1 immunolabelled one postsynaptic element at synapses and also processes well away from the synaptic release site. Since EAAC1 was localized away from synaptic sites, we evaluated the role EAAC1 plays in GABA formation by measuring GABA concentrations via reversed-phase high-performance liquid chromatography following incubation of retinae in enzyme and glutamate uptake inhibitors. Incubation of retinae in D-threo-beta-hydroxyaspartate or D/ L-threo-beta-benzyloxyaspartate, which are known to inhibit the glutamate transporters GLAST1, GLT1, and EAAC1, caused a decrease in GABA synthesis by around 50%. Incubation in 6-diazo-5-oxo- L-norleucine, a phosphate-activated glutaminase inhibitor, decreased GABA formation by 40%. Taken together with the anatomical data, the results of this study suggest that EAAC1 plays very little role in GABA synthesis - indeed GABA formation occurs predominantly from glutamine. By virtue of its location both near and well away from synaptic release sites, EAAC1 may regulate glutamate uptake differentially.
Wiessner
Michael
M
Max-Planck Institut für Hirnforschung, Abteilung für Neuroanatomie, Deutschordenstrasse 46, 60528 Frankfurt am Main, Germany.
Fletcher
Erica L
EL
Fischer
Frauke
F
Rauen
Thomas
T
D025042:Amacrine Cells / Q000378:metabolism / Q000648:ultrastructure; D027322:Amino Acid Transport System X-AG / Q000378:metabolism*; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D004791:Enzyme Inhibitors / Q000494:pharmacology; D027341:Excitatory Amino Acid Transporter 1; D050580:Excitatory Amino Acid Transporter 3; D005968:Glutamate Decarboxylase / Q000037:antagonists & inhibitors / Q000378:metabolism; D050491:Glutamate Plasma Membrane Transport Proteins; D018698:Glutamic Acid / Q000378:metabolism*; D005972:Glutaminase / Q000037:antagonists & inhibitors / Q000378:metabolism; D005973:Glutamine / Q000378:metabolism; D007150:Immunohistochemistry; D008854:Microscopy, Electron; D009433:Neural Inhibition / Q000502:physiology; D009434:Neural Pathways / Q000378:metabolism* / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D012160:Retina / Q000378:metabolism* / Q000648:ultrastructure; D012165:Retinal Ganglion Cells / Q000378:metabolism / Q000648:ultrastructure; D027981:Symporters / Q000378:metabolism*; D013570:Synaptic Membranes / Q000378:metabolism* / Q000648:ultrastructure; D009435:Synaptic Transmission / Q000502:physiology; D005680:gamma-Aminobutyric Acid / Q000096:biosynthesis*
D027322:Amino Acid Transport System X-AG; D000596:Amino Acids; D004791:Enzyme Inhibitors; D027341:Excitatory Amino Acid Transporter 1; D050580:Excitatory Amino Acid Transporter 3; D050491:Glutamate Plasma Membrane Transport Proteins; C493398:Slc1a1 protein, rat; C493392:Slc1a3 protein, rat; D027981:Symporters; D005973:Glutamine; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D005972:Glutaminase; D005968:Glutamate Decarboxylase