title: Possible roles of glutamate transporter EAAT5 in mouse cone depolarizing bipolar cell light responses.
abstract: A remarkable feature of neuronal glutamate transporters (EAATs) is their dual functions of classical carriers and ligand-gated chloride (Cl(-)) channels. Cl(-) conductance is rapidly activated by glutamate in subtype EAAT5, which mediates light responses in depolarizing bipolar cells (DBC) in retinae of lower vertebrates. In this study, we examine whether EAAT5 also mediates the DBC light response in mouse. We took advantage of an infrared illuminated micro-injection system, and studied the effects of the EAAT blocker (TBOA) and a glutamate receptor agonist (LAP4) on the mouse electroretinogram (ERG) b-wave responses. Our results showed that TBOA and LAP4 shared similar temporal patterns of inhibition: both inhibited the ERG b-wave shortly after injection and recovered with similar time courses. TBOA inhibited the b-wave completely at mesopic light intensity with an IC50 value about 1 log unit higher than that of LAP4. The inhibitory effects of TBOA and LAP4 were found to be additive in the photopic range. Furthermore, TBOA alone inhibited the b-wave in the cone operative range in knockout mice lacking DBCRs at a low concentration that did not alter synaptic glutamate clearance activity. It also produced a stronger inhibition than that of LAP4 on the cone-driven b-wave measured with a double flash method in wildtype mice. These electrophysiological data suggest a significant role for EAAT5 in mediating cone-driven DBC light responses. Our immunohistochemistry data indicated the presence of postsynaptic EAAT5 on some DBCCs and some DBCRs, providing an anatomical basis for EAAT5's role in DBC light responses.
authors: Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, TX, USA. Electronic address: ytse@bcm.edu.
authors: Dennis Y
authors: DY
authors: Tse
authors: Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, TX, USA; Department of Ophthalmology, Gyeongsang National University, Jinju, Republic of Korea.
authors: Inyoung
authors: I
authors: Chung
authors: Cullen Eye Institute, Department of Ophthalmology, Baylor College of Medicine, Houston, TX, USA.
authors: Samuel M
authors: SM
authors: Wu
mesh_terms: D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D004596:Electroretinography / Q000187:drug effects; D050582:Excitatory Amino Acid Transporter 5 / Q000502:physiology*; D005971:Glutamates / Q000494:pharmacology; D007150:Immunohistochemistry; D008810:Mice, Inbred C57BL; D023421:Models, Animal; D051245:Retinal Bipolar Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D017949:Retinal Cone Photoreceptor Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects
chemical_list: D050582:Excitatory Amino Acid Transporter 5; D005971:Glutamates; C493387:Slc1a7 protein, mouse; C120673:benzyloxyaspartate; D001224:Aspartic Acid
keywords: Bipolar cells; EAAT5; Electroretinogram; Glutamate transporter; Immunohistochemistry; Retina