title: Retinal bipolar cell input mechanisms in giant danio. II. Patch-clamp analysis of on bipolar cells.
abstract: Glutamate receptors on giant danio retinal on bipolar cells were studied with whole cell patch clamping using a slice preparation. Cone-driven on bipolars (Cbs) and mixed-input on bipolars (Mbs) were identified morphologically. Most Cbs responded to the excitatory amino acid transporter (EAAT) substrate d-aspartate but not to the group III metabotropic glutamate receptor (mGluR) agonist l-(+)-2-amino-4-phosphonobutyric acid (l-AP4) or the AMPA/kainate receptor agonist kainate, suggesting EAATs are the primary glutamate receptors on Cbs. The EAAT inhibitor dl-threo-beta-benzyloxyasparate (TBOA) blocked all light-evoked responses of Cbs, suggesting these responses are mediated exclusively by EAATs. Conversely, all Mbs responded to d-aspartate and l-AP4 but not to kainate, indicating they have both EAATs and group III mGluRs (presumably mGluR6). The light responses of Mbs involve both receptors because they could be blocked by TBOA plus (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG, a group III mGluR antagonist) but not by either alone. Under dark-adapted conditions, the responses of Mbs to green (rod-selective) stimuli were reduced by CPPG but enhanced by TBOA. In contrast, both antagonists reduced the responses to red (cone-selective) stimuli, although TBOA was more effective. Furthermore, under photopic conditions, TBOA failed to eliminate light-evoked responses of Mbs. Thus on Mbs, rod inputs are mediated predominantly by mGluR6, whereas cone inputs are mediated mainly by EAATs but also by mGluR6 to some extent. Finally, we explored the interactions between EAATs and mGluR6 in Mbs. Responses to d-aspartate were reduced by l-AP4 and vice versa. Therefore mGluR6 and EAATs suppress each other, and this might underlie mutual suppression between rod and cone signals in Mbs.
authors.affiliation: Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA, USA. Kwoon_Wong@brown.edu
authors.forename: Kwoon Y
authors.initials: KY
authors.lastname: Wong
authors.forename: Ethan D
authors.initials: ED
authors.lastname: Cohen
authors.forename: John E
authors.initials: JE
authors.lastname: Dowling
mesh_terms: D000613:Aminobutyrates / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D001464:Barium / Q000494:pharmacology; D026603:D-Aspartic Acid / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D004558:Electric Stimulation / Q000379:methods; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D005998:Glycine / Q000031:analogs & derivatives* / Q000494:pharmacology; D066298:In Vitro Techniques; D007546:Isoquinolines / Q000378:metabolism; D007608:Kainic Acid / Q000494:pharmacology; D008027:Light; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D009474:Neurons / Q000145:classification / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018408:Patch-Clamp Techniques / Q000379:methods; D010775:Photic Stimulation / Q000379:methods; D026902:Potassium Channel Blockers / Q000494:pharmacology; D018094:Receptors, Metabotropic Glutamate / Q000037:antagonists & inhibitors; D012160:Retina / Q000166:cytology* / Q000502:physiology; D017949:Retinal Cone Photoreceptor Cells / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D017948:Retinal Rod Photoreceptor Cells / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects; D019789:Tetraethylammonium / Q000494:pharmacology; D013997:Time Factors; D014795:Visual Pathways / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D015027:Zebrafish
chemical_list: D000613:Aminobutyrates; D018690:Excitatory Amino Acid Agonists; D007546:Isoquinolines; D026902:Potassium Channel Blockers; D018094:Receptors, Metabotropic Glutamate; C120673:benzyloxyaspartate; C104331:cyclopropyl-4-phosphonophenylglycine; D001464:Barium; D001224:Aspartic Acid; D018698:Glutamic Acid; D026603:D-Aspartic Acid; D019789:Tetraethylammonium; C017475:lucifer yellow; C012729:2-amino-4-phosphonobutyric acid; D007608:Kainic Acid; D005998:Glycine