title: Calcium-permeable glutamate receptors in horizontal cells of the mammalian retina.
abstract: Mechanisms that mediate the calcium influx in mammalian horizontal cells were studied. Horizontal cells (HCs) enzymatically dissociated from the rabbit retina were recorded by the whole-cell configuration of the patch-clamp technique and by calcium image ratioespectrophotometry of Fura-2 loaded cells. AMPA-preferring glutamate receptors were shown to permeate Ca2+ in mammalian HCs by ionic substitution experiments. Furthermore, after blocking the L-type calcium current with nifedipine (100 microM), calcium current through the AMPA-preferring glutamate receptors was measured. Calcium image ratioespectrophotometry was performed on the dissociated HCs in order to determine the changes in the intracellular calcium ([Ca2+]i). Fura-2 microspectrophotometry showed that in HCs, K+-induced cell depolarization promoted an increase in [Ca2+]i, mediated by the L-type calcium channels, since it was abolished in the presence of nifedipine. The increase in [Ca2+], upon cell depolarization was observed throughout each cell: however, it was maximal at the cell soma. Activation of glutamate receptors in dissociated HCs by glutamate, AMPA or kainate promoted an increase in [Ca2+]i. This increase in [Ca2+]i, was abolished in nominally Ca2+-free solution (0 mM Ca2+); in contrast, nifedipine decreased the glutamate-induced influx of calcium in ca. 50%. The present study demonstrates that calcium may permeate through glutamate receptors expressed in HCs of the rabbit retina.
authors.affiliation: Departamento de Fisiología, Facultad de Farmacia, Universidad de Complutense, Madrid, Spain.
authors.forename: L
authors.initials: L
authors.lastname: Rivera
authors.forename: R
authors.initials: R
authors.lastname: Blanco
authors.forename: P
authors.initials: P
authors.lastname: de la Villa
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015220:Calcium Channels / Q000378:metabolism*; D018690:Excitatory Amino Acid Agonists / Q000494:pharmacology; D016257:Fura-2 / Q000378:metabolism; D007395:Interneurons / Q000378:metabolism*; D015591:Microspectrophotometry; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D010539:Permeability; D011817:Rabbits; D017470:Receptors, Glutamate / Q000378:metabolism*; D012160:Retina / Q000187:drug effects / Q000378:metabolism*; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D015220:Calcium Channels; D018690:Excitatory Amino Acid Agonists; D017470:Receptors, Glutamate; D018350:alpha-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid; D009543:Nifedipine; D002118:Calcium; D016257:Fura-2