title: Metabotropic glutamate receptor 5 and calcium signaling in retinal amacrine cells.
abstract: To begin to understand the modulatory role of glutamate in the inner retina, we examined the mechanisms underlying metabotropic glutamate receptor 5 (mGluR5)-dependent Ca(2+) elevations in cultured GABAergic amacrine cells. A partial sequence of chicken retinal mGluR5 encompassing intracellular loops 2 and 3 suggests that it can couple to both G(q) and G(s). Selective activation of mGluR5 stimulated Ca(2+) elevations that varied in waveform from cell to cell. Experiments using high external K(+) revealed that the mGluR5-dependent Ca(2+) elevations are distinctive in amplitude and time course from those engendered by depolarization. Experiments with a Ca(2+) -free external solution demonstrated that the variability in the time course of mGluR5-dependent Ca(2+) elevations is largely due to the influx of extracellular Ca(2+). The sensitivity of the initial phase of the Ca(2+) elevation to thapsigargin indicates that this phase of the response is due to the release of Ca(2+) from the endoplasmic reticulum. Pharmacological evidence indicates that mGluR5-mediated Ca(2+) elevations are dependent upon the activation of phospholipase C. We rule out a role for L-type Ca(2+) channels and cAMP-gated channels as pathways for Ca(2+) entry, but provide evidence of transient receptor potential (TRP) channel-like immunoreactivity, suggesting that Ca(2+) influx may occur through TRP channels. These results indicate that GABAergic amacrine cells express an avian version of mGluR5 that is linked to phospholipase C-dependent Ca(2+) release and Ca(2+) influx, possibly through TRP channels.
authors.affiliation: Department of Neuroscience, University of Minnesota, Minneapolis, Minnesota, USA.
authors.forename: Romina
authors.initials: R
authors.lastname: Sosa
authors.forename: Brian
authors.initials: B
authors.lastname: Hoffpauir
authors.forename: Michele L
authors.initials: ML
authors.lastname: Rankin
authors.forename: Richard C
authors.initials: RC
authors.lastname: Bruch
authors.forename: Evanna L
authors.initials: EL
authors.lastname: Gleason
mesh_terms: D025042:Amacrine Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D015220:Calcium Channels / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D002642:Chick Embryo; D002645:Chickens; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005456:Fluorescent Dyes; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000378:metabolism; D007150:Immunohistochemistry; D008969:Molecular Sequence Data; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D050052:TRPC Cation Channels; D010738:Type C Phospholipases / Q000378:metabolism; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
chemical_list: D015220:Calcium Channels; D004791:Enzyme Inhibitors; D005456:Fluorescent Dyes; D064529:Receptor, Metabotropic Glutamate 5; D018094:Receptors, Metabotropic Glutamate; D050052:TRPC Cation Channels; D005680:gamma-Aminobutyric Acid; D010738:Type C Phospholipases; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019205:GTP-Binding Protein alpha Subunits, Gs; D020962:Heterotrimeric GTP-Binding Proteins; D011188:Potassium; D002118:Calcium