title: Calcium channel and glutamate receptor activities regulate actin organization in salamander retinal neurons.
abstract: Intracellular Ca2+ regulates a variety of neuronal functions, including neurotransmitter release, protein phosphorylation, gene expression and synaptic plasticity. In a variety of cell types, including neurons, Ca2+ is involved in actin reorganization, resulting in either actin polymerization or depolymerization. Very little, however, is known about the relationship between Ca2+ and the actin cytoskeleton organization in retinal neurons. We studied the effect of high-K+-induced depolarization on F-actin organization in salamander retina and found that Ca2+ influx through voltage-gated L-type channels causes F-actin disruption, as assessed by 53 +/- 5% (n = 23, P < 0.001) reduction in the intensity of staining with Alexa-Fluor488-phalloidin, a compound that permits visualization and quantification of polymerized actin. Calcium-induced F-actin depolymerization was attenuated in the presence of protein kinase C antagonists, chelerythrine or bis-indolylmaleimide hydrochloride (GF 109203X). In addition, phorbol 12-myristate 13-acetate (PMA), but not 4alpha-PMA, mimicked the effect of Ca2+ influx on F-actin. Activation of ionotropic AMPA and NMDA glutamate receptors also caused a reduction in F-actin. No effect on F-actin was exerted by caffeine or thapsigargin, agents that stimulate Ca2+ release from internal stores. In whole-cell recording from a slice preparation, light-evoked 'off' but not 'on' EPSCs in 'on-off' ganglion cells were reduced by 60 +/- 8% (n = 8, P < 0.01) by cytochalasin D. These data suggest that elevation of intracellular Ca2+ during excitatory synaptic activity initiates a cascade for activity-dependent actin remodelling, which in turn may serve as a feedback mechanism to attenuate excitotoxic Ca2+ accumulation induced by synaptic depolarization.
authors.affiliation: Department of Ophthalmology, New York University School of Medicine, 550 First Avenue PHL 843, New York, NY 10016, USA.
authors.forename: Massimiliano
authors.initials: M
authors.lastname: Cristofanilli
authors.forename: Abram
authors.initials: A
authors.lastname: Akopian
mesh_terms: D000199:Actins / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D000470:Alkaloids; D000818:Animals; D053119:Benzophenanthridines; D002118:Calcium / Q000494:pharmacology / Q000502:physiology; D020746:Calcium Channels, L-Type / Q000502:physiology*; D002273:Carcinogens / Q000494:pharmacology; D002470:Cell Survival / Q000187:drug effects; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018698:Glutamic Acid / Q000494:pharmacology; D007211:Indoles / Q000494:pharmacology; D008301:Maleimides / Q000494:pharmacology; D009475:Neurons, Afferent / Q000166:cytology / Q000502:physiology* / Q000648:ultrastructure; D010617:Phenanthridines / Q000494:pharmacology; D011188:Potassium / Q000494:pharmacology; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology; D017470:Receptors, Glutamate / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014562:Caudata / Q000502:physiology*
chemical_list: D000199:Actins; D000470:Alkaloids; D053119:Benzophenanthridines; D020746:Calcium Channels, L-Type; D002273:Carcinogens; D004791:Enzyme Inhibitors; D007211:Indoles; D008301:Maleimides; D010617:Phenanthridines; D017470:Receptors, Glutamate; D018698:Glutamic Acid; C016299:chelerythrine; D011493:Protein Kinase C; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate; D011188:Potassium; D002118:Calcium