title: Calcium activates the light-dependent conductance in melanopsin-expressing photoreceptors of amphioxus.
abstract: Melanopsin, the photopigment of the "circadian" receptors that regulate the biological clock and the pupillary reflex in mammals, is homologous to invertebrate rhodopsins. Evidence supporting the involvement of phosphoinositides in light-signaling has been garnered, but the downstream effectors that control the light-dependent conductance remain unknown. Microvillar photoreceptors of the primitive chordate amphioxus also express melanopsin and transduce light via phospholipase-C, apparently not acting through diacylglycerol. We therefore examined the role of calcium in activating the photoconductance, using simultaneous, high time-resolution measurements of membrane current and Ca(2+) fluorescence. The light-induced calcium rise precedes the onset of the photocurrent, making it a candidate in the activation chain. Moreover, photolysis of caged Ca elicits an inward current of similar size, time course and pharmacology as the physiological photoresponse, but with a much shorter latency. Internally released calcium thus emerges as a key messenger to trigger the opening of light-dependent channels in melanopsin-expressing microvillar photoreceptors of early chordates.
authors.affiliation: Departamento de Biología, Universidad Nacional de Colombia, Bogotá 110231, Colombia;
authors.forename: Gabriel
authors.initials: G
authors.lastname: Peinado
authors.affiliation: Centro Internacional de Fisica, Universidad Nacional de Colombia, Bogotá 110231, Colombia;
authors.forename: Tomás
authors.initials: T
authors.lastname: Osorno
authors.affiliation: Departamento de Biología, Universidad Nacional de Colombia, Bogotá 110231, Colombia; Bell Center, Marine Biological Laboratory, Woods Hole, MA 02543;
authors.forename: María del Pilar
authors.initials: Mdel P
authors.lastname: Gomez
authors.affiliation: Bell Center, Marine Biological Laboratory, Woods Hole, MA 02543; Instituto de Genética, Universidad Nacional de Colombia, Bogotá 110231, Colombia enasi@mbl.edu.
authors.forename: Enrico
authors.initials: E
authors.lastname: Nasi
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism*; D064175:Lancelets / Q000502:physiology*; D008027:Light; D017956:Photoreceptor Cells, Invertebrate / Q000502:physiology*; D017299:Rod Opsins / Q000502:physiology*; D000099210:Melanopsin
chemical_list: D002118:Calcium; D017299:Rod Opsins; D000099210:Melanopsin
keywords: amphioxus; calcium; melanopsin; photoreceptor