title: Melanopsin and mechanisms of non-visual ocular photoreception.
abstract: In addition to rods and cones, the mammalian eye contains a third class of photoreceptor, the intrinsically photosensitive retinal ganglion cell (ipRGC). ipRGCs are heterogeneous irradiance-encoding neurons that primarily project to non-visual areas of the brain. Characteristics of ipRGC light responses differ significantly from those of rod and cone responses, including depolarization to light, slow on- and off-latencies, and relatively low light sensitivity. All ipRGCs use melanopsin (Opn4) as their photopigment. Melanopsin resembles invertebrate rhabdomeric photopigments more than vertebrate ciliary pigments and uses a G(q) signaling pathway, in contrast to the G(t) pathway used by rods and cones. ipRGCs can recycle chromophore in the absence of the retinal pigment epithelium and are highly resistant to vitamin A depletion. This suggests that melanopsin employs a bistable sequential photon absorption mechanism typical of rhabdomeric opsins.
authors.affiliation: Departments of Ophthalmology and and Biological Structure, University of Washington School of Medicine, Seattle, Washington 98104, USA.
authors.forename: Timothy
authors.initials: T
authors.lastname: Sexton
authors.forename: Ethan
authors.initials: E
authors.lastname: Buhr
authors.forename: Russell N
authors.initials: RN
authors.lastname: Van Gelder
mesh_terms: D000818:Animals; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D006801:Humans; D055537:Light Signal Transduction / Q000502:physiology*; D012165:Retinal Ganglion Cells / Q000166:cytology / Q000378:metabolism*; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000378:metabolism; D017299:Rod Opsins / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*; D014801:Vitamin A / Q000378:metabolism; D000099210:Melanopsin
chemical_list: D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D017299:Rod Opsins; D014801:Vitamin A; D000099210:Melanopsin
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