title: Paracrine control of photomembrane removal.
abstract: Photomembrane turnover in vertebrate photoreceptors is regulated by light. Rod outer segments (ROS) shed membrane filled tips at light onset, during the coexistence of two light modulated processes: a dark priming factor and a light induction event. Transduction of these two signals is not direct but appears to involve the neural retina and diffusible paracrine molecules. I propose a model wherein three paracrines control this ROS tip shedding. Melatonin, a lipid soluble dark priming molecule, is synthesized in the dark by all photoreceptor cells, diffusing freely and separating the ROS disk membranes. A second paracrine, dopamine is released from the inner retina whenever light is absorbed by the 502 nm-cones, inhibiting melatonin synthesis. Third, a proposed trophic paracrine, "rostrophin", is released in the dark from internal horizontal cells, and stabilizes the photomembrane. Shedding occurs as rostrophin decreases in the presence melatonin; briefly at light onset or continuously in red or dim white light.
authors.affiliation: Department of Physiology and Cell Biology, University of Kansas, Lawrence 66045-2106.
authors.forename: N A
authors.initials: NA
authors.lastname: Dahl
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000502:physiology*; D004298:Dopamine / Q000502:physiology; D006728:Hormones / Q000502:physiology*; D008027:Light; D008550:Melatonin / Q000096:biosynthesis / Q000502:physiology; D010786:Photoreceptor Cells / Q000502:physiology*; D011894:Rana pipiens; D012160:Retina / Q000502:physiology*; D012374:Rod Cell Outer Segment / Q000502:physiology / Q000648:ultrastructure; D012701:Serotonin / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D006728:Hormones; D012701:Serotonin; D008550:Melatonin; D004298:Dopamine