Beta-ionone activates and bleaches visual pigment in salamander photoreceptors

Vis Neurosci. 2009 May-Jun;26(3):267-74. doi: 10.1017/S0952523809090105. Epub 2009 Jun 5.

Abstract

Vision begins with photoisomerization of 11-cis retinal to the all-trans conformation within the chromophore-binding pocket of opsin, leading to activation of a biochemical cascade. Release of all-trans retinal from the binding pocket curtails but does not fully quench the ability of opsin to activate transducin. All-trans retinal and some other analogs, such as beta-ionone, enhance opsin's activity, presumably on binding the empty chromophore-binding pocket. By recording from isolated salamander photoreceptors and from patches of rod outer segment membrane, we now show that high concentrations of beta-ionone suppressed circulating current in dark-adapted green-sensitive rods by inhibiting the cyclic nucleotide-gated channels. There were also decreases in circulating current and flash sensitivity, and accelerated flash response kinetics in dark-adapted blue-sensitive (BS) rods and cones, and in ultraviolet-sensitive cones, at concentrations too low to inhibit the channels. These effects persisted in BS rods even after incubation with 9-cis retinal to ensure complete regeneration of their visual pigment. After long exposures to high concentrations of beta-ionone, recovery was incomplete unless 9-cis retinal was given, indicating that visual pigment had been bleached. Therefore, we propose that beta-ionone activates and bleaches some types of visual pigments, mimicking the effects of light.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cyclic Nucleotide-Gated Cation Channels / antagonists & inhibitors
  • Dark Adaptation / physiology
  • Dose-Response Relationship, Drug
  • Electric Conductivity
  • In Vitro Techniques
  • Kinetics
  • Larva
  • Membranes / drug effects
  • Membranes / metabolism
  • Membranes / physiology
  • Norisoprenoids / administration & dosage
  • Norisoprenoids / pharmacology*
  • Photoreceptor Cells, Vertebrate / drug effects*
  • Photoreceptor Cells, Vertebrate / metabolism*
  • Photoreceptor Cells, Vertebrate / physiology
  • Retinal Pigments / metabolism*
  • Retinal Rod Photoreceptor Cells / drug effects
  • Retinal Rod Photoreceptor Cells / physiology
  • Rod Cell Outer Segment / drug effects
  • Rod Cell Outer Segment / metabolism
  • Rod Cell Outer Segment / physiology
  • Time Factors
  • Urodela / growth & development
  • Urodela / metabolism*

Substances

  • Cyclic Nucleotide-Gated Cation Channels
  • Norisoprenoids
  • Retinal Pigments
  • beta-ionone