Effect of bleached rhodopsin on signal amplification in rod visual receptors.
Bleaching of rhodopsin markedly desensitizes the vertebrate visual system during a subsequent period of dark adaptation. Previous studies have indicated an origin of bleaching desensitization in the visual pigment itself, but have not identified the mechanism of action. A candidate for the site at which densensitization is initially expressed is the activation of transducin (formation of T*) on the rod disk membranes; this reaction directly involves rhodopsin in its photoactivated (R*) form and mediates initial amplification of the visual signal (reviewed in refs 7-9). We have analysed the effect of bleaching on the sensitivity of a flash-induced light-scattering signal known to monitor the disk-based amplifier, and which has been established as specifically monitoring transducin activation. We have recorded this signal from functioning retinal rods in situ ('ATR' signal) and find that bleaches inducing a pronounced, sustained loss in rod electrophysiological sensitivity do not alter the sensitivity of the ATR response after correction for reduced quantum catch. Our results indicate that the biochemical gain of the R*----T* transduction stage remains unchanged in the presence of bleached pigment and implicate a subsequent reaction as the first to show a sustained, bleaching-dependent gain reduction.
Kahlert
M
M
Institut für biophysik und Strahlenbiologie, Albert-Ludwigs Universität Freiburg, FRG.
Pepperberg
D R
DR
Hofmann
K P
KP
D000818:Animals; D002118:Calcium / Q000502:physiology; D002417:Cattle; D006152:Cyclic GMP / Q000502:physiology; D004594:Electrophysiology; D066298:In Vitro Techniques; D008027:Light; D010786:Photoreceptor Cells / Q000502:physiology*; D012168:Retinal Pigments / Q000502:physiology*; D012243:Rhodopsin / Q000502:physiology* / Q000528:radiation effects; D015398:Signal Transduction; D015293:Transducin / Q000502:physiology
D012168:Retinal Pigments; D012243:Rhodopsin; D015293:Transducin; D006152:Cyclic GMP; D002118:Calcium