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  • Title: Effect of bleached rhodopsin on signal amplification in rod visual receptors.
    Author: Kahlert M, Pepperberg DR, Hofmann KP.
    Journal: Nature; 1990 Jun 07; 345(6275):537-9. PubMed ID: 2161501.
    Abstract:
    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.
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