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B. Battelle, K.S. Alligood; Light–dependent changes in arrestin immunoreactivity in Limulus photoreceptors . Invest. Ophthalmol. Vis. Sci. 2004;45(13):3645.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Light–dependent changes in the distribution of proteins in photoreceptors may play a major role in regulating the photoresponse. The purpose of this study was to examine light–dependent changes in the distribution of arrestin immunoreactivity (arr–ir) in Limulus ventral photoreceptors and to explore possible mechanisms. We also examined the effects of light and darkness on the distribution of Gq alpha. Methods: Ventral photoreceptors were incubated for several days in the dark in chilled organ culture medium, then exposed to light of different intensities and for different durations at room temperature or maintained in the dark. Cells were fixed in methanol/formaldehyde, immunostained to visualize arrestin, opsin, and Gq alpha and viewed with a confocal microscope. In some experiments, cells that had been exposed to light were returned to the dark for different lengths of time. In others, cells were incubated with or without the following drugs before they were exposed to light: cycloheximide to block protein synthesis, cytochalasin D to disrupt the actin cytoskeleton, wortmannin or LY 294002 to inhibit PI3 kinase. Results: The light–driven increase in arr–ir at the rhabdom was rapid even in dim light. It occured within 10 min. The decrease in arr–ir at the rhabdom in the dark was slow, requiring between 3 and 6 hr to reach the fully dark–adapted level. The light–driven increase of arr–ir at the rhabdom was not blocked by cycloheximide, cytochalasin D, wortmannin or Ly294002. Gq–ir was intense at the rhabdom in the dark and in the light. Conclusions: The light–stimulated increase in arr–ir at the rhabdom is rapid and does not require protein synthesis; therefore we conclude it is due to the translocation of the protein from the cytosol. The mechanisms for this translocation are not yet known, but our results suggest it does not require an intact actin cytoskeleton or the syntesis of PIP3. Interestingly, Gq remains at the rhabdom in light–adapted ventral photoreceptors.
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