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Dim background light and Cerenkov radiation from 32P block reversal of rhodopsin phosphorylation in intact frog retinal rods

Published online by Cambridge University Press:  02 June 2009

Michael S. Biernbaum ,
Brad M. Binder  and
M. Deric Bownds
Michael S. Biernbaum
Affiliation:
Laboratory of Molecular Biology, University of Wisconsin, Madison
Brad M. Binder
Affiliation:
Laboratory of Molecular Biology, University of Wisconsin, Madison
M. Deric Bownds
Affiliation:
Laboratory of Molecular Biology and Department of Zoology, University of Wisconsin, Madison
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Abstract

The phosphorylation of photoexcited rhodopsin (Rho*) is thought to inactivate this receptor by inhibiting its interaction with the GTP-binding protein transducin (Gt). Here we report that the time course of phosphorylation-dephosphorylation after bright illumination of intact rod outer and inner segments (ROS-RIS) incubated in 33Pi can be altered if the ROS-RIS are first exposed to levels of dim illumination that cause light adaptation in these ROS-RIS. The dephosphorylation of >107 phosphorylated rhodopsin molecules/ROS following a bright flash can be blocked by prior dim continuous illumination (generating 103 Rho*/ROS/s) that cumulatively bleaches ≍ 105 rhodopsin molecules/ROS. The phenomenon has not been previously noted because these low levels of light are emitted as a result of Cerenkov radiation from the 32P isotope that is usually employed to monitor rhodopsin phosphorylation. The inhibition of rhodopsin dephosphorylation by dim conditioning illumination is observed in intact ROS-RIS but is lost when ROS-RIS are electropermeabilized or fragmented.

Keywords

Vertebrate rodsRhodopsin phosphorylationRhodopsin dephosphorylationCerenkov radiationPhosphatase

Information

Type
Short Communications
Information
Visual Neuroscience , Volume 7 , Issue 5 , November 1991 , pp. 499 - 503
Copyright
Copyright © Cambridge University Press 1991

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