Dim background light and Cerenkov radiation from 32P block reversal of rhodopsin phosphorylation in intact frog retinal rods.
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 greater than 10(7) phosphorylated rhodopsin molecules/ROS following a bright flash can be blocked by prior dim continuous illumination (generating 10(3) Rho*/ROS/s) that cumulatively bleaches approximately 10(5) 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.
Biernbaum
M S
MS
Laboratory of Molecular Biology, University of Wisconsin, Madison 53706.
Binder
B M
BM
Bownds
M D
MD
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D003623:Dark Adaptation; D008029:Lighting; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation / Q000528:radiation effects; D010786:Photoreceptor Cells / Q000528:radiation effects*; D011892:Rana catesbeiana; D012243:Rhodopsin / Q000737:chemistry / Q000528:radiation effects*
D010761:Phosphorus Radioisotopes; D012243:Rhodopsin