The proposed research is designed to utilize the isolated rat retina for an analysis of the mechanisms of rhodopsin-mediated retinal light damage. The experiments involve measurements of metabolic activities following in vitro rhodopsin bleaching at normal (37 degree C) a""""""""d hyperthermic (41-4 degree 5 degree C) incubation temperatures in comparison to non-bleached tissues. The hyperthermic temperatures are the same as those that greatly accelerated rhodopsin-mediated rod cell death in vivo in the rat. It is hypothesized that differences in vitro metabolic activities at 37 degree C and 41 degree C for the same rhodopsin bleach differentiate between non-damaging and damaging reactions. Present work indicates that the light damage studied in the isolated rat retina at 41 degree C expresses itself mainly by a calcium- dependent decrease in the rate of glycolysis which is not accompanied by changes in mitochondrial activities or histological abnormalities.
The specific aims of the proposal are: 1) To explore the possibilities that a low volume incubation medium and the use of long-term dark adapted rats will drive the light-induced damage of the isolated rat retina to stages seen in vivo as manifested by mitochondrial damage, changes in synthetic activities, and histological abnormalities; 2) To study the extent to which manifestations of retinal light damage of the isolated rat retina are reversed by permitting rhodopsin regeneration in vitro following the addition of ll-cis retinal to the medium. This work will provide essential information on the kinetics of the glycolytic inhibition and a separation of reversible an d irreversible components; 3) To continue the analysis as to whether the calcium-dependence of glycolytic inhibition is associated with an increase in the intracellular concentration of calcium and to determine the mechanism of this increase using calcium channel blockers, ionophores, and divalent ion substitutes; and 4) To determine whether rhodopsin bleaching is associated with increased synthesis and release of a compound which may be toxic to cell function. This will involve identification of compounds which appear in the incubation medium, use of radioactive amino acids for measuring synthesis and inhibition of protein synthesis at the levels of transcription and translation. The proposed studies will provide important information not only of rod cell pathology but also of cone cell pathology as exemplified by macular degeneration.
