Complete suppression of protein synthesis during anoxia with no post-anoxia protein synthesis debt in the red-eared slider turtle Trachemys scripta elegans

Two previous studies of the effects of anoxia on protein synthesis in anoxia-tolerant turtles (Trachemys scripta elegans, Chrysemys picta bellii) have generated opposing results. Using the flooding-dose method, we measured the rate of protein synthesis following injection and incorporation of a large dose of radiolabelled phenylalanine to resolve the question of whether anoxia results in a downregulation of protein synthesis. After I h of anoxia, levels of protein-incorporated radiolabel indicated that protein synthesis rates in the intestine, heart, liver, brain, muscle and lungs were not significantly different from those of normoxic controls. However, from 1 to 6h of anoxia, quantities of protein-incorporated radiolabel did not increase, suggesting that protein synthesis had ceased or had decreased below a measurable level. There was also no significant post-anoxia increase in protein synthesis rates above normoxic control levels during 3h of recovery from anoxia. RNA-to-protein ratios did not change significantly in any tissue except the heart, in which RNA levels decreased below normoxic control levels after 6h of anoxia. Except in the heart, downregulation of protein synthesis during anoxia does not appear to be mediated by changes in tissue RNA concentration.