Response of protein synthesis to anoxia and recovery in anoxia-tolerant hepatocytes

Hepatocytes from the western painted turtle (Chrysemys picta bellii) display a profound metabolic suppression under anoxia. Fractional rates of protein synthesis fell by 92% during 12 h anoxia at 25°C and were indistinguishable from the rate obtained with cycloheximide. Normoxic recovery saw protein synthesis increase to 160% of control values and return to normal after 2 h. The GTP-to-GDP ratio, implicated in the control of translation, fell threefold during anoxia. Purine nucleotide phosphate profiles suggest that this change occurs through increasing concentrations of ADP and GDP, with concentrations of ATP and GTP and total purines remaining constant. The normoxic cost for protein synthesis was calculated at 47.6 ± 6.8 mmol ATP/g protein. Normoxic protein synthesis accounted for 36% of overall ATP turnover rates, close to the extent of O₂ consumption inhibitable by cycloheximide (28%). Under anoxia, the proportion of ATP turnover utilized by protein synthesis did not change significantly. ATP turnover rates for urea synthesis reflected a similar pattern, falling 72% under anoxia. These results reflect the cell's ability to suppress protein synthesis under anoxia in a manner that is coordinated with the reduction in total metabolic rate.