DECREASED TOTAL VENTRICULAR AND MITOCHONDRIAL PROTEIN-SYNTHESIS DURING EXTENDED ANOXIA IN TURTLE HEART

The turtle heart provides a model system to study the effects of anoxi a on protein synthesis without the potentially confounding factor of c ontractile failure and decreased ATP levels. Protein synthesis, as mea sured by H-3-labeled phenylalanine incorporation, was studied under co nditions of normoxia and anoxia in isolated perfused turtle [Trachemys (=Pseudemys) scripta elegans] hearts at 15 degrees C. Heart rate, car diac output, and ventricular pressure development were unaffected by 2 or 3 h of anoxia. Despite the anoxia, energy levels in the heart were presumably still high, since contractility was maintained. RNA conten t of ventricle decreased after anoxic perfusion. Rates of total protei n synthesis rates in ventricle were threefold lower under anoxia than under normoxia. These findings suggest that the total level of RNA is one determinant of protein synthesis. Incorporation of label into prot ein extracted from mitochondria was also assessed. The ratio of mitoch ondrial to whole ventricular protein synthesis was significantly lower after anoxia between the synthesis of total cellular protein and prot ein destined fro mitochondria. Isolated mitochondria were still couple d after 2 or 3 h of anoxia. In effect, the mitochondria enter into a s tate of hypometabolism in terms of rates of ATP synthesis and protein synthesis, but functional integrity is maintained. The decrease in pro tein synthesis in general and mitochondrial protein synthesis in parti cular may represent an adaptation to allow the partitioning of the ava ilable energy resources toward mechanical function during anoxia.