Low temperature acclimation decreases rates of protein synthesis in rainbow trout (Oncorhynchus mykiss) heart.

Protein synthesis was assessed in rainbow trout (Oncorhynchus mykiss) hearts perfused with medium containing (3)H phenylalanine. Isolated hearts from fish acclimated to 5° and 15°C were used as the model system, and were perfused at variable test temperatures and pH. Protein synthesis expressed as nmol PHE mg protein(-1) h(-1) was two fold higher in hearts from fish acclimated to 15°C and tested at 15°C and extracellular pH 7.6 than in hearts from fish acclimated to 5°C and tested at 5°C and extracellular pH 8.0. The prime determinant of the decreased rate of protein synthesis was thermal history. Fish acclimated to 5°C had lower levels of RNA mg protein(-1) than fish held at 15°C. There was a direct linear relationship between the rate of protein synthesis in nmol PHE mg protein(-1) h(-1) and RNA content. RNA activity (nmol PHE μg RNA(-1) h(-1) remained constant regardless of thermal history or perfusion condition. Elevated pH resulted in only a marginal decrease in protein synthesis. Test temperature had no effect on in vitro rates of protein synthesis.