Rates of synthesis of actomyosin in atria and ventricles of the perfused working rat heart.

Actomyosin from hearts perfused in vitro with [U-14C] phenylalanine and the remaining plasma amino acids was purified by standard techniques. The rate of actomyosin synthesis was expressed relative to actomyosin protein, to total protein and to total RNA. The rate of atrial total protein synthesis was twice the ventricular rate correlating with the RNA/protein ratios of the compartments. The actomyosin contents relative to total protein were not significantly different in atria and ventricles. The rate of actomyosin synthesis in atria was 2 to 3 times greater than in the ventricles when expressed relative to actomyosin or total protein. Synthesis rates of actomyosin expressed relative to total RNA were similar in the two compartments. These results suggest that the rate of turnover of actomyosin in the atria is 2 to 3 times the ventricular rate and that the greater rate of synthesis of total protein synthesis in atria is reflected in the rate of synthesis of specific intramyocytic proteins.