DIFFERENTIAL ADAPTATION TO ENDURANCE TRAINING BETWEEN HEART AND GASTROCNEMIUS-MUSCLE MITOCHONDRIA IN RATS

The effects of endurance training on mitochondrial gene expression and replication in heart and gastrocnemius muscles were studied in rats. Rats were trained for 12 weeks by treadmill running. Although the hear t weight was significantly increased by the training, activity of cyto chrome oxidase and concentrations of cytochrome b mRNA and mitochondri al DNA in the heart were not altered by the training. On the other han d, those in gastrocnemius muscle were increased about 1.5 fold by the training. When these values were compared between heart and gastrocnem ius muscles, they were 10, 3.3, and 1.7 fold, respectively, higher in the former than in the latter. These results suggest that the mitochon drial gene expression and enzyme activity for the oxidative capacity i n heart are fairly high compared to those in skeletal muscle, therefor e adaptation to the training in heart is attained by increasing the mu scle mass, but not mitochondrial gene expression.