INCREASED MUSCLE CARNITINE PALMITOYLTRANSFERASE-II MESSENGER-RNA AFTER INCREASED CONTRACTILE ACTIVITY

The capacity of skeletal muscle to oxidize fatty acids increases with endurance training. The oxidation of long-chain fatty acids occurs in mitochondria and is initiated by a carnitine-dependent transport step in which three enzymes help fatty acyl groups enter the matrix compart ment. The purpose of this study was to determine whether pretranslatio nal regulation of one of these three enzymes, carnitine palmitoyltrans ferase II (CPT II), as estimated from the level of CPT II mRNA, plays a role in the doubling of CPT activity in skeletal muscle of rats subj ected to daily 2-h bouts of running on treadmills (P. A. Mole, L. B. O scai, and J. O. Holloszy. J. Clin. Invest. 50: 2323-2330, 1971). After 100 min/day of running on motor-driven treadmills for 2 wk, CPT II mR NA in the plantaris muscle was unchanged when normalized per unit of e xtracted RNA but was 50% higher (P < 0.05) over sedentary controls whe n normalized per unit of muscle wet weight. To test whether additional contractile activity would make CPT II mRNA even higher, continuous i ndirect electrical stimulation was imposed on the tibialis anterior mu scles. After 9 days of chronic stimulation, CPT II mRNA was 63, 221, a nd 137% greater than control (P < 0.001) when normalized to extracted RNA, muscle wet weight, and whole muscle, respectively, compared with the muscle in the central rats. These data indicate that pretranslatio nal regulation of CPT II occurs in response to increased contractile a ctivity in skeletal muscle.