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Age-Related Differences in the Effect of Running Training on Cardiac Myosin Isozyme Composition in Rats

^a Department of Exercise Physiology, International Budo University, Chiba, Japan
^b Department of Health Science, Aichi University of Education, Japan

Shuichi Machida, Department of Veterinary Biomedical Sciences, University of Missouri—Columbia, E102 Veterinary Medical Building, 1600 East Rollins Road, Columbia, MO 65211 E-mail: MachidaS{at}missouri.edu.

Decision Editor: James R. Smith, PhD

We examined the effect of running training on age-related changes in cardiac myosin isozyme composition in rats. Female Fischer 344 rats (6, 12, 20, and 27 months old) were divided into two groups: sedentary control and trained. The trained group rats were trained by treadmill running for up to 60 minutes per day, 5 days per week for 8 weeks at up to 30 m per minute. In sedentary control rats, the proportion of V1 myosin, that is, -myosin heavy chain (MyHC) isoform, decreased progressively from 6 to 27 months of age. In the younger age groups (6 or 12 months old), there was a shift from V1 myosin to V3 myosin (ß-MyHC isoform) in trained hearts. However, the training program did not induce a cardiac myosin isozyme transition in older rats (20 or 27 months old). These results suggest that the mechanisms mediating the responses of cardiac muscle to running training alter during aging.