Submitted on August 9, 2005
Accepted on September 15, 2005
Parellel and Divergent Adaptations of Rat Soleus and Plantaris to Chronic Exercise and Hypergravity
Patrick M Fuller1, Kenneth M Baldwin2, and Charles A Fuller1*
1 Neurobiology, Physiology and Behavior, University of California, Davis, Davis, CA, USA
2 Department of Biophysics and Physiology, University of California, Irvine, Irvine, CA, USA
* To whom correspondence should be addressed. E-mail: cafuller{at}ucdavis.edu.
It has been demonstrated that endurance exercise and chronic acceleration, i.e., hypergravity, produce comparable adaptations in a variety of physiological systems, including: decreased adiposity, increased energy metabolism and altered intermediary metabolism. Similar adaptations have not been demonstrated for skeletal muscle per se. To further differentiate between these general responses with respect to gravity and exercise, this study tested the hypothesis that chronic exercise (voluntary wheel running) and chronic acceleration (2G via centrifugation) will induce similar changes in muscle
myosin heavy chain (MHC) isoform expression in rat plantaris, a fast extensor and in rat soleus, a slow 'anti-gravity' extensor. The experimental design involved four groups of mature male rats (n=8/group), 1G (1GW) and 2G (2GW) with running wheels and 1G (1GC) and 2G (2GC) controls without running wheels. The primary observations from the study were: 1) 8 weeks of 2G is an adequate stimulus for MHC compositional changes in rat plantaris and soleus muscle; 2) both exercise and +G caused an increase
in the slow MHC1 isoform in soleus muscle, suggesting that loading is a primary stimulus for this shift; and 3) 2G and exercise appeared to have differential effects on the plantaris muscle MHC isoforms, with 2G causing an increase in MHC2b, and exercise causing a decrease in MHC2b with a concomitant increase in MHC1, suggesting that factors other than enhanced loading, possibly locomotor activity levels, are the primary stimulus for this shift.
