Heat-Stress effects on the myosin heavy chain phenotype of rat soleus fibers during the early stages of regeneration.

INTRODUCTION

We investigated heat-stress effects on the adult myosin heavy chain (MyHC) profile of soleus muscle fibers at an early stage of regeneration.

METHODS

Regenerating fibers in adult rats were analyzed 2, 4, or 6 days after bupivacaine injection. Rats were heat stressed by immersion in water (42 ± 1°C) for 30 minutes 24 hours after bupivacaine injection and every other day thereafter.

RESULTS

No adult MyHC isoforms were observed after 2 days, whereas some fibers expressed only fast MyHC after 4 days. Heat stress increased fast and slow MyHC in regenerating fibers after 6 days. Regenerating fibers expressing only slow MyHC were observed only in heat-stressed muscles. Bupivacaine injection increased the number of Pax7(+) and MyoD(+) satellite cells in regenerating fibers, more so in heat-stressed rats.

CONCLUSION

The results indicate that heat stress accelerates fast-to-slow MyHC phenotype conversion in regenerating fibers via activation of satellite cells.