HEAT-STRESS EFFECTS ON THE MYOSIN HEAVY CHAIN PHENOTYPE OF RAT SOLEUS FIBERS DURING THE EARLY STAGES OF REGENERATION


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Abstract

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. Muscle Nerve52: 1047–1056, 2015

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