[Expression of myosin heavy chain IIx mRNA as a molecular marker of disuse of soleus muscle in rats].

Objective. To make an Achilles tenotomy rat model to observe the change in soleus weight and expression of myosin heavy chain (MHC) isoform mRNA, and to find some clues for elucidating the mechanisms of soleus disuse. Method. Thirty male Sprague-Dawley [correction of Sprangue] rats were divided into 6 groups. On the lst, 3rd, 7th, 14th, 21st and 28th days after Achilles tenotomy, wet weight of soleus (SOL), plantaris (PL), gastrocnemius mediales (MG), and gastrocnemius lateral (LG) muscles were measured. Expression of MHC IIx mRNA was observed by means of reverse transcriptase-polymerase chain reaction (RT-PCR). Result. Wet weight of SOL, MG, LG, and PL decreased significantly on the 3rd day after the tenotomy. The wet weight of these muscles reduced to the minimum on the 7th or 14th days after the tenotomy, and then recovered slightly on the 21st day after the tenotomy. There was only the expression of MHC I and MHC IIa mRNA in normal soleus muscle, but no MHC IIx or MHC IIb mRNA. The expression of MHC IIx mRNA occurred in SOL on the 3rd day after tenotomy and still expressed on the 28th day after tenotomy. There was no expression of MHC IIb mRNA in SOL after Achilles tenotomy. Conclusion. The appearance of atrophy of rat soleus induced by Achilles tenotomy is similar in time and extent with that induced by tail-suspension. The expression of MHC IIx mRNA is shown in rat soleus muscles in Achilles tenotomy and tail-suspension models. The study suggests that expression of MHC IIx mRNA may be used as a molecular marker of soleus muscle disuse in rats.