Key result
Analysis of rat fast and slow muscles showed corresponding proportions of MyHC transcripts, protein isoforms, and fiber types, with slow MyHC-1 mRNA expression in the soleus up to three orders higher than fast transcripts.
Does not inform clinical practice; leaves open whether MyHC coordination extends to human cardiac or skeletal muscle.
We studied the expression of myosin heavy chain isoforms at mRNA and protein levels as well as fiber type composition in the fast extensor digitorum longus (EDL) and slow soleus (SOL) twitch muscles of adult inbred Lewis strain rats. Comparison of the results from Real Time RT-PCR, SDS-PAGE and fiber type analysis showed corresponding proportions of MyHC transcripts (MyHC-1, -2a, -2x/d, -2b), protein isoforms (MyHC-1, -2a, -2x/d, -2b) and fiber types (type 1, 2A, 2X/D, 2B) in both muscles. Furthermore, we found that slow MyHC-1 mRNA expression in the SOL was up to three orders higher than that of fast MyHC transcripts. This finding can explain the predominance of MyHC-1 isoform and fiber type 1 and the absence of pure 2X/D and 2B fibers in the SOL muscle. Based on our data presenting quantitative evidence of corresponding proportions between mRNA level, protein content and fiber type composition, we suggest that the Real Time RT-PCR technique can be used as a routine method for analysis of muscle composition changes and could be advantageous for the analysis of scant biological samples such as muscle biopsies in humans.
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Žurmanová et al. (2013) studied this question. Soleus (SOL) muscle vs. Extensor digitorum longus (EDL) muscle was evaluated on Expression of myosin heavy chain isoforms at mRNA and protein levels and fiber type composition. Analysis of rat fast and slow muscles showed corresponding proportions of MyHC transcripts, protein isoforms, and fiber types, with slow MyHC-1 mRNA expression in the soleus up to three orders higher than fast transcripts.
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