Passive stretch modulates denervation induced alterations in skeletal muscle myosin heavy chain mRNA levels

The effect of denervation and denervation combined with immobilisation in e ither the shortened or lengthened position (passive stretch) upon myosin he avy chain (MyHC) mRNA levels was examined in three rat hind-limb muscles wi th differing phenotypes. Denervation alone caused a reduction in type I and type IIa MyHC transcripts in all three muscles. In contrast denervation ca used a 72% increase in type IIb in the slow postural soleus muscle only whi ch was prevented by immobilisation in the lengthened position. In the same muscle passive stretch also significantly retarded the effects of denervati on upon the type I transcript (from 38% below control levels to 24% below) and type IIa transcript (from 59% to 32% below control levels). The levels of both type I and IIa transcripts, in the fast phasic plantaris muscle, we re both unaffected by stretch combined with denervation when compared to de nervation alone. In the mixed gastrocnemius muscle stretch affected the lev el of the type I but not the type IIa transcript. These data suggest that p assive stretch can modulate MyHC gene expression independently of innervati on but that it does so in a muscle-specific manner.