Myosin heavy chain mRNA transform to faster isoforms in immobilized skeletal muscle: a quantitative PCR study

Jänkälä, Heidi, Veli-Pekka Harjola, NielsErik Petersen, and Matti Härkönen. Myosin heavy chainmRNA transform to faster isoforms in immobilized skeletal muscle: aquantitative PCR study. J. Appl.Physiol. 82(3): 977-982, 1997.A quantitative polymerase chain reaction (PCR) method was used to measure the quantities of type I, IIa, IIx, and IIb myosin heavy chain (MHC) mRNAin total RNA preparations of the soleus, gastrocnemius, and plantarismuscles of normal and hindlimb-immobilized rats. Type IIx and even typeIIb MHC mRNA were demonstrated at extremely low levels in normalsoleus, 2.1 ± 0.4 × 10⁵and 5.0 ± 0.2 × 10⁵molecules of mRNA per microgram total RNA, respectively. Immobilization for 1 wk significantly altered the gene expression of MHC isoforms. Insoleus, both type IIx and IIb MHC genes became significantly upregulated, 24-fold (P < 0.005) and 2.6-fold (P < 0.05),respectively. In gastrocnemius, the level of type IIa MHC mRNAdecreased by 51% (P < 0.01) and thelevel of type IIx MHC mRNA increased by 140%(P < 0.05). In plantaris, the levelof type IIa MHC mRNA decreased by 58%(P < 0.005). In conclusion,immobilization changed the MHC mRNA profile in three different types ofskeletal muscle toward faster isoforms. The quantitative results permitreliable evaluation of changes in mRNA levels.