MYOSIN HEAVY-CHAIN MESSENGER-RNA TRANSFORM TO FASTER ISOFORMS IN IMMOBILIZED SKELETAL-MUSCLE - A QUANTITATIVE PCR STUDY

A quantitative polymerase chain reaction (PCR) method was used to meas ure the quantities of type I, IIa, IIx, and IIb myosin heavy chain (MH C) mRNA in total RNA preparations of the soleus, gastrocnemius, and pl antaris muscles of normal and hindlimb-immobilized rats. Type IIx and even type IIb MHC mRNA were demonstrated at extremely low levels in no rmal soleus, 2.1 +/- 0.4 X 10(5) and 5.0 +/- 0.2 X 10(5) molecules of mRNA per microgram total RNA, respectively. Immobilization for 1 wk si gnificantly altered the gene expression of MHC isoforms. In soleus, bo th type IIx and IIb MHC genes became significantly upregulated, 24-fol d (P < 0.005) and 2.6-fold (P < 0.05), respectively. In gastrocnemius, the level of type IIa MHC mRNA decreased by 51% (P < 0.01) and the le vel of type IIx MHC mRNA increased by 140% (P < 0.05). In plantaris, t he level of type IIa MHC mRNA decreased by 58% (P < 0.005). In conclus ion, immobilization changed the MHC mRNA profile in three different ty pes of skeletal muscle toward faster isoforms. The quantitative result s permit reliable evaluation of changes in mRNA levels.