Reverse transcriptase-polymerase chain reaction detects induction of cardiac-like α myosin heavy chain mRNA in low frequency stimulated rabbit fast-twitch muscle

Using reverse transcriptase-polymerase chain reaction we quantified in rabbit skeletal muscles expression levels of the highly homologous cardiac α and β myosin heavy chain (αMHC, βMHC) mRNA isoforms. Masseter muscle displayed highest levels of a cardiac-like αMHC mRNA. This isoform was present at 20-fold lower amounts in slow soleus and at 200-fold lower levels in several fast-twitch muscles. Low-frequency stimulation periods exceeding 20 days drastically induced the αMHC mRNA in fast tibialis anterior. The αMHC mRNA was 140-fold elevated after 60 days when βMHC mRNA had increased 50-fold. Our results demonstrate the wide distribution of a cardiac-like αMHC mRNA in skeletal muscle and its marked induction during fast-to-slow transition as induced by low-frequency stimulation.