Reverse transcriptase-polymerase chain reaction detects induction of cardiac-like alpha 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 alpha and beta myosin heavy chain (alpha MHC, beta MHC) mRNA isoforms. Masseter muscle displayed highest levels of a cardiac-like alpha MHC 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 alpha MHC mRNA in fast tibialis anterior. The alpha MHC mRNA was 140-fold elevated after 60 days when beta MHC mRNA had increased 50-fold. Our results demonstrate the wide distribution of a cardiac-like alpha MHC mRNA in skeletal muscle and its marked induction during fast-to-slow transition as induced by low-frequency stimulation.