Changes in skeletal muscle myosin heavy chain isoform content during congestive heart failure.

Recent investigations have suggested that changes in contractile protein expression contribute to reductions in skeletal muscle function during congestive heart failure (CHF). Myosin heavy chain (MHC), a major contractile protein, has been shown to undergo alterations in protein isoform expression during CHF. The purpose of this investigation was twofold: (1) to determine whether muscles of the same functional group undergo similar changes in MHC expression, and (2) determine whether the magnitude of alterations in MHC is related to the severity of CHF. Using the rat coronary ligation model, mild and severe forms of CHF were produced and muscles of the plantar flexor group were analyzed. Whole-muscle MHC isoform proportions were not altered in the soleus and white gastrocnemius muscle, however significant increases in the percentage of fast MHC isoforms (7-9% increases in MHC IIx and IIb expression) were found in the red gastrocnemius muscle. In addition, there were significant proportional increases (8%) in MHC type IIb at the expense of MHC type IIx in the plantaris muscle. Many of the changes in the proportions of MHC isoforms were significantly correlated with indices of CHF severity. This indicates that changes in skeletal muscle MHC isoform expression are related to the severity of CHF and suggests that some peripheral skeletal muscles are more susceptible to shifts in MHC expression due to CHF. These changes in MHC isoform expression may contribute to alterations in the physiological performance of skeletal muscle and exercise capacity during CHF.