Myosin heavy chains in skeletal muscles of the common shrew (Sorex araneus): absence of a slow isoform and transitions of fast isoforms with ageing.

Myosin heavy chain (MHC) composition in seven skeletal muscles of the common shrew (Sorex araneus) was analysed by gradient SDS-PAGE and immunoblotting with monoclonal antibodies. Characteristic for the studied muscles (diaphragm, lateral gastrocnemius, medial gastrocnemius, masseter, plantaris, soleus and tibialis anterior) was a total absence of the slow isoform, MHCI; all muscles were exclusively composed of two fast isoforms MHCIId and MHCIIb. In young adults the amount of MHCIId varied between 34% (tibialis anterior) and 97% (masseter). In over-wintered senescent individuals MHCIId was clearly the dominant isoform in all muscles studied; the lowest MHCIId content was measured for tibialis anterior (69%), while in diaphragm, masseter and soleus it was practically the sole isoform (over 96%). Ageing associated isoform transition from MHCIIb to MHCIId occurred in all seven muscles studied (P < 0.05).