Spatial distribution of myosin heavy chain isoforms and lactate dehydrogenase M4 in the limb musculature of two crossbred lambs.

Sixteen different skeletal muscle samples were distributed in the cross-section of eight hip and thigh muscles. Contractile characteristics were assessed by measuring myosin heavy chain (MHCI, MHCIIa, MHCIIb) composition by electrophoresis. Glycolytic capacity was estimated by immunochemical quantitation of the LDH-M4. Histochemistry was used as a reference. The MHC isoform composition of most of the muscles in this study was heterogeneous. When an intramuscular transversal regionality was observed (semitendinosus, vastus lateralis, vastus medialis and rectus femoris muscles), MHCI percentage increased toward deeper layers, while MHCIIb and LDH-M4 decreased. The pattern of MHCIIa isoform distribution was less evident. Within semimembranosus and gluteus medius muscles, proportions of MHC isoforms were constant. Gradients of variation of MHCI and MHCIIb isoforms across rectus femoris and vastus medialis muscles were sharper than those of semitendinosus and vastus lateralis muscles. For the vastus lateralis muscle, these gradients may also be modified according to the breed. Breed effect was mainly shown by MHCIIb and MHCI isoforms and was not observed at all the sampling points of the muscles. These observations show that breed effect on muscle contractile and metabolic characteristics is not uniformly expressed throughout the muscle. Results of a comparison may differ according to the muscle and sampling location.