Contractile properties of different types of dog muscle fibres.

In this work we studied the functional properties of canine myosin isoforms in skeletal and specialized muscles of the dog such as semimembranosus, vastus lateralis, lungissimus dorsi, diaphragm and thyroarytenoideus. We determined the isometric tension (Po), maximum shortening velocity (Vo) of single fibres and the speed (Vf) of actin filament sliding on myosin extracted from single muscle fibres in an in vitro motility assay (IVMA). Single fibres were identified on the basis of their myosin isoform composition, determined by gel electrophoresis. The results obtained showed the progressive increase of Vo in the order 1/slow<2A<2X<2B thus confirming the identification of the myosin isoforms carried out on the basis of their primary structure. Furthermore, the results indicated a close proportionality between Vo and Vf, thus suggesting that the diversity in Vo can be attributed to the different myosin isoform composition.