Histochemical and morphometric study of fiber types in ten skeletal muscles of healthy young adult cats

A histochemical and morphometric study of fiber types in a variety of skeletal muscles of healthy young adult cats was undertaken to provide normative data not available previously. Using a standardized system of nomenclature, fiber types 1, 2A, 2B, and 2C were identified in most cat muscles on the basis of myosin ATPase staining at pH 4.45. Type-2M fibers were present in temporalis (TEM) and masseter (MAS) muscles. Type-1 fibers predominated in medial head of triceps (MHT) and soleus muscles. Type-2B fibers were dominant in biceps femoris, lateral head of gastrocnemius, cranial tibial, long head of triceps, and superficial digital flexor muscles; type-2A fibers were dominant in buccinator muscle samples; and type-2M fibers were dominant in TEM and MAS muscles. Numbers of type-2C fibers did not exceed 2 to 3% of the myofiber population in any muscle. In CT and LHT muscles, a gradient of fiber type distribution was observed, with significant (P < 0.05) increase in numbers of type-1 and type-2A fibers in deeper regions of the muscles. The distribution of fiber types was compartmentalized in MHT and MAS specimens. Diameter of type-2B fibers was significantly (P < 0.05) larger than that of type-1 and type-2A fibers in biceps femoris, lateral head of gastrocnemius, cranial tibial, long head of triceps, and superficial MHT muscles. Diameter of type-2M fibers was significantly (P < 0.05) larger than that of type-1 fibers in TEM and MAS muscles. The soleus type-1 muscle fibers were the largest fibers encountered in any muscle. In MHT muscle, fiber diameter of type-1 and type-2B fibers varied significantly (P < 0.05) in oxidative and glycolytic compartments. Variability coefficients were less than 200 in all muscles. In every muscle specimen, the number of fibers with internal nuclei was less than or equal to 2%.