HISTOCHEMICAL AND MORPHOMETRIC STUDY OF FIBER TYPES IN 10 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-2 M 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 gas trocnemius, cranial tibial, long head of triceps, and superfici al digital flexor muscles; type-2A. fibers were dominant in buccinator muscle samples; and type-2M fibers were dominant in TEM and MAS muscl es. Numbers of type-2C fibers did not exceed 2 to 3% of the myofiber p opulation in any muscle. In cr and LHT muscles, a gradient of fiber ty pe 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) lar ger than that of type-1 and type-2A fibers in biceps femoris, lateral head of gastrocnemius, cranial tibial, long head of triceps, and super ficial 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 so leus type-1 muscle fibers were the largest fibers encountered in any m uscle. In MHT muscle, fiber diameter of type-1 and type-2B fibers vari ed significantly (P < 0.05) in oxidative and glycolytic compartments. Variability coefficients were less than 200 in all muscles. In every m uscle specimen, the number of fibers with internal nuclei was less tha n or equal to 2%.