COMPARISON OF MUSCLE-CELL FIBER TYPES AND OXIDATIVE CAPACITY IN GRACILIS, RECTUS FEMORIS, AND TRICEPS BRACHII MUSCLES IN THE FERRET (MUSTELA-PUTORIUS-FURO) AND THE DOMESTIC DOG (CANIS-FAMILIARIS)

Muscle cell fiber types in gracilis, rectus femoris, and long head of triceps brachii muscles of ferrets and dogs were identified on serial sections stained for myosin ATPase after preincubation at pH values of 9.8, 4.6, and 4.3 and for NADH-tetrazolium reductase (NADH-TR) activi ty. Although fiber types I and II were identified, the ATPase stain di d not demonstrate classic type IIA/IIB fiber differences in either spe cies. However, two type II fiber subtypes could be distinguished in th e ferret because they differed slightly in staining intensity with ATP ase at pH 4.3 and markedly with NADH-TR. One ferret type II fiber (des ignated II dark or IID) was smaller, slightly darker on ATPase, more o xidative on NADH-TR, and comprised more muscle volume than the other t ype II fiber (designated II light IIL). The IID fibers of ferret may r epresent the IID/X fibers of other authors. Both ferret type II fiber subtypes stained darker at pH 4.3 than canine II fibers. The NADH-TR s taining indicated high oxidative activity in canine and ferret type I fibers. In contrast, type 11 fibers in the dog and IIL fibers in the f erret were moderately oxidative. Canine type IIC fibers were intermedi ate between type I and type II, whereas in the ferret, type IIC fibers were highly oxidative, as were type IID fibers. Ferret muscles are mo re oxidative than canine muscles according to NADH-TR staining. Also, ferret muscles possess 40-100% higher citrate synthase activity as com pared to canine muscles. (C) 1993 Wiley-Liss, Inc.