Limb myosin heavy chain isoproteins and muscle fiber types in the adult goat (Capra hircus)

The primary focus of this study was the accurate classification of limb ske letal muscle fiber types in adult goats (Capra hircus) according to the myo sin heavy chain (MHC) isoform they express. Combined methodologies of gel e lectrophoresis, immunoblotting, immunohistochemistry, myofibrillar ATPase ( mATPase), and quantitative metabolic enzyme histochemistry of M. semitendin osus samples were developed. Three MHCs were identified and tentatively des ignated as types I, IIA, and IIX. Five fiber types were defined immunohisto chemically according to their MHC content: I, I + IIA, IIA, IIAX, and IIX. The hybrid fast-twitch fibers (IIAX) totaled 21% of the fiber population an alyzed. The three major pure fibers (I, IIA, and IIX) could be objectively separated upon the basis of their mATPase activities after acid and alkalin e preincubations. The prominent number of hybrid fibers, however, could not be delineated with these mATPase methods. Metabolic and size properties of muscle fibers varied according to their MHC content, but overlapped the fu ll range of muscle fiber phenotypes. These integrated data demonstrate that type II skeletal muscle fibers of small ruminants have been misclassified in previous studies. The immunohistochemical approach developed in the pres ent study offers new prospects for muscle fiber typing in caprine experimen tal studies and meat production technologies. Anat Rec 264:284-293, 2001. ( C) 2001 Wiley-Liss, Inc.