The histochemical classification of muscle fibers

Abstract

Histochemical studies have shown that red and white mammalian muscles are not homogeneous and that, regardless of the enzyme reaction employed, most white muscles possess three types of fibers and most red muscles possess one or two fiber types. Inasmuch as different nomenclatures for the three basic fiber types have been proposed (according to the histochemical technique used), we have attempted to reconcile these differences and achieve a unified nomenclature. Using serial sections of rat and cat muscle, the three fiber types ( A, B, and C) revealed by the succinic dehydrogenase reaction were compared with the three types (α, β, and αβ) revealed by the actomyosin adenosine triphosphatase (ATPase) reaction. The B fibers of both rat and cat are β (base-labile ATPase). However, the cat's A fibers are α (acid-labile ATPase) and the rat's are αβ (hybrid, or intermediate in pH labilty). Conversely, the cat's C fibers are αβ and the rat's are α. Thus, these classifications cannot be reconciled between species. Inasmuch as fiber typing is used extensively in clinical investigations of human diseases and in biochemical and physiological studies on mammals, it is important that the species, muscles, and enzymes studied be considered in interpreting results and that oversimplification of the three fiber types into a dual classification be avoided.