Enzyme‐ and immunohistochemical aspects of skeletal muscle fibers in brown bear (Ursus arctos)

Abstract

To further elucidate the pattern of MHC isoform expression in skeletal muscles of large mammals, in this study the skeletal muscles of brown bear, one of the largest mammalian predators with an extraordinary locomotor capacity, were analyzed. Fiber types in longissimus dorsi, triceps brachii caput longum, and rectus femoris muscles were determined according to the myofibrillar ATPase (mATPase) histochemistry and MHC isoform expression, revealed by a set of antibodies specific to MHC isoforms. The oxidative (SDH) and glycolytic enzyme (alpha-GPDH) capacity of fibers was demonstrated as well. By mATPase histochemistry five fiber types, i.e., I, IIC, IIA, IIAX, IIX were distinguished. Analyzing the MHC isoform expression, we assume that MHC-I, -IIa, and -IIx are expressed in the muscles of adolescent bears. MHC-I isoform was expressed in Type-I fibers and coexpressed with presumably -IIa isoform, in Type-IIC fibers. Surprisingly, two antibodies specific to rat MHC-IIa stained those fast fibers, that were histochemically and immunohistochemically classified as Type IIX. This assumption was additionally confirmed by complete absence of fiber staining with antibody specific to rat MHC-IIb and all fast fiber staining with antibody that according to our experience recognizes MHC-IIa and -IIx of rat. Furthermore, quite high-oxidative capacity of all fast fiber types and their weak glycolytic capacity also imply for MHC-IIa and -IIx isoform expression in fast fibers of bear. However, in adult, full-grown animal, only MHC-I and MHC-IIa isoforms were expressed. The expression of only two fast isoforms in bear, like in many other large mammals (humans, cat, dog, goat, cattle, and horse) obviously meets the weight-bearing and locomotor demands of these mammals.

Distribution Pattern of Muscle Fiber Types in the Perivertebral Musculature of Two Different Sized Species of Mice

“…In the current study, only three fiber types were distinguished out of the continuum of so far identified muscle fiber (sub)types. Type IIX fibers, if occurring in the murine perivertebral musculature were thus conflated with the fibers referred to as IIB because of their highly similar oxidative capacity and pH stability of their myosin ATPase (e.g., Pette et al, 1999;Smerdu et al, 2009). In our study, the fibers were first classified as slow and fast fibers according to the pH stability of their myosin ATPase and then subclassified using their oxidative capacity and associated fatigue resistance.…”

“…Type IIX fibers are histochemically very similar to Type IIB fibers and MHC IIx has been shown to be expressed in fibers histochemically identified as Type IIB, but both types differ in their contractile properties (Pette et al, 1999;Smerdu et al, 2009). In contrast to small mammals, results on larger species have shown that only MHC IIa and IIx were expressed but not MHC IIb (e.g., cat: Talmadge et al, 1996;dog: Snow et al, 1982;Š trbenc et al, 2004;goat: Argü ello et al, 2001;sheep: Maier et al, 1992;human: Smerdu et al, 1994;Ennion et al, 1995;horse: Rivero et al, 1996;Eizema et al, 2003;cattle: Tanabe et al, 1998;brown bear: Smerdu et al, 2009).…”

High oxidative capacity and type IIx fibre content in springbok and fallow deer skeletal muscle suggest fast sprinters with a resistance to fatigue

“…A fourth fibre type (type IIB expressing MHC IIb), fast twitch glycolytic, is primarily abundant in limb muscles of rodents (Pette and Staron, 1993;Delp and Duan, 1996;. Although small quantities of this fibre type were detected in cheetah, llama and pig limb muscles, it seems that this fibre type is reserved for more specialised muscles, such as those in the eye, and is undetectable in horse, cattle, black and blue wildebeest, blesbuck, kudu, lion, caracal and brown bear (Quiroz-Rothe and Rivero, 2001;Toniolo et al, 2005;Smerdu et al, 2009;Hyatt et al, 2010;Kohn et al, 2011b;Kohn et al, 2011a).…”

Black wildebeest skeletal muscle exhibits high oxidative capacity and a high proportion of type IIx fibres

“…humans, horses, lions and black bears) are primarily composed of three fibre types, namely types I, IIa and IIx (Gollnick et al, 1972;Rivero et al, 2007;Smerdu et al, 2009;Kohn et al, 2011). They derive their individual characteristics from the type of myosin heavy chain (MHC) isoform each expresses.…”