Gene/Protein Disease Symptom Drug Enzyme Compound
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Postural muscles have many type I myofibers, which reacted strongly for acid-stable myosin ATPase and were unreactive for alkali-stable myosin ATPase (Ariano et al., J. Histochem. Cytochem., 21:51-55, 1973; Armstrong et al., Am. J. Anat., 163:87-98, 1982; Smith et al., J. Neurophysiol., 40:503-513, 1977). House shrews (Suncus murinus) keep abducting their limbs in locomotion and hardly lift their trunk off the ground. The limb muscles of Suncus were examined by histochemical methods to determine whether the locomotory and postural behavior is related to the proportion of type I myofibers. The observation of whole cross sections from the triceps surae, flexor digitorum superficialis, quadriceps femoris, and caudally situated muscles in the thigh showed that all myofibers of these muscles were unreactive for acid-stable myosin ATPase and strongly reactive for alkali-stable myosin ATPase: Those were classified as type II myofibers. Type II myofibers showed a weak (type IIB), moderate (type IIAB), or strong (type IIA) reaction for NADH tetrazolium reductase. Part of type IIA myofibers reacted weakly to moderately for menadione-linked glycerol-3-phosphate dehydrogenase (m-GPD), which predominated in the soleus muscle. Type IIAB, type IIB, and the remainder of type IIA myofibers reacted strongly for m-GPD. The limb muscles contained subtypes of type II myofibers but no type I myofibers. In Suncus murinus, type I myofibers specialized for a postural maintenance may not be required because all myofibers function exclusively for propulsion.
Anat Rec 1990 Sep
PMID:Composition of myofiber types in limb muscles of the house shrew (Suncus murinus): lack of type I myofibers. 214 5

The fatigue characteristics and the activities of oxidative and glycolytic enzymes were determined in tetrodotoxin (TTX)-induced disuse muscles and in muscles of animals recovering from TTX-induced disuse (TTX-rec). In addition, the effects of additional daily exercise (grid-climbing and swimming) on the fatigue and metabolic profiles of muscles from TTX-rec and control animals were investigated. The activities of citrate synthase (CS), phosphofructokinase (PFK), and alpha-glycerophosphate dehydrogenase (alpha-GPD) were depressed following 28 days of inactivity produced by the chronic neural application of TTX. The response of these muscles to a pattern of stimulation that has been used to classify fast-twitch motor units according to their fatigability (6) (330 ms, 40 Hz, l/s, 4 min) was not affected to any great extent by inactivity, except for a loss in the ability to summate or maintain forces during each 330-ms burst, as fatigue developed. After 28 days of recovery, the concentration of CS had returned to normal, whereas the concentrations of PFK and alpha-GPD remained depressed. TTX-rec muscles, on the other hand, appeared more resistant to fatigue than control muscles, based on several indices of muscle fatigue. Control and TTX muscles responded similarly to daily training. Swimming but not climbing increased the activity of CS and the fatigue resistance of the muscle. Neither exercise influenced the activity of PFK and alpha-GPD. Although the activity of CS was influenced by the level of neuromuscular usage, the former did not appear to play a dominant role in determining the fatigue resistance of the muscle, emphasizing the need to consider other factors as primary determinants of muscle fatigue.
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PMID:Recovery of muscle from tetrodotoxin-induced disuse and the influence of daily exercise. 2. Muscle enzymes and fatigue characteristics. 297 Sep 77

A comparison of the anatomy, fiber type profiles, and contractile properties of the wrist flexor muscles was undertaken in the cat. Isometric contractile characteristics were measured for each muscle. Three muscle fiber types, FG, FOG, and SO, were differentiated by staining cross sections of each muscle for ATPase, NADH diaphorase, SDH, and alpha-GPD activities. The wrist flexor muscles ranged from less than 1% to 49% SO fiber content; with two of the five heads of the flexor digitorium profundus (FDP) having 1% or less SO fibers (FDP1-1.07%, FDP5-0.81%) and the humeral head of the flexor carpi ulnaris muscle (FCUh) having the greatest content of SO fibers. The mean contraction time (CT) plus one-half relaxation time for an isometric twitch was correlated with the percentage of SO fibers and ranged from 40.5 to 111.8 ms. Except for the FCU (37ms), the CT was less than 25 ms for the wrist flexor muscles. The uniarticular wrist flexor muscles, the flexor carpi radialis (FCR), and the FCU had the highest percentage of SO fibers and were more fatigue-resistant that the multiarticular muscles. Considerable differences exist in muscle structure, fiber type proportions, and contractile properties between the FCR and FCU, which may be related to functional differences between the two sides of the wrist that may exist during the placement of the foot during locomotion.
Anat Rec 1981 Mar
PMID:Morphological organization and contractile properties of the wrist flexor muscles in the cat. 725 81