Gene/Protein Disease Symptom Drug Enzyme Compound
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Intrafusal muscle fibers of the extraocular muscles (EOMs) of the sheep, cow, and pig were studied histochemically and immunohistochemically. In sheep and cow spindles, three intrafusal fiber types, namely the bag1, bag2, and chain fibers, were identified by a combination of standard histochemical methods and immunohistochemical staining with antibodies selective for slow-tonic (antitonic ALD) and slow twitch (anti-I BA-D5) myosin. The bag1 and bag2 fibers appeared immunologically different on the basis of their differential reactivity with the two antisera. Anti-tonic ALD preferentially stained the bag1 fibers, whereas anti-I BA-D5 labeled the bag2 fibers. Chain fibers did not react with either antisera. In the pig EOM spindles, in general, one bag and some chain intrafusal fibers were identified. The bag fiber was labeled by anti-tonic ALD, but it did not react with the anti-I BA-D5. These findings point to the existence in pig EOM spindles of only one bag fiber antigenically similar to the bag1 fiber of the other species examined.
Anat Rec 1990 Jul
PMID:An immunohistochemical approach to the intrafusal fibers of extraocular muscle spindles in sheep, cow, and pig. 214 87

Transmission of contractile tension from skeletal muscle fibers to connective tissue elements is thought to occur at the muscle-tendon junctions, specialized regions at the extreme ends of the fibers. Previous work has suggested that the structure of this region may be quantitatively modified to match the contractile properties of the fibers. Using scanning electron microscopy, transmission electron microscopy, and stereological analysis, we have analyzed the three-dimensional structure, and have quantitatively compared the muscle-tendon junctions, of slow and fast fibers of the anterior (ALD) and posterior (PLD) latissimus dorsi muscles of the chicken. The ends of ALD and PLD fibers are found to be structurally different in some respects but to be similar with respect to their surface specializations, which are believed to function in the transmission of tension. Quantitative analysis of these specializations indicates that, when referred to similar cross-sectional areas of myofilaments, the fast fibers of the PLD have approximately 40% more surface area devoted to force transmission than do the slow fibers of the ALD. These observations are consistent with the idea that the amount of cell surface specialized for force transmission is related to the functional properties of the muscle fiber.
Anat Rec 1987 Jul
PMID:A stereological comparison of the muscle-tendon junctions of fast and slow fibers in the chicken. 363 40

The sarcolemma, sarcoplasmic reticulum (SR), and T system of the anterior (tonic) and posterior (fast twitch) latissimus dorsi muscles of the chicken have been examined by the freeze-fracture technique, and quantitative data on the P and E fracture faces have been obtained. The fractured plasma membranes reveal (a) profiles of surface caveolae, (b) randomly distributed intramembranous particles ranging in size from 40-100 A in diameter, and (c) orthogonal assemblies composed of groups of 60 A particles in close association, and differences with respect to all three structures are present between the tonic (ALD) and fast twitch (PLD) muscles. In the ALD muscle, the surface caveolae are more uniformly distributed and have smaller openings than in the PLD muscle; the former muscle also has a two-fold higher caveolae density than the latter muscle. The intramembranous particles are more numerous in the ALD than in the PLD muscle in both fracture faces, but the orthogonal assemblies are fewer. The functional significance of these differences in the two fiber types are discussed. The fractured membranes of the SR have intramembranous particles (IMPs) approximately 80 A in diameter, with a two-fold higher packing density in the PLD than in the ALD muscle. This difference is present in both the longitudinal and cisternal components of the SR. In addition, there are collar-like expansions (CLE's) in the SR of the ALD muscle which are particularly poor in intramembranous particles. These particles are considered to represent Ca2+ transport ATP-ase, and the reduced density of IMP's could be a significant factor in the low calcium uptake and and slow relaxation characteristics of the ALD muscle.
Anat Rec 1980 Oct
PMID:A freeze-fracture study of the anterior and posterior latissimus dorsi muscle of the chicken. 721 1

Most of the sounds of human speech are produced by vibration of the vocal folds, yet the biomechanics and control of these vibrations are poorly understood. In this study the muscle within the vocal fold, the thyroarytenoid muscle (TA), was examined for the presence and distribution of slow tonic muscle fibers (STF), a rare muscle fiber type with unique contraction properties. Nine human TAs were frozen and serially sectioned in the frontal plane. The presence and distribution pattern of STF in each TA were examined by immunofluorescence microscopy using the monoclonal antibodies (mAb) ALD-19 and ALD-58 which react with the slow tonic myosin heavy chain (MyHC) isoform. In addition, TA muscle samples from adjacent frozen sections were also examined for slow tonic MyHC isoform by electrophoretic immunoblotting. STF were detected in all nine TAs and the presence of slow tonic MyHC isoform was confirmed in the immunoblots. The STF were distributed predominantly in the medial aspect of the TA, a distinct muscle compartment called the vocalis which is the vibrating part of the vocal fold. STF do not contract with a twitch like most muscle fibers, instead, their contractions are prolonged, stable, precisely controlled, and fatigue resistant. The human voice is characterized by a stable sound with a wide frequency spectrum that can be precisely modulated and the STF may contribute to this ability. At present, the evidence suggests that STF are not presented in the vocal folds of other mammals (including other primates), therefore STF may be a unique human specialization for speech.
Anat Rec 1999 10 01
PMID:Slow tonic muscle fibers in the thyroarytenoid muscles of human vocal folds; a possible specialization for speech. 1048 12