Fiber Type Characteristics Research Articles

Regulation of concentrations of glycolytic enzymes and creatine-phosphate kinase in “fast-twitch” and “slow-twitch” skeletal muscles of the chicken

The distinctive contractile and metabolic characteristics of different skeletal muscle fiber types are associated with different protein populations in these cells. In the present work, we investigate the regulation of concentrations of three glycolytic enzymes (aldolase, enolase, glyceraldehyde-3-phosphate dehydrogenase) and creatine-phosphate kinase in “fast-twitch” (breast) and “slow-twitch” (lateral adductor) muscles of the chicken. Results of short-term amino acid incorporation experiments conducted both in vivo and with muscle explants in vitro showed that these enzymes turnover at different rates and that aldolase turns over 2 to 3 times faster than the other three enzymes. However, these differences in turnover rates were difficult to detect in long-term double-isotope incorporation experiments, presumably because extensive reutilization of labeled amino acids occurred during these long-term experiments. Mature muscle fibers synthesize these four cytosolic enzymes at very high rates. For example, 11 to 14% of the total labeled leucine incorporated into protein by breast muscle fibers was found in the enzyme aldolase. Results of short-term amino acid incorporation experiments also showed that the relative rates of synthesis of the three glycolytic enzymes were about fourfold higher in mature “fast-twitch” muscle fibers than in mature “slow-twitch” ones while the relative rates of synthesis of creatine-phosphate kinase were similar in the two fiber types. The relative rates of synthesis of these four enzymes and cytosolic proteins in general were found to be very similar in immature muscles of both types. More profound changes in the relative rates of synthesis of major cytosolic proteins, including the glycolytic enzymes, occurred during postembryonic maturation of fast-twitch fibers than occurred during maturation of slow-twitch fibers. Our work demonstrates that (1) the synthesis of creatine-phosphate is independently regulated with respect to the synthesis of the glycolytic enzymes in muscle fibers; and (2) the approximate fourfold higher steady-state concentrations of glycolytic enzymes in fast-twitch muscle fibers as compared with slow-twitch fibers are determined predominantly by regulatory mechanisms operating at the level of protein synthesis rather than protein degradation. Our demonstration that more profound changes in the relative rates of synthesis of major cytosolic proteins occur during maturation of fast-twitch fibers as compared with slow-twitch fibers is discussed in terms of the mode(s) of fiber-type differentiation proposed by others.

A Comparative Study of Fibre Type Characteristics and Terminal Innervation in Head and Axial Muscle of the Carp (Cyprinus Carpio L.) : a Histochemical and Electron-Microscopical Study

In the axial muscles and in a head muscle (m. hyohyoideus) of the carp two slow (red) and three fast (white, large pink and small pink) fibre types were distinguished on the basis of reactions with antisera, the pH stability of ATPase and succinatedehydrogenase activity. The gradual transition in histochemical characteristics between small and large pink fibres and the occurrence of stadia intermediate between myosatellite cells and small muscle fibres suggest that the small fibres are a growth stage. Density of nerve terminations was highest on red fibres, which is in accordance with physiological data. White axial muscle fibres had the lowest termination density. Pink fibres of the m. hyohyoideus had significantly more terminations per millimeter fibre length than pink fibres of the axial muscles. Vesicle densities per endplate profile and per synaptic contact were similar in all types. Endplates on white fibres had narrower synaptic clefts and vesicles that were slightly more elliptical than those on other types. The presence of swollen mitochondria in endplates on red head muscle fibres may reflect the continuous rhytmic activity of these fibres. The absence of subjunctional folds on slow as well as on fast fibres suggest that endplates on both types release but little acetylcholine per stimulus.

Influence of Breed Type, Sex, Feeding Systems, and Muscle Bundle Size on Bovine Fiber Type Characteristics

ABSTRACTFiber type numbers, percentages and diameter were evaluated in two experiments. Experiment 1 contained Angus and Angus cross cattle consisting of 48 steers and 48 heifers with half of each sex fed grain while the other half were fed grain‐on‐grass. Experiment 2 contained 12 Angus and 12 Simmental cross steers slaughtered at four feeding system endpoints. Steers tended to have a higher percentage of βR and a lower percentage of αW fibers than heifers; The percentage of βR fibers increased in the longissimus and semi‐membranosus, while the αW fibers decreased. The percentage of αW fibers in the biceps femoris and semitendinosus muscles increased over the longer feeding period while the percentage βR tended to decrease. Breed appeared to have little effect on histological traits in the longissimus and semimembranosus muscles. Bundle size had no effect on fiber type diameter; however, in all muscles there was a tendency for the βR population to increase as bundle size increased.

Histochemical Characteristics of Muscle Fiber Types in the Posterior Cricoarytenoid Muscle

The muscle fiber type composition of the human posterior cricoarytenoid muscle (PCA) was examined using a large battery of histochemical techniques. Staining for myosin ATPase (pH 9.9) indicated that the muscles were composed of 52% ± 11.8 SD type 1 (slowly contracting) fibers and 48% ± 11.9 SD type 2 (rapidly contracting) fibers. In order to obtain information concerning the probable fatigue resistance of the type 2 fibers, serial sections were processed to determine the relative extent of ATPase inactivation at various pH levels in the acid range and to obtain data concerning the relative activities of oxidative and glycolytic enzymes and their substrates. The great majority of the type 2 fibers were of the 2A (fatigue resistant) fiber type. This indication of a capacity for prolonged activity was substantiated by the presence of high activities of succinic dehydrogenase, a mitochondrial enzyme which is involved in oxidative metabolism. Type 2C fibers (generally considered to be an undifferentiated fiber type) were also present but relatively rare. The overall enzyme profiles of many of the muscle fibers in the human PCA differed from those typical of fibers having the same alkaline ATPase and acid ATPase characteristics in most other mammalian muscles. Since muscle fiber biochemistry reflects the activity pattern of the motor unit, these unusual enzyme profiles may be the result of activity patterns that are associated with the inspiratory cycle and/or patterns of activity that are relatively specific to the PCA. Four of the ten muscles examined had unequivocal evidence of muscle fiber type grouping, a manifestation of partial denervation followed by reinnervation. This is interesting since most of the cases were in the fifth decade. Muscle fiber type grouping has been shown to occur selectively in certain other human muscles and to increase with age, eventually resulting in muscle atrophy. This suggests the possibility that the human PCA is for some reason selectively vulnerable to partial denervation and indicates the need for more extensive data concerning the relationship of muscle fiber type grouping in the PCA and other laryngeal muscles to age.

A morphometric analysis of human muscle fibers with relation to fiber types and adaptations to exercise

Muscle biopsies were obtained from the vastus lateralis of 14 male subjects: 3 long distance runners, 2 world class power lifters and 9 active, although not highly trained, individuals used as controls. The fibers were investigated by electron microscopy and the mitochondrial volume percent, lipid volume percent and Z-line width were analyzed morphometrically. With the combined data a direct correlation was found between mitochondrial volume percent and lipid volume percent, lipid volume percent and Z-line width and mitochondrial volume percent and Z-line width. The muscle fibers were classified as slow-twitch oxidative (SO), fast-twitch-oxidative-glycolytic (FOG) and fast-twitch-glycolytic (FG) based on relationships found in the data and well established properties of muscle fiber types. Although no distinct patterns emerged, a good approximation of fiber type characteristics was obtained, and values for volume percent of central mitochondria, volume percent lipid and Z-line width are reported. The fibers classified as SO were characterized by having wide Z-lines, a high mitochondrial volume percent and high lipid volume percent. The fast-twitch fibers (fibers with narrow Z-lines) were separated into 2 groups, those with high mitochondrial volume percent (FOG) and those with low mitochondrial volume percent (FG). No distinction could be made between the fast-twitch subgroups with regard to Z-line width. The fibers from distance runners differed from those from controls by exhibiting a greater capacity for aerobic activity as evidenced by the increased volume percent of mitochondria and lipid in both slow- and fast-twitch fibers. The high strength, anaerobic activity of the world class power lifters was reflected by the low mitochondrial volume percent of many fast-twitch fibers (FG) and the decreased lipid stores in all fibers.

Muscle histochemistry and muscle function.

A short review of the histochemical characteristics of the different muscle fibre types is given. The possibility of changing contraction time, strength, and endurance by physical training is discussed.

Compensatory adaptations of skeletal muscle fiber types to a long-term functional overload

We investigated selected histochemical and histometrical characteristics of the heterogeneous fiber types of rat skeletal muscle following long-term compensatory muscle growth. Sixty days following surgical removal of the synergistic gastrocnemius muscle, the compensated ipsilateral plantaris and soleus muscles and the corresponding control muscles from the contralateral leg were excised and stained histochemically for myofibrillar ATPase and DPNH-diaphorase activities. The number of fibers per cross-section was determined by a direct count from transverse sections taken from the midportion of the muscles. Fiber area was determined by direct planimetry. The plantaris and soleus muscles hypertrophied 103% and 45%, respectively, within 60 days. Compensatory hypertrophy of the plantaris muscle was accompanied by a significant but disproportionate increase in the cross-sectional areas of the three muscle fiber types. There was an approximate 4-fold increase in the number of slow-twitch-oxidative (SO) fibers observed per transverse section. The hypertrophied plantaris muscle exhibited a significantly greater number of fibers per cross-section (29%) than the respective control muscle. The compensated soleus muscle consisted of nearly 100% SO fibers compared to 83% for the control soleus muscle.

Ultrastructural differentiation of skeletal muscle fibers and their diversity

The ultrastructural changes occurring during postnatal differentiation of the plantaris and soleus muscles were investigated in kittens. Neonatal muscle fibers vary somewhat according to maturity as well as Z-line width and relative volume of sarcoplasmic reticulum (variables most characteristic of a given fiber type). A clear-cut classification of fiber type, however, evolves during the postnatal period—intermediate fibers differentiate first while white fibers differentiate last. Functional overload, induced by ablation of the synergistic gastrocnemius, does not significantly alter the prime characteristics of fiber type (e.g., Z-line width) but rather exerts an influence on accelerating myofibril proliferation, which occurs both by splitting and by de novo formation. White fibers are modified by enhancing their mitochondrial population. These results support previous histochemical studies and affirm the contention that certain fiber characteristics (structural and enzymatic) are determined genetically and expressed through neural factors, while other characteristics are subject to modification by alterations in function.

Intrafusal fibre types in rat limb muscle spindles: morphological and histochemical characteristics.

Morphological, histochemical and ultrastructural characteristics of intrafusal fibre types were studied in rat muscle spindles. The existence of three intrafusal fibre types, namely the typical bag, the intermediate bag and the chain fibres was confirmed. Intrafusal fibres differ in diameter, length and number of nuclei in the equatorial zone. Histochemically, typical bag fibres exhibit both alkali- and acid-stable ATPase activity and low SDH activity. Intermediate bag fibres possess low alkali-stable ATPase activity; after acid-preincubation, however, they have low activity only in the juxtaequatorial region, whereas in the polar zones they exhibit high acid-stable ATPase activity. The SDH activity varies from moderate to high. The chain fibres exhibit high alkali-stable and low acid-stable ATPase and high SDH activity in the extensor digitorum longus muscle, whereas in the soleus muscle the acid-stable ATPase activity varies from a low one to a high one, either among individual chain fibres in one spindle, and/or repeatedly along the fibre length. Since there are regional differences in morphological characteristics and in staining properties of intrafusal fibres, a reliable identification of intrafusal fibre types can only be achieved by an analysis of serial sections.

Metabolic Characteristics of Fibre Types in Human Skeletal Muscle

Muscle biopsy samples were obtained from healthy subjects in order to evaluate quantitative differences in single fibres of substrate (glycogen and triglyceride) and ion concentrations (Na+ and K+) as well as enzyme activity levels (succinate-dehydrogenase, SDH; phosphofructokinase, PFK; 3-hydroxyacyl-CoA-dehydrogenase, HAD; myosin ATPase) between human skeletal muscle fibre types. After freeze drying of the muscle specimen fragments of single fibres were dissected out and stained for myofibrillar-ATPase with preincubations at pH's of 10.3, 4.6, 4.35. Type I ("red") and II A,B, and C ("white") fibres could then be identified. Glycogen content was the same in different fibres, whereas triglyceride content was highest in Type I fibres (2-3 X Type II). No significant differences were observed for Na+ and K+ between fibre types. The activity for the enzymes studied were quite different in the fibre types (SDH and HAD, Type I is approximately 1.5 X Type II; PFK Type I is approximately 0.5 X Type II, Myosin ATPase Type I is approxiamtely 0.4 X Type II). The subgroups of Type II fibres were distinguished by differences in both SDH and PFK activities (SDH, Type II C is greater than A is greater than B; PFK, Type II B is greater than A is approximately C). It is concluded that contractile and metabolic characteristics of human skeletal fibres are very similar to many other species. One difference, however, appears to be than no Type II fibres have an oxidative potential higher than Type I fibres.

Electron microscopical investigation of asbestos fibers.

Examination of asbestos fibers by electron microscopical techniques enables the observer to distinguish among the fiber types by morphological and structural characteristics. Chrysotile asbestos fibers are composed of bundles of fibrils. Fibers are often curvilinear with splayed ends. Individual fibrils consist of a central capillary defined by an electron dense crystalline wall. With increasing time of electron bombardment, the capillary wall decreases in thickness, deforms, and is encapsulated in an electron translucent material. The change in electron opacity is considered to be a product of structural disruption brought about by dehydroxylation due to electron radiation. A well recognized sequential deformation pattern may be used for identification purposes.Amphibole fibers tend to be straight, splintery, and electron-opaque, although curved fibers are occasionally observed. Diffraction contrast figures are visible as dark bands moving parallel and at right angles to the fiber axis. Crocidolite forms the shortest and thinnest fibers, followed in size by amosite and anthophyllite. Size distribution characteristics of the amphibole fiber types are different. The selected area electron diffraction pattern for chrysotile is unique. Reflections range in forms from streaked to arcuate. Reflection intensity and shape are related to the degree of openness of the fiber bundle and the extent of physical degradation of the fiber. The amphibole asbestos fibers possess diffraction patterns having similar characteristics prohibiting individual identification. Microchemical analysis is required for identification in such cases.A discussion of the industrial hygiene threshold limit values for ampliphibole asbestos fibers is presented. The discussion is based on their differing size distribution characteristics.

Characteristics of skeletal muscle fiber types in the miniature pig and the effect of training.

The fiber types present in miniature pig skeletal muscle were determined with enzyme histochemical techniques. Three distinct fiber types were found: a fast white fiber, a fast intermediate fiber, and a slow red fiber. The fiber types found in miniature pig (large mammal) skeletal muscle were different from those in rat (rodent) skeletal muscle where the fiber types are classified as fast white, slow intermediate, and fast red. The fiber type distribution in miniature pig skeletal muscle was not altered by either an endurance or sprint running program, despite physiologically measurable training effects. It is concluded that enzyme histochemistry is a good qualitative tool for assessing the fiber types present in a muscle but lacks the sensitivity to measure or quantitate changes due to training.

Behavior and histochemistry of functionally isolated cat ankle extensors

A division of labor between cat ankle extensors has been previously proposed. It was suggested that gastrocnemius has the speed and power of contraction for phasic movements whereas soleus is suited for sustained activity and full extension. A more recent study showed that plantaris in the cat provides a substantial contribution to locomotor activities when the other two ankle extensors are denervated. We extended chronic behavioral observations of isolated muscles to all three ankle extensors and also examined fiber type characteristics. Soon after surgery, when plastic changes in muscles would be minimal, cats with the gastrocnemius isolated performed normally in almost all postural and locomotor tasks. Cats with either the soleus or plantaris isolated failed to extend the ankle fully after surgery, but they could run and jump adequately. The relatively good locomotor performance of soleus points to the hitherto unrecognized versatility of its type I fibers. Long term effects of isolation included some gradual improvement in performance over six weeks and increased numbers of type I fibers in the plantaris muscle. In contrast, no fiber conversion was observed in the isolated gastrocnemius, which had performed so well after surgery. We conclude that while in normal intact cats specialized roles may exist for these muscles, their intrinsic versatility permits them a broader range of actions than previously has been assumed.

Effect of neonatal neurectomy on differentiation of fiber types in rat skeletal muscle

The differentiation of fiber types in normal and denervated muscles [gastrocnemius, extensor digitorum longus (EDL) and soleus] of the rat was compared by histochemical and electron microscopic techniques. By myosin ATPase test with acid (pH 4.35) and alkali (pH 10.4) preincubations the muscle fibers of the newborn rat reacted equally strongly and did not show selective staining characteristic of type I and type II fibers. By electron microscopy also there was no evidence of fiber type differentiation; the thickness of Z bands and amounts of sarcoplasmic reticulum and mitochondria appeared to be comparable in all fibers. Fiber types were well differentiated in control muscles at 2–3 weeks after birth, but not in the denervated muscles. In the latter ATPase test with acid preincubation showed fibers with weak and strong staining but there was no reciprocal relationship with the staining after alkali preincubation. By electron microscopy there was some difference in the amount of sarcoplasmic reticulum in EDL and soleus fibers but not in respect to Z bands and mitochondria. It was concluded that differentiation of typical fiber type characteristics did not occur following neonatal denervation.

Body composition, aerobic capacity, and density of muscle capillaries in young and old men.

Body composition, aerobic capacity, and density of muscle capillaries in young and old men.