2b Fibers Research Articles

Skeletal muscle fiber size in untrained and endurance-trained horses

Summary The mean area and minimal diameter of 3 histochemically determined myofiber types (1, 2A, and 2B; myosin ATPase in acid buffer) were calculated in middle gluteal muscle biopsy specimens from 62 stallions, 47 Andalusians and 15 Arabians, ranging in age from 6 to 12 years. Fourteen Andalusians and 7 Arabians were untrained, and the remainder were actively endurance-trained. The 6-month training schedules involved walking, slow trotting, and cantering. Fourteen Andalusians were moder-ately endurance-trained, whereas the other 19 Andalusians and 8 Arabians were strongly endurance-trained. Significant differences were not recorded between untrained and endurance-trained Arabians with respect to the area (type 1, 3,194 ± 869 μm2 and 3,150 ± 370 μm2; type 2A, 3,819 ± 890 μm2 and 3,380 ± 356 μm2; and type 2B, 4,872 ± 962 μm2 and 4,417 ± 646 μm2) or minimal diameter (type 1, 52.2 ± 7.4 μm and 52.8 ±3.1 μm; type 2A, 58.1 ± 6.7 μm and 55.0 ± 2.8 μm; and type 2B, 65.3 ± 6.4μm and 63.4 ± 4.3 μm) of the 3 fiber types, nor between untrained and endurance-trained Andalusians with respect to the area (untrained, 3,990 ± 690 μm2; moderately endurance-trained, 3,882 ± 347 μm2; and strongly endurance-trained, 3,758 ± 510 μm2) and minimal diameter (untrained, 58.1 ± 4.7 μm; moderately endurance-trained, 59.7 ± 2.7 μm; and strongly endurance-trained, 58.7 ± 4.5 μm) of 2A fibers. Moderately endurance-trained Andalusians had larger 2B fibers (area 18.6%; minimal diameter 14.3%) than untrained Andalusians, and the minimal diameter of type-1 and type-2B fibers was greater in strongly endurance-trained Andalusians than in untrained Andalusians (9.5% for type 1; 10.0% for type 2B). These results suggest minimal effects of endurance training on the myofiber size of adult Andalusians and Arabians, but a tendency toward increased type-1 and -2B fiber size was found for Andalusians.

Arrangement of fiber types within fascicles of human vastus lateralis muscle

A total of 106 fascicles at 6 predetermined areas of the vastus lateralis muscle from 9 healthy men, aged 18 to 40 years, were analyzed. Fibers in a fascicle were divided into layers according to their relation to the perimysium. In each layer the proportions of type 1 and 2, subdivided into 2a, 2b, and 2c fibers were determined and normalized by the fiber type proportion in the whole fascicle. A consistent arrangement of fiber types within the fascicles was obtained, regardless of subject, sampling site, fiber type proportion, and fascicle size. A high proportion of 2b fibers on the border, a prevalence of type 1 fibers in the layer beneath, and a rather uniform distribution of 2a fibers in all layers are the main characteristics of the distribution of fibers in a fascicle. Developmental processes in fiber type differentiation most probably constitute the basis for fiber type arrangement, which can further be influenced by local factors.

A histometric analysis of skeletal myofibers following 90 min of tourniquet ischemia and reperfusion

Routine tourniquet use causes sublethal hypoxic cellular injury and results in edema formation. Using a histochemical morphometric technique, edema caused by 90 min of tourniquet-induced ischemia and 3 hr of reperfusion is measured in the different muscle fibers of a primate model. The degree of cellular swelling is shown to be related to the fiber's metabolic dependence upon oxygen. After reperfusion, predominantly oxidative type 1 fibers show a 29% increase in diameter, P < 0.0005, type 2a fibers which are both oxidative and glycolytic increase by 7%, P < 0.005, and the glycolytic type 2b fibers increase by 5%, P < 0.01. A 48% increase in interfiber distance occurs with reperfusion, P < 0.01. By quantifying the different fibers' responses to ischemic injury, this method may be of use in investigating the pathophysiology and prevention of reperfusion injury and the post-tourniquet syndrome.

Muscle Pathology in Polymyalgia Rheumatica: Histochemical and Immunohistochemical Study.

Immunohistochemical studies were performed on muscle biopsy specimens of polymyalgia rheumatica (PMR) to evaluate the extent of muscle and peripheral nerve involvement. The routine histochemistry revealed a mild variation of fiber size, type 2 fiber atrophy and type 2A or 2B fiber deficiency. In 63% of the PMR cases small angular fibers, pyknotic nuclear clumps or target-targetoid fibers were observed, suggesting neurogenic changes, although abnormalities were mild in degree. In immunocytochemical studies, neither major histocompatibility complex (MHC) class 1 nor class 2 products were expressed on the muscle surface membrane of PMR. But regarding intramuscular vessels, MHC class 2 products were distinctly visualized. On serial sections, combined deposits of IgG and Clq in perimysial arteries were seen in 38% of PMR. These results suggest that arteries of small caliber might be involved in immunopathological processes, causing muscle and peripheral nerve damage.

Skeletal muscle in the diabetic mouse: histochemical and morphometric analysis.

Despite the extensive literature concerning the neuropathy associated with diabetes, only limited information describes changes in the associated muscle. The objective of this study was to evaluate the histochemical and morphometric characteristics of diabetic muscle in the C57BL/KsJ db-m strain of mouse. The histochemical analysis of myofiber type for the diabetic mouse revealed that the extensor digitorum longus muscle consisted of 53.1% type 2a, 46.0% type 2b, and 0.9% type 1 myofibers, a significant shift from the percentages found in the nondiabetic litter mates (44.4% type 2a, 55.6% type 2b, no type 1). Computer-assisted morphometric analysis of myofiber size by fiber type indicated a significant difference in myofiber size for the type 2b fibers in muscles from diabetic mice. Similarly, there was a shift in the fiber size distribution to include a greater number of small type 2b myofibers when compared to controls. Skeletal muscle from diabetic mice exhibited a significant change in the percentage of fiber types, with an increase in the number of type 2a fibers, a fiber type grouping that implies possible denervation and reinnervation, and a decrease in myofiber size. These findings may explain why some diabetic patients complain of muscle weakness.

Three myosin heavy chain isoforms in type 2 skeletal muscle fibres

Mammalian skeletal muscles consist of three main fibre types, type 1,2A and 2B fibres, with different myosin heavy chain (MHC) composition. We have now identified another fibre type, called type 2X fibre, characterized by a specific MHC isoform. Type 2X fibres, which are widely distributed in rat skeletal muscles, can be distinguished from 2A and 2B fibres by histochemical ATPase activity and by their unique staining pattern with seven anti-MHC monoclonal antibodies. The existence of the 2X-MHC isoform was confirmed by immunoblotting analysis using muscles containing 2X fibres as a major component, such as the normal and hyperthyroid diaphragm, and the soleus muscle after high frequency chronic stimulation. 2X-MHC contains one determinant common to 2B-MHC and another common to all type 2-MHCs, but lacks epitopes specific for 2A- and 2B-MHCs, as well as an epitope present on all other MHCs. By SDS-polyacrylamide gel electrophoresis 2X-MHC shows a lower mobility compared to 2B-MHC and appears to comigrate with 2A-MHC. Muscles containing predominantly 2X-MHC display a velocity of shortening intermediate between that of slow muscles and that of fast muscles composed predominantly of 2B fibres.

Fiber type differentiation and myosin expression in regenerating rat muscles.

The relation between fiber type differentiation and the expression of slow and fast myosin isoforms was examined in regenerating rat muscles after injection of a myotoxic agent, bupivacaine. The histochemical myosin ATPase reaction for fiber typing demonstrated that immature type 2C fibers differentiated into type 1, 2A and 2B fibers. Slow and fast myosin isoforms were demonstrated immunohistochemically using antibodies raised against myosins extracted from the slow-twitch soleus and fast-twitch tensor fasciae latae muscles of mature guinea pigs (anti-SOL, anti-TFL). The results showed that immature type 2C fibers destined to differentiate into type 1 fibers first reacted with anti-TFL only, and later reacted with both anti-TFL and anti-SOL, whereas those destined to differentiate into type 2A and 2B fibers reacted with anti-TFL only throughout regeneration. The significance of the myosin isoforms that react with anti-TFL in immature type 2C fibers was discussed.

Cross reactive identification of types 1 and 2C fibers in human skeletal muscles with monoclonal anti-neurofilament (200 kd) antibody.

Types 1 and 2C fibers in human skeletal muscle were cross-reactively identified with monoclonal anti-bovine neurofilament (200 kd) antibody. Thirty seven biopsy samples including sixteen vastus lateralis muscles, twelve lumbar paravertebral muscles, six gluteus medius muscles, two flexor carpi ulnaris muscles, and one flexor pollicis longus muscle, were examined. Serial transverse sections were stained histochemically with myofibrillar ATPase (pH 10.4, 4.6, 4.3) and DPNH-tetrazolium reductase reactions, and immunochemically using the avidin-biotin-peroxidase complex with the primary antibodies of monoclonal anti-bovine neurofilament (200 kd, 160 kd, 70 kd) antibodies and anti-bovine glial filament acidic protein antibody. The immunochemical reaction with anti-NF (200 kd) antibody could distinguish two kinds of fibers; positive and negative in all of the specimens. No fiber was recognized with other antibodies. Myosin ATPase reactions in serial sections proved that the positively stained fibers with anti-NF (200 kd) antibody were types 1 and 2C fibers and negative fibers types 2A and 2B fibers. At present, it is not known what substance is responsible for the cross-reaction with the monoclonal anti-NF (200 kd) antibody in types 1 and 2C fibers, but this unique antibody would be valuable in two aspects: one concerns the problem of the evolution of fiber types, and the other the utility as another supplemental method to conventional myosin ATPase scheme.

Type 2B muscle fibre deficiency in myotonia and paramyotonia congenita: A genetically determined histochemical fibre type pattern?

The histochemical ATPase fibre type pattern was examined in muscle biopsy samples obtained from patients with recessive myotonia, paramyotonia and from one patient with dominant myotonia. Absence (⩽5%) of 2B fibres was a genuine finding in the minority of the cases. In additional cases of recessive myotonia, a deficiency (⩽15%) of 2B fibres was observed. Absence or deficiency of 2B fibres was not related to the minor myopathic alterations or to (para-)myotonic activity. It is hypothesised that absence of 2B fibres is a dominant or a recessive autosomal trait, and deficiency of 2B fibres is a recessive trait. Reported findings and our own observations suggest the possibility of a genetic combination of myotonia and absence/deficiency of 2B fibres. Implications of these hypotheses are proposed.

Arthrogryposis multiplex congenita: Histochemical study of biopsied muscles

Morphometric analysis was performed after histochemical staining on 12 biopsied muscles of the affected limbs from 12 patients with arthrogryposis multiplex congenita. Except for one muscle, samples demonstrated variation in fiber size associated with abnormal fiber type distribution suggesting abnormal innervation: large groups of atrophic fibers in one muscle, either type 1 or 2 fiber predominance with occasional fiber type grouping in five, a complete lack of type 2 fibers in one, type one fiber atrophy in one, both type 2A and 2B fiber atrophy in two, and increased number of type 2C fibers in four. In most patients with arthrogryposis multiplex congenita, a defect in neural influence on the developing muscles may be responsible for the absence or maldevelopment of some muscle groups. Underdeveloped muscles are then assumed to induce imbalance of agonists and antagonists resulting in permanent contractures.

Muscle fibre type differentiation and satellite cell population in Werdnig-Hoffmann disease

Quantitative analyses of the muscle fibre type distribution and satellite cell population were performed on biceps muscles from control infants 6–30 months of age and patients with Werdnig-Hoffmann (WH) disease aged 1–13 months. In muscles of control infants, type 1 fibres ranged from 34.5 to 52.5% of a total of 500 muscle fibres, similar to the percentage in adult muscle. The distribution of type 2A and 2B fibres varied slightly at different ages (type 2A, 19.3–42.8%; type 2B, 21.1–39.2%). Type 2C fibres ranged from 0.2 to 3.4% and did not tend to decrease with age up to 30 months. The ratio of satellite cells to total subsarcolemmal nuclei was 8.4 ± 1.6% (5–21 months). In muscles in Werdnig-Hoffmann (WH) disease, undifferentiated type 2C fibres were significantly increased in number, ranging from 10.4 to 84.2% ( P < 0.005). The prevalence of the fibres was not necessarily proportional to the clinical severity, the onset of the disease, or the age at biopsy. Satellite cells in WH disease were significantly increased in number (14.4 ± 3.1%) in comparison with control infants ( P < 0.005). The satellite cells in WH disease appeared quiescent without morphological characteristics of “activation”.

The size of the myofibers in mature grafts of the mouse extensor digitorum longus muscle.

The histochemical profile of stabilized orthotopically grafted mouse extensor digitorum longus muscles (EDL) and fiber type diameter distribution in the graft was compared with control muscles. Histochemical fiber typing, based on myofibrillar ATPase reactions, indicated that type 1 fiber accounted for less than 1%, type 2a fibers for 30%, and type 2b fibers for 69% of the total fiber population of the graft. In control muscles of 56-day-old and 156-day-old mice, type 1 fibers accounted for less than 1%, type 2a fibers for 36%, and type 2b fibers for 63% of the total fiber population of normal muscles. The regenerating myofibers in stabilized grafts failed to achieve the normal fiber diameter. The type 2b fibers exhibited greater growth inhibition than did type 2a fibers.

Muscle changes in protein-deprived young rats: A morphometrical, histochemical and ultrastructural study

Rats were reared on a standard diet up to the age of 6 weeks when they were divided into two groups. One was fed on a diet containing 14% protein and the other on a diet with only 1.5% protein. The size of the various fibre types of the EDL muscle of both groups was assessed at 6 and 25 weeks of age. All the fibre types of protein-deprived rats were smaller compared to the age-matched controls, the difference being most evident in the 2B fibres. In the protein-deprived rats the 2B fibres atrophied while the type 1 and type 2A fibres simply failed to grow. Histochemical and ultrastructural examination revealed a marked reduction of the subsarcolemmal mitochondria after prolonged protein deprivation; normally large accumulations of mitochondria are seen preferentially in type 2A fibres.

THE EFFECTS OF THYROIDECTOMY ON THE EXTRAOCULAR MUSCLES OF THE RAT: A HISTOCHEMICAL STUDY

The effects of thyroidectomy on the metabolic properties of the rat extraocular muscles have been studied using histochemical techniques. Six months after removal of the thyroid gland a significant increase in the proportion of Type 1 fibres was found in the central zone of the superior rectus (SR) and in the levator palpebrae superioris muscles. Other changes included an increased proportion of Type 2a' fibres and reduced proportions of Type 2a and 2b fibres in the central zone of the SR, and an increased proportion of type 2a, and a reduced proportion of Type 2a" fibres in the peripheral zone of the SR, Mr and So. In addition, there was a mild hypertrophy of Type 1 fibres in the MR, and a mild atrophy of Type 2 fibres in each of the muscles studies. The physiological significance of these findings is discussed.

Actomyosin ATPase. II. Fiber typing by histochemical ATPase reaction.

A new method for fiber typing based on staining for actomyosin Ca,Mg-ATPase is presented. Inclusion of ethanol in the medium enhanced the differentiation of type 2A and 2B fibers. With this technique, type 1, 2A, and 2B fibers can be distinguished in a single-step procedure for human biopsy samples.

Congenital fiber type disproportion in identical twins

Eighteen-month-old identical twins with the muscle histological characteristics of congenital fiber type disproportion are reported. The fiber typing system of pH-dependent adenosine triphosphatase was used to analyze the size and percentage of type 1, 2A, and 2B fibers in muscle tissue obtained by needle biopsy. Both twins had significantly larger type 2 than type 1 fibers, with 2B fibers representing the largest type. One patient also had type 1 predominance at the expense of a reduction in 2B (2B deficiency). The probands as well as other family members had transient delayed motor development, macrocephaly, and normal intelligence. A biopsy obtained from 1 of these family members failed to demonstrate a similar histological abnormality. The disorder is nonprogressive in this family, as evidenced by minimal disability in the older members and gradual improvement in the probands.