Type 2b Fibers Research Articles

Fiber type and regional differences in oxidative capacity and glycogen content in the hamster diaphragm.

The purpose of this study was to define variability of the oxidative capacity and glycogen content between different fiber types and regions of the hamster diaphragm. Using histochemical and microphotometric techniques, the oxidative capacity (identified by nicotinamide-adenine dinucleotide tetrazolium reductase reaction end product) and glycogen levels (identified by the periodic acid-Schiff stain test) were examined in three myofibrillar ATPase (M-ATPase) fiber types and four diaphragmatic regions: sternal, anterior costal, thoracic surface of the crural (thor/crur), and abdominal surface of the crural (abd/crur). Most regional differences were found between the crus and the rest of the diaphragm. There were no differences in the oxidative capacity between diaphragmatic regions in the types 1 and 2a fibers, but the type 2b fibers in the thor/crur region had the greatest oxidative capacity and the 2b fiber in the sternal region had the lowest oxidative capacity. There were differences in glycogen content between diaphragmatic regions for all of the three M-ATPase fiber types. Variability in oxidative capacity between fiber types was demonstrated in all regions except the thor/crur region. Variation in glycogen content between fiber types was only demonstrated in the two surfaces of the crus. The type 2b fiber demonstrated the most differences from types 1 and 2a fibers in oxidative capacity and glycogen content in the different diaphragmatic regions, whereas the types 1 and 2a fibers demonstrated few differences from each other in these features across the different diaphragmatic regions.(ABSTRACT TRUNCATED AT 250 WORDS)

Mammalian skeletal muscle fibers distinguished by contents of phosphocreatine, ATP, and Pi.

We tested the proposition that muscle cell types have different contents of phosphocreatine (PCr), ATP, and Pi by 31P NMR spectroscopy and HPLC analyses of adult rat and mouse muscles containing various volume fractions of different fiber types. There was a 2-fold difference in the PCr content between muscles with a high volume fraction of fiber types 1 and 2x versus those with fast-twitch (types 2a and 2b) fiber types. Pi content was low, and PCr and ATP contents were high in muscles with large contents of type 2b and 2a fibers; the reverse was true in muscles with a large volume fraction of type 1 and 2x fibers. There is a large range in the Pi/PCr ratios in normal resting muscles, from less than 0.05 in type 2 to 0.51 in type 1 fibers, depending upon the distribution of their component fiber types. In all muscles, the peak area resulting from the beta phosphate of ATP constituted approximately 13% of the sum of all peak areas observable in the 31P spectrum. Fiber types 2a and 2b were not distinguishable, and the content of type 2x fibers was similar to type 1 fibers. From the profile of these metabolites, we could distinguish only two classes of fibers. For type 2a and 2b fibers, the intracellular concentrations were 8 mM ATP, 39 mM total creatine, 32 mM PCr, 0.8 mM Pi, and 8 microM ADP. For type 1 and 2x fibers, these quantities were 5 mM ATP, 23 mM total creatine, 16 mM PCr, 6 mM Pi, and 11 microM ADP. Thus our results establish an additional criterion upon which to distinguish skeletal muscle cells, one based on the resting content of bioenergetically important metabolites. These results also provide the basis for estimating skeletal muscle fiber-type composition from noninvasive NMR spectroscopic data.

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.

Taurine content and distribution in equine skeletal muscle.

Taurine (TAU) is found in large but variable amounts in the skeletal muscles of many species. It has been reported that slow twitch muscles in the rat exhibit higher TAU levels than fast twitch muscles. Variation in muscle taurine content may be attributable to differences in the fibre type composition of different muscles. TAU content (mmol kg-1 dry muscle) and percentage type-1, type-2A, and type-2B fibre section area (f.s.a.) were measured in muscle samples taken from up to six sites in the middle gluteal muscle of four horses and one pony at post mortem and in biopsy samples taken from twenty Thoroughbred horses in race training. TAU was positively correlated to type-1 f.s.a. (r = 0.94, p < 0.001) in both post mortem samples and biopsies from horses in race-training. Multiple linear regression analysis was used to estimate the TAU content of individual fibre types when present at 100%. TAU is almost exclusively localized in type-1 fibres. The TAU content of type-1 and type-2A fibres was estimated to be 45.4 mmol kg-1 d.m. and 4.5 mmol kg-1 d.m. respectively in the post mortem horses, and 32.4 mmol kg-1 d.m. and 7.9 mmol kg-1 d.m. respectively in the horses in training. TAU was estimated to be absent from type-2B fibres in both horse groups.

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.

Hyperkalemic periodic paralysis in horses

Summary Eleven horses (3 mares, 7 stallions, 1 gelding) with clinical and biochemical evidence of hyperkalemic periodic paralysis were studied. Each horse had history of episodic weakness, muscular tremors, or collapse, which lasted for periods of a few minutes to hours. Diagnosis was based on hyperkalemia in association with a spontaneous episode of paralysis or by precipitation of an episode by oral administration of potassium chloride. Clinical and biochemical events were documented during spontaneous and induced episodes of muscular weakness. During episodes, electrocardiographic findings were consistent with hyperkalemia. Electromyography performed between episodes revealed fibrillation potentials and positive sharp waves, complex repetitive discharges, and myotonic discharges. Histologic changes in muscle biopsy specimens varied from no overt changes in some horses to vacuolation in type-2B fibers with mild degenerative changes in other horses. Electron microscopy of myofibers revealed dilatations of the sarcoplasmic reticulum. Analysis of blood samples taken serially during induced attacks in 5 horses revealed marked hyperkalemia (5.5 to 9.0 mEq/L), with normal acid-base status, hemoconcentration, and modest changes in muscle-derived enzymes. Close correlation (r2 = 0.882) between total plasma protein and plasma potassium concentrations was observed and indicated a shift of fluid out of the extracellular fluid compartment. Treatment of either spontaneous or induced episodes by iv administration of calcium, glucose, or bicarbonate resulted in rapid recovery. Dietary management or daily administration of acetazolamide effectively controlled episodes. An affected mare was bred to an affected stallion, and 3 affected offspring were produced by embryo transfer. Blood samples from another extended family of affected horses were analyzed for identification of a genetic marker. Blood typing, including 22 loci, revealed no linkage with erythrocytic or serum markers. Lymphocyte typing for equine lymphocytic antigen markers also failed to reveal any linkage.

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.

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.

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”.

Mailing muscle biopsy samples for histochemical processing. Conditions and morphometric approach to the alterations induced by storage.

Muscle samples obtained in patients with different neuromuscular diseases were stored at 0 degree C for periods of 6-12h and were subsequently frozen for histochemical processing. Compared to reference samples which had been immediately frozen, the individual test sections displayed different degrees of swelling of the muscle fibres. After 12h of storage the mean diameters had increased by 20% in type-1 and type-2A fibres and by 16% in type-2B fibres. With shorter periods type-2B fibres also showed the smallest amounts of increase in mean fibre diameter. The distribution of fibre diameters, variability coefficients and atrophy and hypertrophy factors showed corresponding changes but rarely fell outside the range defined from the reference sections. The histological, histochemical and cytological quality of the sections remained satisfactory. The decrease in glycogen content during storage appeared to be crucial. Time for mailing samples can be extended up to 27h without essential loss of histo-and cytochemical quality of the sections at the light microscopic level.

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.

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.