Fast-twitch Oxidative Fibers Research Articles

Mitochondrial dynamics define muscle fiber type by modulating cellular metabolic pathways

Skeletal muscle is highly developed after birth, consisting of glycolytic fast-twitch and oxidative slow-twitch fibers; however, the mechanisms of fiber-type-specific differentiation are poorly understood. Here, we found an unexpected role of mitochondrial fission in the differentiation of fast-twitch oxidative fibers. Depletion of the mitochondrial fission factor dynamin-related protein 1 (Drp1) in mouse skeletal muscle and cultured myotubes results in specific reduction of fast-twitch muscle fibers independent of respiratory function. Altered mitochondrial fission causes activation of the Akt/mammalian target of rapamycin (mTOR) pathway via mitochondrial accumulation of mTOR complex 2 (mTORC2), and rapamycin administration rescues the reduction of fast-twitch fibers invivo and invitro. Under Akt/mTOR activation, the mitochondria-related cytokine growth differentiation factor 15 is upregulated, which represses fast-twitch fiber differentiation. Our findings reveal a crucial role of mitochondrial dynamics in the activation of mTORC2 on mitochondria, resulting in the differentiation of muscle fibers.

Systemic delivery of AAVrh74.tMCK.hCAPN3 rescues the phenotype in a mouse model for LGMD2A/R1

Limb girdle muscular dystrophy (LGMD) 2A/R1, caused by mutations in the CAPN3 gene and CAPN3 loss of function, is known to play a role in disease pathogenicity. In this study, AAVrh74.tMCK.CAPN3 was delivered systemically to two different age groups of CAPN3 knockout (KO) mice; each group included two treatment cohorts receiving low (1.17 × 1014 vg/kg) and high (2.35 × 1014 vg/kg) doses of the vector and untreated controls. Treatment efficacy was tested 20 weeks after gene delivery using functional (treadmill), physiological (in vivo muscle contractility assay), and histopathological outcomes. AAV.CAPN3 gene therapy resulted in significant, robust improvements in functional outcomes and muscle physiology at low and high doses in both age groups. Histological analyses of skeletal muscle showed remodeling of muscle, a switch to fatigue-resistant oxidative fibers in females, and fiber size increases in both sexes. Safety studies revealed no organ tissue abnormalities; specifically, there was no histopathological evidence of cardiotoxicity. These results show that CAPN3 gene replacement therapy improved the phenotype in the CAPN3 KO mouse model at both doses independent of age at the time of vector administration. The improvements were supported by an absence of cardiotoxicity, showing the efficacy and safety of the AAV.CAPN3 vector as a potential gene therapy for LGMDR1.

Targeted deletion of Kcne3 impairs skeletal muscle function in mice.

KCNE3 (MiRP2) forms heteromeric voltage-gated K+ channels with the skeletal muscle-expressed KCNC4 (Kv3.4) α subunit. KCNE3 was the first reported skeletal muscle K+ channel disease gene, but the requirement for KCNE3 in skeletal muscle has been questioned. Here, we confirmed KCNE3 transcript and protein expression in mouse skeletal muscle using Kcne3-/- tissue as a negative control. Whole-transcript microarray analysis (770,317 probes, interrogating 28,853 transcripts) findings were consistent with Kcne3 deletion increasing gastrocnemius oxidative metabolic gene expression and the proportion of type IIa fast-twitch oxidative muscle fibers, which was verified using immunofluorescence. The down-regulated transcript set overlapped with muscle unloading gene expression profiles (≥1.5-fold change; P < 0.05). Gastrocnemius K+ channel α subunit remodeling arising from Kcne3 deletion was highly specific, involving just 3 of 69 α subunit genes probed: known KCNE3 partners KCNC4 and KCNH2 (mERG) were down-regulated, and KCNK4 (TRAAK) was up-regulated (P < 0.05). Functionally, Kcne3-/- mice exhibited abnormal hind-limb clasping upon tail suspension (63% of Kcne3-/- mice ≥10-mo-old vs. 0% age-matched Kcne3+/+ littermates). Whereas 5 of 5 Kcne3+/+ mice exhibited the typical biphasic decline in contractile force with repetitive stimuli of hind-limb muscle, both in vivo and in vitro, this was absent in 6 of 6 Kcne3-/- mice tested. Finally, myoblasts isolated from Kcne3-/- mice exhibit faster-inactivating and smaller sustained outward currents than those from Kcne3+/+ mice. Thus, Kcne3 deletion impairs skeletal muscle function in mice.-King, E. C., Patel, V., Anand, M., Zhao, X., Crump, S. M., Hu, Z., Weisleder, N., Abbott, G. W. Targeted deletion of Kcne3 impairs skeletal muscle function in mice.

MicroRNA-mRNA regulatory networking fine-tunes the porcine muscle fiber type, muscular mitochondrial respiratory and metabolic enzyme activities

BackgroundMicroRNAs (miRNAs) are small non-coding RNAs that play critical roles in diverse biological processes via regulation of gene expression including in skeletal muscles. In the current study, miRNA expression profile was investigated in longissimus muscle biopsies of malignant hyperthermia syndrome-negative Duroc and Pietrain pigs with distinct muscle metabolic properties in order to explore the regulatory role of miRNAs related to mitochondrial respiratory activity and metabolic enzyme activity in skeletal muscle.ResultsA comparative analysis of the miRNA expression profile between Duroc and Pietrain pigs was performed, followed by integration with mRNA profiles based on their pairwise correlation and computational target prediction. The identified target genes were enriched in protein ubiquitination pathway, stem cell pluripotency and geranylgeranyl diphosphate biosynthesis, as well as skeletal and muscular system development. Next, we analyzed the correlation between individual miRNAs and phenotypical traits including muscle fiber type, mitochondrial respiratory activity, metabolic enzyme activity and adenosine phosphate concentrations, and constructed the regulatory miRNA-mRNA networks associated with energy metabolism. It is noteworthy that miR-25 targeting BMPR2 and IRS1, miR-363 targeting USP24, miR-28 targeting HECW2 and miR-210 targeting ATP5I, ME3, MTCH1 and CPT2 were highly associated with slow-twitch oxidative fibers, fast-twitch oxidative fibers, ADP and ATP concentration suggesting an essential role of the miRNA-mRNA regulatory networking in modulating the mitochondrial energy expenditure in the porcine muscle. In the identified miRNA-mRNA network, a tight relationship between mitochondrial and ubiquitin proteasome system at the level of gene expression was observed. It revealed a link between these two systems contributing to energy metabolism of skeletal muscle under physiological conditions.ConclusionsWe assembled miRNA-mRNA regulatory networks based on divergent muscle properties between different pig breeds and further with the correlation analysis of expressed genes and phenotypic measurements. These complex networks relate to muscle fiber type, metabolic enzyme activity and ATP production and may contribute to divergent muscle phenotypes by fine-tuning the expression of genes. Altogether, the results provide an insight into a regulatory role of miRNAs in muscular energy metabolisms and may have an implication on meat quality and production.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2850-8) contains supplementary material, which is available to authorized users.

Comparison of M.Semitendinosus Morphometry and Structure in Gilts and Barrows at Market Age

Abstract The aim of this paper was to investigate the differences in morphometric characteristics and histological structure of m. semitendinosus, between gilts and barrows of German Landrace breed at the end of the fattening period. Morphometric characteristics (weight, length, diameter and cross sectional area) of m. semitendinosus were not significantly different, while gender as a factor influenced the histological properties of this muscle. A very high statistical difference (p&lt;0.01) in the total number of muscle fibers in m. semitendinosus was determined, with gilts having a higher total fiber number. The cross sectional area of fast twitch oxidative (FTO) fibers was significantly higher (p&lt;0.05) in barrows. Gender did not affect the distribution of different fiber types: in both gender, the most present fiber types (48-52 %) were fast twitch glycolitic (FTG), FTO fibers represented 27-30 % of the total fiber number, while slow twitch oxidative fibers (STO) were the least represented (≈ 20 %).

The relationship of pork longissimus muscle pH to mitochondrial respiratory activities, meat quality and muscle structure

The way the pH falls post-slaughter has an impact on meat quality. Pork longissimus muscles (n=48) were sorted in fast- (FG) (n=15) and normal glycolysing (NG) (n=33) muscles according to the post-slaughter pH 45 min values (FG<6.0; NG>6.0). FG muscles (5.84±0.04) compared with NG muscles (6.27±0.04) were accompanied with higher temperature, electrical conductivity, lightness and yellowness, and reduced grill loss and shear force values (P<0.05), but there were no pH-dependent changes of the drip loss and redness results. FG muscles had higher (P<0.05) percentages of fast-twitch glycolytic and lower proportions of fast-twitch oxidative and slow-twitch oxidative (P<0.05) muscle fibres. The study confirms the relationship of pH value to meat quality and muscle fibre characteristics also showing that pH values have no impact on intrinsic mitochondrial respiratory function.

Comparison of different skeletal muscles from growing domestic pigs and wild boars

Abstract. The domestication process of pigs was associated with substantial morphological and physiological changes. The aim of this study was to comparatively investigate muscle microstructure and biochemical properties of four different skeletal muscles (M. longissimus, M. semitendinosus, M. psoas major, M. rhomboideus) in growing domestic pigs (n=5) and wild boars (n=4). The superiority of domestic pigs in body and muscle growth at three months of age was reflected by a 4-fold body weight and higher absolute weights of heart, liver and muscles. Relative muscle weights of M. psoas major and M. rhomboideus were reduced, whereas a 1.6-fold heavier M. semitendinosus was observed in domestic pigs compared with wild boars. In addition, the muscle cross-sectional area was greater in all muscles of domestic pigs resulting from about 3-fold fibre cross-sectional area, whereas total fibre number remained unchanged. As a consequence of intensified fibre hypertrophy, the fibre area per capillary is higher in all muscles of domestic pigs. Thus, the impaired supply with oxygen and nutrients may be one reason for the shift to the glycolytic muscle metabolism as indicated by a greater proportion of fast-twitch glycolytic fibres at the expense of fast-twitch oxidative fibres. This is also reflected by a higher ratio of lactate dehydrogenase to isocitrate dehydrogenase activity. Our data suggest that the intensified muscle growth was realized by myofibre hypertrophy at unchanged myofibre number in growing domestic pigs. It seems that domestication-induced changes were most pronounced in M. semitendinosus as the exterior ham muscle which may be related to muscle specific selection for lean growth.

Comparison of microstructural traits of &amp;lt;i&amp;gt;Musculus longissimus lumborum&amp;lt;/i&amp;gt; in wild boars, domestic pigs and wild boar/domestic pig hybrids

Abstract. The aim of the present study was to compare the histological structure of muscles in wild boars, pigs and wild boar/domestic pig hybrids by determining the percentage of different muscle fibre types and diameters and the intramuscular fatty tissue content of the Musculus longissimus lumborum (LL). The study involved 24 males representing three groups: wild boars (6 animals), pigs (12 animals: 6 of Polish Landrace and 6 of Duroc breeds) and wild boar/domestic pig hybrids (6 animals). Wild boar/domestic pig hybrids were obtained by crossing DU pigs with wild boars. Samples of the LL were frozen in liquid nitrogen. Frozen muscle samples were cut into 10- μm sections. These were later placed on a glass slide and stained using different histochemical reactions: NADH-TR and myofibrillar ATP-ase activity to distinguish muscle fibre types and Oil Red staining to determine the intramusuclar fatty tissue content. The highest proportion of slow twitch oxidative fibres and fast twitch oxidative fibres, being indicative of high meat value, was characteristic of wild boar muscles. The lowest diameters of all three muscle fibre types, associated with the largest number of fibres in the analysed area, suggest that the meat had the most delicate structure. Compared to wild boars, wild boar/domestic pig hybrids showed a decrease in the percentage of oxidative fibres and an increase in the percentage of glycolytic fibres. The diameters of all muscle fibre types in this group of animals were similar to those obtained in pigs.

The ontogeny of aerobic and diving capacity in the skeletal muscles of Weddell seals

Our objective was to determine the ontogenetic changes in the skeletal muscles of Weddell seals that transform a non-diving pup into an elite diving adult. Muscle biopsies were collected from pups, juveniles and adults and analyzed for changes in fiber type, mitochondrial density, myoglobin concentrations and aerobic, lipolytic and anaerobic enzyme activities. The fiber type results demonstrated a decrease in slow-twitch oxidative (Type I) fibers and a significant increase in fast-twitch oxidative (Type IIA) fibers as the animals mature. In addition, the volume density of mitochondria and the activity of lipolytic enzymes significantly decreased as the seals matured. To our knowledge, this is the first quantitative account describing a decrease in aerobic fibers shifting towards an increase in fast-twitch oxidative fibers with a significant decrease in mitochondrial density as animals mature. These differences in the muscle physiology of Weddell seals are potentially due to their three very distinct stages of life history: non-diving pup, novice diving juvenile, and elite deep diving adult. During the first few weeks of life, pups are a non-diving terrestrial mammal that must rely on lanugo (natal fur) for thermoregulation in the harsh conditions of Antarctica. The increased aerobic capacity of pups, associated with increased mitochondrial volumes, acts to provide additional thermogenesis. As these future elite divers mature, their skeletal muscles transform to a more sedentary state in order to maintain the low levels of aerobic metabolism associated with long-duration diving.

The ontogeny of skeletal muscle adaptations that enable long deep dives in Weddell seals

Our objective was to determine the ontogenetic changes in the skeletal muscles of Weddell seals that transform a non‐diving pup into an elite diving adult. Muscle biopsies were collected from pups, juveniles and adults and analyzed for changes in fiber type, mitochondrial density, myoglobin concentrations, and aerobic, lipolytic and anaerobic enzyme activities. The fiber type results showed a decrease in type I fibers with a significant increase in type IIA fibers as the animals mature. In addition, the volume density of mitochondria and the activity of lipolytic enzymes significantly decreased as the seals matured. To our knowledge, this is the first quantitative account describing a decrease in aerobic fibers shifting towards an increase in fast‐twitch oxidative fibers with a significant decrease in mitochondrial density as the animals mature. These differences in muscle physiology are due to their three stages of life history. During the first few weeks of life, pups are a non‐diving terrestrial mammal that must rely on natal fur for thermoregulation in the harsh conditions of Antarctica. The increased aerobic capacity of pups, associated with increased mitochondrial volumes, acts to provide additional thermogenesis. As these future elite divers mature, their skeletal muscles transform to a more sedentary state in order to maintain the low levels of aerobic metabolism associated with long duration diving.

Computational modeling indicates anaerobic glycogenolytic ATP synthesis contributes little to quadriceps energy balance during exhaustive bicycling exercise

It has been proposed that anaerobic glycogenolysis may contribute as much as 20% to cellular ATP synthesis during contractile work on basis of indirect evidence from 31P NMR spectroscopic measurements of proton balance in human limb muscles (1). Here, this hypothesis was tested more rigorously using a systems biology approach. We constructed a computational model of energy metabolism in muscle composed of slow‐twitch oxidative, fast‐twitch oxidative and fast‐twitch glycolytic fibers incorporating mitochondrial and glycogenolytic ATP synthetic pathways operating in parallel. Next, we measured the in vivo dynamics of phosphocreatine (PCr), Pi, hexose monophosphates (HMP) and H+ concentrations in quadriceps muscle of human subjects performing in‐magnet bicycling exercise using gated 31P NMR spectroscopy (2). The measured PCr dynamics were then compared to model simulations for different magnitudes of glycogenolytic ATP synthetic flux. In contrast to previous indirect analyses (1), we found that anaerobic ATP synthesis contributions of only 10% or less sufficed to explain energy balance during exercise; this in spite of massive activation of glycogenolysis as evidenced by large accumulations of HMP of up to 10 mM directly following exercise (2).

Body composition, muscle fibre characteristics and postnatal growth capacity of pigs born from sows supplemented with L-carnitine

Recently, it has been shown that supplementation of sows with L-carnitine increases their plasma concentrations of insulin-like growth factor (IGF)-I, and it has been hypothesized that this may stimulate fetal myogenesis. This study was performed to investigate whether piglets of sows supplemented with L-carnitine differ in muscle fibre characteristics, chemical body composition and postnatal growth capability from pigs of control sows. Muscle fibre characteristics and chemical body composition were determined at weaning in 21 piglets of control sows and 21 piglets of sows treated with L-carnitine with similar body weights; postnatal growth capability was determined from weaning until slaughter at a body weight of 118 kg in 80 pigs of control sows and 80 pigs of sows treated with L-carnitine which had also similar body weights at weaning. Piglets of sows supplemented with L-carnitine did not differ in number, area, diameter and type (percentages of slow twitch oxidative + fast twitch oxidative fibres, and fast twitch glycolytic fibres) of muscle fibres in m. longissimus dorsi and m. semitendinosus and in chermical body composition (concentrations of dry matter, crude protein, crude fat) from piglets of control sows. Postnatal growth capability (body weight gains, feed conversion ratio) from weaning to slaughter as well as carcass composition (carcass yield, meat thickness, fat thickness) was also not different between pigs of sows treated with L-carnitine and pigs of control sows. In conclusion, data of this study do not support the hypothesis that L-carnitine supplementation of sows during pregnancy enhances fetal muscle fibre development and increases postnatal growth capability of the offspring.

An association between genotypes at the porcine loci &amp;lt;i&amp;gt;MSTN (GDF8)&amp;lt;/i&amp;gt; and &amp;lt;i&amp;gt;CAST&amp;lt;/i&amp;gt; and microstructural characteristics of &amp;lt;i&amp;gt;m. longissimus lumborum&amp;lt;/i&amp;gt;: a preliminary study

Abstract. The aim of the study was to evaluate the association between the microstructure characteristics of longissimus lumborum (LL) muscle and the genotype at porcine loci MSTN and CAST. The study was carried out on 132 unrelated pigs – 93 crosses of Pietrain and (Polish Large White x Polish Landrace) and 39 Stamboek castrated males. Crosses Pi x (PLW x PL), with an equal proportion of castrated males (n=46) and females (n=47), were of genotype CC or CT at the locus RYR1, whereas Stamboek pigs were of genotype CC at this locus. The diameters of slow-twitch oxidative (STO), fast-twitch oxidative (FTO) and fast-twitch glycolytic (FTG) fibers, their per cent share in a bundle and number of fibers per 1 mm2 were determined. Moreover, the analyses covered the frequency of occurrence of pathological fibers, including giant and angular fibers. The parameters examined, characterising the microstructure of LL muscle, were not found to be related to the presence of the C→T polymorphism in exon 3 of the MSTN gene, identified by enzyme TaqI. However, it was shown that the diameters of the STO, FTO and FTG fibres in the LL muscle were significantly smallest in the Stamboek pigs with genotype FF at locus CAST compared to both the remaining genotypes. Among the crosses Pi x (PLW x PL) this genotype was not observed. The content of FTG fibres in a bundle proved to be related to the CAST genotype in Stamboek pigs. The frequency of pathological fibres in the LL muscle was the lowest in pigs with genotype EE at the locus CAST, but only in the case of the crosses Pi x (PLW x PL) was this relation statistically significant. The studies should be continued to determine whether such relations occur in other pig breeds. The frequency of pathological fibres affects meat quality and thus the polymorphism of the CAST gene could be of importance in selection.

Exercise Stimulates Pgc-1α Transcription in Skeletal Muscle through Activation of the p38 MAPK Pathway

Peroxisome proliferator-activated receptor gamma co-activator 1alpha (PGC-1alpha) promotes mitochondrial biogenesis and slow fiber formation in skeletal muscle. We hypothesized that activation of the p38 mitogen-activated protein kinase (MAPK) pathway in response to increased muscle activity stimulated Pgc-1alpha gene transcription as part of the mechanisms for skeletal muscle adaptation. Here we report that a single bout of voluntary running induced a transient increase of Pgc-1alpha mRNA expression in mouse plantaris muscle, concurrent with an activation of the p38 MAPK pathway. Activation of the p38 MAPK pathway in cultured C2C12 myocytes stimulated Pgc-1alpha promoter activity, which could be blocked by the specific inhibitors of p38, SB203580 and SB202190, or a dominant negative p38. Furthermore, the p38-mediated increase in Pgc-1alpha promoter activity was enhanced by increased expression of the downstream transcription factor ATF2 and completely blocked by ATF2DeltaN, a dominant negative ATF2. Skeletal muscle-specific expression of a constitutively active activator of p38, MKK6E, in transgenic mice resulted in enhanced Pgc-1alpha and cytochrome oxidase IV protein expression in fast-twitch skeletal muscles. These findings suggest that contractile activity-induced activation of the p38 MAPK pathway promotes Pgc-1alpha gene expression and skeletal muscle adaptation.

A relationship between the PCR-RFLP polymorphism in porcine MYOG, MYOD1 and MYF5 genes and microstructural characteristics of m. longissimus lumborum in Pietrain × (Polish Large White × Polish Landrace) crosses

Muscle fibre formation takes place during embryonic development and is regulated by the MyoD gene family, which consists of four genes, MYOD1, myogenin, MYF5 and MRF4. A relationship was studied between MYOD1, myogenin and MYF5 genotypes and microstructural characteristics of the m. longissimus lumborum in pigs &amp;ndash; crosses: Pietrain &amp;times; (Polish Large White &amp;times; Polish Landrace). The data included 115 unrelated animals slaughtered at about 105 kg live body weight. Within 45 min after exsanguination, samples were taken from the m. longissimus lumborum, frozen in liquid nitrogen and later analysed for the diameter of slow-twitch oxidative, fast-twitch oxidative and fast-twitch low-oxidative fibres, their proportion in a bundle, the proportion of pathological changes and number of fibres per unit area. The RYR1 and MyoD genotypes were determined using the PCR-RFLP technique. A significant or highly significant relation was observed between the diameter of all types of muscle fibres and genotype RYR1 &amp;ndash; the highest values were recorded for homozygotes TT (genetically stress-sensitive). A relation between MyoD genotypes and microstructural characteristics of the m. longissimus lumborum was analysed on a group of 93 animals of the genotype CC or CT at locus RYR1. Sex appeared to have no significant effect on the muscle microstructural traits in this group of animals. The content of fast-twitch oxidative fibres (FTO) was significantly related to the MYF5 genotype, whereas that of fast-twitch low-oxidative fibres (FT) was affected by the MYOD1 and MYF5/DdeI genotypes. The proportion of angular fibres in a bundle was related to MYF5/HinfI genotype. The results showed that MyoD genes could be considered as candidate genes for some microstructural characteristics of m. longissimus lumborum in pigs. &amp;nbsp;

Cyclosporin A treatment increases rat soleus muscle oxidative capacities.

Previous studies suggested that administration of cyclosporin A (CsA), an immunosuppressive agent, contributes to the increased fatigability of heart transplant recipients. The aim of this study was to investigate whether CsA itself, without vehicle, affects the function of mitochondria maintained in situ, in rats treated with CsA (25mg/kg/day) dissolved in ethanol and olive oil. Treatment with CsA induced a 16% decrease in slow myosin heavy chain (MHC) associated with a 225% increase in fast MHCIIa. The proportion of fibers expressing type IIa MHC increased as a result of CsA treatment. Soleus from the CsA-treated animals showed an increase in both basal (+85%) and maximal (+37%) mitochondrial respiration (P < 0.001), consistent with a 24% increase in citrate synthase activity, whereas the apparent Km for adenosine diphosphate was unchanged. By itself, CsA has no deleterious effects on muscle oxidative capacity but induces alterations in energy metabolism in accordance with the increased proportion of fast-twitch oxidative fibers.

SELECTIVE CHANGES IN MUSCLE FIBER SIZE FOLLOWING BONE FRACTURE IN AGED RATS

PURPOSE The purpose of this study was to investigate the effect of bone fracture-induced muscle atrophy on the histochemical property of muscle fibers in aged rats. METHODS All experimental procedures were approved by the institutional Animal Care and Use Committee at Kyoto University. Ten male and female Wistar Kyoto rats (aged:88.7 □} 3.2 wk) were subdivided into four groups based upon gender and the presence of fractures or non-fractures of the metatarsal bone of the right hindlimb paw: …3) male fractur ed (M-FR, n=5); …) non-fractur ed (M-NFR, n=5); … μ) female fractured (F-FR, n=5); …¶) non-fractured (F-NFR, n=5). The soleus muscles were dissected from both hindlimbs and analyzed for histochemical properties. Myofibrillar adenosine triphosphatase (ATPase) histochemical staining procedure was used to determine muscle fiber type and calculate the percentage distribution and cross-sectional area (CSA) of each fiber type. RESULTS The wet weight of the soleus muscles of the leg with the fractured paw decreased by 9.6% in M-FR and decreased by 10.0% in F-FR compared to M-NFR and F-NFR, respectively (p > 0.05). However, the wet weight of the soleus muscle of the contralateral, nonfractured site of both M-FR and F-FR groups displayed a hypertrophic compensation and was increased by 12% in M-FR and increased by 3.3% in F-FR (p > 0.05). The CSA of the fast-twitch oxidative glycolytic (FOG) fibers hypertrophied by 40% (p < 0.05) in the soleus muscles of the leg with the fractured paw in the M-FR compared with M-NFR group. In contrast, there was no change in CSA of the FOG of soleus muscle between the female groups. CONCLUSION The data suggest that stress-induced increases in male androgen hormones upregulated the synthesis of contractile proteins of the fast twitch oxidative and glycolytic fibers.

Morphometric and Histochemical Study of the Human Vocal Muscle

The present study was conducted on vocal muscles removed at autopsy from adult individuals (10 men and 8 women, ages ranging from 48 to 78 years) with no laryngeal disease. Histologic analysis was performed with hematoxylin and eosin staining, and histochemical analysis was performed by nicotinamide-adenine-dinucleotide tetrazolium reductase, succinate dehydrogenase, and acid and alkaline myofibrillar adenosine triphosphatase reactions. The histochemical reactions showed that the muscle consists of slow-twitch oxidative (SO), fast-twitch glycolytic (FG), and fast-twitch glycolytic oxidative (FOG) fibers distributed in mosaic form. The frequencies of SO, FOG, and FG fibers were 40.50%, 54.75%, and 4.75%, respectively. The higher frequency of SO and FOG oxidative fibers characterizes the muscle as having aerobic metabolism, resistance to fatigue, and fast contraction. The mean minimum diameters were 31.37 microm for SO fibers and 36.46 microm for FOG and FG fibers.

Histochemische und morphometrische Untersuchungen der Muskulatur der Vordergliedmaße des Schafes in bezug zu ihrer Funktion Teil 2. Beuger und Strecker der Karpal- und Zehengelenke

Muscle tissue was obtained from eight forearm muscles of six male sheep (180 days old) and stained for NADH tetrazolium oxidoreductase and myofibrillar ATPase after preincubation at pH 4.3. The fiber diameter and the percentage were determined of three fiber types: slow twitch oxidative (STO), fast twitch oxidative (FTO) and fast twitch glycolytic fibers (FTG). The extensor carpi radialis muscle had the lowest percentage of STO fibers. It is a fast extensor of the carpal joint. The superficial digital flexor muscle (FS) is located in the superficial region of the forearm has shown the highest percentage of STO fibers (50%). These fibers were also considerable larger (57 microns) than the STO fibers of the deep digital flexor muscle (39 microns). The FS supports the elbow joint extensors in the fixation of the elbow joint during the standing position (static work) and flexes the digital joints in motion (dynamic work). At first muscle function decides the quality and the quantity of the muscle fibers. Then other factors, e.g. capillarization, determine the distribution of fiber types. Muscles which have to work static-tonically require a higher content of large slow twitch fibers regardless of whether these muscles are located close to the limb axis or in the periphery. They resist lastingly gravity. Thus they are antigravity muscles. In the forearm they are the superficial digital flexor muscle, flexor carpi ulnaris muscle, and extensor carpi ulnaris muscle, which always have more than 30% STO-fibers.

Histochemische und morphometrische Untersuchungen der Muskulatur der Vordergliedmaße des Schafes in bezug zu ihrer Funktion: Teil 1. Beuger und Strecker des Ellbogengelenkes

Muscle tissue was removed from the extensors and flexors of the elbow joint of six male sheep (180 days old) and stained for NADH tetrazolium oxidoreductase and myofibrillar ATPase after preincubation at pH 4.3 in order to identify three fiber types: slow twitch oxidative (STO), fast twitch oxidative (FTO) and fast twitch glycolytic fibers (FTG). The medial head of the M. triceps brachii and the anconaeus muscle had the largest fibers (> 50 and 60 microns). The smallest muscle fibers (35-43 microns) were found in the dorsal part of the long head of the triceps muscle. The medial head of the triceps muscle and the anconaeus muscle possessed a very high percentage of STO-fibers (90 and 100%) and FTG-fibers were absent in these muscles. In the other extensors and flexors of the elbow joint the STO-percentage amounted to less than 30%. The dorsal part of the long head of the triceps muscle contained only 13% STO-fibers, but had the highest percentage of FTG-fibers (49%), which is representative of fast-muscles. The muscles of the elbow joint perform both static and dynamic functions. The medial head of the triceps brachii muscle and the anconaeus muscle possess the complement of enzymes which permits them to fulfil the work of extensors in the standing position. Therefore, they are typical of antigravity muscles. The histochemical structure of the other extensors and flexors reflect their function in motion. The lateral and long head of triceps muscle oppose the flexors and extend the elbow joint of the raised limb in the swing phase, during the landing phase they also function to support the other extensors of the elbow.