Proportion Of Type IIB Fibres Research Articles

Muscle fiber characteristics and postmortem quality of longissimus thoracis, psoas major and semitendinosus from Chinese Simmental bulls.

Using Chinese Simmental cattle semitendinosus, psoas major, and longissimus thoracis samples, we assessed muscle fiber characteristics and postmortem quality. The type I, IIA, and IIB fiber diameters were greater in semitendinosus and longissimus thoracis relative to psoas major, with psoas major, semitendinosus, and longissimus thoracis having the highest respective percentages of type I, IIB, and IIA fibers. Psoas major had the highest R 248 and R 250 values and lowest R 258 values at 1‐ and 6‐hr postmortem. Psoas major had the lowest Warner–Bratzler shear force (WBSF), hardness, and chewiness values. The trends of WBSF, hardness, and chewiness changes decreased with increasing aging time. Semitendinosus had higher changes in WBSF than psoas major, and the number % type I fibers was correlated negatively with % changes of WBSF. Therefore, muscles with a high proportion of type IIB fibers and a low proportion of type I had lower tenderness and higher tenderization rate. Further research should be done to seek the optimal composition of muscle fiber type in order to improve beef quality, as muscle fiber type has opposite effect of tenderness background and tenderization rate.

Treatment with the essential amino acid L-tryptophan reduces masticatory impairments in experimental cerebral palsy

ABSTRACT Purpose Children with cerebral palsy (CP) often exhibit difficulties in feeding resulting from deficits in chewing. This study investigates the therapeutic potential of L-tryptophan (TRI) to reduce deficits in chewing in rats subjected to an experimental model of CP. Methods A total of 80 Wistar albino rats were used. Pups were randomly assigned to 4 experimental groups: Control Saline, Control TRI, CP Saline, and CP TRI groups. The experimental model of CP was based on the combination of perinatal anoxia associated with postnatal sensorimotor restriction of the hind limbs. TRI was administered subcutaneously during the lactation period. Anatomical and behavioral parameters were evaluated during maturation, including body weight gain, food intake, chewing movements, relative weight and the distribution of the types of masseter muscle fibers. Results The induction of CP limited body weight gain, decreased food intake and led to impairment in the morphological and functional parameters of chewing. Moreover, for a comparable amount of food ingested, CP TRI animals grew the most. In addition, supplementation with TRI improved the number of chewing movements, and increased the weight and proportion of type IIB fibers of the masseter in rats subjected to CP. Conclusion These results demonstrate that experimental CP impaired the development of mastication and that TRI supplementation increased masticatory maturation in animals subjected to CP.

Perinatal undernutrition associated to experimental model of cerebral palsy increases adverse effects on chewing in young rats

The aim of the present study was to investigate the effect of perinatal undernutrition on the sensorimotor pattern of chewing in rats submitted to cerebral palsy experimental model. A total of 60 male Wistar rats were randomly distributed into four groups: Nourished/Control (NC, n=15), Nourished/Cerebral Palsy (NCP, n=15); Undernourished/Control (UC, n=15) and Undernourished/Cerebral Palsy (UCP, n=15). Animals of cerebral palsy (CP) group were subjected to an experimental model based on the combination of perinatal anoxia associated with sensorimotor restriction of the hindlimb. In the rats were evaluated body weight gain, intake of breast milk, feed post-weaning consumption, parameters of the chewing, intra-oral sensitivity and muscle properties (muscle weight and distribution of types of fibers) of the masseter and digastric. Animals from undernourished CP group showed greater reduction in most data evaluated including body weight (P<0.05), food intake post-weaning (P<0.05), frequency of chewing cycles (P<0.05), duration of the reactions of “taste” (P<0.05), muscle weight and decrease of the proportion of type IIB fibers in the masseter muscle (P<0.05). These results demonstrated in rats submitted a cerebral palsy that perinatal undernutrition intensifies the damage in morphological and functional parameters of chewing.

Resistance Training Alters the Proportion of Skeletal Muscle Fibers but Not Brain Neurotrophic Factors in Young Adult Rats.

Antonio-Santos, J, Ferreira, DJS, Gomes Costa, GL, Matos, RJB, Toscano, AE, Manhães-de-Castro, R, and Leandro, CG. Resistance training alters the proportion of skeletal muscle fibers but not brain neurotrophic factors in young adult rats. J Strength Cond Res 30(12): 3531–3538, 2016—Resistance training (RT) is related to improved muscular strength and power output. Different programs of RT for rats have been developed, but peripheral and central response has not been evaluated directly in the same animal. To test the hypothesis that RT induces central and peripheral adaptations, this study evaluated the effects of a RT on the performance of a weekly maximum overload test, fiber-type typology, and brain neurotrophic factors in young adult rats. Thirty-one male Wistar rats (65 ± 5 days) were divided in 2 groups: nontrained (NT, n = 13) and trained (T, n = 18). Trained group was submitted to a program of RT ladder climbing, gradually added mass, 5 days per week during 8 weeks at 80% of individual maximum overload. This test was weekly performed to adjust the individual load throughout the weeks for both groups. After 48 hours from the last session of exercise, soleus and extensor digital longus (EDL) muscles were removed for myofibrillar ATPase staining analysis. Spinal cord, motor cortex, and cerebellum were removed for RT-PCR analysis of BDNF and insulin-like growth factor-1 (IGF-1) gene expression. In EDL muscle, T animals showed an increase in the proportion of type IIb fibers and a reduction of type IIa fibers. Insulin-like growth factor-1 gene expression was reduced in the cerebellum of T animals (NT: 1.025 ± 0.12; T: 0.57 ± 0.11). Our data showed that 8 weeks of RT were enough to increase maximum overload capacity and the proportion of glycolytic muscle fibers, but there were no associations with the expression of growth neurotrophic factors.

The influence of fiber size distribution of type IIB on carcass traits and meat quality in pigs

The effects of detailed characteristics such as the size and proportion of type IIB fibers in longissimus thoracis muscle on carcass traits and pork quality were investigated. A total of 96 pigs were classified into four groups by the proportion of different IIB fiber sizes. Group NS (high proportion of both small- and normal-sized IIB fibers) had a higher total number (136.4) and density (231.31) of type IIB fibers, backfat thickness (37.20mm) and intramuscular fat content (4.77%) than the other groups (P<0.05), whereas Group NS had the lowest values of cross-sectional area (3413.85μm2) and diameter (60.15μm) of type IIB fiber among the groups (P<0.05). Pig muscles with higher percentage of large IIB fibers exhibit tougher, lighter and more exudative meat than pig muscles with a higher proportion of small- or normal-sized IIB fibers. Therefore, an increase in the proportion of large IIB fibers causes poor quality of pork.

Bovine sire selection based on maintenance energy affects muscle fiber type and meat color of F1 progeny1

A total of 42 F(1) Red Angus progeny from sires divergent in maintenance energy (ME(M)) EPD were analyzed to determine whether selecting for sire ME(M) would alter end-product meat quality. Data from animals were grouped based on the divergence of the ME(M) EPD of their sire from the Red Angus Association-reported breed average and defined as either high or low, the assumption being that high-ME(M) cattle are less efficient because their maintenance requirements represent a larger proportion of their dietary intake. Steer progeny (n = 7) from the high group produced bottom round steaks with a greater a* (redness) color value (P = 0.02) after 5 d in a simulated retail display when compared with bottom round steaks from the low group (n = 18). Bottom round steaks from the high group had a greater b* (yellowness) color value at d 1 (P = 0.03) and d 5 (P = 0.01) of retail display. Samples from the biceps femoris were taken at 12 mo (from both steers and heifers) and 15 mo (from steers only) of age for fiber type proportion analysis. At 12 mo of age, steers from the low group had more type I fibers (P = 0.02), whereas steers from the high group had more type IIb fibers (P = 0.01). Furthermore, samples from steers in the low group at 15 mo had more type I fibers (P = 0.02), and steers from the high group maintained more type IIb fibers (P = 0.02). No changes in fiber type proportions were observed between the high- and low-ME(M) EPD heifers (n = 17). Relative mRNA abundance of genes involved in the synthesis, storage, and breakdown of glycogen were analyzed as a variable important for meat quality, but no statistical differences were observed. At 12 mo age, glycogenin (glyc) was negatively correlated with the proportion of type IIa fibers (r = -0.32 and P = 0.12) as well as with the proportion of type IIb fibers (r = -0.42 and P = 0.03) in the biceps femoris of the steers. In samples taken from the biceps femoris at 15 mo age, glyc was negatively correlated with the proportion of type IIa fibers (r = -0.42 and P = 0.03) in the steers. This indicates that relative mRNA expression of glyc may serve as a marker of muscle glycogen storage capacity in steers. Thus, selection for efficient Red Angus beef cattle based on sire ME(M) EPD does not adversely affect meat quality in F(1) progeny, based on the variables assessed in this study. Furthermore, selection for progeny from low-ME(M) EPD sires may improve fresh meat quality within Red Angus beef cattle.

Effect of pulmonary rehabilitation on muscle remodelling in cachectic patients with COPD

It is known that non-cachectic patients with chronic obstructive pulmonary disease (COPD) respond well to pulmonary rehabilitation, but whether cachectic COPD patients are capable of adaptive responses is both important and unknown. 10 cachectic and 19 non-cachectic COPD patients undertook high-intensity cycling training, at the same relative intensity, for 45 min x day(-1), 3 days x week(-1) for 10 weeks. Before and after rehabilitation vastus lateralis muscle biopsies were analysed morphologically and for the expression of muscle remodelling factors (insulin-like growth factor (IGF)-I, myogenic differentiation factor D (MyoD), tumour necrosis factor (TNF)-alpha, nuclear factor (NF)-kappaB and myostatin) and key components of ubiquitin-mediated proteolytic systems (muscle ring finger protein (MURF)-1 and Atrogin-1). Rehabilitation improved peak work-rate and the 6-min walk distance similarly in non-cachectic (18+/-3% and 42+/-13 m, respectively) and cachectic (16+/-2% and 53+/-16 m, respectively) patients, but quality of life only improved in non-cachectic COPD. Mean muscle fibre cross-sectional area increased in both groups, but significantly less in cachectic (7+/-2%) than in non-cachectic (11+/-2%) patients. Both groups equally decreased the proportion of type IIb fibres and increased muscle capillary/fibre ratio. IGF-I mRNA expression increased in both groups, but IGF-I protein levels increased more in non-cachectic COPD. MyoD was upregulated, whereas myostatin was downregulated at the mRNA and protein level only in non-cachectic patients. Whilst rehabilitation had no effect on TNF-alpha expression, it decreased the activation of the transcription factor NF-kappaB in both groups by the same amount. Atrogin-1 and MURF-1 expression were increased in cachectic COPD, but it was decreased in non-cachectic patients. Cachectic COPD patients partially retain the capacity for peripheral muscle remodelling in response to rehabilitation and are able to increase exercise capacity as much as those without cachexia, even if they exhibit both quantitative and qualitative differences in the type of muscle fibre remodelling in response to exercise training.

Functional assessment of skeletal muscle in intact mice lacking myostatin by concurrent NMR imaging and spectroscopy

Inhibiting myostatin (mstn) causes spectacular increase in muscle mass, spurring research for therapeutic approaches against neuromuscular disorders. Yet, possible functional deterioration and compromised force production have been reported in isolated muscle of null mstn(-/-) mice. We analyzed vascular and metabolic response to repeated electro-stimulated exercise in vivo in mstn(-/-) mice compared with FVB wild-type controls (WT), using interleaved multi-parametric functional nuclear magnetic resonance (NMR) imaging and spectroscopy. At steady-state exercise, specific force of plantar flexion, phosphocreatine consumption measured by phosphorus spectroscopy and maximum perfusion measured by arterial spin-labeled (ASL) NMR imaging were identical in both groups. After exercise, phosphorus spectroscopy revealed reduced oxidative mitochondrial capacity in mstn(-/-), whereas early recovery perfusion was identical and oxygen extraction, estimated from the blood oxygen level-dependent (BOLD) contrast, was decreased when compared with WT. Hyperemia was prolonged, indicating specific regulation of the perfusional response in mstn(-/-) mice. Histology showed an increased proportion of type IIb fibers in hypertrophied muscles, but the distribution of capillary contacts per fiber between oxidative and glycolytic fibers was unaltered in mstn(-/-) compared with WT. These integrated results formed coherent evidence of a congruous, non-pathologic shift toward a more glycolytic metabolism in this model of mstn(-/-).

Comparison of muscle fibre characteristics and production traits among offspring from Meishan dams mated to different sires

This study evaluated how various porcine sires affected muscle fibre characteristics, with respect to production traits. Sires from Berkshire, Duroc, Meishan, and Yorkshire pigs were mated to Meishan dams (BM, DM, MM, and YM offspring, respectively). A total of 96 pigs were evaluated for muscle fibre characteristics and production traits. The progeny from Duroc and Yorkshire sires had the greatest number of total fibres (P<0.05) and exhibited less backfat thickness (P<0.001) and larger loin muscle areas (P<0.05) than BM pigs. The DM and BM crossbreds showed higher marbling (P<0.01), and colour scores (P<0.05), as well as lower shear force scores (P<0.001). The MM pigs had greater proportional area of type IIb muscle fibres (P<0.05), and also displayed higher drip loss (P<0.01), higher lightness (P<0.001), and a greater incidence of PSE pork (pale, soft, and exudative; 25%) than DM, BM, and YM. These results showed that a greater number of total muscle fibres without increasing the cross sectional area of fibres improved lean meat production, and that a lower proportion of type IIb fibres was associated with better meat quality. For these reasons, the Duroc sire × Meishan dam crossbreed emerged as the most appropriate mating type examined herein to simultaneously enhance both lean meat production and meat quality.

Associations of Serum Adiponectin with Skeletal Muscle Morphology and Insulin Sensitivity

Skeletal muscle morphology and function are strongly associated with insulin sensitivity. The objective of the study was to test the hypothesis that circulating adiponectin is associated with skeletal muscle morphology and that adiponectin mediates the relation of muscle morphology to insulin sensitivity. This was a cross-sectional investigation of 461 men aged 71 yr, participants of the community-based Uppsala Longitudinal Study of Adult Men study. Measures included serum adiponectin, insulin sensitivity measured with euglycemic insulin clamp technique, and capillary density and muscle fiber composition determined from vastus lateralis muscle biopsies. In multivariable linear regression models (adjusting for age, physical activity, fasting glucose, and pharmacological treatment for diabetes), serum adiponectin levels rose with increasing capillary density (beta, 0.30 per 50 capillaries per square millimeter increase; P = 0.041) and higher proportion of type I muscle fibers (beta, 0.27 per 10% increase; P = 0.036) but declined with a higher proportion of type IIb fibers (beta, -0.39 per 10% increase; P = 0.014). Using bootstrap methods to examine the potential role of adiponectin in associations between muscle morphology and insulin sensitivity and the associations of capillary density (beta difference, 0.041; 95% confidence interval 0.001, 0.085) and proportion of type IIb muscle fibers (beta difference, -0.053; 95% confidence interval -0.107, -0.002) with insulin sensitivity were significantly attenuated when adiponectin was included in the models. Circulating adiponectin concentrations were higher with increasing skeletal muscle capillary density and in individuals with higher proportion of slow oxidative muscle fibers. Furthermore, our results indicate that adiponectin could be a partial mediator of the relations between skeletal muscle morphology and insulin sensitivity.

Preferential motor unit loss in the SOD1G93A transgenic mouse model of amyotrophic lateral sclerosis

The present study investigated motor unit (MU) loss in a murine model of familial amyotrophic lateral sclerosis (ALS). The fast-twitch tibialis anterior (TA) and medial gastrocnemius (MG) muscles of transgenic SOD1(G93A) and SOD1(WT) mice were studied during the presymptomatic phase of disease progression at 60 days of age. Whole muscle maximum isometric twitch and tetanic forces were 80% lower (P < 0.01) in the TA muscles of SOD1(G93A) compared to SOD1(WT) mice. Enumeration of total MU numbers within TA muscles showed a 60% reduction (P < 0.01) within SOD1(G93A) mice (38 +/- 7) compared with SOD1(WT) controls (95 +/- 12); this was attributed to a lower proportion of the most forceful fast-fatigable (FF) MU in SOD1(G93A) mice, as seen by a significant (P < 0.01) leftward shift in the cumulative frequency histogram of single MU forces. Similar patterns of MU loss and corresponding decreases in isometric twitch force were observed in the MG. Immunocytochemical analyses of the entire cross-sectional area (CSA) of serial sections of TA muscles stained with anti-neural cell adhesion molecule (NCAM) and various monoclonal antibodies for myosin heavy chain (MHC) isoforms showed respective 65% (P < 0.01) and 28% (P < 0.05) decreases in the number of innervated IIB and IID/X muscle fibres in SOD1(G93A), which paralleled the 60% decrease (P < 0.01) in the force generating capacity of individual fibres. The loss of fast MUs was partially compensated by activity-dependent fast-to-slower fibre type transitions, as determined by increases (P < 0.04) in the CSA and proportion of IIA fibres (from 4% to 14%) and IID/X fibres (from 31% to 39%), and decreases (P < 0.001) in the CSA and proportion of type IIB fibres (from 65% to 44%). We conclude that preferential loss of IIB fibres is incomplete at 60 days of age, and is consistent with a selective albeit gradual loss of FF MUs that is not fully compensated by sprouting of the remaining motoneurons that innervate type IIA or IID/X muscle fibres. Our findings indicate that disease progression in fast-twitch muscles of SOD1(G93A) mice involves parallel processes: (1) gradual selective motor axon die-back of the FF motor units that contain large type IIB muscle fibres, and of fatigue-intermediate motor units that innervate type IID/X muscle fibres, and (2) activity-dependent conversion of motor units to those innervated by smaller motor axons innervating type IIA fatigue-resistant muscle fibres.

Heterogeneity of fiber characteristics in the rat masseter and digastric muscles

The functional requirements in muscle use are related to the fiber type composition of the muscles and the cross-sectional area of the individual fibers. We investigated the heterogeneity in the fiber type composition and fiber cross-sectional area in two muscles with an opposing function, namely the digastric and masseter muscles (n = 5 for each muscle) of adult male rats, by means of immunohistochemical staining according to their myosin heavy chain (MyHC) content. The digastric and masseter muscles were taken from Wistar strain male rats 10 weeks old. In the masseter six predefined sample locations were examined; in the digastric four. Most regions showed dominant proportions of type IIA and IIX fibers. However, both muscles also revealed a regional heterogeneity in their fiber type distribution. In the digastric, type I fibers were detected only at the central and deep areas of the anterior and posterior belly, respectively. Meanwhile, the peripheral area of the anterior belly contained a higher proportion of type IIB fibers. In the masseter, the type I fibers were absent. In the superficial masseter the distribution of IIA and IIB fibers was significantly different between the superior and inferior regions. In the deep masseter, regional differences were observed among all four examined areas, of which the posterolateral region contained the highest proportion of type IIB fibers. The cross-sectional areas of type IIB fibers were always the largest, followed by the type IIX and IIA fibers. Only a few differences in cross-sectional area of corresponding fiber types were detected between the various sites. In conclusion, the masseter and digastric muscles showed an obvious heterogeneity of fiber type composition and fiber cross-sectional area. Their heterogeneity reflects the complex role of the both muscles during function. This detailed description of the fiber type composition can serve as a reference for future studies examining the muscular adaptations after the onset of various diseases in the masticatory system.

Morphometry, ultrastructure, myosin isoforms, and metabolic capacities of the “mini muscles” favoured by selection for high activity in house mice

Prolonged selective breeding of mice ( Mus musculus) for high levels of voluntary wheel running has favoured an unusual phenotype (“mini muscles”), apparently caused by a single Mendelian recessive allele, in which most hind-limb muscles are markedly reduced in mass, but have increased mass-specific activities of mitochondrial enzymes. We examined whether these changes reflect changes in fibre size, number or ultrastructure in normal and “mini-muscle” mice within the two (of four) selectively bred lines (lab designations L3 and L6) that exhibit the phenotype at generations 26 and 27. In both lines, the gastrocnemius and plantaris muscles are smaller in mass (by > 50% and 20%, respectively) in affected individuals. The mass-specific activities of mitochondrial enzymes in the gastrocnemius and plantaris muscles were increased in the mini phenotype in both lines, with stronger effects in the gastrocnemius muscle. In the gastrocnemius, the % myosin heavy chain (MHC) IIb was reduced by 50% in L3 and by 30% in L6, whereas the % MHC IIa and I were higher, particularly in L3. Fibre number in the plantaris muscle did not significantly differ between mini and normal muscles, although muscle mass was a significant positive correlate of fibre number. Small fibres were more abundant in mini than normal muscles in L3. Mitochondrial volume density was significantly higher in mini than normal muscle fibres in L3, but not in L6. Microscopy revealed a surprising attribute of the mini muscles: an abundance of small, minimally differentiated, myofibril-containing cells positioned in a disorderly fashion, particularly in the surface layer. We hypothesise that these unusual cells may be satellite cells or type IIb fibres that did not complete their differentiation. Together, these observations suggest that mice with the mini phenotype have reduced numbers of type IIb fibres in many of their hind-limb muscles, leading to a decrease in mass and an increase in mass-specific aerobic capacity in muscles that typically have a high proportion of type IIb fibres. Moreover, the several statistically significant interactions between muscle phenotype and line indicate that the effect of the underlying allele is altered by genetic background.

Exercise Performance and Skeletal Muscles in Patients With Advanced Chagas Disease

This study was designed to evaluate the peripheral muscle metabolic and structural characteristics in patients with advanced Chagas disease (ChD), and whether they were related with exercise performance. Cross-sectional study. Outpatient cardiomyopathy clinic of a university hospital. We studied 11 stage II patients, 8 stage III patients, and 11 healthy volunteers. All patients underwent exercise testing and peripheral muscle biopsies. The muscles were also studied in control subjects. Muscle biopsy specimens were analyzed for histochemical characteristics. In six patients, the muscle was studied ultrastructurally. The data demonstrate more glycolytic and less oxidative capacity of the peripheral muscle in patients with advanced ChD (increased proportion of type IIb fibers, increased proportion of fibers with low nicotinamide adenine dinucleotide diaphorase activity, high proportion of darkly stained fibers for alpha-glycerophosphate dehydrogenase activity, and lower levels of citrate synthase). Many capillaries in patients with ChD had an abnormal aspect: they were either closed or showed a thicker wall. The ultrastructural study also showed fiber atrophy and abnormal capillaries even in patients with normal functional capacity. Some muscle characteristics (enzyme activity, mean cross-sectional area of the fiber, and capillarity) related with exercise parameters (anaerobic threshold, and peak oxygen pulse). These findings indicate that patients with advanced ChD have decreased oxidative capacity and a shift to anaerobic metabolism in the skeletal muscle. They also suggest that muscular abnormalities are related to oxygen delivery, which is probably reduced in part by the abnormal muscle microvasculature. Those changes could affect oxygen extraction, and therefore exercise tolerance in these patients.

Muscle morphology, self‐reported physical activity and insulin resistance syndrome

In a population-based sample of 475 men the associations between muscle morphology, self-reported physical activity (PA) and insulin resistance (IR) syndrome were investigated. Also, we studied to what degree muscle morphology contributes to the association between PA and IR syndrome. Muscle morphology and the components of IR syndrome were compared in four groups categorized according to self-reported habitual PA data. We found a significantly higher percentage of type I fibres, fibre area and number of capillaries around the fibres and a lower proportion of type IIB fibres with higher level of PA. The relative distribution of type I fibres and capillarization were positively related to high density lipoprotein (HDL) cholesterol and negatively to serum triglycerides (TG) and plasminogen activator inhibitor-1 (PAI-1) activity. The percentage of type IIB fibres was were inversely related to HDL cholesterol and positively to serum TG, PAI-1 activity and resting heart rate. Insulin sensitivity was positively and independently related to PA level (P < 0.001). Regression analysis including all relevant variables regarding insulin sensitivity indicated that the significant explanatory variables left in the equation were body mass index (BMI), glucose intolerance, PAI-1 activity, serum free fatty acid concentration, proportion of type IIB fibres, HDL cholesterol level, drug treatment, PA level, and waist-to-hip ratio, which together explained 55% of the variation in the insulin sensitivity index. In conclusion, both fibre type distribution and muscle capillary density might contribute to the beneficial effect of PA on IR syndrome.

Bilateral effect of a unilateral occlusal splint on the expression of myosin heavy-chain isoforms in rat deep masseter muscle

Many studies have shown that various myosin isoforms are involved in muscle contraction. A search for specific antibodies directed against the myosin heavy chain (MHC) resulted in the identification of at least two main classes, referred to as MHC type I and type II. In this study, immunohistology and gel electrophoresis were used to determine the proportion of MHC isoforms in rat deep masseter muscle at different times after the insertion of an unilateral occlusal splint. An increasing proportion of MHC type I isoforms was found in both deep masseters soon after splinting, and this trend continued until 7 days after splint insertion. The type I fibres were clearly distributed on either side of the central axis of the muscle. At 15 days, a significant decrease in the percentage of the type IIb MHC isoform was observed on the occlusal splint side compared to the contralateral side. After 30 days of unilateral splinting, the proportion of type IIb fibres on the splint side returned to baseline whereas on the contralateral side there was an increase in the proportion of this type. The results suggest an initial adaptation after the unilateral occlusal disturbance in which muscles of both sides react in the same way; later, the muscles of each side adapt their expression of MHC isoforms according to altered functional demand.

Physical fitness, muscle morphology, and insulin-stimulated limb blood flow in normal subjects.

The response of limb blood flow to insulin is highly variable even in normal subjects. We examined whether physical fitness or differences in muscle morphology contribute to this variation. Maximal aerobic power, muscle fiber composition and capillarization, and the response of forearm glucose extraction and blood flow to a sequential hyperinsulinemic euglycemic clamp (serum insulin 374 +/- 10, 816 +/- 23, and 2,768 +/- 78 pmol/l) were determined in 16 normal males (age 25 +/- 1 yr, body mass index 24 +/- 1 kg/m2). Maximal aerobic power correlated positively with the proportion of type I fibers (r = 0.67, P < 0.01) and negatively with the proportion of type IIb fibers (r = -0.73, P < 0.01). Fiber composition but not blood flow correlated significantly with forearm and whole body glucose uptake. All doses of insulin significantly increased forearm blood flow, maximally by 123 +/- 21%. The ratio of capillaries per fiber was significantly correlated with basal and insulin-stimulated blood flow (0.58- 0.76, P < 0.05-0.01). Mean arterial blood pressure and the insulin-induced increase in blood flow were inversely correlated (r = -0.59, P < 0.05). We conclude that variation in glucose extraction is significantly determined by muscle fiber composition, whereas variation in insulin-stimulated blood flow is closely associated with muscle capillarization.

Myosin isoforms and muscle fiber characteristics in equine gluteus medius muscle

To date, four different myosin heavy chain (MyHC) isoforms have been identified in adult skeletal muscle of a number of species: types I, IIa, IIx or IId, and IIb. The aim of this study was to investigate the distribution of various MyHC isoforms in the equine gluteus medius and gluteus profundus muscles in relation with several morphometric variables of muscle fibers. Samples from different depths of the gluteus medius muscle (2, 4, 6, and 8 cm) and gluteus profundus muscle of five sedentary horses were examined by MyHC gel electrophoresis, monoclonal antibodies staining against fast, slow and neonatal MyHC isoforms, myosin adenosine triphosphatase (m-ATPase) activity, nicotinamide adenine dinucleotide tetrazolium reductase, alpha-glycerophosphate dehydrogenase, and alpha-amylase-PAS. Data about relative frequencies, sizes, and capillaries of the various histochemical fiber types were collected by morphometry. Three MyHC isoforms were present in the gluteus medius muscle. Two of them comigrated with type I and IIa MyHC isoforms of rat diaphragm (used as a control). The third isoform showed an electrophoretic mobility closer to type IIx than to the IIb MyHC isoform of rat diaphragm. Only two MyHC isoforms (type I and IIa) were detected in the gluteus profundus muscle. In both muscles, type I fibers (high m-ATPase activity at pH 4.5) only reacted with the anti slow-MyHC antibody and both type IIA and IIB fibers (low and moderate m-ATPase activity at pH 4.5, respectively) only reacted with the anti fast-MyHC antibody. No cross-reactivity of fibers positive for both antibodies was found except for the scarce type IIC fibers. Fiber types and capillaries were heterogeneously distributed across the gluteus medius muscle. The deeper regions of this muscle were found to contain a higher percentage of type I fibers, a large number of capillaries and a lower proportion of type IIB fibers compared to the superficial regions of the muscle. The gluteus profundus muscle had more abundant and larger type I fibers than the deepest sampling site of the gluteus medius muscle. These results show the existence of three different MyHC isoforms in the equine gluteus medius muscle and that fiber types and MyHC isoforms are heterogeneously distributed within this muscle. The distribution of slow-twitch and fast-twitch MyHCs among the fibers determined by immunohistochemistry was in agreement with histochemically identified type I and type II fibers, respectively.

Myosin isoforms and muscle fiber characteristics in equine gluteus medius muscle

Background To date, four different myosin heavy chain (MyHC) isoforms have been identified in adult skeletal muscle of a number of species: types I, IIa, IIx or IId, and IIb. The aim of this study was to investigate the distribution of various MyHC isoforms in the equine gluteus medius and gluteus profundus muscles in relation with several morphometric variables of muscle fibers. Methods Samples from different depths of the gluteus medius muscle (2, 4, 6, and 8 cm) and gluteus profundus muscle of five sedentary horses were examined by MyHC gel electrophoresis, monoclonal antibodies staining against fast, slow and neonatal MyHC isoforms, myosin adenosine triphosphatase (m-ATPase) activity, nicotinamide adenine dinucleotide tetrazolium reductase, α-glycerophosphate dehydrogenase, and α-amylase-PAS. Data about relative frequencies, sizes, and capillaries of the various histochemical fiber types were collected by morphometry. Results Three MyHC isoforms were present in the gluteus medius muscle. Two of them comigrated with type I and IIa MyHC isoforms of rat diaphragm (used as a control). The third isoform showed an electrophoretic mobility closer to type IIx than to the IIb MyHC isoform of rat diaphragm. Only two MyHC isoforms (type I and IIa) were detected in the gluteus profundus muscle. In both muscles, type I fibers (high m-ATPase activity at pH 4.5) only reacted with the anti slow-MyHC antibody and both type IIA and IIB fibers (low and moderate m-ATPase activity at pH 4.5, respectively) only reacted with the anti fast-MyHC antibody. No cross-reactivity of fibers positive for both antibodies was found except for the scarce type IIC fibers. Fiber types and capillaries were heterogeneously distributed across the gluteus medius muscle. The deeper regions of this muscle were found to contain a higher percentage of type I fibers, a large number of capillaries and a lower proportion of type IIB fibers compared to the superficial regions of the muscle. The gluteus profundus muscle had more abundant and larger type I fibers than the deepest sampling site of the gluteus medius muscle. Conclusions These results show the existence of three different MyHC isoforms in the equine gluteus medius muscle and that fiber types and MyHC isoforms are heterogeneously distributed within this muscle. The distribution of slow-twitch and fast-twitch MyHCs among the fibers determined by immunohistochemistry was in agreement with histochemically identified type I and type II fibers, respectively. © 1996 Wiley-Liss, Inc.

Aerobic capacity and skeletal muscle properties of normoxic and hypoxic rats in response to training.

The aim of this study was to determine, in the rat, the effects of chronic exposure (7-9 weeks) to normobaric hypoxia (FIO2=0.13, equivalent to 3700 m altitude) on cardiac and skeletal muscle properties, on maximal oxygen uptake (VO2max), and endurance time to exhaustion (ETE). In addition, we evaluated the impact of endurance training (90 min of treadmill running per day, 5 days per week, for 9 weeks) on these parameters. The results were compared to normoxic rats fed ad libitum (NAL) and to normoxic pair-weight (NPW) animals in order to take into account the influence of hypoxia on growth rate. It was found that, in sedentary rats, hypoxia results in stunted growth, adrenal atrophy, a significant reduction of cross-sectional area of fast-twitch (type II) fibres, a reduced capillary-to-fibre ratio (C/F), and a reduced oxidative capacity (decreases in citrate synthase and 3-hydroxy-Acyl CoA dehydrogenase activities) of the plantaris muscle. These effects are mainly related to the anorexic effects of prolonged exposure to hypoxia. Nevertheless, hypoxic (H) rats displayed higher VO2max and ETE values when compared either to NAL or to NPW animals. Endurance training resulted, in all groups (H, NAL, NPW), in a significant change of the fibre type distribution of the plantaris which displayed an increased number of type IIA fibres and a decreased proportion of type IIB fibres. In addition, the C/F ratio and cross-sectional area of fast-twitch fibres were normalized by superimposition of training on hypoxia. Both VO2max and ETE were significantly higher in trained H rats than in NAL, but these improvements were mainly related to the reduced body weight induced by hypoxia. These data suggest that the greater aerobic capacity and tolerance for prolonged exercise induced by chronic exposure to hypoxia can be mainly accounted for by the anorexic effects of hypoxia, although other factors (e.g. increase in oxygen carrying capacity induced by hypoxia acclimatization) may play a significant role in some circumstances (e.g. in sedentary rats).