Myosin Heavy Chain Content Research Articles

Does oxidative stress modulate limb muscle atrophy in severe COPD patients?

Oxidative stress may differentially regulate protein loss within peripheral muscles of severe chronic obstructive pulmonary disease (COPD) patients exhibiting different body composition. Oxidation levels of proteins, myosin heavy chain (MyHC) and myonuclei, superoxide anion, antioxidants, actin, creatine kinase, carbonic anhydrase-3, ubiquitin-proteasome system, redox-signalling pathways, inflammation and muscle structure, and damage were quantified in limb muscles of severe COPD patients with and without muscle wasting, and in sedentary controls. Compared with controls, in the quadriceps of muscle-wasted COPD patients, levels of protein carbonylation, oxidation of MyHC and myonuclei, superoxide anion production, superoxide dismutase, total protein ubiquinitation, E2(14k), atrogin-1, FoxO1 and p65 were higher, while content of MyHC, creatine kinase, carbonic anhydrase-3, myogenin, and fast-twitch fibre size were decreased. Importantly, in nonwasted COPD patients, where MyHC was more oxidised than in controls, its content was preserved. Muscle inflammation and glutathione levels did not differ between patients and controls. In all patients, muscle structure abnormalities were increased, while muscle force and exercise capacity were reduced. In severe COPD, while muscle oxidative stress increases regardless of their body composition, protein ubiquitination and loss of MyHC were enhanced only in patients exhibiting muscle atrophy. Oxidative stress does not seem to directly modulate muscle protein loss in these patients.

Endurance training decreases the non‐linearity in the oxygen uptake–power output relationship in humans

In this study, we hypothesized that 5 weeks of cycling endurance training can decrease the magnitude of the non-proportional increase in oxygen uptake (V(O(2))) to power output relationship (V(O(2)) 'excess') at exercise intensities exceeding the lactate threshold (LT). Ten untrained, physically active men performed a bout of incremental cycling exercise until exhaustion before and after training. The mitochondrial DNA copy number, myosin heavy chain composition and content of uncoupling protein 3 and sarcoplasmic reticulum Ca(2+)-ATPases (SERCAs) were analysed in muscle biopsies taken from vastus lateralis before and after training. The training resulted in an enhancement of the power-generating capabilities at maximal oxygen uptake (V(O(2)max)) by ∼7% (P = 0.002) despite there being no changes in V(O(2)max) (P = 0.49). This effect was due to a considerable reduction in the magnitude of the V(O(2)) 'excess' (P < 0.05) above the LT. A decrease in plasma ammonia concentration was found during exercise after training (P < 0.05). A downregulation of SERCA2 in vastus lateralis (P = 0.006) was observed after training. No changes in myosin heavy chain composition, selected electron transport chain proteins, uncoupling protein 3 or the mitochondrial DNA copy number (P > 0.05) were found after training. We conclude that the training-induced increase in power-generating capabilities at V(O(2)max) was due to attenuation of the V(O(2)) 'excess' above the LT. This adaptive response seems to be related to the improvement of muscle metabolic stability, as judged by a lowering of plasma ammonia concentration. The enhancement of muscle metabolic stability after training could be caused by a decrease in ATP usage at a given power output owing to downregulation of SERCA2 pumps.

Early-phase muscular adaptations in response to slow-speed versus traditional resistance-training regimens

Thirty-four untrained women participated in a 6-week program to investigate slow-speed versus "normal" speed resistance-training protocols. Subjects were divided into: slow-speed (SS), normal-speed/traditional-strength (TS), normal-speed/traditional muscular endurance (TE), and non-exercising control (C) groups. Leg press, squats, and knee extensions were performed 2 days/week for the first week and 3 days/week for the remaining 5 weeks (~2 min rest). The SS group performed 6-10 repetitions maximum (6-10RM) for each set with 10 s concentric (con) and 4 s eccentric (ecc) contractions. The TS and TE groups performed sets of 6-10RM and 20-30RM, respectively, at "normal" speed (1-2 s/con and ecc contractions). TE and SS trained at the same relative intensity (~40-60% 1RM), whereas TS trained at ~80-85% 1RM. Pre- and post-training muscle biopsies were analyzed for fiber-type composition, cross-sectional area (CSA), and myosin heavy chain (MHC) content. The percentage of type IIX fibers decreased and IIAX increased in all three training groups. However, only TS showed an increase in percentage of type IIA fibers. CSA of fiber types I, IIA, and IIX increased in TS. In SS, only the CSA of IIA and IIX fibers increased. These changes were supported by MHC data. No significant changes for any parameters were found for the C group. In conclusion, slow-speed strength training induced a greater adaptive response compared to training with a similar resistance at "normal" speed. However, training with a higher intensity at "normal" speed resulted in the greatest overall muscle fiber response in each of the variables assessed.

Titin and diaphragm dysfunction in mechanically ventilated rats

PurposeDiaphragm weakness induced by mechanical ventilation may contribute to difficult weaning from the ventilator. For optimal force generation the muscle proteins myosin and titin are indispensable. The present study investigated if myosin and titin loss or dysfunction are involved in mechanical ventilation-induced diaphragm weakness.MethodsMale Wistar rats were either assigned to a control group (n = 10) or submitted to 18 h of mechanical ventilation (MV, n = 10). At the end of the experiment, diaphragm and soleus muscle were excised for functional and biochemical analysis.ResultsMaximal specific active force generation of muscle fibers isolated from the diaphragm of MV rats was lower than controls (128 ± 9 vs. 165 ± 13 mN/mm2, p = 0.02) and was accompanied by a proportional reduction of myosin heavy chain concentration in these fibers. Passive force generation upon stretch was significantly reduced in diaphragm fibers from MV rats by ca. 35%. Yet, titin content was not significantly different between control and MV diaphragm. In vitro pre-incubation with phosphatase-1 decreased passive force generation upon stretch in diaphragm fibers from control, but not from MV rats. Mechanical ventilation did not affect active or passive force generation in the soleus muscle.ConclusionsMechanical ventilation leads to impaired diaphragm fiber active force-generating capacity and passive force generation upon stretch. Loss of myosin contributes to reduced active force generation, whereas reduced passive force generation is likely to result from a decreased phosphorylation status of titin. These impairments were not discernable in the soleus muscle of 18 h mechanically ventilated rats.Electronic supplementary materialThe online version of this article (doi:10.1007/s00134-012-2504-5) contains supplementary material, which is available to authorized users.

Myosin Heavy Chain Expression and Oxidative Modifications in Diabetic Rat Hearts

In this study, we tested the hypotheses that 1) diabetes-induced disturbances in cardiac my-ATPase activity would be attributed to not only myosin heavy chain (MHC) isoform transitions, but also reduced amounts in MHC protein; and 2) if diabetes results in declines in the MHC protein content, this change would relate to oxidative damage to MHC. Diabetes was induced by a single intraperitoneal injection of streptozotocin. After 6 weeks of injection, the left ventricles were excised for mechanical and biochemical analyses. Peak twitch tension and the rate of force development in papillary muscles were decreased by 23.4% and 34.1%, respectively. A 33.5% reduction in myofibrillar ATPase activity occurred in conjunction with a 9.5% decrease in MHC protein as well as MHC isoform transitions towards a slower phenotype. The decreased MHC content was not accompanied by elevations in carbonyl groups present in MHC. Whole muscle analyses indicated that the contents of malondialdehyde and reduced glutathione were elevated. These results suggest that decreases in the MHC content may be associated, at least in part, with a diabetes-related inactivation of cardiac my-ATPase and may not be due to accumulation of oxidative damage to protein.

Urocortins Improve Dystrophic Skeletal Muscle Structure and Function through Both PKA- and Epac-Dependent Pathways

In Duchenne muscular dystrophy, the absence of dystrophin causes progressive muscle wasting and premature death. Excessive calcium influx is thought to initiate the pathogenic cascade, resulting in muscle cell death. Urocortins (Ucns) have protected muscle in several experimental paradigms. Herein, we demonstrate that daily s.c. injections of either Ucn 1 or Ucn 2 to 3-week-old dystrophic mdx(5Cv) mice for 2 weeks increased skeletal muscle mass and normalized plasma creatine kinase activity. Histological examination showed that Ucns remarkably reduced necrosis in the diaphragm and slow- and fast-twitch muscles. Ucns improved muscle resistance to mechanical stress provoked by repetitive tetanizations. Ucn 2 treatment resulted in faster kinetics of contraction and relaxation and a rightward shift of the force-frequency curve, suggesting improved calcium homeostasis. Ucn 2 decreased calcium influx into freshly isolated dystrophic muscles. Pharmacological manipulation demonstrated that the mechanism involved the corticotropin-releasing factor type 2 receptor, cAMP elevation, and activation of both protein kinase A and the cAMP-binding protein Epac. Moreover, both STIM1, the calcium sensor that initiates the assembly of store-operated channels, and the calcium-independent phospholipase A(2) that activates these channels were reduced in dystrophic muscle by Ucn 2. Altogether, our results demonstrate the high potency of Ucns for improving dystrophic muscle structure and function, suggesting that these peptides may be considered for treatment of Duchenne muscular dystrophy.

Black wildebeest skeletal muscle exhibits high oxidative capacity and a high proportion of type IIx fibres

The aim of the study was to investigate the skeletal muscle characteristics of black wildebeest (Connochaetes gnou) in terms of fibre type and metabolism. Samples were obtained post mortem from the vastus lateralis and longissimus lumborum muscles and analysed for myosin heavy chain (MHC) content. Citrate synthase (CS), 3-hydroxyacyl co A dehydrogenase (3HAD), phosphofructokinase (PFK), lactate dehydrogenase (LDH) and creatine kinase (CK) activities were measured spectrophotometrically to represent the major metabolic pathways in these muscles. Both muscles had less than 20% MHC I, whereas MHC IIa and MHC IIx were expressed in excess of 50% in the vastus lateralis and longissimus lumborum muscles, respectively. Overall fibre size was 2675±1034 μm(2), which is small compared with other species. Oxidative capacity (CS and 3HAD) in both muscles was high and did not differ from one another, but the longissimus lumborum had significantly (P<0.05) higher PFK, LDH and CK activities. No relationships were observed between fibre type and the oxidative and oxygen-independent metabolic capacity as measured by specific enzyme activities. This study confirms the presence of both fast-twitch fibres and high oxidative capacity in black wildebeest, indicating an animal that can run very fast but is also fatigue resistant.

Effects of Two Different Half-Squat Training Programs on Fatigue During Repeated Cycling Sprints in Soccer Players

This study compared the effects of two different half-squat training programs on the repeated-sprint ability of soccer players during the preseason. Twenty male professional soccer players were divided into 2 groups: One group (S-group) performed 4 sets of 5 repetitions with 90% of their 1-repetition maximum (1RM), and the other group (H-group) performed 4 sets of 12 repetitions with 70% of 1RM, 3 times per week for 6 weeks, in addition to their common preseason training program. Repeated-sprint ability was assessed before and after training by 10 × 6-second cycle ergometer sprints separated by 24 seconds of passive recovery. Maximal half-squat strength increased significantly in both groups (p < 0.01), but this increase was significantly greater in the S-group compared with the H-group (17.3 ± 1.9 vs. 11.0 ± 1.9%, p < 0.05). Lean leg volume (LLV) increased only in the H-group. Total work over the 10 sprints improved in both groups after training, but this increase was significantly greater in the second half (8.9 ± 2.6%) compared with the first half of the sprint test (3.2 ± 1.7%) only in the S-group. Mean power output (MPO) expressed per liter of LLV was better maintained during the last 6 sprints posttraining only in the S-group, whereas there was no change in MPO per LLV in the H-group over the 10 sprints. These results suggest that resistance training with high loads is superior to a moderate-load program, because it increases strength without a change in muscle mass and also results in a greater improvement in repeated sprint ability. Therefore, resistance training with high loads may be preferable when the aim is to improve maximal strength and fatigue during sprinting in professional soccer players.

High‐Intensity Resistance Training with Insufficient Recovery Time Between Bouts Induce Atrophy and Alterations in Myosin Heavy Chain Content in Rat Skeletal Muscle

The aim of this study was to test whether high-intensity resistance training with insufficient recovery time between bouts, could result in a decrease of muscle fiber cross-sectional area (CSA), alter fiber-type frequencies and myosin heavy chain (MHC) isoform content in rat skeletal muscle. Wistar rats were divided into two groups: trained (Tr) and control (Co). Tr group were subjected to a high-intensity resistance training program (5 days/week) for 12 weeks, involving jump bouts into water, carrying progressive overloads based on percentage body weight. At the end of experiment, animals were sacrificed, superficial white (SW) and deep red (DR) portions of the plantaris muscle were removed and submitted to mATPase histochemical reaction and SDS-PAGE analysis. Throughout the experiment, both groups increased body weight, but Tr was lower than Co. There was a significant reduction in IIA and IID muscle fiber CSA in the DR portion of Tr compared to Co. Muscle fiber-type frequencies showed a reduction in Types I and IIA in the DR portion and IID in the SW portion of Tr compared to Co; there was an increase in Types IIBD frequency in the DR portion. Change in muscle fiber-type frequency was supported by a significant decrease in MHCI and MHCIIa isoforms accompanied by a significant increase in MHCIIb isoform content. MHCIId showed no significant differences between groups. These data show that high-intensity resistance training with insufficient recovery time between bouts promoted muscle atrophy and a transition from slow-to-fast contractile activity in rat plantaris muscle.

Age-Related Changes in Myosin Light and Heavy Chain Isoforms’ Composition in Gluteus Medius Muscle of Sedentary Akhal-Teke Horses

The primary purpose of the present study was to examine age dependence of gluteus medius muscle phenotypic plasticity with regard to myosin light chain (MyLC) and myosin heavy chain (MyHC) isoform expression of sedentary Akhal-Teke horses. A total of 23 Akhal-Teke horses (11 horses, 1.5 to 2.5-year-old; nine horses, 9 to 20-year-old; and three horses, 21 to 23.5-year-old) were studied. A muscle biopsy of depth 60 mm from the left gluteus medius muscle was obtained. MyHC and MyLC isoform pattern was determined in three age groups. The current study demonstrated that in the 21 to 23.5-year-old age group, the relative content of MyHC I isoform and MyLC 1slow isoform decreased significantly. The results of the current study indicate that gluteus medius muscle of Akhal-Teke horses consists of a relatively high percentage of MyHC I and IIa isoforms, which together compose about 50% of MyHC. MyHC IIa and IIx isoforms together compose 88% to 94% of MyHC isoforms. Age-related decrease of the relative content of MyHC I and MyLC 1slow isoforms in gluteus medius muscle starts in Akhal-Teke horses older than 20 years.

Differential muscular myosin heavy chain expression of the pectoral and pelvic girdles during early growth in the king penguin (Aptenodytes patagonicus) chick

Continuous growth, associated with a steady parental food supply, is a general pattern in offspring development. So that young chicks can acquire their locomotor independence, this period is usually marked by a fast maturation of muscles, during which different myosin heavy chain (MyHC) isoforms are expressed. However, parental food provisioning may fluctuate seasonally, and offspring therefore face a challenge to ensure the necessary maturation of their tissues when energy is limited. To address this trade-off we investigated muscle maturation in both the pectoral and pelvic girdles of king penguin chicks. This species has an exceptionally long rearing period (1 year), which is prolonged when parental food provisioning is drastically reduced during the sub-Antarctic winter. Approximately 1 month post hatching, chicks acquire a functional pedestrian locomotion, which uses pelvic muscles, whereas swimming, which uses the pectoral muscles, only occurs 1 year later. We therefore tested the hypothesis that the MyHC content of the leg muscles reaches a mature state before those of the pectoral muscles. We found that leg muscle MyHC composition changed with the progressive acquisition of pedestrian locomotion, whereas pectoral muscle fibres reached their mature MyHC profile as early as hatching. Contrary to our predictions, the acquisition of the adult profile in pectoral muscles could be related to an early maturation of the contractile muscular proteins, presumably associated with early thermoregulatory capacities of chicks, necessary for survival in their cold environment. This differential maturation appears to reconcile both the locomotor and environmental constraints of king penguin chicks during growth.

Decreased Prevalence of Myosin Heavy Chain Hybrid Isoforms in Lifelong Endurance Trained Octogenarians

An increased prevalence of myosin heavy chain (MHC) hybrid muscle fibers (MHC I/IIa, IIax, and/or I/IIax) and the MHC IIx isoform is associated with elderly, sedentary, spinal cord injured, and bed ridden populations. Accordingly, highly trained young athletes typically express few MHC hybrid fibers and little MHC IIx isoform. To date there is no data pertaining to lifelong exercisers in their ability to maintain a comparable fiber type distribution as they age. PURPOSE: To examine single muscle fiber MHC composition in lifelong endurance athletes (n=9, 81±1 y, 68±3 kg, BMI=23±1 kg/m2) and compare to age-matched, independent living, healthy men (n=6; 82±1 y, 77±5 kg, BMI=26±1 kg/m2). The endurance athletes were cross-country skiers, including a former Olympic champion and several national/regional champions, with a history of aerobic exercise and frequent participation in an annual 90 km ski race and other related endurance events throughout their entire adult life (∼61 years/subject). METHODS: Muscle biopsies were obtained from the vastus lateralis. A total of 1905 muscle fibers for the athletes and 1246 muscle fibers for the non-athletes were isolated and analyzed electrophoretically (SDS-PAGE) for MHC content (∼209 fibers/subject). RESULTS: Athletes had a greater percentage (P<0.05) of MHC I fibers than non-athletes (54% vs. 33%). The athletes had fewer (P<0.05) MHC IIax fibers (6% versus 16%) and total hybrid fibers (13 ± 2% vs. 24 ± 5%) compared to non-athletes. The athletes had only 7% of fibers with any MHC IIx isoform present (MHC IIax + MHC IIx + MHC I/IIax) while 29% of the fibers from non-athletes contained the MHC IIx isoform (P<0.05). CONCLUSION: Muscle fibers from elite octogenarian athletes showed more pure MHC I and less MHC hybrid isoforms and MHC IIx isoform than non-athletic octogenarians. This pattern is consistent with the phenotype of well-trained young endurance athletes. This may suggest that lack of activity and not aging per se is the primary cause of an increased prevalence of hybrid fibers and MHC IIx expression with aging. The ability of the octogenarian athletes to retain a high percentage of the pure MHC I and IIa isoforms suggests an advantageous skeletal muscle health phenotype with advanced age.

Myosin‐actin cross‐bridge kinetics explain variation in single skeletal muscle fiber function in humans

Our objective was to determine if myosin-actin cross-bridge kinetics, measured in their intact myofilament lattice, could account for variation in skeletal muscle fiber type specific performance among healthy and diseased humans. We applied small amplitude sinusoidal analysis for the first time to human skeletal muscle fibers obtained from 9 heart failure patients and 6 controls of similar age and activity level. In both groups, myosin heavy chain (MHC) isoform contractile velocity (I<IIA<IIX) was inversely related to myosin-actin attachment time (ton). The rate of myosin transition between weakly- and strongly-bound states (2πb) increased with MHC velocity, suggesting the myosin-actin detachment time (toff) decreases with faster contractions. These results suggest that total myosin-actin cycle time (ton + toff) decreases with contractile velocity due to reductions in both ton and toff in humans. Heart failure patients had an increased ton, which compensated for their reduced cross-bridge number due to MHC content loss, resulting in similar isometric tensions compared to healthy controls. Collectively, these results indicate the usefulness of cross-bridge kinetics and highlight their potential use for examining the effects of disease, muscle activity and aging on single fiber function. Support: NIH HL-077418 and AG-031303

Fiber Myosin Heavy Chain Polymorphism is Associated with a Heightened Susceptibility to Eccentric Damage

The purpose of this study was to model the relationship between fiber myosin heavy chain (MHC) isoform content and susceptibility to damage by a standardized eccentric contraction (+25% change in fiber length; 50% of unloaded shortening velocity, Vo). Damage was quantified as the pre- to post-eccentric change in Ca2+-activated force. Chemically skinned fibers from the soleus and EDL of C57BL/6 mice were studied in order to obtain MHC monomorphic (type I, IIa, IIx, IIb) and polymorphic (I/IIa, IIa/IIx, IIx/IIb) fibers. Fiber MHC isoform content was determined by SDS-PAGE. The mean (±SE) pre- to post-eccentric change in force was −5.2 ± 0.5 kN/m2 (n = 24) for type I fibers, −18.3 ± 1.5 (7) for I/IIa, −5.3 ± 0.7 (27) for IIa, −18.1 ± 2.3 (5) for IIa/IIx, −5.4 ± 0.6 (34) for IIx, −17.8 ± 1.1 (11) for IIx/IIb, and −5.7 ± 0.8 (24) for IIb. Multiple linear regression indicated that, independent of MHC content, greater pre-specific force was associated with a slightly greater post-force deficit (slope = 0.94). With pre-eccentric force held constant, no relationship was found between fiber Vo and post-eccentric force (p = 0.716) . In contrast, data were well described by a model using pre-eccentric force and MHC polymorphism as predictors (p < 0.001; r2 = 0.97): post-force of monomorphic fibers = 0.94(pre-force) + 2.04 kN/m2 post-force of polymorphic fibers = 0.94(pre-force) - 12.15 kN/m2 The significant difference (p < 0.001) in model y-intercepts reveals that, at similar pre-eccentric specific force, MHC polymorphism was associated with a 14 kN/m2 greater eccentric-induced reduction in force vs. monomorphic fibers. We conclude that MHC polymorphism is associated with a heightened sensitivity to high mechanical strain at the level of the myofilament lattice or cytoskeleton.

Electromyographic Data on Myosin Heavy Chain Content of TMD Masticatory Muscles

Electromyographic Data on Myosin Heavy Chain Content of TMD Masticatory Muscles

Electromyographic Data on Myosin Heavy Chain Content of TMD Masticatory Muscles

Electromyographic Data on Myosin Heavy Chain Content of TMD Masticatory Muscles

Muscle Wasting and Impaired Myogenesis in Tumor Bearing Mice Are Prevented by ERK Inhibition

BackgroundThe onset of cachexia is a frequent feature in cancer patients. Prominent characteristic of this syndrome is the loss of body and muscle weight, this latter being mainly supported by increased protein breakdown rates. While the signaling pathways dependent on IGF-1 or myostatin were causally involved in muscle atrophy, the role of the Mitogen-Activated-Protein-Kinases is still largely debated. The present study investigated this point on mice bearing the C26 colon adenocarcinoma.Methodology/Principal FindingsC26-bearing mice display a marked loss of body weight and muscle mass, this latter associated with increased phosphorylated (p)-ERK. Administration of the ERK inhibitor PD98059 to tumor bearers attenuates muscle depletion and weakness, while restoring normal atrogin-1 expression. In C26 hosts, muscle wasting is also associated with increased Pax7 expression and reduced myogenin levels. Such pattern, suggestive of impaired myogenesis, is reversed by PD98059. Increased p-ERK and reduced myosin heavy chain content can be observed in TNFα-treated C2C12 myotubes, while decreased myogenin and MyoD levels occur in differentiating myoblasts exposed to the cytokine. All these changes are prevented by PD98059.Conclusions/SignificanceThese results demonstrate that ERK is involved in the pathogenesis of muscle wasting in cancer cachexia and could thus be proposed as a therapeutic target.

Comparative study on the effect of acid- and alkaline-aided extractions on mechanically separated turkey meat (MSTM): Chemical characteristics of recovered proteins

The study was undertaken to determine the physico-chemical properties of proteins isolated from mechanically separated turkey meat (MSTM) by a pH-shifting technique. The effect of four pH values (2.5, 3.5, 10.5 and 11.5) was investigated. Protein yield did not show any statistical difference between the extractions carried out at pH 2.5, 10.5 and 11.5. However, yield was considerably lower when pH of extraction was 3.5 ( P = 0.0097). Total protein extractability and myofibrillar protein hydrophobicity showed the same pattern, with the highest values at pH 10.5 and the lowest at pH 2.5. No significant ( P > 0.05) differences were found between the various pH of extractions on total, neutral and polar lipids, which on average were equal to 92.3%, 93.0% and 90.7%, respectively. TBARs analysis showed no difference between acid and alkaline treatments; however, the values were significantly lower compared to raw MSTM ( P < 0.0001). SDS-PAGE analysis showed a greater concentration of myosin heavy chain and actin in protein isolates compared to raw MSTM. Amino acid analysis of isolates showed higher concentration of glutamic acid and reduced levels of histidine and methionine compared to raw MSTM. Uronic acid and hydroxyproline analysis revealed that most of the proteoglycans and collagen were deposited in the sediment fraction obtained during the centrifugation step following protein solubilization.

The effects of eccentric contraction on myofibrillar proteins in rat skeletal muscle

The present study investigated the effects of eccentric muscle contractions (ECC) on the content of myofibrillar proteins (my-proteins) and the catalytic activity of myofibrillar ATPase (my-ATPase) in skeletal muscles. Rat extensor digitorum longus and tibialis anterior muscles were exposed to 200-repeated ECC or isometric contractions (ISC) and used for measures of force output and for biochemical analyses, respectively. Whereas in ISC-treated muscles, full restoration of tetanic force was attained after 2days of recovery, force developed by ECC-treated muscles remained depressed (P<0.05) after 6days. The total my-protein content and the relative content of myosin heavy chain (MHC) in total my-proteins were unaltered during 4days of recovery after ECC, but fell (P<0.05) to 55.9 and 63.4% after 6days of recovery, respectively. my-ATPase activity expressed on a my-protein weight basis was unaltered immediately after ECC. However, it decreased (P<0.05) to 75.3, 45.3, and 49.3% after 2, 4 and 6days of recovery, respectively. Total maximal calpain activity measured at 5mM Ca(2+) was significantly augmented (P<0.05) after 2days of recovery, reaching a level of threefold higher after 6days. These alterations were specific for ECC and not observed for ISC. These results suggest that depressions in my-ATPase activity contribute to ECC-induced decreases in force and power which can take a number of days to recover.

Capillary Supply in Relation to Myosin Heavy Chain Fibre Composition of Human Intrinsic Tongue Muscles

The capillary supply and myosin heavy chain (MyHC) composition of three different intrinsic tongue muscles was analysed in the anterior and posterior regions of the human tongue with biochemical and immunohistochemical techniques. Mean capillary density for the whole tongue was 796 ± 82 cap/mm², without regional differences. The overall number of capillaries around each fibre (CAF) was higher in the posterior than in the anterior region (2.5 vs. 2.1, p = 0.009). However, correcting for regional differences in fibre size, CAF per fibre area was higher in the anterior region (4.3 vs. 3.0, p < 0.001). Muscle fibres containing fast MyHCs predominated in the anterior region (78.7%), consisting of MyHCIIa (58.5%), MyHCIIx (1.0%), MyHCIIa+MyHCIIx (11.3%) and MyHCI+MyHCIIa (7.9%). Fibres containing slow MyHC predominated in the posterior region (65.2%), consisting of MyHCI (45.5%) and MyHCI+MyHCIIa (19.7%). A minor fibre population (<2%) contained unusual MyHC isoforms, namely MyHC foetal, MyHC slow-tonic, MyHC α-cardiac or MyHC embryonic. The microvascularization of the human tongue was twice as high as in human limb muscles. Regional similarities in capillary supply, but differences in fibre phenotype composition, suggest that human tongue muscle fibres are fatigue resistant independently of MyHC content. High frequency of hybrid fibres, that is fibres co-expressing two or more MyHC isoforms, indicates a wider spectrum of fibre contractile properties than in limb muscles. In conclusion, human intrinsic tongue muscles showed internal specialization in distribution of MyHC isoforms and capillary supply, but not in the expression of unusual MyHCs.