Proportion Of Myosin Heavy Chain Research Articles

The influence of skeletal muscle mitochondria and sex on critical torque and performance fatiguability in humans.

Critical torque (CT) represents the highest oxidative steady state for intermittent knee extensor exercise, but the extent to which it is influenced by skeletal muscle mitochondria and sex is unclear. Vastus lateralis muscle biopsy samples were collected from 12 females and 12males -matched for relative maximal oxygen uptake normalized to fat-free mass (FFM) (F: 57.3 (7.5) ml(kg FFM)-1 min-1 ; M: 56.8 (7.6) ml(kg FFM)-1 min-1 ; P=0.856) - prior to CT determination and performance fatiguability trials. Males had a lower proportion of myosin heavy chain (MHC) I isoform (40.6 (18.4)%) compared to females (59.5 (18.9)%; P=0.021), but MHC IIa and IIx isoform distributions and protein markers of mitochondrial content were not different between sexes (P > 0.05). When normalized to maximum voluntary contraction (MVC), the relative CT (F: 42.9 (8.3)%; M: 37.9 (9.0)%; P=0.172) and curvature constant, W' (F: 26.6 (11.0) Nms(Nm)-1 ; M: 26.4 (6.5) Nms(Nm)-1 ; P=0.962) were not significantly different between sexes. All protein biomarkers of skeletal muscle mitochondrial content, as well as the proportion of MHC I isoform, positively correlated with relative CT (0.48<r<0.70; P<0.05), and the proportion of MHC IIx isoform correlated positively with relative W' (r=0.57; P=0.007). Indices of performance fatiguability were not different between males and females for MVC- and CT-controlled trials (P > 0.05). Greater mitochondrial protein abundance was associated with attenuated declines in potentiated twitch torque for exercise at 60% MVC (P<0.05); however, the influence of mitochondrial protein abundance on performance fatiguability was reduced when exercise was prescribed relative to CT. Whether these findings translate to whole-body exercise requires additional research. KEY POINTS: The quadriceps critical torque represents the highest intensity of intermittent knee extensor exercise for which an oxidative steady state is attainable, but its relationship with skeletal muscle mitochondrial protein abundance is unknown. Matching males and females for maximal oxygen uptake relative to fat-free mass facilitates investigations of sex differences in exercise physiology, but studies that have compared critical torque and performance fatiguability during intermittent knee extensor exercise have not ensured equal aerobic fitness between sexes. Skeletal muscle mitochondrial protein abundance was correlated with critical torque and fatigue resistance for exercise prescribed relative to maximum voluntary contraction but not for exercise performed relative to the critical torque. Differences between sexes in critical torque, skeletal muscle mitochondrial protein abundance and performance fatiguability were not statistically significant. Our results suggest that skeletal muscle mitochondrial protein abundance may contribute to fatigue resistance by influencing the critical intensity of exercise.

Genotype Score for Iron Status Is Associated with Muscle Fiber Composition in Women.

Human muscle fiber composition is heterogeneous and mainly determined by genetic factors. A previous study reported that experimentally induced iron deficiency in rats increases the proportion of fast-twitch muscle fibers. Iron status has been reported to be affected by genetic factors. As the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms are strongly associated with iron status in humans, we hypothesized that the genotype score (GS) based on these polymorphisms could be associated with the muscle fiber composition in humans. Herein, we examined 214 Japanese individuals, comprising of 107 men and 107 women, for possible associations of the GS for iron status with the proportion of myosin heavy chain (MHC) isoforms (I, IIa, and IIx) as markers of muscle fiber composition. No statistically significant correlations were found between the GS for iron status and the proportion of MHC isoforms in all participants. When the participants were stratified based on sex, women showed positive and negative correlations of the GS with MHC-IIa (age-adjusted p = 0.020) and MHC-IIx (age-adjusted p = 0.011), respectively. In contrast, no correlation was found in men. In women, a 1-point increase in the GS was associated with 2.42% higher MHC-IIa level and 2.72% lower MHC-IIx level. Our results suggest that the GS based on the TMPRSS6 rs855791 T/C and HFE rs1799945 C/G polymorphisms for iron status is associated with muscle fiber composition in women.

Effects of maternal dietary supplementation of phytosterol esters during gestation on muscle development of offspring in mice

The development of muscle in the embryo, which is crucial for postnatal skeletal muscle growth, has been investigated widely. Much has been learned during the past several decades about the role of maternal nutrition in the outcome of pregnancy. Protein and carbohydrate levels during pregnancy have been shown to be important in the development of offspring, especially muscle development. However, the maternal effects of steroids were still not clear. Phytosterol esters (PEs) are produced by the esterification of phytosterols and fatty acids and have many beneficial functions, such as anti-inflammation and hypolipemic functions. Through the effect of regulation on lipid metabolism, can pregnant mice fed with PEs show any programming effect on the muscle development of offspring? In our study, PEs were supplied to the maternal diet, and changes in maternal lipid metabolism and the development of offspring skeletal muscle were detected. As a result, the amniotic fluid total bile acid (TBA) and total cholesterol (TC) levels were decreased; the growth of offspring was significantly faster than that of the control group until 6 weeks of age. Adult offspring had a higher lean mass index and grip strength. In skeletal muscle, the proportion of myosin heavy chain (MHC) 1 was significantly decreased, while the proportion of MHC 2 b was increased. In conclusion, maternal PEs significantly reduced sterols in the amniotic fluid, while skeletal muscle development was promoted in the offspring.

The Muscle Fiber Profiles, Mitochondrial Content, and Enzyme Activities of the Exceptionally Well-Trained Arm and Leg Muscles of Elite Cross-Country Skiers.

As one of the most physically demanding sports in the Olympic Games, cross-country skiing poses considerable challenges with respect to both force generation and endurance during the combined upper- and lower-body effort of varying intensity and duration. The isoforms of myosin in skeletal muscle have long been considered not only to define the contractile properties, but also to determine metabolic capacities. The current investigation was designed to explore the relationship between these isoforms and metabolic profiles in the arms (triceps brachii) and legs (vastus lateralis) as well as the range of training responses in the muscle fibers of elite cross-country skiers with equally and exceptionally well-trained upper and lower bodies. The proportion of myosin heavy chain (MHC)-1 was higher in the leg (58 ± 2% [34–69%]) than arm (40 ± 3% [24–57%]), although the mitochondrial volume percentages [8.6 ± 1.6 (leg) and 9.0 ± 2.0 (arm)], and average number of capillaries per fiber [5.8 ± 0.8 (leg) and 6.3 ± 0.3 (arm)] were the same. In these comparable highly trained leg and arm muscles, the maximal citrate synthase (CS) activity was the same. Still, 3-hydroxy-acyl-CoA-dehydrogenase (HAD) capacity was 52% higher (P < 0.05) in the leg compared to arm muscles, suggesting a relatively higher capacity for lipid oxidation in leg muscle, which cannot be explained by the different fiber type distributions. For both limbs combined, HAD activity was correlated with the content of MHC-1 (r2 = 0.32, P = 0.011), whereas CS activity was not. Thus, in these highly trained cross-country skiers capillarization of and mitochondrial volume in type 2 fiber can be at least as high as in type 1 fibers, indicating a divergence between fiber type pattern and aerobic metabolic capacity. The considerable variability in oxidative metabolism with similar MHC profiles provides a new perspective on exercise training. Furthermore, the clear differences between equally well-trained arm and leg muscles regarding HAD activity cannot be explained by training status or MHC distribution, thereby indicating an intrinsic metabolic difference between the upper and lower body. Moreover, trained type 1 and type 2A muscle fibers exhibited similar aerobic capacity regardless of whether they were located in an arm or leg muscle.

MiR-204-5p regulates C2C12 myoblast differentiation by targeting MEF2C and ERRγ

Myogenic differentiation, which occurs in the process of muscle development, is a highly ordered process. Increasing evidence indicates that microRNAs (miRNAs) are important regulators in myogenic processes. In this study, we found that miR-204-5p expression gradually decreased when myoblasts were induced to differentiate. Our results suggested that miR-204-5p blunted myoblast differentiation, which was accompanied with a decreased proportion of myosin heavy chain (MyHC)-positive cells in myoblasts with augmented expression of miR-204-5p. Furthermore, overexpression of miR-204-5p significantly decreased the MyHC composition of slow-twitch fibers in myoblasts. Luciferase activity assays confirmed that miR-204-5p directly targeted the 3′-untranslated region (3′-UTR) of myocyte enhancer factor 2C (MEF2C) and estrogen-related receptor gamma (ERRγ). Small interfering RNA (siRNA) technology successfully inhibited the expression of MEF2C and ERRγ. Interference with MEF2C or ERRγ inhibited myoblast differentiation and the formation of slow-twitch fibers. Meanwhile, co-transfection of either si-MEF2C or si-ERRγ with miR-204-5p mimics resulted in a more severe attenuation of myogenic differentiation. In summary, this study demonstrates that miR-204-5p inhibits myoblast differentiation by targeting MEF2C and ERRγ. Our findings suggest that miR-204-5p is a potential regulator that could influence myogenesis.

Role of selected polymorphisms in determining muscle fiber composition in Japanese men and women.

Genetic polymorphisms and sex differences are suggested to affect muscle fiber composition; however, no study has investigated the effects of genetic polymorphisms on muscle fiber composition with respect to sex differences. Therefore, the present study examined the effects of genetic polymorphisms on muscle fiber composition with respect to sex differences in the Japanese population. The present study included 211 healthy Japanese individuals (102 men and 109 women). Muscle biopsies were obtained from the vastus lateralis to determine the proportion of myosin heavy chain (MHC) isoforms (MHC-I, MHC-IIa, and MHC-IIx). Moreover, we analyzed polymorphisms in α-actinin-3 gene (ACTN3; rs1815739), angiotensin-converting enzyme gene (ACE; rs4341), hypoxia-inducible factor 1 α gene (rs11549465), vascular endothelial growth factor receptor 2 gene (rs1870377), and angiotensin II receptor, type 2 gene (rs11091046), by TaqMan single-nucleotide polymorphism genotyping assays. The proportion of MHC-I was 9.8% lower in men than in women, whereas the proportion of MHC-IIa and MHC-IIx was higher in men than in women (5.0 and 4.6%, respectively). Men with the ACTN3 RR + RX genotype had a 4.8% higher proportion of MHC-IIx than those with the ACTN3 XX genotype. Moreover, men with the ACE ID + DD genotype had a 4.7% higher proportion of MHC-I than those with the ACE II genotype. Furthermore, a combined genotype of ACTN3 R577X and ACE insertion/deletion (I/D) was significantly correlated with the proportion of MHC-I (r = −0.23) and MHC-IIx (r = 0.27) in men. In contrast, no significant correlation was observed between the examined polymorphisms and muscle fiber composition in women. These results suggest that the ACTN3 R577X and ACE I/D polymorphisms independently affect the proportion of human skeletal muscle fibers MHC-I and MHC-IIx in men but not in women.NEW & NOTEWORTHY In men, the RR + RX genotype of the α-actinin-3 gene (ACTN3) R577X polymorphism was associated with a higher proportion of myosin heavy chain (MHC)-IIx. The ID + DD genotype of the angiotensin-converting enzyme gene (ACE) insertion/deletion (I/D) polymorphism, in contrast to a previous finding, was associated with a higher proportion of MHC-I in men. In addition, the combined genotype of these polymorphisms was correlated with the proportion of MHC-I and MHC-IIx in men. Thus ACTN3 R577X and ACE I/D polymorphisms influence the muscle fiber composition in Japanese men.

Pseudouridine synthase 1 deficient mice, a model for Mitochondrial Myopathy with Sideroblastic Anemia, exhibit muscle morphology and physiology alterations.

Mitochondrial myopathy with lactic acidosis and sideroblastic anemia (MLASA) is an oxidative phosphorylation disorder, with primary clinical manifestations of myopathic exercise intolerance and a macrocytic sideroblastic anemia. One cause of MLASA is recessive mutations in PUS1, which encodes pseudouridine (Ψ) synthase 1 (Pus1p). Here we describe a mouse model of MLASA due to mutations in PUS1. As expected, certain Ψ modifications were missing in cytoplasmic and mitochondrial tRNAs from Pus1−/− animals. Pus1−/− mice were born at the expected Mendelian frequency and were non-dysmorphic. At 14 weeks the mutants displayed reduced exercise capacity. Examination of tibialis anterior (TA) muscle morphology and histochemistry demonstrated an increase in the cross sectional area and proportion of myosin heavy chain (MHC) IIB and low succinate dehydrogenase (SDH) expressing myofibers, without a change in the size of MHC IIA positive or high SDH myofibers. Cytochrome c oxidase activity was significantly reduced in extracts from red gastrocnemius muscle from Pus1−/− mice. Transmission electron microscopy on red gastrocnemius muscle demonstrated that Pus1−/− mice also had lower intermyofibrillar mitochondrial density and smaller mitochondria. Collectively, these results suggest that alterations in muscle metabolism related to mitochondrial content and oxidative capacity may account for the reduced exercise capacity in Pus1−/− mice.

Role of cyclic AMP sensor Epac1 in masseter muscle hypertrophy and myosin heavy chain transition induced by β2-adrenoceptor stimulation.

The predominant isoform of β-adrenoceptor (β-AR) in skeletal muscle is β2-AR and that in the cardiac muscle is β1-AR. We have reported that Epac1 (exchange protein directly activated by cAMP 1), a new protein kinase A-independent cAMP sensor, does not affect cardiac hypertrophy in response to pressure overload or chronic isoproterenol (isoprenaline) infusion. However, the role of Epac1 in skeletal muscle hypertrophy remains poorly understood. We thus examined the effect of disruption of Epac1, the major Epac isoform in skeletal muscle, on masseter muscle hypertrophy induced by chronic β2-AR stimulation with clenbuterol (CB) in Epac1-null mice (Epac1KO). The masseter muscle weight/tibial length ratio was similar in wild-type (WT) and Epac1KO at baseline and was significantly increased in WT after CB infusion, but this increase was suppressed in Epac1KO. CB treatment significantly increased the proportion of myosin heavy chain (MHC) IIb at the expense of that of MHC IId/x in both WT and Epac1KO, indicating that Epac1 did not mediate the CB-induced MHC isoform transition towards the faster isoform. The mechanism of suppression of CB-mediated hypertrophy in Epac1KO is considered to involve decreased activation of Akt signalling. In addition, CB-induced histone deacetylase 4 (HDAC4) phosphorylation on serine 246 mediated by calmodulin kinase II (CaMKII), which plays a role in skeletal muscle hypertrophy, was suppressed in Epac1KO. Our findings suggest that Epac1 plays a role in β2-AR-mediated masseter muscle hypertrophy, probably through activation of both Akt signalling and CaMKII/HDAC4 signalling.

Noninvasive Estimation of Myosin Heavy Chain Composition in Human Skeletal Muscle

Information on muscle fiber type composition is of great importance in muscle physiology and athletic performance. Because there are only a few techniques available that noninvasively and accurately provide an estimate of muscle fiber type composition, the development of additional and alternative approaches is required. Twenty-seven participants (21 men, 6 women) with an average age of 43 ± 18 yr, height of 175 ± 7 cm, and mass of 74 ± 12 kg participated in the study. Delay, contraction, and half relaxation times were calculated from tensiomyographic radial twitch responses of the vastus lateralis muscle. Univariate and multiple linear regression analyses were used to correlate the proportion of myosin heavy chain I (%MHC-I) in a biopsy obtained from the same muscle with a single and all three radial twitch parameters. Delay, contraction, and half relaxation times all correlated with %MHC-I (r = 0.612, 0.878, and 0.669, respectively, at P ≤ 0.001). When all three parameters were included in a multiple linear regression, the correlation with the %MHC-I was even better (R = 0.933, P < 0.001). These data suggest that time parameters of the skeletal muscle mechanical radial twitch response, measured with a contact linear displacement sensor, can be used as an accurate noninvasive predictor of the %MHC-I in a muscle.

48 MUSCLE CHARACTERISTICS OF BOVINE CLONE OFFSPRING F1 COMPARED WITH CLONES

Information on clone offspring F1 is limited, especially in species with a long inter-generation interval such as cattle. As cloned cattle exhibit a slight delay in muscle maturation until puberty (Jurie et al. 2009 Animal 3, 244-250), the present study aimed to investigate the contractile and metabolic muscle characteristics of F1 at 8, 12, and 18 months of age. Repeated biopsies of the semitendinosus muscle were collected on 10 F1 heifers born after AI of cloned cows at the experimental farm of INRA. Muscle characteristics of these offspring were compared with those of 9 female clones and 8 AI control heifers previously biopsied at the same ages. All animals (clones, F1, and controls) were female Holstein, born and raised under the same conditions in the same farm. Biopsy samples were stored frozen at -80°C until analysis for contractile and metabolic characteristics. The type of contractile fibers was determined from the proportion of the different myosin heavy chain (MyHC) isoforms separated by electrophoresis. Oxidative metabolism was assessed by isocitrate dehydrogenase (ICDH) and cytochrome-c oxidase (COX) activities (μmol min-1 per gram of muscle). Data were analyzed separately for each time of biopsy using the GLM procedure of SAS (SAS Institute, Cary, NC, USA). The statistical model contained the group as fixed effect. When a significant effect was detected, differences between least squares means were further separated by the PDIFF option of SAS. Comparison of contractile characteristics from the 3 groups of animals is presented in Table 1. The proportion of MyHC I (slow oxidative isoform) and MyHC IIx (fast glycolytic isoform) in the muscles of F1 was not significantly different from those of controls at 8 and 12 months of age. F1 had different muscle contractile properties compared with clones at 12 months of age. At 8 months of age, F1 had greater ICDH activity than controls (1.39 ± 0.22 v. 0.54 ± 0.007; P ≤ 0.002) and greater COX activities (11.4 ± 1.6 v. 4.2 ± 0.9; P ≤ 0.003), but this was not observed later on. Altogether, these data indicate that the muscles of F1 were more oxidative than those of controls. This was not related to a higher percentage of type I fibers but rather to a higher percentage of type IIA fibers. A delay in muscle maturation was only partially found in F1. Table 1.Contractile characteristics (mean ± SE) of the semitendinosus muscle from controls (n = 8), clones (n = 9) and clone offspring (F1, n = 10) heifers

Comparison of cloned and non-cloned Holstein heifers in muscle contractile and metabolic characteristics

Muscle contractile and metabolic characteristics were studied on nine cloned and eight non-cloned (control) heifers. The animals were submitted to repeated biopsies of the semitendinosus (ST) muscle at the ages of 8, 12, 18 and 24 months. The contractile type was determined from the proportion of the different myosin heavy chain (MyHC) isoforms separated by electrophoresis. Glycolytic metabolism was assessed by lactate dehydrogenase (LDH) activity, and oxidative metabolism was assessed by isocitrate dehydrogenase (ICDH), cytochrome-c oxidase (COX) and β-hydroxyacyl-CoA dehydrogenase (HAD) activities. In cloned heifers at 8 months of age, there was a greater proportion of MyHC I (slow oxidative isoform) and MyHC IIa (fast oxido-glycolytic isoform), a lower proportion of MyHC IIx (fast glycolytic isoform), greater COX and HAD activity and a lower LDH/ICDH ratio compared with control heifers. Thus, young cloned heifers had slower muscle types associated with a more oxidative muscular metabolism than control heifers. From 12 months of age onwards, no significant differences were observed between cloned and control heifers. A delay in muscle differentiation and maturation in cloned heifers is hypothesised and discussed.

Distribution of Myosin Heavy Chain Isoform in Human Extraocular Muscles

Purpose: To provide quantitative data on the distribution of MyHCeom and compare the proportion of myosin heavy chain (MyHC) isoforms between the central and peripheral regions of human extraocular muscles (EOMs). Methods: Medial rectus, lateral rectus, superior rectus, inferior rectus, superior oblique, and inferior oblique muscle samples were taken from three men with brain death. To examine the longitudinal distribution of myosin isoforms, the muscles were divided into central and peripheral portions of equal length. Electrophoresis and densitometry were used to quantify the distribution of MyHC isoforms. Results: Electrophoresis of whole-muscle extracts of sampled EOMs revealed four MyHC bands that were identified as MyHCI, MyHCeom, MyHCIIa, and MyHCIIx. The proportion of MyHCeom was higher in the central region, whereas the proportion of MyHCIIa was higher in the peripheral region. The relative proportions of MyHCI, MyHCeom, and MyHCIIa were not significantly different among the EOMs. There was a tendency for higher levels of MyHCIIx in the inferior rectus muscle. Conclusions: The proportion of MyHCeom was higher in the central region of human EOMs. Further studies are needed to investigate the consequences of this distributional difference on the function of EOMs.

Adaptive responses to creatine loading and exercise in fast-twitch rat skeletal muscle

We investigated the effects of chronic creatine loading and voluntary running (Run) on muscle fiber types, proteins that regulate intracellular Ca2+, and the metabolic profile in rat plantaris muscle to ascertain the bases for our previous observations that creatine loading results in a higher proportion of myosin heavy chain (MHC) IIb, without corresponding changes in contractile properties. Forty Sprague-Dawley rats were assigned to one of four groups: creatine-fed sedentary, creatine-fed run-trained, control-fed sedentary, and control-fed run-trained animals. Proportion and cross-sectional area increased 10% and 15% in type IIb fibers and the proportion of type IIa fibers decreased 11% in the creatine-fed run-trained compared with the control-fed run-trained group (P < 0.03). No differences were observed in fast Ca2+-ATPase isoform SERCA1 content (P > 0.49). Creatine feeding alone induced a 41% increase (P < 0.03) in slow Ca2+-ATPase (SERCA2) content, which was further elevated by 33% with running (P < 0.02). Run training alone reduced parvalbumin content by 50% (P < 0.05). By comparison, parvalbumin content was dramatically decreased by 75% (P < 0.01) by creatine feeding alone but was not further reduced by run training. These adaptive changes indicate that elevating the capacity for high-energy phosphate shuttling, through creatine loading, alleviates the need for intracellular Ca2+ buffering by parvalbumin and increases the efficiency of Ca2+ uptake by SERCAs. Citrate synthase and 3-hydroxyacyl-CoA dehydrogenase activities were elevated by run training (P < 0.003) but not by run training + creatine feeding. This indicates that creatine loading during run training supports a faster muscle phenotype that is adequately supported by the existing glycolytic potential, without changes in the capacity for terminal substrate oxidation.

Effect of fiber type on postmortem proteolysis in longissimus muscle of Landrace and Korean native black pigs

The current study was conducted to characterize objective meat quality, fiber type and their relations to postmortem proteolysis in longissimus muscle of Landrace and Korean native black (KNP) pigs. Longissimus muscles from each 10 market-weighted male pigs were removed after conventional slaughtering and chilling procedures, and aged for 1 or 7 days at 4 °C to determine WB-shear force, objective meat color, proportion of myosin heavy chain I (MyHC I), intramuscular fat content and rate of proteolysis by a proteomics approach. KNP had a significantly ( p < 0.05) higher content of MyHC I, and that concurred with greatly ( p < 0.05) higher intramuscular fat content and Hunter a ∗ value, and significantly ( p < 0.05) lower drip loss than those seen in Landrace. One-dimension SDS-PAGE indicated that GAPDH, troponin I and creatine kinase were prominent proteolytic products during chiller ageing. By applying a gel-based proteome analysis, 26 proteins were identified, which showed different degradation properties during ageing between the breeds. Biopsied sample revealed that myosin regulatory light chain 2, myosin light chain isotype v/sb, fatty acid-binding protein and albumin were expressed at a greatly higher level for KNP, but their relation to fiber type (or genetic background) is unclear. It was particular noticeable that different actin isoforms showed various degradation behavior during ageing time.

RNA content differs in slow and fast muscle fibers: implications for interpretation of changes in muscle gene expression.

Quantification of a specific muscle mRNA per total RNA (e.g., by Northern blot analysis) plays a crucial role in assessment of developmental, experimental, or pathological changes in gene expression. However, total RNA content per gram of a particular fiber type may differ as well. We have tested this possibility in the distinct fiber types of adult rat skeletal muscle. Sections of single fibers were hybridized against 28S rRNA as a marker for RNA content. Quantification of the hybridization showed that the 28S rRNA content decreases in the order I>IIA>IIX>IIB, where Type I fibers show a five- to sixfold higher expression level compared to Type IIB fibers. Results were verified with an independent biochemical determination of total RNA content performed on pools of histochemically defined freeze-dried single fibers. In addition, the proportion of myosin heavy chain (MHC) mRNA per microgram of total RNA was similar in slow and fast fibers, as demonstrated by Northern blot analysis. Consequently, Type I fibers contain five- to sixfold more MHC mRNA per microgram of tissue than IIB fibers. These differences are not reflected in the total fiber protein content. This study implies that proper assessment of mRNA levels in skeletal muscle requires evaluation of total RNA levels according to fiber type composition.

Changes in functional characteristics and myosin heavy chain composition in m. vastus medialis before and after arthroscopy for knee injury.

The aim of this study was to investigate the influence of restriction of movement on the functional characteristics and myosin heavy chain composition of m. vastus medialis. The subjects of this study were 13 arthroscopically treated patients with meniscus lesions (both men and women, mean age 28 years). All measurements were performed and biopsies were taken bilaterally before and 6 months after knee arthroscopy. Thigh girth was measured to determine the degree of atrophy. A tendency towards decreased thigh girth in the injured leg was noted. As an estimate of functional characteristics, maximum voluntary contraction (MVC) was measured. The MVC of the injured limb was lower than that of the non-injured limb (mean values 548.2 +/- 54.1 and 705.4 +/- 48.2 N respectively; P < 0.05). The myosin heavy chain (MHC) composition was determined electrophoretically. The proportion of MHC I isoform decreased from 59.35% to 47.97% (P < 0.05).

EFFECTS OF CHITOSAN ON GELLING PROPERTIES OF LOW QUALITY SURIMI

ABSTRACT In order to produce a strong and elastic gel from low quality walleye pollock surimi, use of chitosan was examined. The strength of gels was nearly doubled by the addition of 1.5% chitosan when salted surimi pastes were set below 25C. In contrast, chitin did not cause any changes in the physical texture of gels. When salted surimi pastes containing 1.5% chitosan were set at 20C, a large decrease in the proportion of myosin heavy chain was observed with a concomitant increase in components with molecular weights heavier than myosin heavy chain. Since the addition of EGTA, an inhibitor of transglutaminase, to surimi reduced gel strength and minimized myosin heavy chain polymerization, it is suggested that the enhancing effect ofchitosan on the gel formation of walleye pollock surimi could be due to the activity of the endogenous transglutaminase known to be present in this surimi.