Muscle protein turnover in endurance training: a review.

There has been much debate about skeletal muscle capacity to adapt to long-lasting endurance exercise. Exercise in the aerobic zone of metabolism does not result in hypertrophy of skeletal muscle fibres but increases their oxidative capacity. The duration and intensity of an exercise session determines the time period of depressed muscle protein synthesis and increased degradation rate during the recovery period after exercise. Protein turnover characterizes the renewal processes of muscle proteins and the functional capacity of muscle. The turnover rate of myofibrillar proteins is slow in comparison with mitochondrial proteins and depends on the oxidative capacity of muscle fibres. The turnover rate of myofibrillar proteins in the same muscle is different and is also different within the myosin molecule between myosin heavy and light chain isoforms. The turnover rate of muscle proteins in endurance training shows the adaptation of skeletal muscle to long-lasting exercise via remodelling of muscle structures. Adaptational coordination between myofibrillar and mitochondrial compartments shows the physiological role and adaptational capacity of skeletal muscle to endurance training. It is challenging to use muscle protein turnover for the purposes of monitoring the training process of endurance athletes, optimizing training programs and preventing overtraining.

Myosin heavy chain pattern in the Akhal-Teke horses.

This study investigates the myosin heavy chain (MyHC) isoform composition in the gluteus medius muscle of the Akhal-Teke horses using SDS-PAGE (sodium dodecyl sulfate polyacrylamide gel electrophoresis). Fifteen horses aged between 1.5 and 23.5 years were used in this study and divided into three age groups: 1.5 to 4 (n = 6), 9 to 13 (n = 5) and 18.5 to 23.5 years (n = 4). The average content of the MyHC I isoform was 11.72 ± 1.07% (variation between individuals: 7.09% to 20.14%). The relative content of the MyHC IIa and IIx isoforms was subsequently 38.20 ± 1.46% (30.73% to 48.78%) and 50.07 ± 1.10% (43.8% to 56.78%) from the total MyHC. The MyHC pattern in the skeletal muscles of the Akhal-Teke horses shows that the muscles of these horses have a high capacity both for endurance and speed.

Changes in fast-twitch muscle oxidative capacity and myosin isoforms modulation during endurance training.

AIM: The purpose of this study was to investigate the effect of endurance training on changes in myosin heavy (MyHC) and light (MyLC) chains expression, their turnover rate in fast-twitch (FT) skeletal muscles, and relations with changes in contractile proteins degradation rate and muscle oxidative capacity. METHODS: Wistar rats were run at 35 m/min for 6 weeks (from 10 min to 60 min per day, from 1.8 kJ to 7 kJ per training session and power of work was 1.5 W). The FT muscles were used for measurement of myosin isoforms and oxidative capacity. Double isotope method ((3)H/(14)C) was used. RESULTS: During endurance training in plantaris and extensor digitorum longus (EDL) muscles the relative content of MyHC IIb isoform decreased while there was an increase in the relative content of MyHC IIa and IId isoforms. MyLC 3(fast) isoform increased in FT muscles. Degradation rate of MyHC isoforms increased during endurance training simultaneously with the increase of contractile proteins degradation and increase of cytochrome aa3 content in FT muscles. Endurance training increased MyHC I, IIa and IId isoform turnover rate, whereas MyHC IIb and MyLC isoforms turnover rate did not change significantly. CONCLUSIONS: Adaptation of FT skeletal muscles to endurance training shows coordination between increase in oxidative capacity and faster turnover rate of MyHC isoforms in contractile apparatus. FT muscles show high potential of recruitment in endurance training.

The profile and distribution of myosin heavy chain isoforms in middle-aged sedentary persons.

AIM: Human lifestyle has drastically changed during the past century as the share of physical work in daily life has decreased. The purpose of the present study was to examine the distribution of myosin heavy chain (MHC) isoforms in middle-aged sedentary persons, to compare the proportion of MHC isoforms of middle-aged and young sedentary persons and to demonstrate the effect of physical activity of MHC isoforms in middle-aged sedentary persons. METHODS: Eighty-nine middle-aged sedentary and 13 young sedentary persons volunteered for the study. Thirty middle-aged sedentary subjects participated in strength-conditional exercise program during 9 months. Vertical jumping height and maximal anaerobic work capacity were measured. Muscle samples were taken from vastus lateralis muscle. MHC isoform composition was determined by SDS-PAGE. RESULTS: Variation of MHC I and MHC IIa isoforms in middle-age sedentary persons demonstrated normal distribution. Significant differences of MHC isoform proportions between middle-aged and young sedentary participants were not observed. The proportion of MHC IIx decreased significantly after the exercise period that significantly improved the maximal anaerobic power and jumping height of participants. CONCLUSIONS: Normal distribution illustrated the proportion of MHC I and MHC IIa isoforms in 89 middle-aged sedentary persons while significant differences of MHC isoforms proportion between young and middle-aged sedentary persons were not observed. Even small increase of physical activity improved physical performance and decrease the MHC IIx proportion of middle-aged sedentary persons. Physically active lifestyle in middle age, when age-related changes have not started yet, may delay age-related changes in skeletal muscle.

Endurance training: volume-dependent adaptational changes in myosin.

The purpose of this study was to find the effect of different endurance training volumes on the composition and turnover of myosin. Sixteen-week-old male rats of the Wistar strain were divided into three different volume-based training groups. Changes in myosin heavy chain (MyHC), myosin light chain (MyLC) isoforms' composition, their synthesis rate, as well as myosin binding C-protein synthesis rate, and muscle protein degradation rate were measured. In slow-twitch (ST) soleus (Sol) muscle MyHC I isoform relative content increased and MyHC IIa isoform decreased during excessive increase in the volume of endurance training (ET). In plantaris (Pla) muscle excessive increase in ET volume decreased MyHC I and IIb isoforms, and increased MyHC IIa and IId relative content. In extensor digitorum longus (EDL) muscle the relative content of MyHC IId isoform increased during ET, but excessive increase in training volume decreased it. In Pla muscle the relative content of MyLC 1 (slow) isoform decreased during ET, but excessive increase in ET volume decreased the relative content of MyLC 3 (fast) isoform in both fast-twitch (FT) muscles. Decrease in MyHC and myosin binding C-protein synthesis rate in Pla muscle had significant correlation with ET volume (r = - 0.537, p < 0.05 and r = - 0.727, p < 0.001 subsequently). MyHC I and IIb isoforms and MyLC 3 (fast) isoform in Pla muscle and MyHC IIb, IId and MyLC 3 (fast) isoforms in EDL muscle are the most sensitive to the increase in ET volume. Excessive increase in ET volume leads to a decrease in physical working capacity. The degradation of muscle protein increased during ET in all groups.

Composition and turnover of contractile proteins in volume-overtrained skeletal muscle.

The purpose of this study was to find the composition shift of myosin heavy chain (MyHC) isoforms in overtraining in fast- and slow-twitch skeletal muscles and different changes in MyHC isofom composition, synthesis and turnover rate between 4-week and 6-week overtraining. Male Wistar rats were randomly assigned to 4-week and 6-week endurance training, 4-week and 6-week overtraining groups. Plantaris (Pla), extensor digitorum longus (EDL), and soleus (Sol) muscles were studied. Daily excretion of 3-methylhistidine (3-MeHis) pool as an indicator for protein degradation increased in the 4-week and 6-week overtraining group to 4.04 +/- 0.21 and 4.32 +/- 0.23 %/day subsequently in comparison with the control group (2.16 +/- 14 %/day, p < 0.001). In Pla muscle MyHC I isoform synthesis rate was 33 200 +/- 2150 (after 6-week overtraining 27 100 +/- 1800, p < 0.05), IIa 32 600 +/- 2100; IId 27 300 +/- 1890 and IIb isoform 20 100 +/- 1600 (after 6-week overtraining 15 500 +/- 1400, p < 0.05) dpm/M leucine/min. Actin synthesis rate increased in fast-twitch muscles during 4- and 6-week overtraining, and in soleus muscle during 6-week overtraining. In EDL and Sol muscle MyHC isoform composition during 6-week overtraining did not change significantly. During the 6-week overtraining the relative content of MyHC I and IIb isoforms decreased and IIa and IId isoforms increased in Pla muscle. The initial increase of MyHC IIb isoform after 4-week overtraining shows the higher stability of this isoform in comparison with MyHC I isoform in fast-twitch muscles during high volume exercise.

The effect of mechanical loading on the MyHC synthesis rate and composition in rat plantaris muscle.

The aim of this study was to investigate the response of protein synthesis rate, particularly myosin heavy chain (MyHC) isoforms synthesis and the magnitude of its isoform transformation in fast-twitch plantaris muscle, to different modes of prolonged mechanical loading. Different protocols of mechanical loading were used: resistance training (RT), compensatory hypertrophy (CH) of m. plantaris after tenotomy of m. gastrocnemius and a combination of the two previous loadings (RT + CH). During the different modes of loading, plantaris muscle hypertrophy in RT group was approximately 10 %, CH approximately 40 % and CH + RT approximately 44 %. MyHC I and IID isoform synthesis rate increased in all experimental groups, as well as their relative content. MyHC IIA relative content decreased during RT and RT + CH and increased during CH. MHC IIB isoform relative content decreased in all experimental groups, but compared with CH in CH + RT MyHC IIB isoform content increased in plantaris muscle. These results demonstrate that different modes of mechanical loading resulted in the selective up- and down-regulation of MyHC isoforms in fast-twitch skeletal muscle. The synthesis rate and relative content of the two fastest isoforms of MyHC IIB and IID are regulated to different directions during mechanical loading.

Radiotherapy treatment planning for patients with non-small cell lung cancer using positron emission tomography (PET).

PURPOSE: Many patients with non-small cell lung cancer (NSCLC) receive external beam radiation therapy as part of their treatment. Three-dimensional conformal radiation therapy (3DCRT) commonly uses computed tomography (CT) to accurately delineate the target lesion and normal tissues. Clinical studies, however, indicate that positron emission tomography (PET) has higher sensitivity than CT in detecting and staging of mediastinal metastases. Imaging with fluoro-2-deoxyglucose (FDG) PET in conjunction with CT, therefore, can improve the accuracy of lesion definition. In this pilot study, we investigated the potential benefits of incorporating PET data into the conventional treatment planning of NSCLC. Case-by-case, we prospectively analyzed planning target volume (PTV) and lung toxicity changes for a cohort of patients. MATERIALS AND METHODS: We have included 11 patients in this study. They were immobilized in the treatment position and CT simulation was performed. Following CT simulation, PET scanning was performed in the treatment position using the same body cast that was produced for CT simulation and treatment. The PTV, along with the gross target volume (GTV) and normal organs, was first delineated using the CT data set. The CT and PET transmission images were then registered in the treatment planning system using either manual or automated methods, leading to consequent registration of the CT and emission images. The PTV was then modified using the registered PET emission images. The modified PTV is seen simultaneously on both CT and PET images, allowing the physician to define the PTV utilizing the information from both data sets. Dose-volume histograms (DVHs) for lesion and normal organs were generated using both CT-based and PET+CT-based treatment plans. RESULTS: For all patients, there was a change in PTV outline based on CT images versus CT/PET fused images. In seven out of 11 cases, we found an increase in PTV volume (average increase of 19%) to incorporate distant nodal disease. Among these patients, the highest normal-tissue complication probability (NTCP) for lung was 22% with combined PET/CT plan and 21% with CT-only plan. In other four patients PTV was decreased an average of 18%. The reduction of PTV in two of these patients was due to excluding atelectasis and trimming the target volume to avoid delivering higher radiation doses to nearby spinal cord or heart. CONCLUSIONS: The incorporation of PET data improves definition of the primary lesion by including positive lymph nodes into the PTV. Thus, the PET data reduces the likelihood of geographic misses and hopefully improves the chance of achieving local control.

Radiation Dose Assessment for I-131 Therapy of Thyroid Cancer Using I-124 PET Imaging.

The goal for this work was to develop a method to determine the feasibility of estimating absorbed dose distribution of I-131 thyroid therapy using I-124 PET images of residual thyroid lesions with the dose constraint of 200 cGy to blood, that is a surrogate for bone marrow toxicity. A dose response study has been carried out on 3 patients with papillary thyroid carcinoma. Those patients were given 15-37 MBq of I-124 along with 74-185 MBq of I-131. PET imaging was performed 2-4 hour and then at 24 hour and either 48 hour, or 72 hour post-infusion. Lesion masses were computed from PET images using an adaptive thresholding technique. The definition of the boundary enabled determination of the iodine activity within the lesion. Time-activity curves were fitted to estimate the cumulated activity and therefore the absorbed dose per MBq administered. Daily blood and total body counts were performed on the patients using a multichannel analyzer with windows set for both I-131 (364 keV) and I-124 (511 keV). Cross-talk corrections from one isotope into the alternate window was determined using a standard of each respective isotope. At maximum-tolerated-activity (MTA) that delivers 200 cGy radiation dose to the blood, the dose to lesions from I-131 varied from 0.04 to 2.44 cGy/MBq (1.57-90.48 rads/mCi) with effective half-lives for I-124 ranging from 0.58 to 1.86 days. The three-dimensional absorbed dose distribution in the thyroid lesions was calculated by convolving the activity values with an I-131 point-source kernel using a Fast Hartley Transform. The calculated mean absorbed dose distribution was displayed as isodose lines on PET images that can be used to refine the amount of administered activity. PET with I-124 may improve the absorbed dose estimates from radioiodine therapy with I-131 in the treatment of thyroid cancer. The capability of estimating I-131 mean absorbed dose distributions from serial I-124 PET images can lead to patient-specific treatment planning for thyroid therapy.

The effect of autografting on the myosin composition in skeletal muscle fibers.

The purpose of the study was to investigate the changes in myosin heavy chain (MHC) and myosin light chain (MLC) isoforms following autotransplantation of extensor digitorum longus muscles. Muscles were grafted in "standard" and "nerve-intact" conditions. MHC and MLC isoforms were analyzed by sodium dodecyl sulphate gel electrophoresis. Changes in MHC isoforms 10, 30, and 60 days after grafting were similar in the "standard" and the "nerve-intact" grafts. In contrast to MHC, changes in MLC were different in the 10th day groups, but the same in the 30th day groups. Sixty days after grafting the content of MLC isoforms was the same as the control muscles. These data indicate that transient loss of functional innervation, even for a short time, has permanent effect on the composition of MHC but not MLC isoforms in regenerating skeletal muscle fibers.

Effect of muscular activity on the turnover rate of actin and myosin heavy and light chains in different types of skeletal muscle.

In endurance-trained rats the myosin HC have a more rapid turnover rate than in control animals in all three types of skeletal muscle fibres, but in sprint-trained rats only in fast-glycolytic and fast-oxidative-glycolytic fibres. A comparison of the actin turnover rate in sprint- and endurance-trained animals shows that in both groups there are more rapid turnover rates in all types of muscle fibres in comparison with control rats. During long-lasting exhaustive exercise the turnover rate of myosin HC decreases. Twelve hours after exercise, myosin LC 2 and 3, and actin have a more rapid turnover than in control rats. Changes in the turnover rate of muscle contractile proteins during exercise and the recovery period after exercise reflect the functional conditions of the contractile apparatus in different types of skeletal muscle fibres and have a physiological significance.

Effect of glucocorticoids on contractile apparatus of rat skeletal muscle.

Skeletal muscles which have a high oxidative potential are less sensitive to the catabolic action of dexamethasone. In fast-twitch white muscles, where the oxidative capacity is low, the alkaline proteinase activity as well as the rise in the number of lysosomes was more pronounced. It seems that the glucocorticoid-caused myopathy is a result of elevated degradation of contractile proteins. This process of degradation of contractile proteins begins in the myosine filaments and then spreads to the thin filaments and the z-line.

[Relation between changes in the blood levels of beta-endorphin and various hormones during physical exercise]. / Vzaimootnosheniia mezhdu izmeneniiami soderzhaniia beta-éndorfina i riada gormonov v krovi vo vremia myshechnoi raboty.

Dynamics of beta-endorphin, corticotropin, cortisol, somatotropin, insulin and triiodothyronine content were studied using bicycle ergometer in blood of 22 persons during 2 hrs exercises. After an initial increase the beta-endorphin content was subsequently decreased. At the same time, the decrease in the neuropeptide content was accompanied by repeated elevation within the second hr of the exercise, mainly in persons exhibiting high working capacity, while in other persons the hormone concentration decreased below the initial level at the end of the exercise. These alterations in the content of beta-endorphin correlated distinctly with dynamics of pituitary-adrenocortical hormones variation. In untrained persons the initial increase in beta-endorphin content was especially distinctly related to the elevation in somatotropin and to a decrease in insulin content in blood. Concentration of triiodothyronine in blood was altered independently of the alterations of other hormones.

[Effect of increased functional activity of skeletal muscles on the turnover rate of heavy and light chains in myosin]. / Vliianie povyshennoi funktsional'noi aktivnosti skeletnykh myshts na skorost' obnovleniia tiazhelykh i legkikh tsepei miozina.

Incorporation of 14C-leucine into light chains (LC) of myosin was distinctly increased and into heavy chains (HC)--decreased during physical exercises. Within first six hours after the exercises synthesis of HC maintained at the reduced level, then it was gradually elevated and distinctly activated after 48 hrs rest. Incorporation of 14C-leucine into LC of myosin was unaltered at the post-exercise period. During swimming turnover of LC myosin was accelerated and after physical activity it maintained at the level of controls. The rate of HC myosin turnover was not distinctly altered both during physical activity and within the first day after the loading. The rate of HC myosin turnover was augmented within 48 hrs after exercises.

[Glucocorticoids in intracellular catabolism of myosin and actin]. / Gliukortikoidy vo vnutrikletochnom katabolizme miozina i aktina.

The catabolic effect of glucocorticoids on the structural proteins of contractile apparatus seems to be realized through the increased alkaline proteinase activity and accelerated synthesis of light enzyme subunits. The administration of large amounts of glucocorticoids increased the excretion of 3-methylhistidine in rats by 60%. Digestion of isolated myofibrils with alkaline proteinase resulted in the degradation of myosin heavy chain and actin. The turnover rate of actin and myosin heavy chain was decreased.

Effect of muscular activity on the turnover rate of actin and myosin heavy and light chains in different types of skeletal muscle. I. Changes in the turnover rate of myosin and actin during and after single-bout physical activity.

During a single-bout of 6-h swimming, myosin heavy chain (HC) and actin in m. gastrocnemius turned over more slowly than they did in the pre-exercise period, whereas the turnover rate of myosin light chain (LC) increased; 48 h after swimming, actin and myosin HC had a significantly higher turnover rate, but the turnover rate of myosin LC remained at the pre-exercise level. Exercise caused a remarkable decrease in the incorporation of the 14C leucine into actin and myosin HC, but an increase in the incorporation into myosin LC. An elevation of the synthesis rate of actin and myosin HC was observed 48 h after exercise. Myofibrillar proteinase activity at alkaline pH reached its maximum level during exercise, but the same was observed for the proteolytic activity at acid pH 6 h and at neutral pH 24 h after exercise.

Effect of glucocorticoids on the turnover rate of actin and myosin heavy and light chains on different types of skeletal muscle fibres.

The catabolic action of glucocorticoids on the molecular level of the two main muscular proteins, myosin and actin, was found to depend on the type of muscle fibres. The synthesis rate of actin and myosin heavy chain was decreased in all types of muscle fibres, and in myosin light chain only in the slow-twitch red fibres. The turnover rate of actin and myosin heavy chain was also found decreased in all types of muscle fibres. The myosin light chains turned over more rapidly in dexamethasone-treated than in the control rats in all types of muscle fibres except in the case of the slow-twitch red ones as was shown by single and double isotope methods. Dexamethasone treatment enhanced the urinary 3-methylhistidine excretion in rats by 60%.

[Adaptation of skeletal muscle and myocardium to increased motor activity in hypo- and athyroid rats]. / Adaptatsiia skeletnykh i serdechnoi myshts k povyshennoi dvigatel'noi aktivnosti u gipo- i atireoidnykh krys.

Changes in contractility and synthesis of protein were studied in different types of muscles of hypo- and athyroid ratts during adaptation to physical exercise. Intensity of the exercises used corresponded to metabolic power output of 70% VO2max. Thyroidectomy caused a significant decrease in Mg2+ activated actomyosin ATPase activity and in content of RNA in myocardium and in fast oxidative-glycogenolytic and glycogenolytic skeletal muscle fibers. Exercises, intensity of which corresponded to metabolic power output of 70% VO2max led to a more distinct decrease in Mg2+ activated actomyosin ATPase activity in fast glycogenolytic muscle fibers, but in fast oxidative-glycogenolytic fibers the enzymatic activity was increased up to the level comparable with that of intact animals. Rhysical working capacity of athyroid rats was lower by 40% as compared with intact trained animals. Hypothyroidism, induced by means of administration of KJ into previously trained rats, caused a decrease in physical working capacity by 25%.

[Role of the thyroid gland in skeletal muscle adaptation to increased motor activity]. / Rol' shchitovidnoi zhelezy pri adaptatsii skeletnykh myshts k povyshennoi dvigatel'noi aktivnosti.

Experiments in 16-week old male Wistar strain rats showed that deficiency of thyroid hormones caused a decrease of cytochrome aa3, RNA, myofibrillar and sarcoplasmic protein contents in m. quadriceps femoris, Mg2+ activated actomyosin ATPase activity and physical working capacity of untrained and trained animals also reduced. Physical activity the intensity of which corresponded to metabolic power output of 190%. Vo2max stimulated thyroid function, elicited a significant elevation of blood thyroxine level, oxidative potential and intensity of protein synthesis in m. quadriceps femoris, the character of these changes depending on the type of muscle fibers. The stimulation of thyroid function caused an elevation of muscle content of cytochrome aa3 and content of RNA, especially in the glycolytic fibers of hypothyroid rats.

[Effect of increased functional activity on the contractile function of skeletal muscle]. / Vliianie povyshennoi funktsional'noi aktivnosti na sokratitel'nuiu funktsiiu skeletnykh myshts.

The adaptation of rats to the exercise program the intensity of which corresponded to metabolic power output of 190% VO2max, did not produce any significant changes in Mg2+ and Ca2+ activated ATPase activity in the different types of skeletal muscle fibers. The increase in the cross-sectional area of glycolytic muscle fibers was due to the hypertrophy of all cellular structures, especially the srcoplasmic reticulum. The sytochrome aa3 concentration increased by 23%. The submaximal exercise program (130% VO2max) elicited a significant elevation of Mg2+ activated actomyosin ATPase activity in the oxydative-glycolytic muscles and a decrease of the latter enzyme activity in glycolytic muscles. The endurance exercise (70% VO2max) caused a small decrease in Mg2+ activated actomyosin ATPase activity in the oxydative-glycolytic muscles and an increase in the oxydative ones. The character of the adaptive response of the actomyosin ATPase in different types of skeletal muscle fibers depends on the intensity and duration of the running program.