Number Of Sarcomeres Research Articles

Decline running produces more sarcomeres in rat vastus intermedius muscle fibers than does incline running.

Unaccustomed eccentric exercise, in which a muscle is lengthened while generating tension, is well known to cause injury and pain. A rapid training effect has been demonstrated in a number of eccentric exercises. The mechanism for both the damage and the training has been unknown. Morgan proposed that the damage is caused by sarcomere length instabilities during operation on the descending limb of the sarcomere length-tension curve and that the training effect is an increase in the number of sarcomeres connected in series in a muscle fiber, thus avoiding the descending limb (Biophys. J. 57: 209-221, 1990). We tested this proposal by exercising rats on a treadmill set at either an incline or a decline of 16 degrees, an exercise that has previously been shown to cause damage in untrained rats and a training effect. The vastus intermedius muscles were fixed and were digested in acid, and the fiber and sarcomere lengths of representative fibers were measured. From these measurements, the mean number of sarcomeres per fiber was found for the different training regimes. A clear and repeatable difference was found, supporting Morgan's prediction of more sarcomeres after decline running, although with some differences in response that depended on the age of the rats.

Sarcomere number plays an important role in joint mechanics

Sarcomere number plays an important role in joint mechanics

Ultrastructure of Developing Flight Muscle in Drosophila. I. Assembly of Myofibrils

In order to evaluate the effects of specific mutations on sarcomere assembly and function in vivo, we describe the course of normal development of Drosophila indirect flight muscle (IFM) in staged pupae using electron microscopy. We find that no contractile assemblies remain in larval muscle remnants invaded by imaginal myoblasts, establishing that myofibrils in IFM assemble de novo. Stress-fiber-like structures or other template structures are not prominent before or during sarcomere assembly. By 42 hr pupation (eclosion ∼112 hr), thick and thin filaments have appeared simultaneously in slender, interdigitated arrays between regularly spaced Z-bodies. Each tiny, uniformly striated myofibril forms within a "sleeve" of microtubules, and both microtubules and myofibrils are attached to the cell membrane at each end of the fiber from the initial stages of assembly. Later in pupation, the microtubule "sleeves" disassemble. Sarcomere number appears to remain constant. We saw no evidence that terminal sarcomeres are sites for addition of new sarcomeres or that Z-lines split transversely, producing new, very short sarcomeres. Rather, initial thick and thin filaments and sarcomeres are much shorter than adult length. Sarcomere length increases smoothly and coordinately from ∼1.7 to ∼3.2 μm, reflecting increase in filament lengths and indicating that myosin and actin molecules must be incorporated into filaments after sarcomere formation. Myofilaments are not seen scattered in the cytoplasm at any time, nor do we detect filaments that could be in the process of being "trolleyed" along myofibrils into positions of lateral register. Myofibril diameter increases uniformly from ∼4-thick filaments to ∼36-thick filaments across, by peripheral addition of myofilaments. At each successive stage, all sarcomeres in a fiber attained similar length and diameter. Initial thick filaments are solid but within several hours these and all subsequently assembled thick filaments appear hollow. Initial Z-bodies do not show any internal lattice and are more irregularly shaped than adult Z-discs.

Biomechanics of Balance in the Hand

The mechanical balance of a hand has nothing to do with having equally strong muscles on opposite sides of each joint. It has to do with the balance of torque at a sequence of joints while the hand is exerting force on external objects that need to be controlled by the hand. The balance may be calculated or seem to be satisfactory when, for example, the tension in finger flexors is sufficient to hold the fingers flexed around an object that is being moved against external force. During such activity balance is not achieved until other muscles such as wrist extensors exert enough tension to hold the wrist stable against the flexion torque generated at the wrist by the same finger flexors. Any attempt to restore muscle balance in the hand must take into account the way in which the body responds by itself to loss of balance after injury or paralysis. It does this by changing the number of sarcomeres in each muscle fiber as well as by trick movements used to circumvent paralysis or other failure of normal balance.

Histomorphologic Changes in Expanded Skeletal Muscle in Rats

Tissue expansion is one of the powerful tools for various reconstructive procedures and has proven to provide more available local tissues. However, limited attention has been given to the characteristics of expanded skeletal muscle. Using a rat model (n = 41), we expanded the rat gracilis muscle and investigated the histomorphologic changes in the expanded skeletal muscle. By expansion, the gracilis muscle after 3 weeks increased 50.4 to 58.4 percent in length and 60.5 percent in width and decreased 39.0 to 42.0 percent in thickness. Histologically, the expanded muscle demonstrated a normal striation and no signs of inflammation or necrosis. The cross-sectional areas of muscle fibers indicated that expanded muscle consisted of predominantly smaller fibers. Vasculature in the expanded muscle demonstrated a longer network of arteries and a more obvious and developed arterial arcade. The average number of sarcomeres in a fiber estimated from the sarcomere length and fiber length was significantly greater (46.5 percent) in the expanded muscle. These findings suggest that the expansion of skeletal muscle is not a "stretching" process of muscle but rather a growth process of the muscle accompanied by an increase in the number of sarcomeres per fiber. Furthermore, the expanded skeletal muscle appears to preserve normal skeletal muscle architecture, vasculature, and function while undergoing the ischemic stress of expansion.

Muscle length-force characteristics in relation to muscle architecture: a bilateral study of gastrocnemius medialis muscles of unilaterally immobilized rats

The geometry of rat gastrocnemius medialis muscle (GM) was studied at different muscle lengths. In addition, the number of sarcomeres in series within fibres was estimated. For muscles of immobilized legs (i.e. GM was held at in vivo smallest length) as well as those of the contralateral legs, comparison was made with controls of similar age. Immobilization periods of 4 and 6 weeks were used. For immobilized GM muscles, the number of sarcomeres in series was lower only within distal fibres after 4 weeks of immobilization. Aponeuroses were 25% shorter after both immobilization periods and no differences were found for fibre and aponeurosis angle. For GM of contralateral legs no difference with respect to controls was found regarding the number of sarcomeres in series. Aponeuroses were approximately 15% shorter and the fibre and the aponeurosis angle were also smaller. Based on these geometrical differences, it was expected that both experimental muscles should exert force over a smaller range of muscle length than controls. However, for immobilized muscles a similar range of length was found for which a possible explanation could be the more compliant aponeurosis. For contralateral muscle a 2-mm larger length range as well as a change of distribution of optimal fibre length with respect to optimal muscle length was found. For immobilized muscles indications of a distribution of optimal fibre lengths were also found but these did not differ from those of the controls. The results for contralateral muscles would indicate that the distribution may be changed under the influence of an altered use of the limb and that this may be an important factor determining the length range of active force generation.

Sarcomere length-joint angle relationships of seven frog hindlimb muscles.

The sarcomere length-joint angle relationship was measured in 7 different muscle-joint complexes (n = 43 muscles) of the frog hindlimb (Rana pipiens). Muscles studied included the cruralis, iliacus internus, gastrocnemius, gluteus magnus, gracilis major, semimembranosus and the semitendinosus. Muscle-joint complexes were mounted in a jig and submerged in chilled Ringer's solution. Joints were rotated throughout their range of motion, while sarcomere length was measured by laser diffraction. Muscles were then formalin fixed and architectural properties determined by microdissection of individual muscle fibers. Sarcomere length change per degree of joint rotation (dLs/d theta) ranged from a low of 3.7 nm/degree for the cruralis muscle acting at the knee to a high of 12.5 nm/degree for the semitendinosus muscle acting at the hip. Values for dLs/d theta were significantly different between all muscles (p < 0.001), and dLs/d theta values for muscles acting at the hip were significantly greater than those for muscles acting at the knee (p < 0.005). dLs/d theta was negatively correlated with fiber length, suggesting a balance between fiber length and moment arm in most muscle-joint systems. However, many exceptions to this generalization were noted. These data suggest that different muscle-joint systems are 'designed' for differential contribution of muscle force production to the joint torque profile. The low variability of these data also suggests that sarcomere number is tightly regulated in these muscle-joint systems but not simply as a result of the total in vivo muscle excursion.

Effects of growth on architecture and functional characteristics of adult rat gastrocnemius muscle

Changes of architecture of adult rat gastrocnemius medialis muscle (GM) due to growth were studied in relation to length-force characteristics. Myofilament lengths were unchanged, indicating constant sarcomere length-force characteristics. Number of sarcomeres within fibers was unchanged as a consequence of growth, allowing persistence of differences between proximal and distal fibers in all age groups. Distal fiber length at muscle optimum length was shorter for the 14- than for the 10- and 16-week age groups despite a lack of difference of number of sarcomeres. This is indicative of a shift of optimum length. Some evidence for the occurrence of distribution of fiber optimum lengths with respect to muscle optimum length was found in other age groups as well, albeit of a smaller magnitude. Muscle and aponeurosis length increased substantially with growth. Functional effects of increased aponeurosis lengths were increased contributions to muscle length changes by the aponeurosis, allowing smaller fiber contributions in older animals. Fiber angle increased approximately 5 degrees with growth. Despite the differences of architecture indicated above, muscle length range between optimum length and active slack length was constant. This was probably caused by widening of this length range in the youngest age group by variations of architecture within the muscle. It is concluded that adaptation of aspects of muscle architecture is an important mechanism for adult muscle growth in rat GM. Of these aspects regulation of muscle length seems a dominant factor.

Use of intermittent stretch in the prevention of serial sarcomere loss in immobilised muscle.

After immobilisation of muscle in a shortened position there is a reduction of muscle fibre length due to a loss of serial sarcomeres. Experiments have been carried out to determine whether short, daily periods of stretch prevent sarcomere loss and the resultant loss of range of joint motion. It was found that periods of stretch as short as 1/2 h daily were sufficient not only to prevent loss of sarcomeres but actually to cause an increase in the number of sarcomeres in series. Range of joint motion was normal. Such short periods of stretch were also found to prevent much of the muscle atrophy normally associated with immobilisation in the shortened position.

Muscle growth and exercise

This paper first reviews muscle growth and then considers the influence of exercise in growth. Knowledge about how muscle cells grow and some factors that may influence the growth pattern are discussed first since these effects must be considered before the influence of exercise becomes clear. Growth of muscle can occur in three ways: (1) by an increase in muscle cell numbers, (2) by an increase in muscle fiber diameter, and (3) by an increase in fiber length. All three of these mechanisms are involved in muscle growth. However, growth in cell numbers is limited to the prenatal and immediately postnatal period, with the animals and man being born with or soon reaching their full complement of muscle cells. Thus, growth occurs by either hypertrophy of the existing muscle fibers by adding additional myofibrils to increase the muscle mass or by adding new sarcomeres to the ends of the existing muscle fibers to increase their length. Both of these mechanisms occur during the growth process. Growth in the girth of the muscle fibers appears to take place by splitting of the myofibrils. This may be stimulated by development of stress creating an unequal pressure with splitting at the Z-band and development of additional SR and T-tubule systems. This adds to the diameter or girth of myofibers without any hyperplasia. The growth in length occurs at either end of the fibers and results in addition of new sarcomeres. In both cases, new myofibrillar protein must be synthesized and deposited in the muscle cells. It is suggested that adaptation by adding or removing sarcomeres is physiologically determined by the degree of force a muscle can generate that is in turn dependent on the degree of overlap of the thick and thin filaments. Thus, the amount of tension would control the number of in-series sarcomeres in a single muscle fiber. Nutrition is also known to play an important role in muscle and was discussed from the standpoint of the effects of nutritional adequacy and restriction. Although a nutritionally balanced and calorically adequate diet is required to achieve optimum muscle growth, it may be less efficient in terms of protein deposition than a moderately restricted diet. Muscle and bone deposition, however, can be limited on severely restricting the dietary intake. Although fat deposition is the first tissue to suffer on a severely restricted diet, muscle and bone follow next with the nervous system, brain and eyes being the last systems to be affected.(ABSTRACT TRUNCATED AT 400 WORDS)

Morphological and contractile characteristics of rat cardiac myocytes from maturation to senescence.

Morphological and contractile characteristics of individual myocytes isolated from rats of 2, 6-9, and 24-25 mo of age were measured. The average myocyte length measured under high power light microscopy in unattached cells increased from 133 microns at 2 mo to 146 microns at 6-9 mo to 162 microns at 24-25 mo of age. The average slack sarcomere length was 1.85, 1.83, and 1.82 microns at 2, 6-9, and 24-25 mo, respectively. The average cell volume measured via Coulter counter techniques approximately doubled between 2 and 24 mo. During the electrically stimulated twitch in individual unloaded myocytes contracting from slack length the absolute amplitude of cell shortening increased with age, but when expressed relative to cell length or as sarcomere shortening the age effect was obliterated. Neither the maximal velocity of myocyte shortening (cell length/s) nor the calculated maximal sarcomere shortening velocity varied with age. The time course of the twitch increased with aging, due largely to an increase in the time to peak shortening. Thus aging is associated with an increase in cell size due to the addition of sarcomeres. Except for a prolonged time course, the twitch contraction characteristics normalized for cell length and sarcomere number in unloaded ventricular myocytes contracting over a range of sarcomere lengths below the slack length do not change appreciably with age.

Adaptation of skeletal muscle to immobilization in a shortened position

This study determined the morphological changes and adaptations that occur following immobilization of rat soleus and gastrocnemius muscles when the ankle joint is placed in complete plantar flexion for 2, 5, 7, 14, 21, and 28 days by means of plaster casts. Previous studies of such shortened muscles have shown that the number of sarcomeres in series is reduced, but how the sarcomeres are reduced has not been determined. We observed that the fibers in the mid-belly region of the muscles demonstrated a progressive degenerative process over the first few weeks. Myofibrils across the entire width of the affected fibers underwent dissolution. However, by 4 weeks new myofibrils were being formed, and sarcomere lengths appeared normal. Portions of the fibers near the tendon underwent segmental necrosis. These findings are similar to the response of the soleus and gastrocnemius muscles to tenotomy and are clinically relevant to orthopedic procedures that maintain muscles in shortened conditions for prolonged periods.

発育期マウス骨格筋の筋節長, 筋節数および筋張力の変化

発育期マウス骨格筋の筋節長, 筋節数および筋張力の変化

養殖マダイの肉質改善に関する研究 Ｉ 養殖マダイの肉質に対する遊泳運動の効果

The effect of swimming exercise on retardation of softening of flesh was examined with cultured red sea-bream Pagrus major (2 years old) exercised for 0 (control) or 12h a day during 1, 2 or 4 weeks in water flow of 2.5 BL (body length)/s. Fish were instantly killed by exsanguination and stored in ice for 12 days. Pieces of ordinary muscle of the dorsal part and caudal part were sampled from the iced fish every 2 days up to the 12th day, and myofibrils were prepared from the muscle. The number of sarcomeres composing the myofibrils was counted under a microscope. The fre-quency in percentage of F1-4, myofibrils composed of 1 to 4 sarcomeres, was used as an index of softness of the flesh. The frequency of F1-4 increased during storage faster in the cultured fish than in the wild ones, and slower in exercised fish than in nonexercised ones among cultured fish, especially at the caudal muscle. These results suggest that the flesh texture of cultured red sea-bream may be improved by swimming exercise.

Structure of abdominal muscles in the hamster: effect of elastase-induced emphysema.

The present study examined the effects of elastase-induced emphysema on the structure of the external oblique and transverse abdominis muscles and a non-respiratory muscle, the extensor digitorum longus. Muscle structure was assessed from the cross-sectional area (CSA) and percent of individual fiber types in histochemically stained sections and from the number of sarcomeres arranged in series along the length of individual fibers. Data were obtained in eight hamsters with emphysema and nine saline-injected controls. In the normal (control) animals the external oblique was thicker but contained fewer sarcomeres than the transverse abdominis. Fiber size was similar in the two muscles. In the transverse abdominis the percents of fast-glycolytic and fast-oxidative fibers were greater and smaller, respectively, than in the external oblique. Lung volume of emphysematous hamsters was 168% of control values (P less than 0.001). In emphysematous compared with control animals, the CSA of fast-twitch fibers in the external oblique and transverse abdominis was significantly reduced. Fiber length and sarcomere number were significantly decreased in the transverse abdominis but not in the external oblique in emphysematous hamsters. In contrast, fiber size and composition of the extensor digitorum longus was similar in emphysematous and control animals. These data indicate that cellular responses of the ventilatory muscles to chronic hyperinflation and altered thoracic geometry induced by emphysema are not present in limb skeletal muscle. We speculate that changes in fiber length and CSA of fast fibers in the abdominal expiratory muscles reflect responses to chronic alterations in the mechanics of breathing that may affect muscle load, length, or the pattern of activity.

Length-tension relationship of abdominal expiratory muscles: effect of emphysema.

The present study examined the active and passive length-tension relationship of the abdominal expiratory muscles in vitro during electrically stimulated contractions. Studies were performed on isolated strips of transverse abdominis and external oblique muscle from nine adult hamsters with normal lung function. The effect of chronic hyperinflation on the two muscles was assessed in eight hamsters with elastase-induced emphysema. In normal animals the maximal active tension per cross-sectional area (Po) was equal in the two muscles. The absolute muscle fiber length at which Po occurred (Lo) was less for the external oblique than the transverse abdominis and the length-tension curve operated at shorter fiber lengths. However, the change in tension produced by an increase or decrease in muscle length expressed in relative terms (i.e., as %Lo) was greater for the transverse abdominis than the external oblique. Mean total lung capacity of emphysematous animals was 198% of control. Po of the transverse abdominis and external oblique were the same in emphysematous and control animals. However, Lo and the length-tension curve of the transverse abdominis occurred at shorter fiber lengths in emphysematous animals because of a reduction in the number of sarcomeres in series along the fiber. The length-tension curve and the number of sarcomeres in the external oblique was the same in emphysematous and control animals. These results in normal animals indicate that the magnitude of the change in active and passive tension produced by a change in muscle length differs in the transverse abdominis and external oblique. Moreover, chronic hyperinflation of the thorax produced by elastase injection alters the length-tension relationships of some but not all the expiratory muscles.

In Vitro and In Vivo Protein Synthesis Rates in a Crustacean Muscle During the Moult Cycle

ABSTRACT In vivo protein synthesis rates were measured in the carpopodite extensor muscle of the shore crab, Carcinus maenas, following a single, high-dose injection of [3H]phenylalanine, which stabilized specific radioactivities in the free pools. In intermoult animals the percentage of protein mass synthesized per day (the fractional rate of protein synthesis) was 1·15% day−1 for the whole extensor muscle. The small, slow-type tonic fibres in the extensor had fractional rates of protein synthesis some 2·1 times higher than those of the large, fast-type phasic fibres. Measurement of protein synthesis rates of extensor muscles from intermoult animals using an in vitro incubation over 2h gave fractional synthesis rates three times lower than those found in in vivo experiments. Compared with the intermoult animals, six- and three-fold increases in fractional synthesis rates were found in the extensor muscles from stages immediately preceding and following ecdysis, respectively. Microdissection of the muscle fibres revealed that the increased synthesis in postecdysial animals was occurring mainly at the external cuticular end of the muscle fibres. Autoradiographic analysis confirmed the cuticular end of the muscles as the major site of muscle protein synthesis. We conclude that the postecdysial increase in muscle fibre length and the associated increase in the sarcomere number is accompanied by an increase in protein synthesis in the muscles.

Motor endplate position of rat gastrocnemius muscle.

In this study, the relative endplate position of fibers of rat gastrocnemius caput mediale (GM) muscle was determined by counting numbers of sarcomeres. Isolated fibers were teased from the proximal, intermediate, and distal regions of the muscle. Endplates of distal fibers were located on the proximal third of their lengths. Endplates of intermediate fibers were located at half fiber length, and for proximal fibers, a variable endplate position was obtained: in half of the muscles studied, endplates occurred around the proximal one-third and in the other half near the midpoint of the fiber. Endplate position relative to fiber length was thus found to be dependent on the region of the muscle. Changes in the orientation of endplate zone relative to the muscle belly is likely to take place with changes in muscle length, as shown by a planimetric muscle model. It is argued that architecture of pennate muscles may highly affect characteristics of motor unit potentials.

MULTIWIRE DETECTOR AND DATA ACQUISITION SYSTEM FOR TIME RESOLVED EXPERIMENTS

R6sum6 - Un systsme pour effectuer des mesures cinetiques aux rayons X sur des muscles est decrit, de mzme que le logiciel d'acquisition de donnkes et d'analyse des rksultats. Plusieurs exemples d'application sont donnks. Abstract - A system for making time-resolved X-ray measurements from muscle is described in this paper along with real-time software for data acquisition and software for further analysis. Several examples illustrating the use of the system are also given. The technique of time resolved X-ray diffraction is a powerful tool for studying dynamic processes in structural biology where ordered structures are involved, and has proven of particular value in the study of vertebrate skeletal muscle. The principal ideas behind the technique are relatively simple - one needs to record the X-ray pattern from a contracting muscle in a stroboscopic manner, the data being recorded in such a way that it is possible to distinguish patterns from different phases of muscle contraction. It is possible to calculate the extent of changes in the molecular structure as a function of time from the changes in the X-ray pattern provided one has knowledge of the starting structure 191; partial information is available for vertebrate muscle from a number of techniques, including electron microscopy, biochemistry and conventional X-ray diffraction studies. The basic contractile muscle unit, the sarcomere, shown in Fig 1, consists of two types of inter-digitating protein filaments 181. The 'thick' filaments, consisting mainly of myosin are about 1.6 pm in length and have an array of 'projections' along most of its length arranged in a helical fashion. The thin filaments are about 1 pm in length and consist mainly of actin with smaller quantities of the regulatory proteins tropomyosin and troponin. The thin filaments are attached to the Z-lines, the distance between two Z-lines being approximately 2.3 pm at normal body length. It is believed that during contraction the projections on the thick filament form cross-bridges with the thin filament and go through a 'conformational' change which produces a relative sliding movement between the two filaments. The polarity of the filaments is reversed half-way along the sarcomere so that opposing forces are generated in the two halves. A large number of sarcomeres generate force in series and in parallel which is transmitted to the skeleton through the tendons to allow external work to be performed.

Muscle fibre length and bone length in adult mice during dietary restriction and refeeding

The dietary intake of male mice was restricted to 70% by weight of the ad lib intake of control littermates between days 75 and 96 post partum. Eight mice were killed at 96 days of age and compared with controls. A further group of eight mice then resumed ad lib feeding until they had regained the control body weight, when they were killed and also compared with controls. Muscle weight, fibre length, sarcomere length and sarcomere number per fibre were measured in the biceps brachii and tibialis anterior muscles. The lengths of the femur, tibia, humerus and radius were measured and remained unchanged throughout the study. Muscle weight, fibre length and the number of sarcomeres per fibre were significantly reduced in both muscles following dietary restriction but regained their control values after a return to normal feeding. Sarcomere length remained unchanged throughout the study. The pattern of fibre length changes, due entirely to alterations in sarcomere number, is similar to that reported in young mice. The reduction in sarcomere number during dietary restriction was due to a loss of established sarcomeres.