Muscle Fibres Of Different Types Research Articles

Accumulation of STIM1 is associated with the degenerative muscle fibre phenotype in ALS and other neurogenic atrophies.

Upon denervation, skeletal muscle fibres initiate complex changes in gene expression. Many of these genes are involved in muscle fibre remodelling and atrophy. Amyotrophic lateral sclerosis (ALS) leads to progressive neurodegeneration and neurogenic muscular atrophy (NMA). Disturbed calcium homeostasis and misfolded protein aggregation both in motor neurones and muscle fibres are key elements of ALS pathogenesis that are mutually interdependent. Therefore, we hypothesized that the calcium sensor STIM1 might be abnormally modified and involved in muscle fibre degeneration in ALS and other types of NMA. We examined ALS and NMA patient biopsy and autopsy tissue and tissue from G93A SOD1 mice by immunohistochemistry and immunoblotting. In normal human and mouse muscle STIM1 was found to be differentially expressed in muscle fibres of different types and to concentrate at neuromuscular junctions, compatible with its known role in calcium sensing. Denervated muscle fibres of sALS and NMA cases and SOD1 mice showed diffusely increased STIM1 immunoreactivity along with ubiquitinated material. In addition, distinct focal accumulations of STIM1 were observed in target structures within denervated fibres of sALS and other NMA as well as SOD1 mouse muscles. Large STIM1-immunoreactive structures were found in ALS-8 patient muscle harbouring the P56S mutation in the ER protein VAPB. These findings suggest that STIM1 is involved in several ways in the reaction of muscle fibres to denervation, probably reflecting alterations in calcium homeostasis in denervated muscle fibres.

Healthy ageing through regulated proteostasis

During metazoan life, protein homeostasis (proteostasis) declines with age due to impaired proteasome activity. The signalling pathways activated by growth factors that regulate proteostasis and their importance to ageing are just emerging. In this issue, Liu et al report a crucial role of epidermal growth factor (EGF) in regulating Caenorhabditis elegans lifespan through the RAF/MAPK pathway. EGF signalling activates the ubiquitin–proteosome system (UPS) and represses the chaperone machinery by modulating the expression of several ageing‐related genes (gerontogenes). This strategic switch in controlling global protein turnover provides novel insights into the molecular mechanisms driving ageing in multi‐cellular organisms.

Fibre type related changes in the metabolic profile and fibre diameter of human vastus medialis muscle after anterior cruciate ligament rupture

Vastus medialis muscles of patients with chronic anterior instability of the knee after anterior cruciate ligament rupture were analysed to investigate changes in defined muscle fibres of the diseased leg in comparison to the healthy leg of the same patient. Metabolic and morphological parameters were obtained by cytophotometrical measurements of the activities of succinate dehydrogenase (a marker of oxidative metabolism) and glycerol-3-phosphate dehydrogenase (a marker of glycolytic metabolism) of slow-oxidative (SO), fast-oxidative glycolytic (FOG) and fast-glycolytic (FG) fibre types in serial sections and by measuring the minimal fibre diameters of type I (slow) and type II (fast) fibres. We found decreased glycolytic activity and a shift to more oxidative metabolism in each fibre type suggesting diminished fast force and shift to endurance force development. The latter was interpreted as a sign of active compensation for the knee instability. Significantly decreased minimal fibre diameters to 85.9% in type I fibres, and to 88.7% in type II fibres of the diseased muscle were measured, indicating the fibre atrophy. Our findings suggest that the atrophied muscle fibres of the affected vastus medialis muscle adapt to the altered conditions by changing their metabolic profile. Muscle fibres of different types were found to be affected similarly.

Speeds of Actin Translocation in Vitro by Myosins Extracted from Single Rat Muscle Fibres of Different Types

As skeletal muscle fibres mostly express a single myosin isoform, they are a potential source of pure myosin isoforms. A technique is described that allows extraction and identification of pure myosin isoforms from single fibres, and testing of such myosins in an in vitro motility assay (IVMA). The results show that the extraction procedure does not alter myosin function and support the view that single fibres are reliable sources of purified myosin isoforms for IVMA.

Tension/stiffness ratio of skinned rat skeletal muscle fibre types at various temperatures.

It is well known that shortening velocity and maximal tension of muscle preparations are strongly dependent on experimental temperature. Conversely, studies about temperature effects on muscle fibre stiffness are scarce. In the present study, we measured tension and stiffness of maximally Ca2+-activated skinned rat skeletal muscle fibres of different types over a wide temperature range. All fibre types exhibited a similar tension/stiffness ratio at each experimental temperature. This ratio increased almost linearly from 6 to 18 nm when the temperature was raised from 6 to 34 degrees C. Our results are discussed in the light of the drastic discrepancies reported for the amount of compliance inside and outside the attached myosin cross-bridges of activated muscle fibres (Ford et al. 1981, Huxley et al. 1994, Kojima et al. 1994, Wakabayashi et al. 1994, Higuchi et al. 1995). The relation between these compliances had been deduced from various experimental approaches executed at different temperatures. The large temperature sensitivity of the tension/stiffness ratio found in this study provides evidence for the assumption that the compliance outside the cross-bridges increases with rising temperature. This view would reconcile the contrasting results reported for the relation of compliances inside and outside the attached cross-bridges.

Both Myoblast Lineage and Innervation Determine Fiber Type and Are Required for Expression of the Slow Myosin Heavy Chain 2 Gene

Skeletal muscle fibers express members of the myosin heavy chain (MyHC) gene family in a fiber-type-specific manner. In avian skeletal muscle it is the expression of the slow MyHC isoforms that most clearly distinguishes slow- from fast-contracting fiber types. Two hypotheses have been proposed to explain fiber-type-specific expression of distinct MyHC genes during development—an intrinsic mechanism based on the formation of different myogenic lineage(s) and an extrinsic, innervation-dependent mechanism. We developed a cell culture model system in which both mechanisms were evaluated during fetal muscle development. Myoblasts isolated from prospective fast (pectoralis major) or slow (medial adductor) fetal chick muscles formed muscle fibers in cell culture, none of which expressed slow MyHC genes. By contrast, when muscle fibers formed from myoblasts derived from the slow muscle were cocultured with neural tube, the muscle fibers expressed a slow MyHC gene, while muscle fibers formed from myoblasts of fast muscle origin continued to express only fast MyHC. Motor endplates formed on the fibers derived from myoblasts of both fast and slow muscle origin in cocultures, and slow MyHC gene expression did not occur when neuromuscular transmission or depolarization was blocked. We have cloned the slow MyHC gene that is expressed in response to innervation and identified it as the slow MyHC 2 gene, the predominant adult slow isoform. cDNAs encoding portions of the three slow myosin heavy chain genes (MyHC1, slow MyHC 2, and slow MyHC 3) were isolated. Only slow MyHC 2 mRNA was demonstrated to be abundant in the cocultures of neural tube and muscle fibers derived from myoblasts of slow muscle origin. Thus, expression of the slow MyHC 2 gene in thisin vitrosystem indicates that formation of slow muscle fiber types is dependent on both myoblast lineage (intrinsic mechanisms) and innervation (extrinsic mechanisms), and suggests neither mechanism alone is sufficient to explain formation of muscle fibers of different types during fetal development.

Activities of creatine kinase isoenzymes in single skeletal muscle fibres of trained and untrained rats.

Biochemical changes in the creatine kinase isoenzyme compositions in single muscle fibres of different types in rats were induced by endurance running training. Single muscle fibres were dissected from the soleus and extensor digitorum longus muscles of Wistar-strain male rats trained on a motor-driven treadmill for 16 weeks. Each fibre was typed histochemically (SO, slow-twitch oxidative; FOG, fast-twitch oxidative glycolytic; FG, fast-twitch glycolytic), and the activities of total creatine kinase and its four isoenzymes (CK-MM, -MB, -BB, and mitochondrial creatine kinase) were measured. The endurance training did not affect the total creatine kinase activity, but resulted in significantly increased activities of CK-MB and CK-BB in SO and FOG fibres, and the mitochondrial enzyme activity in FOG and FG fibres. Endurance training induced biochemical changes in the isoenzyme compositions, specifically in FOG fibres. These results suggest that changes in creatine kinase isoenzymes with endurance training reflect changes in the energy metabolism in the different muscle fibres, supporting the hypothesis that the different isoenzymes play different roles in energy transduction.

Profiles of creatine kinase isoenzyme compositions in single muscle fibres of different types

Creatine kinase (CK) isoenzyme compositions of different types of single muscle fibres dissected from soleus (SOL) and extensor digitorum longus (EDL) muscles from rats were examined. CK isoenzymes were separated into cytoplasmic (CK-MM, CK-MB, CK-BB) (muscle, brain and hybrid types, respectively) and mitochondrial (m-CK) isoenzymes. Total CK and CK-MM activities showed the highest activities in fast-twitch glycolytic fibres (FG), lower in fast-twitch oxidative glycolytic (FOG) and the lowest in slow-twitch oxidative (SO) fibres. Conversely, the activity of m-CK was highest in SO, lowest in FG and intermediate in FOG fibres. The activity of CK-MB was highest in SO and lower in FOG and FG fibres. However, the activities of total CK and CK isoenzymes in a single muscle fibre type were not distinguishable from those of another type, and the profiles of CK isoenzyme compositions from the same type of single muscle fibres overlapped over a considerable range. The relationships between the four CK isoenzymes activities in single muscle fibres of different types were not similar. These results suggest that CK isoenzymes of single muscle fibres of different types play different roles in intracellular energy metabolism. Therefore, it is supposed that the CK isoenzyme compositions of single muscle fibres are suitable for their contractive and metabolic properties.

Identification of motoneurons in the spinal cord of the zebrafish (Brachydanio rerio), with special reference to motoneurons that innervate intermediate muscle fibers

We investigated the location and size distribution of motoneurons that innervate red, intermediate and white muscle fibers in the axial musculature of the zebrafish (Brachydanio rerio). Motoneurons were identified by retrograde labeling from the respective myotomal compartments with horseradish peroxidase applied either in small polyacrylamide gel fragments or as pure crystals. We found a spatial relationship between the three myotomal muscle fiber types and the corresponding motoneurons. The white motoneurons are grouped in the dorsal part of the motorcolumn, near the central canal. Motoneurons of the red and intermediate muscle are clustered in the ventral part of the motorcolumn. The average position of the red motoneurons is ventral to that of the intermediate motoneurons. Some sizes are distributed over wide overlapping ranges, spanning from 41 to 352 microns 2 for red and intermediate and from 56 to 894 microns 2 for white motoneurons. These data are discussed in relation to the recruitment order of myotomal muscle fibers of different types as revealed by electromyographic recordings in fish, and the so called "size principle" for motoneuron recruitment.

Topographical localization of muscle glycogen: an ultrahistochemical study in the human vastus lateralis

The fine structural pattern of glycogen storage in resting and sprint-exercised human vastus lateralis muscle fibres of different types was analysed using ultrahistochemical methods. Three male subjects (31-36 years) performed 60 consecutive, supramaximal bouts of bicycle exercise, each starting every 1 min and having a duration of 8 s (including approximately 3 s of acceleration). The load was estimated to correspond to 200% of VO2-max. Five other subjects (22-27 years) constituted controls. Ultrathin sections stained with periodic acid-thiosemicarbazide-silver proteinate (PA-TSC-SP) clearly revealed a compartmental distribution of glycogen. Glycogen is stored at five topographically, and probably also functionally, different locations. They are the subsarcolemmal, intermyofibrillar, para-Z-disc, N2-line, and H-zone spaces. During the exercise, glycogen from the N2-line and para-Z-disc locations is preferentially utilized. Serial sections stained with uranyl acetate and lead citrate demonstrated that glycogen stores of the type 2 fibres were more depleted than those of type 1 fibres. The implications of the differential intracellular glycogen storage are discussed.

Ultrastructural and metabolic profiles on single muscle fibers of different types after hindlimb suspension in rats.

The relationships between ultrastructural and metabolic profiles in different types of single muscle fiber after hindlimb suspension in rats were examined. Glycolytic (lactate dehydrogenase, LDH; phosphofructokinase, PFK) and oxidative (succinate dehydrogenase, SDH; malate dehydrogenase, MDH) enzyme activities in extensor digitorum longus (EDL) and soleus (SOL) muscles were measured. Relative mitochondrial and lipid droplet volumes were also measured in single muscle fiber of different types. Glycolytic enzyme activity in EDL muscle and oxidative enzyme activity in soleus muscle decreased following suspension for 2 weeks. LDH and PFK activities in fast-twitch (FG, fast-twitch glycolytic; FOG, fast-twitch oxidative glycolytic) fibers and oxidative enzymes in FOG and FG fibers decreased following suspension. Relative mitochondrial volume decreased significantly in all types (SO, slow-twitch oxidative; FOG, and FG) of fibers following suspension. The mitochondrial volume in SO fiber of the control group was significantly (p less than 0.01) higher than that of suspended group; however, SDH and MDH activities were not different between the control and suspended groups. The structural and metabolic changes following hindlimb suspension were influenced by different factors, respectively. Changes in ultrastructural and metabolic profiles in response to the hindlimb suspension differed according to the type of fibers.

Determination of metabolic profiles on single muscle fibres of different types.

Single muscle fibres separated from extensor digitorum longus (EDL) as well as soleus (SOL) in the Wistar strain male rat in relaxing solution were typed histochemically, then glycolytic and oxidative enzyme activities were determined on the same fibres. Glycolytic enzyme lactate dehydrogenase (LDH), phosphofructokinase (PFK), pyruvate kinase (PK) and creatine kinase (CK) showed highest activities in fast-twitch glycolytic (FG), lower in fast-twitch oxidative glycolytic (FOG) and lowest in slow-twitch oxidative (SO) fibres. Also oxidative enzyme succinate dehydrogenase (SDH) and malate dehydrogenase (MDH) showed highest activities in SO, lower in FOG and lowest in FG fibres. The activities of LDH, PFK, PK and CK in FOG fibres separated from EDL showed higher activity compared to those separated from SOL, whereas the opposite result was obtained for the activities of SDH and MDH. Enzyme activities in a single muscle fibre type were not distinguishable from those of another type, and the activity profiles overlapped over a considerable range. The correlations among the separate enzyme activities of CK, LDH and MDH obtained from the same single fibre overlapped over a considerable range.

Characteristics of synaptic currents in frog muscle fibers of different types.

A study was made of synaptic currents in voltage-clamped muscle fibers of the frog. Fast, submaxillaris, and slow muscle fibers are innervated by nerve fibers of different conduction velocities. To avoid spatial complications, transmitter release by nerve impulses was restricted to the site of recording and reduced to single quanta (unitary endplate currents: uepc). Following nerve stimulation, the time course of transmitter release was longer and more variable in slow and submaxillaris muscle fibers than in the fast fibers. The time constant of decay of uepc in submaxillaris and slow fibers was, respectively, about 1.8 and 2.9 times slower than the decay of uepc in fast fibers. This is due mainly to differences in the lifetime of the channels opened by acetylcholine. The neuromuscular junctions in submaxillaris muscle fibers are bouton-like or longer branched contacts; and the unitary currents in the bouton junctions have a slower time course. It is concluded that the synaptic membrane in the different types of muscle fibers has synaptic acetylcholine-operated channels that have different kinetic properties, and that these properties are determined by the type of axon that innervates the muscle fiber.

Temperature-dependent calcium sensitivity changes in skinned muscle fibres of rat and toad.

Single mechanically skinned muscle fibres of different types (fast- and slow-twitch mammalian; slow and twitch amphibian) were successively activated in solutions of various Ca2+ concentrations at different temperatures. An increase in temperature from 5 to 22 degrees C reversibly shifted the isometric steady-state force-pCa curves towards higher Ca2+ concentration for individual fibres of each of the muscle types. A further increase in temperature to 35 degrees C in mammalian fibres resulted in an additional decrease in Ca2+ sensitivity. The temperature dependence of Ca2+ sensitivity was greater in the 'faster' fibre types: fast-twitch greater than slow-twitch; twitch greater than slow. The maximum isometric force response, P0, of both rat and toad skinned fibres was found to be strongly dependent on temperature below 22 degrees C. No detectable force could be induced by Ca2+ in mammalian muscle fibres at 0-1 degree C while in toad fibres P0 decreased by about 90% when temperature dropped from 20 to 0 degree C. Since in mechanically skinned fibres of other amphibians (Bufo bufo, Rana species) P0 is only marginally affected it is likely that the P0-temperature relations are indicative of the range of temperature over which the muscles are normally functional. The P0-temperature relations of skinned muscle fibres closely resembled the P0-temperature relations of tetanically stimulated intact muscle preparations from the same species of animals suggesting that the contractile apparatus is mainly responsible for the variation of force response with temperature in intact muscle.

Myoglobin levels in individual human skeletal muscle fibers of different types.

An attempt was made to determine the relationship of myoglobin content to specific fiber types in human muscle. Biopsies were obtained from biceps brachii, vastus lateralis, and gastrocnemius muscles of untrained subjects and from the vastus lateralis muscle of a highly trained athlete at peak training and at intervals of no training (detraining). Individual muscle fibers were assayed, by quantitative microanalytical methods, for myoglobin, lactate dehydrogenase, malate dehydrogenase, citrate synthase, beta-hydroxyacyl-coenzyme A dehydrogenase, and adenylokinase activities all on the same fiber. The enzyme levels were used to classify the fibers into type I or II. The results show that the content of myoglobin in human muscle does not differ greatly between fiber types in contrast to other species. The type II fibers contained, on the average, at least two-thirds as much myoglobin as type I fibers. The concentration of myoglobin did not change in either fiber type during detraining (84 days), despite marked changes in lactate dehydrogenase, adenylokinase and the three oxidative enzymes.