-
The Journal of Physiology Oct 2003The purpose of this study was to determine whether there was an age-related decline in the isometric and isotonic contractile function of permeabilized slow (MHC I) and... (Comparative Study)
Comparative Study
The purpose of this study was to determine whether there was an age-related decline in the isometric and isotonic contractile function of permeabilized slow (MHC I) and fast (MHC IIa) single muscle fibres. Vastus lateralis muscle fibres from six young men (YM; 25 +/- 1 years), six young women (YW; 25 +/- 1 years), six old men (OM; 80 +/- 4 years) and six old women (OW; 78 +/- 2 years) were studied at 15 degrees C for in vitro force-velocity properties, peak force and contractile velocity. Peak power was 23-28 % lower (P < 0.05) in MHC I fibres of YW compared to the other three groups. MHC IIa peak power was 25-40 % lower (P < 0.05) in OW compared to the other three groups. No difference was found in MHC I and IIa normalized peak power among any of the groups. Peak force was lower (P < 0.05) in the YW (MHC I fibres) and OW (MHC IIa fibres) compared to the other groups. Differences in peak force with ageing were negated when normalized to cell size. No age-related differences were observed in single fibre contractile velocity of MHC I and IIa fibres. These data show that YW (MHC I) and OW (MHC IIa) have lower single fibre absolute peak power and peak force compared to men; however, these differences are negated when normalized to cell size. General muscle protein concentrations (i.e. total, sarcoplasmic and myofibrillar) from the same biopsies were lower (4-9 %, P < 0.05) in the OM and OW. However, myosin and actin concentrations were not different (P > 0.05) among the four groups. These data suggest that differences in whole muscle strength and function that are often observed with ageing appear to be regulated by quantitative rather than qualitative parameters of single muscle fibre contractile function.
Topics: Actins; Adult; Aged; Aged, 80 and over; Aging; Female; Humans; Isometric Contraction; Isotonic Contraction; Male; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Myosins
PubMed: 12837929
DOI: 10.1113/jphysiol.2003.044966 -
Journal of Anatomy Apr 1999Muscle spindles in 2 synergistic avian skeletal muscles, the anterior (ALD) and posterior (PLD) latissimus dorsi, were studied by light and electron microscopy to... (Comparative Study)
Comparative Study
Muscle spindles in 2 synergistic avian skeletal muscles, the anterior (ALD) and posterior (PLD) latissimus dorsi, were studied by light and electron microscopy to determine whether morphological or quantitative differences existed between these sensory receptors. Differences were found in the density, distribution and location of muscle spindles in the 2 muscles. They also differed with respect to the morphology of their capsules and intracapsular components. The slow ALD possessed muscle spindles which were evenly distributed throughout the muscle, whereas in the fast PLD they were mainly concentrated around the single nerve entry point into the muscle. The muscle spindle index (number of spindles per gram wet muscle weight) in the ALD was more than double that of its fast-twitch PLD counterpart (130.5+/-2.0 vs 55.4+/-2.0 respectively, n = 6). The number of intrafusal fibres per spindle ranged from 1 to 8 in the ALD and 2 to 9 in the PLD, and their diameters varied from 5.0 to 16.0 microm and 4.5 to 18.5 microm, respectively. Large diameter intrafusal fibres were more frequently encountered in spindles of the PLD. Unique to the ALD was the presence of monofibre muscle spindles (12.7% of total spindles observed in ALD) which contained a solitary intrafusal fibre. In muscle spindles of both the ALD and PLD, sensory nerve endings terminated in a spiral fashion on the intrafusal fibres in their equatorial regions. Motor innervation was restricted to either juxtaequatorial or polar regions of the intrafusal fibres. Outer capsule components were extensive in polar and juxtaequatorial regions of ALD spindles, whereas inner capsule cells of PLD spindles were more numerous in juxtaequatorial and equatorial regions. Overall, muscle spindles of the PLD exhibited greater complexity with respect to the number of intrafusal fibres per spindle, range of intrafusal fibre diameters and development of their inner capsules. It is postulated that the differences in muscle spindle density and structure observed in this study reflect the function of the muscles in which they reside.
Topics: Animals; Chickens; Female; Male; Microscopy, Electron; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle Spindles; Muscle, Skeletal
PubMed: 10386776
DOI: 10.1046/j.1469-7580.1999.19430381.x -
Histochemistry and Cell Biology Jul 2023It is generally accepted that carnosine (β-alanyl-L-histidine) content is higher in glycolytic than in oxidative muscle fibres, but the underlying mechanisms...
It is generally accepted that carnosine (β-alanyl-L-histidine) content is higher in glycolytic than in oxidative muscle fibres, but the underlying mechanisms responsible for this difference remain to be elucidated. A first study to better understand potential mechanisms involved was undertaken (1) to determine whether differences in the expression of carnosine-related enzymes (CARNS1, CNDP2) and transporters (SLC6A6, SLC15A3, SLC15A4, SLC36A1) exist between oxidative and glycolytic myofibres and (2) to study the effect of carnosine on myoblast proliferative growth and on carnosine-related gene expression in cultured myoblasts isolated from glycolytic and oxidative muscles. Immunohistochemistry analyses were conducted to determine the cellular localization of carnosine-related proteins. Laser-capture microdissection and qPCR analyses were performed to measure the expression of carnosine-related genes in different myofibres isolated from the longissimus dorsi muscle of ten crossbred pigs. Myogenic cells originating from glycolytic and oxidative muscles were cultured to assess the effect of carnosine (0, 10, 25 and 50 mM) on their proliferative growth and on carnosine-related gene expression. The mRNA abundance of CNDP2 and of the studied carnosine transporters was higher in oxidative than in glycolytic myofibres. Since carnosine synthase (CARNS1) mRNA abundance was not affected by either the fibre type or the addition of carnosine to myoblasts, its transcriptional regulation would not be the main process by which carnosine content differences are determined in oxidative and glycolytic muscles. The addition of carnosine to myoblasts leading to a dose-dependent increase in SLC15A3 transcripts, however, suggests a role for this transporter in carnosine uptake and/or efflux to maintain cellular homeostasis.
Topics: Swine; Animals; Carnosine; Muscle, Skeletal; Muscle Fibers, Skeletal; RNA, Messenger
PubMed: 37171629
DOI: 10.1007/s00418-023-02193-6 -
Animal : An International Journal of... Jun 2020Intramuscular connective tissue (IMCT) is mainly composed of several fibrils (known as total collagen (TCol)) linked between each other by different chemical cross-links...
Intramuscular connective tissue (IMCT) is mainly composed of several fibrils (known as total collagen (TCol)) linked between each other by different chemical cross-links (CLs), the whole being embedded in a matrix of proteoglycans (PGs). In the field of beef quality, there is limited information on the role of CLs and PGs. Accordingly, several authors suggest that, to investigate the role of IMCT, it is important to investigate them just like TCol and insoluble collagen (ICol). In muscle, there are two other components, the muscle fibres and intramuscular fat (IMF) content. There are limited data on the relationships between these three components of muscle and then on possibility to independently manipulate these characteristics in order to control the final quality of meat. The present study aimed to investigate whether consistent relationships exist between these different components of muscle. Therefore, the present study compared four muscles of two cattle types (dairy and beef) to determine associations between TCol, ICol, CLs and PGs. Data were analysed across and within muscle (M) and animal type (AT) based on residuals. There was a strong M and AT effect for all muscle characteristics and an interaction M × AT for type I muscle fibres and IMF. Correlations between TCol, ICol and their CLs were M- and AT-independent. Total proteoglycans were positively correlated with TCol and ICol in a muscle-dependent manner irrespective of AT, but no correlation was found with CLs. On the contrary, CLs were negatively correlated with the ratio TPGs : TCol in an M-dependent manner, irrespective of AT. TCol, ICol and CLs were positively and negatively correlated with type IIA and IIB+X muscle fibres only in longissimus thoracis (LT) muscle, regardless the AT. Insoluble collagen was the only parameter of IMCT to be correlated with type I muscle fibres but only in LT muscle, irrespective of AT. There was no correlation between PGs and muscle fibre types, but PGs were the only IMCT component to be related with IMF in an M-dependent manner, irrespective of AT. Finally, there was no correlation between muscle fibre types and IMF content within M and AT. This study revealed that there is a strong relationship between IMCT components irrespective of M, an M-dependent relationship between the IMCT components and muscle fibre types and few (only with PGs) or no relationship between IMF and IMCT and muscle fibres.
Topics: Animals; Body Composition; Cattle; Connective Tissue; Muscle Fibers, Skeletal
PubMed: 31941561
DOI: 10.1017/S1751731119003422 -
Journal of Biomechanics May 2024Connective tissues can be recognized as an important structural support element in muscles. Recent studies have also highlighted its importance in active force...
Connective tissues can be recognized as an important structural support element in muscles. Recent studies have also highlighted its importance in active force generation and transmission between muscles, particularly through the epimysium. In the present study, we aimed to investigate the impact of the endomysium, the connective tissue surrounding muscle fibers, on both passive and active force production. Pairs of skeletal muscle fibers were extracted from the extensor digitorum longus muscles of rats and, after chemical skinning, their passive and active force-length relationships were measured under two conditions: (i) with the endomysium between muscle fibers intact, and (ii) after its dissection. We found that the dissection of the endomysium caused force to significantly decrease in both active (by 22.2 % when normalized to the maximum isometric force; p < 0.001) and passive conditions (by 25.9 % when normalized to the maximum isometric force; p = 0.034). These findings indicate that the absence of endomysium compromises muscle fiber's not only passive but also active force production. This effect may be attributed to increased heterogeneity in sarcomere lengths, enhanced lattice spacing between myofilaments, or a diminished role of trans-sarcolemmal proteins due to dissecting the endomysium. Future investigations into the underlying mechanisms and their implications for various extracellular matrix-related diseases are warranted.
Topics: Animals; Rats; Muscle Fibers, Skeletal; Rats, Wistar; Connective Tissue; Sarcomeres; Male; Muscle, Skeletal; Biomechanical Phenomena; Isometric Contraction; Muscle Contraction
PubMed: 38723428
DOI: 10.1016/j.jbiomech.2024.112134 -
Experimental Physiology Oct 2021What is the central question of this study? While muscle fibre atrophy in response to immobilisation has been extensively examined, intramuscular connective tissue,...
NEW FINDINGS
What is the central question of this study? While muscle fibre atrophy in response to immobilisation has been extensively examined, intramuscular connective tissue, particularly endomysium, has been largely neglected: does endomysium content of the soleus muscle increase during bed rest? What is the main finding and its importance? Absolute endomysium content did not change, and previous studies reporting an increase are explicable by muscle fibre atrophy. It must be expected that even a relative connective tissue accumulation will lead to an increase in muscle stiffness.
ABSTRACT
Muscle fibres atrophy during conditions of disuse. Whilst animal data suggest an increase in endomysium content with disuse, that information is not available for humans. We hypothesised that endomysium content increases during immobilisation. To test this hypothesis, biopsy samples of the soleus muscle obtained from 21 volunteers who underwent 60 days of bed rest were analysed using immunofluorescence-labelled laminin γ-1 to delineate individual muscle fibres as well as the endomysium space. The endomysium-to-fibre-area ratio (EFAr, as a percentage) was assessed as a measure related to stiffness, and the endomysium-to-fibre-number ratio (EFNr) was calculated to determine whether any increase in EFAr was absolute, or could be attributed to muscle fibre shrinkage. As expected, we found muscle fibre atrophy (P = 0.0031) that amounted to shrinkage by 16.6% (SD 28.2%) on day 55 of bed rest. ENAr increased on day 55 of bed rest (P < 0.001). However, when analysing EFNr, no effect of bed rest was found (P = 0.62). These results demonstrate that an increase in EFAr is likely to be a direct effect of muscle fibre atrophy. Based on the assumption that the total number of muscle fibres remains unchanged during 55 days of bed rest, this implies that the absolute amount of connective tissue in the soleus muscle remained unchanged. The increased relative endomysium content, however, could be functionally related to an increase in muscle stiffness.
Topics: Animals; Bed Rest; Humans; Muscle Fibers, Skeletal; Muscle, Skeletal; Myocardium
PubMed: 34387385
DOI: 10.1113/EP089734 -
Scientific Reports Mar 2023Muscle fibres possess unique visco-elastic properties, which generate a stabilising zero-delay response to unexpected perturbations. This instantaneous response-termed...
Muscle fibres possess unique visco-elastic properties, which generate a stabilising zero-delay response to unexpected perturbations. This instantaneous response-termed "preflex"-mitigates neuro-transmission delays, which are hazardous during fast locomotion due to the short stance duration. While the elastic contribution to preflexes has been studied extensively, the function of fibre viscosity due to the force-velocity relation remains unknown. In this study, we present a novel approach to isolate and quantify the preflex force produced by the force-velocity relation in musculo-skeletal computer simulations. We used our approach to analyse the muscle response to ground-level perturbations in simulated vertical hopping. Our analysis focused on the preflex-phase-the first 30 ms after impact-where neuronal delays render a controlled response impossible. We found that muscle force at impact and dissipated energy increase with perturbation height, helping reject the perturbations. However, the muscle fibres reject only 15% of step-down perturbation energy with constant stimulation. An open-loop rising stimulation, observed in locomotion experiments, amplified the regulatory effects of the muscle fibre's force-velocity relation, resulting in 68% perturbation energy rejection. We conclude that open-loop neuronal tuning of muscle activity around impact allows for adequate feed-forward tuning of muscle fibre viscous capacity, facilitating energy adjustment to unexpected ground-level perturbations.
Topics: Musculoskeletal System; Locomotion; Muscle Fibers, Skeletal; Computer Simulation; Time Factors; Muscle Contraction; Muscle, Skeletal
PubMed: 36941316
DOI: 10.1038/s41598-023-31179-6 -
The Journal of Physiology Apr 1986Differences in contractile activation by Ca2+ and Sr2+ between various types of normal and dystrophic murine muscle fibres were investigated using mechanically skinned...
Differences in contractile activation by Ca2+ and Sr2+ between various types of normal and dystrophic murine muscle fibres were investigated using mechanically skinned fibres derived from soleus and extensor digitorum longus (e.d.l.) muscles of normal and dystrophic mice of strain 129ReJ. In terms of contractile activation, the normal e.d.l. muscle was found to consist of one relatively homogeneous population of muscle fibres characterized by steep force-pCa and force-pSr curves, low sensitivity to Ca2+ and very low sensitivity to Sr2+. Normal soleus muscles contained two fibre populations of similar size which could be distinguished on the basis of their contractile activation properties. The first fibre population was characterized mainly by its shallow force-pCa and force-pSr curves, high Ca2+ sensitivity, high Sr2+ sensitivity and the occurrence of large, slow force oscillations of myofibrillar origin. The second fibre population was characterized by force-pCa and force-pSr curves of steepness intermediate between those of normal e.d.l. and those of the first fibre population of normal soleus, by faster myofibrillar force oscillations and by low sensitivity to Ca2+ and Sr2+. The dystrophic e.d.l. fibre population had contractile characteristics which were distinct from those of the three types of normal fibre populations. However, some characteristics of the dystrophic e.d.l. fibres were very similar to those of the normal e.d.l. fibre population. Of all the fibre types investigated, dystrophic e.d.l. fibres were the least sensitive to Ca2+. Dystrophic soleus muscle contained a single homogeneous population of fibres which shared some common contractile activation characteristics with both of the fibre populations present in normal soleus muscle. However, of all fibre types investigated, the dystrophic soleus fibres were the most sensitive to Ca2+. Because of this characteristic, these fibres formed a distinct population. The maximum tensions induced by Ca2+ and Sr2+ were usually smaller in dystrophic fibres than in normal fibres obtained equivalent muscles. In conclusion, various normal murine muscle fibre types can be identified on the basis of differences in the mechanism of force activation by Ca2+ and Sr2+. Furthermore, it is possible to detect significant physiological differences in the mechanism of force activation brought about by murine muscular dystrophy.
Topics: Animals; Calcium; In Vitro Techniques; Mice; Muscle Contraction; Muscles; Muscular Dystrophy, Animal; Myofibrils; Sarcomeres; Strontium
PubMed: 3746681
DOI: 10.1113/jphysiol.1986.sp016060 -
Journal of Anatomy Sep 2013Adult muscle size and fibre-type composition are heritable traits that vary substantially between individuals. We used inbred mouse strains in which soleus muscle mass...
Adult muscle size and fibre-type composition are heritable traits that vary substantially between individuals. We used inbred mouse strains in which soleus muscle mass varied by an order of magnitude to explore whether properties of muscle spindles can also be influenced by genetic factors. Skip-serial cross-sections of soleus muscles dissected from 15 male mice of BEH, BEL, C57BL/6J, DUH, LG/J and SM/J strains were analysed for number of muscle spindles and characteristics of intrafusal and extrafusal fibres following ATPase staining. The BEL and DUH strains determined the range of: soleus mean size, a 10-fold difference from 2.1 to 22.3 mg, respectively; the mean number of extrafusal fibres, a 2.5-fold difference from 497 to 1249; and mean fibre-cross-sectional area, three-fold difference, e.g. for type 1 fibres, from 678 to 1948 μm². The range of mean proportion of type 1 fibres was determined by C57BL/6J (31%) and DUH (64%) strains. The mean number of spindles per muscle ranged between nine (LG/J) and 13 (BEL) (strain effect P < 0.02). Genetic correlations between spindle count and muscle weight or properties of extrafusal fibres were weak and not statistically significant. However, there was a strong correlation between the proportion of spindles with more than one bag2 fibre and the proportion of extrafusal fibres that were of type 1, and strain-dependent variation in the numbers of such spindles was statistically significant. The numbers of intrafusal fibres per spindle ranged from 2 to 8, with the most common complement of four found in 75.6% of spindles. There were no significant differences between the strains in the mean numbers of intrafusal fibres; however, the variance of the number was significantly less for the C57BL/6J strain than for any of the others. We conclude that abundance of muscle spindles and their intrafusal-fibre composition are substantially determined by genetic factors, which are different from those affecting muscle size and properties of the extrafusal fibres.
Topics: Analysis of Variance; Animals; Male; Mice; Mice, Inbred Strains; Muscle Spindles; Muscle, Skeletal; Phenotype
PubMed: 23834369
DOI: 10.1111/joa.12076 -
The Journal of Physiology Apr 20001. Changes in muscle strength, vastus lateralis fibre characteristics and myosin heavy-chain (MyoHC) gene expression were examined in 48 men and women following 3 weeks...
1. Changes in muscle strength, vastus lateralis fibre characteristics and myosin heavy-chain (MyoHC) gene expression were examined in 48 men and women following 3 weeks of knee immobilization and after 12 weeks of retraining with 1866 eccentric, concentric or mixed contractions. 2. Immobilization reduced eccentric, concentric and isometric strength by 47 %. After 2 weeks of spontaneous recovery there still was an average strength deficit of 11 %. With eccentric and mixed compared with concentric retraining the rate of strength recovery was faster and the eccentric and isometric strength gains greater. 3. Immobilization reduced type I, IIa and IIx muscle fibre areas by 13, 10 and 10 %, respectively and after 2 weeks of spontaneous recovery from immobilization these fibres were 5 % smaller than at baseline. Hypertrophy of type I, IIa and IIx fibres relative to baseline was 10, 16 and 16 % after eccentric and 11, 9 and 10 % after mixed training (all P < 0.05), exceeding the 4, 5 and 5 % gains after concentric training. Type IIa and IIx fibre enlargements were greatest after eccentric training. 4. Total RNA/wet muscle weight and ty I, IIa and IIx MyoHC mRNA levels did not change differently after immobilization and retraining. Immobilization downregulated the expression of type I MyoHC mRNA to 0.72-fold of baseline and exercise training upregulated it to 0.95 of baseline. No changes occurred in type IIa MyoHC mRNA. Immobilization and exercise training upregulated type IIx MyoHC mRNA 2.9-fold and 1.2-fold, respectively. For the immobilization segment, type I, IIa and IIx fibre area and type I, IIa and IIx MyoHC mRNA correlated (r = 0.66, r = 0.07 and r = -0.71, respectively). 5. The present data underscore the role muscle lengthening plays in human neuromuscular function and adaptation.
Topics: Adult; Electromyography; Exercise; Female; Gene Expression Regulation; Humans; Immobilization; Isometric Contraction; Male; Muscle Contraction; Muscle Fibers, Fast-Twitch; Muscle Fibers, Slow-Twitch; Muscle, Skeletal; Myofibrils; Myosin Heavy Chains; RNA; RNA, Messenger; Time Factors
PubMed: 10747199
DOI: 10.1111/j.1469-7793.2000.00293.x