Дисертації: "Single muscle fibres"

1

Vawda, Farouk. "Effects of hydrostatic pressure on single intact muscle fibres." Thesis, University of Bristol, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.294625.

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2

Kalakoutis, Michaeljohn. "Specific force in human single muscle fibres with specific reference to ageing." Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/specific-force-in-human-single-muscle-fibres-with-specific-reference-to-ageing(99224606-619b-46f8-87d4-a175a2ade014).html.

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The loss of muscle strength in the elderly is greater than the loss of muscle mass, termed specific force (SF) loss, and indicates that a decrease in muscle quality contributes to age-related muscular weakness. The present PhD thesis has studied age-related SF loss in human skeletal muscle using a skinned single muscle fibre model. A large variation in published skinned fibre SF measurements was found to exist in the literature. Therefore, a systematic review and meta-analysis was performed to identify factors causing this variability. The majority of publications were objectively divided into four research groups based on shared authorship. Methodological differences between research groups contributed to ~30% of the variance in the literature, suggesting that they are an important contributor to the variance in published SF values. Different research groups use different activating solutions to study skinned fibres, and were assessed experimentally. Skinned fibres were exposed to different, but commonly used activating solutions (termed A and B). A significantly higher SF and a shorter time to half peak tension (t50) was measured from the same fibres in solution B compared with solution A. The use of TES in solution B instead of Imidazole as a pH buffer largely caused the SF difference, and a lower Cl- concentration and the use of Glutathione in solution B partly caused the faster t50. These findings indicate that the use of different activating solutions likely affects the variance of published SF values. The final study in this thesis compared SF between skinned fibres from physically active and comparatively frail elderly cohorts to a young, healthy group. MHC I fibre SF was significantly higher in solution B than A within all groups. No significant differences in SF, myosin content (SDS PAGE) or order (X-ray diffraction) were observed between groups. These findings suggest that physical activity does not affect age-related skinned fibre SF loss and that SF is related to skinned fibre myosin content.

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3

Qaisar, Rizwan. "Myonuclear Organization and Regulation of Muscle Contraction in Single Muscle Fibres : Effects of Ageing, Gender, Species, Endocrine Factors and Muscle Size." Doctoral thesis, Uppsala universitet, Klinisk neurofysiologi, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-167723.

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The skeletal muscle fibre is a syncitium where each myonucleus regulates the gene products in a finite volume of cytoplasm i.e., the myonuclear domain (MND). A novel image analysis algorithm applied to confocal images, analyzing MND size and myonuclear spatial distribution in 3-dimensions in single skeletal muscle fibres has been used in this project. The goal was to explore the modulation of myonuclei count and MND size in response to muscle adaptation processes. The effects of ageing, gender, hormones, muscle hypertrophy and body size were investigated on MND size. A strong linear relationship was found between MND size and body size in the muscle fibres from mammals representing a 100,000-fold difference in body size. Independent of species, MND size was highly dependent on MyHC isoform type and mitochondrial contents of skeletal muscle fibres. In hypertrophic mice, a significant effect of MND size on specific force and myosin content was observed. This effect was muscle fibre type-specific and shows that the bigger MNDs in fast-twitch EDL muscle fibres are optimally tuned for force production while smaller MNDs in slow-twitch soleus muscle fibres have a much more dynamic range of hypertrophy without functional compromise. This indicates a critical volume individual myonuclei can support efficiently for a proportional gain in muscle fibre force and size. In human muscle fibres, spatial organization of myonuclei was affected by both ageing and MyHC isoform expression. In fibres expressing type I MyHC isoform, an increased MND size variability and myonuclear aggregates were observed in old age although average MND size was unchanged. In contrast, in type IIa fibres, the average MND size was smaller reflecting smaller size of muscle fibres. Those changes may influence the transcriptional activity per myonucleus and/or local cooperatively of myonuclei in a gender and muscle fibre-type specific manner. Finally, hormone replacement therapy was shown to negate menopause-related functional impairment in skeletal muscle fibres. The positive effect on force was due to quantitative effect in fibres expressing fast myosin isoform while the effect was both quantitative and qualitative in fibres expressing slow myosin isoform. The effect on MND size was fibre type dependent and was achieved by significantly reducing domain size in slow- but not the fast-twitch muscle fibres. Together, our data suggest that modulation of myonuclei count and MND size is a mechanism contributing to remodelling of skeletal muscle in muscle adaptation process. These findings should be considered when developing therapeutic approaches towards restoring muscle mass and strength in muscle wasting conditions.

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4

Küenzi, Erich. "On the effect of 2,3-butanedione monoxime on contractile properties of single frog skeletal muscle fibres /." Bern, 1990. http://www.ub.unibe.ch/content/bibliotheken_sammlungen/sondersammlungen/dissen_bestellformular/index_ger.html.

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5

Karatzaferi, Christina. "Human muscle fatigue and recovery : relationship between high-energy phosphate turnover and myosin heavy chain isoform expression in single human skeletal muscle fibres." Thesis, Manchester Metropolitan University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.324541.

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6

Selvin, David. "Regulation of Myoplasmic Ca2+ During Fatigue in KATP Channel Deficient FDB Muscle Fibres." Thèse, Université d'Ottawa / University of Ottawa, 2013. http://hdl.handle.net/10393/26174.

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It is known that muscles that lack KATP channel activity generate much greater unstimulated [Ca2+]i and force than normal muscles during fatigue. The increase in unstimulated force in KATP channel deficient muscles is abolished by a partial inhibition of L-type Ca2+ channels, suggesting that it is due to a Ca2+ influx through L-type Ca2+ channels and a subsequent increased myoplasmic Ca2+. However, there is also evidence that the increase in resting force is abolished by NAC, a ROS scavenger. The objective of this study was to reconcile these observations by studying the hypothesis that “the increase in resting [Ca2+]i during fatigue in KATP channel deficient muscles starts with an excess Ca2+ influx through L-type Ca2+ channels, followed by an excess ROS production that causes a further increase in resting [Ca2+]i”. To test the hypothesis, single FDB fibres were fatigued with one tetanic contraction/sec for 180 sec. KATP channel deficient fibres were obtained i) by exposing wild type muscle fibers to glibenclamide, a KATP channel blocker and ii) by using fibres from Kir6.2-/- mice, which are null mice for the Kir6.2 gene that encodes for the protein forming the channel pore. Verapamil, a L-type Ca2+ channel blocker, applied at 1 μM, significantly reduced resting [Ca2+]i during fatigue in glibenclamide-exposed wild type fibres. NAC (1 mM) also reduced resting [Ca2+]i in glibenclamide-exposed muscles. The results suggest that the increase in resting [Ca2+]i during fatigue in KATP channel deficient FDB fibres is due to an influx through L-type Ca2+ channels, and an excess ROS production.

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7

Pilipowicz, Orest J. "Early satellite cell activation on isolated single muscle fibers." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 2000. http://www.collectionscanada.ca/obj/s4/f2/dsk1/tape2/PQDD_0019/MQ53205.pdf.

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8

Ghent, Heidi. "Fiber Type-specific Desmin Content in Human Single Muscle Fibers." BYU ScholarsArchive, 2006. https://scholarsarchive.byu.edu/etd/381.

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Contractile and cytoskeletal protein concentrations have been shown to differ on the basis of fiber type in whole muscle homogenates. The purpose of this study was to compare the content of the intermediate filament protein, desmin, between type I and type IIa single muscle fibers from a mixed muscle in human subjects. Biopsies were taken from the vastus lateralis of six recreationally active males. Approximately 150 single muscle fibers were dissected from each sample and analyzed using SDS-PAGE to determine myosin heavy chain (MHC) composition. Following identification, muscle fibers were pooled into two groups (MHC I and MHC IIa). Desmin and actin content within the pooled samples was determined via immunoblotting. On average, muscle samples were composed of 51 ± 7 % type I, 2 ± 1% type I/IIa, 27 ± 5% type IIa, 19 ± 4% type IIa/IIx and 1 ± 1% type IIx MHC single fibers. Desmin and actin contents were 40% and 34% higher in type I fibers compared to type IIa fibers, respectively (P < 0.05). However the desmin to actin ratio was similar between pooled type I and IIa single muscle fibers within the vastus lateralis. These data suggest that desmin and actin content is a function of muscle fiber type. These differences in cytoskeletal protein content may have implications for differences in contractile function and eccentric damage characteristics between fiber types.

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9

Snyder, Heidi Ghent. "Fiber type-specific desmin content in human single muscle fibers /." Diss., CLICK HERE for online access, 2006. http://contentdm.lib.byu.edu/ETD/image/etd1253.pdf.

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10

Hind, Albadrani. "Optimizing the Approach for Maintaining Single Muscle Fibers in Culture." Thesis, Université d'Ottawa / University of Ottawa, 2014. http://hdl.handle.net/10393/31900.

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The skeletal muscle is a dynamic tissue that has the ability to change and modify itself to fit the level of required activity; a phenomenon called muscle plasticity. Most studies of muscle plasticity are carried out in situ, a condition for which it is difficult to study and discern between the intrinsic properties of skeletal muscle, the myokines released by muscle fibers and the neurotrophic factors released by neurons innervating skeletal muscles that play various roles in the mechanisms of muscle plasticity. Another approach is to study the morphological and contractile properties of single adult muscle fibers under culture conditions for which one can fully control the level of activity and exogenous factors affecting muscle plasticity. However, the survival of single muscle fiber in culture is very low as most fibers degenerated or supercontracted within 5-7 days. The first objective of this study was to optimize fiber survival in culture. The application of chronic stimulation and beta-adrenergic agonists are two major factors that prevent muscle atrophy and loss of force in denervated muscles in situ. So, objective two was to determine if chronically stimulated single fibers in culture also improve fiber survival and contractile characteristic under culture conditions. The third objective was the same for salbutamol, a beta 2-adrenergic agonist. In regard to the optimization of fiber survival, the Minimum Essential Medium (MEM) was a better medium than Dulbecco’s Modified Eagle Medium (DMEM), changing 50% of the culture medium every two days also improved fiber survival compared to changing the medium every day. Interestingly, inhibiting the proliferation of satellite cells with AraC largely improved fiber survival when fibers were kept under resting conditions, but not when they were chronically stimulated. Finally, under conditions in which proliferation of satellite cells was inhibited, the use of a collagen/laminin mixture as adhering substrate to improve fiber adhesion to glass coverslip gave rise to a better fiber survival than Matrigel that contains not only collagen and laminin but several growth factors. The results suggest i) that when satellite cells (or fibroblasts) are allowed to proliferate they appear to contribute to the degeneration of fibers under resting conditions and ii) that the release of myokines by skeletal muscle fibers (or cytokines by other cells) likely play a role in fiber survival. Contrary to the situation in situ, neither the chronic stimulation nor salbutamol improved fiber survival and contractile characteristics of muscle fibers in culture suggesting that some important factors in culture are missing to allow chronic stimulation and salbutamol to reduce muscle atrophy and loss of force.

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11

Tomalka, André [Verfasser], and Tobias [Akademischer Betreuer] Siebert. "Determination of biomechanical and architectural muscle properties : from single muscle fibre to whole muscle mechanics / André Tomalka ; Betreuer: Tobias Siebert." Stuttgart : Universitätsbibliothek der Universität Stuttgart, 2018. http://d-nb.info/1162497270/34.

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12

Stary, Creed Michael. "Contraction-induced elevation of heat shock protein 72 mRNA content in isolated single skeletal muscle fibers." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3211911.

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Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed Jul 10, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references.

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13

Tan, Jing [Verfasser], and Thomas [Akademischer Betreuer] Klopstock. "Laser capture microdissection of single muscle fibers for mitochondrial proteomic investigations / Jing Tan ; Betreuer: Thomas Klopstock." München : Universitätsbibliothek der Ludwig-Maximilians-Universität, 2019. http://d-nb.info/1205664874/34.

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14

Henning, Franclo. "Mechanisms underlying the development of weakness in idiopathic inflammatory myopathies: an in vitro single muscle fibre contractility study." Doctoral thesis, University of Cape Town, 2018. http://hdl.handle.net/11427/29317.

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Introduction: Polymyositis (PM), dermatomyositis (DM) and necrotising autoimmune myopathy (NAM) form part of the spectrum of idiopathic inflammatory myopathies (IIMs). Although the pathogenic mechanisms are different, the unifying feature is that of weakness caused, in some way or another, by an inflammatory attack on muscle. The mechanism by which weakness develops is still unclear, but experimental animal data suggest that dysfunction of the contractile apparatus might contribute to muscle weakness in these conditions. This study investigated the contractile function of single muscle fibres from patients with IIMs in vitro. Methods: Muscle biopsies obtained from patients with IIMs and healthy controls were dissected and chemically permeabilised. Single muscle fibres were dissected out and subjected to contractility measurement based on standard protocols utilising a permeabilised single fibre system. Specific force (SF; maximum force normalised to cross-sectional area), was calculated for each fibre and compared between the two groups. In addition, maximum shortening velocity and power output were assessed in some of the fibres, and calcium sensitivity in the rest. The myosin heavy chain composition of each fibre was determined by means of gel electrophoresis. Results: A total of 178 fibres from IIM cases and 174 fibres from controls were studied. Specific (normalised) force was 23%, 24% and 29% lower in the IIM group for all fibre types combined, type I fibres, and type IIa fibres, respectively. Shortening velocity and maximum power output were significantly higher in the IIM group for both type I and IIa fibres, compared to controls, while calcium sensitivity was higher in type IIa fibres from IIM cases than controls. Discussion: The findings from this study suggest that weakness in IIMs may, at least in part, be caused by dysfunction of the contractile apparatus leading to impaired contractile force. The higher shortening velocity, power output and calcium sensitivity in fibres from IIM cases probably represents compensatory mechanisms. Although the mechanism by which contractile function is affected has not been investigated, animal studies suggest a role for TNF-α. The findings of this study provide a basis for further investigation into the mechanisms underlying weakness in IIMs.

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15

Cristea, Alexander. "Effects of Ageing and Physical Activity on Regulation of Muscle Contraction." Doctoral thesis, Uppsala University, Department of Neuroscience, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-9198.

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The aims of this study were to investigate the mechanisms underlying (1) the ageing-related motor handicap at the whole muscle, cellular, contractile protein and myonuclear levels; and (2) ageing-related differences in muscle adaptability.

In vivo muscles function was studied in the knee extensors. Decreases were observed in isokinetic and isometric torque outputs in old age in the sedentary men and women and elite master sprinters. A 20-week long specific sprint and resistance training successfully improved the maximal isometric force and rate of force development in a subgroup of master sprinters.

In vitro measurements were performed in muscle biopsies from the vastus lateralis muscle. Immunocytochemical and contractile measurements in single membrane permeabilized muscle fibres demonstrated ageing- and gender-related changes at the myofibrillar level. In sedentary subjects, data showed a preferential decrease in the size of muscle fibres expressing type IIa MyHC in men, lower force generating capacity in muscle fibres expressing the type I MyHC isoform in both men and women and lower maximum velocity of unloaded shortening (V₀) in fibres expressing types I and IIa MyHC isoforms in both men and women. The master sprinters also experienced the typical ageing-related reduction in the size of fast-twitch fibres, a shift toward a slower MyHC isoform profile and a lower V₀ of type I MyHC fibres, which played a role in the decline in explosive force production capacity. The fast-twitch fibre area increased after the resistance training period. A model combining single muscle fibre confocal microscopy with a novel algorithm for 3D imaging of myonuclei in single muscle fibre segments was introduced to study the spatial organisation of myonuclei and the size of individual myonuclear domains (MNDs). Significant changes in the MND size variability and myonuclear organization were observed in old age, irrespective gender and fibre type. Those changes may influence the local quantity of specific proteins per muscle fibre volume by decreased and/or local cooperativity of myonuclei in a gender and muscle fibre specific manner.

In conclusion, the ageing-related impairments in in vivo muscle function were related to significant changes in morphology, contractile protein expression and regulation at the muscle fibre level. It is suggested that the altered myonuclear organisation observed in old age impacts on muscle fibre protein synthesis and degradation with consequences for the ageing-related changes in skeletal muscle structure and function. However, the improved muscle function in response to a 20-week intense physical training regime in highly motivated physically active old subjects demonstrates that all ageing-related in muscle function are not immutable.

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16

Reisman, Elizabeth. "Analysis Of Changes In Mitochondrial Proteins In Single Muscle Fibres With Different Types Of Training." Thesis, 2020. https://vuir.vu.edu.au/42803/.

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Mitochondria are involved in many essential cell functions, including the production of energy and cellular metabolism. Hence, a better understanding of how mitochondria adapt to different interventions may have implications for both health and performance. The ability to distinguish fibre-specific changes may help resolve some of the debate concerning the effects of different types of exercise on mitochondrial biogenesis. Skeletal muscle fibres represent a large proportion of cell types in humans, with specialised contractile and metabolic functions that depend on a large number of associated proteins with extensive posttranslational modifications. Many of these skeletal muscle proteins are present in a cell-specific or a fibre-type dependent manner. However, while the size principle has clearly demonstrated the recruitment of different fibre types with exercise of different intensities, the methods for studying mitochondrial protein adaptations have mostly been confined to the analysis for whole-muscle samples that contain a mixture of type I and II fibres. Recent advances in proteomics by mass spectrometry (MS) allow for the quantification of thousands of proteins in small biological samples, providing the potential to analyse changes in mitochondrial proteins in single muscle fibres. This research describes a proteomic workflow for fibre typing and the subsequent identification of mitochondrial proteins within single human skeletal muscle fibres by MS, even when fibres have been prepared in a high detergent matrix. Fibre types were verified based on the relative abundance of myosin heavy chain (MYH) isoforms, which was determined by dividing the intensity-based absolute quantification of the respective isoform (MYH1, MYH2, MYH4, MYH7) by the sum of the intensities of all four MYH isoforms. This protocol also allows for incorporation of tandem mass tag (TMT) labelling for increased identification of lowly abundant proteins using a TMTpro-16 plex. This permitted a three-tiered comparison of mitochondrial protein content from different fibre types applied to a post vs. pre exercise training study design comparing two different types of exercise training performed by 23 men. The developed proteomic workflow quantified the levels of 536 known mitochondrial proteins, representing more than 45% of the total mitochondrial proteins in single muscle fibres. Analysis of proteins associated with known cellular pathways within the mitochondria demonstrated distinct trends of fibre-type specific protein responses to different types of exercise. This research aims to further the application of proteomic technologies to better understand how specific mitochondrial proteins are altered in response to the stress of exercise at the resolution of single skeletal muscle fibres.

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17

Wyckelsma, Victoria. "Na+, K+-ATPase in single skeletal muscle fibres and the effects of ageing, training and inactivity." Thesis, 2014. https://vuir.vu.edu.au/25863/.

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The Na+,K+-ATPase (NKA) is a key protein involved in the maintenance of skeletal muscle excitability and comprises 2 subunits (α and β), each of which express multiple isoforms at a protein level in skeletal muscle (α1-3 and β1-3). The fibre-specific expression, adaptability and roles of each isoform in human skeletal muscle are explored in this thesis. Research utilising muscle biopsies typically uses samples obtained from the vastus lateralis muscle, which in healthy young people comprises similar proportions of type I and II fibres. Analyses using whole muscle pieces don’t allow the detection of fibre-type specific differences and changes occurring at a cellular level. Hence analysis of skeletal muscle samples at the single fibre level offers important advantages in understanding NKA regulation. This thesis therefore investigated the isoform abundance of the NKA in human skeletal muscle single fibres and their adaptability following intense repeated-sprint exercise (RSE) training in healthy young adults (Study 1); with ageing (Study 2) and after high-intensity interval training (HIT) in the elderly (Study 3) and after voluntary inactivity and resistance training in healthy young adults (Study 4).

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18

Shoepe, Todd C. "Contractile function of single muscle fibers from chronically resistance trained humans." Thesis, 2001. http://hdl.handle.net/1957/29965.

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Resistance training is widely prescribed for rehabilitation of injuries and as a method to improve athletic performance. It is accepted that resistance training increases the maximal force production of whole muscle and it has been suggested that the velocity of shortening can increase as well. However, little is known about the effects of resistance training at the cellular level. Therefore, we investigated morphology, force production, velocity, and force-velocity-power relationships of single chemically skinned muscle fibers from chronically resistance trained humans, including cross sectional area (CSA), peak Ca²⁺ -activated force production (P₀), specific tension (P₀/CSA), unloaded shortening velocity (V₀), and isotonic contractions. The untrained group (NT) group consisted of sedentary males (n=6, age =27 ± 2 yrs) while the chronically trained group (CHRT) group consisted of males with 7.7 ± 0.4 yrs resistance training experience (n=6, 22 ± 1 yrs). Maximum voluntary isometric and isokinetic knee extensor strength were measured along with 6 repetition maximum (6RM) free weight bench press and leg press. Muscle biopsies were obtained from the vastus lateralis. Chemically skinned single muscle fibers were mounted between a force transducer and servo-controlled motor and subjected to slack tests to determine peak Ca²⁺ -activated force (P₀) and unloaded shortening velocity (V₀). Isotonic load clamps were used to determine the force-velocity-power relationship. All fiber experiments were performed at 15°C. Fiber myosin heavy chain (MHC) content was determined by gel electrophoresis. The CHRT group was 119% and 81% stronger for 6RM leg press and bench press respectively. Peak isometric torque was 28% greater for the CHRT subjects and was significantly higher at all isokinetic speeds tested. No differences were seen in strength or isokinetic power between groups after normalization for lean body mass. CHRT fibers (n=213) expressing type I, IIa, and I₀a/IIx MHC were significantly greater in CSA (+41%, +51%, and +33%, respectively) and produced significantly greater P₀ (+37%, +48%, and +34%, respectively) than NT fibers (n=236). However, P₀/CSA was not different between CHRT and NT groups. Fibers expressing type IIa/IIx fibers produced greater P₀/CSA than IIa which produced greater P₀/CSA than type I. The P₀/CSA relationship between fibers within groups was type IIa/IIx>IIa>I and was significant for both groups. Fiber V₀ was not different between groups. Absolute power was significantly greater in the CHRT for all fiber types whereas power normalized for fiber volume was not different between groups. This resulted in a significantly greater force at peak power for all but type IIa/IIx fibers and trends for greater velocity at peak power. Single-cell contractile function in terms of V₀ and P₀/CSA, measured under standardized conditions, appears to be unaltered as a result of long term CHRT in young adult males. Group differences in absolute P₀ can be attributed solely to the greater CSA of the CHRT fibers. Long-term CHRT is not associated with a difference in fiber V₀. Therefore, the greater power was due entirely to the greater force. These data suggest that differences in whole muscle strength and power between NT and CHRT groups are primarily due to differences in fiber CSA rather than differences in cross-bridge mechanisms of contraction. Supported by National Institute of Health grant R3AR46392A.
Graduation date: 2002

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19

Zhang, Helia (Haoyue). "Satellite cell activation in adult zebrafish (Danio rerio) single muscle fibre cultures." 2013. http://hdl.handle.net/1993/21970.

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Satellite cells (SCs) are muscle stem cells that stay in a metabolically and mitotically quiescent state in adult skeletal muscle until activated. In mammals, SCs are activated and enter into the cell cycle for growth and regeneration. The mechanism initiating SC activation in vivo and in vitro, mediated by nitric oxide (NO) and hepatocyte growth factor (HGF) is described in the mouse model, but not in other species. Here, we assessed SC activation by counting bromodeoxyuridine (BrdU)-immuno-positive cells, and found that SC activation in zebrafish single muscle-fibre cultures is also NO and HGF dependent, peaking at 1 mM isosorbide dinitrate (ISDN, an NO donor drug) and 10 ng/mL HGF respectively, using dose-response experiments. Moreover, HGF signalling via the c-Met receptor is involved in the SC activation pathway and is considerably affected by temperature (i.e., 21 °C). Overall, understanding NO-HGF-c-Met signalling in SC activation gives new insights on fish muscle growth and conservation of regulatory pathways between species.

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20

Foster, Aurora. "Mechanisms and Mitigation of Skeletal Muscle Fatigue in Single Fibers from Older Adults." 2019. https://scholarworks.umass.edu/masters_theses_2/772.

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Skeletal muscle fatigue is the contraction-induced decline in whole muscle force or power, and can be greater in older versus young adults. Fatigue primarily results from increased metabolism elevating phosphate (Pi) and hydrogen (H+), which alters myosin-actin interactions; however, which steps of the myosin-actin cross-bridge cycle are changed and their reversibility are unclear. PURPOSE: This study sought to: 1) Examine the effects of elevated Pi and H+ on molecular and cellular function, and 2) Test the ability of deoxyadenosine triphosphate (dATP), an alternative energy to adenosine triphosphate (ATP), to reverse the contractile changes induced with high Pi and H+. METHODS: Maximal tension (force/cross-sectional area), myofilament mechanics and myosin-actin cross-bridge kinetics were measured in 214 single fibers (104 type 1) from the vastus lateralis of eight (4 men) healthy, sedentary older adults (71±1.3 years) under normal (5 mM Pi, pH 7.0), simulated fatigue (30 mM Pi, pH 6.2) and simulated fatigue with dATP conditions. RESULTS: Tension declined with high Pi and H+ in slow- (type I, 23%) and fast-contracting (type II, 28%) fibers due to fewer strongly bound myosin heads (28-48%) and slower cross-bridge kinetics (longer myosin attachment times (ton) (18-40%) and reduced rates of force production (18-30%)). Type I myofilaments became stiffer with high Pi and H+ (48%), which may have partially mitigated fatigue-induced tension reduction. Elevated Pi and H+ with dATP moderately improved force production similarly in both fiber types (8-11%) compared to high Pi and H+ with ATP. In type I fibers, high Pi and H+ with dATP returned the number of myosin heads strongly bound and ton to normal, while the rate of force production became faster than normal (16%). In type II fibers, high Pi and H+ with dATP did not change the number of myosin heads bound, but cross-bridge kinetics were 16-23% faster than normal. CONCLUSION: These results identified novel fiber-type specific changes in myosin-actin cross-bridge kinetics and myofilament stiffness that help explain fatigue-related force reduction in human single skeletal muscle fibers as well as an alternative energy source that partially to fully reverses contractile changes of elevated Pi and H+ that occur with fatigue.

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21

Stelzer, Julian E. (Julian Emanuel). "Protein isoform-function relationships of single skeletal muscle fibers from weight-bearing and hindlimb suspended mice." Thesis, 2002. http://hdl.handle.net/1957/31160.

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The goals of this research were to a) characterize the protein-function relationships of skeletal muscle single fibers from the mouse hindlimb b) examine mouse-strain related differences in myosin heavy chain composition (MHC) and single fiber contractile function, and c) quantify changes in fiber size and contractile function in response to 7 days of non-weight bearing. This research is significant because mechanistic approaches to understanding relationships between muscle protein expression, contractile function, and mechanical loading will likely benefit from a transition from the traditional laboratory rat to genetically modified mouse models. The methods used in this research feature an in vitro skinned-fiber preparation and single-fiber gel electrophoresis. Hindlimb muscles of mice were excised, and dissected into smaller bundles from which single muscle fibers were isolated. Single fibers were placed in skinning solution that permeabilized the fiber's membrane. The ends of skinned single muscle segments were attached to stainless steel troughs, which were connected to an isometric force transducer and a direct-current position motor. This system allowed the measurement of the fiber's cross-sectional area (CSA), peak isometric force (P��), and unloaded maximal shortening velocity (V��) during maximal Ca��-activating. The identification of the fiber's MHC content was subsequently achieved by electrophoresis of a sample of each fiber segment. The results showed that the C57BL/6 mouse soleus muscle contains a MHC composition (20% type I) that is dramatically different than the ICR and CBA/J mouse strains (50% type I, respectively). Type I fibers from the C57BL/6 mouse had V�� that was 25% lower than type I fibers from ICR and CBA/J mice. Following 7 days of hindlimb suspension (HS) all strains experienced significant soleus muscle and single-fiber atrophy and decreases in the absolute and specific (force/fiber CSA) of type I and II fibers. However, type I fibers from C57BL/6 mice showed no change in V�� whereas type I fibers from ICR and CBA/J showed increased V��. In conclusion, this research demonstrates that unlike the rat and human models of non-weight bearing, mouse soleus type I and II fibers are equally affected by HS with respect to decreases in fiber CSA and force. However, type I fiber V�� was elevated only in mouse strains with solei containing at least 50% type I MHC. These findings challenge the current view that non-weight bearing affects slow fibers more than fast fibers, and suggests that changes in single fiber contractile function with HS may be influenced in part by the MHC distribution of the muscle.
Graduation date: 2003

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Дисертації з теми "Single muscle fibres"

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