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| 4. |
- Kadi, Fawzi, et al.
(author)
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The effects of physical activity and estrogen treatment on rat fast and slow skeletal muscles following ovariectomy.
- 2002
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In: Journal of muscle research and cell motility. - Dordrecht : Springer. - 0142-4319 .- 1573-2657. ; 23:4, s. 335-9
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Journal article (peer-reviewed)abstract
- Decreased estrogen production is associated with changes in the skeletal, cardiovascular and muscular systems. At the level of skeletal muscles, it has been shown that a reduction in force production occurs at menopause but the underlying mechanisms are still unknown. The aim of the study was to investigate the effects of ovariectomy on myosin heavy chain (MyHC) composition. Additionally, we studied the effects of physical activity and the combined effects of physical activity and estrogen treatment on MyHC content in ovariectomised (OX) animals. Twenty-five rats were randomly assigned to five different groups: controls, runners, OX, ovariectomised runners and ovariectomised runners receiving estrogen. Exercise consisted of voluntary running for 5 weeks. Two muscles were analysed: m. extensor digitorum longus, EDL, (fast muscle) and m. soleus (slow muscle). MyHC content was analysed on 8% gel electrophoresis. The level of running activity is reduced in OX animals and estrogen administration is associated with the normalisation of the level of physical activity. Ovariectomy induces a shift from fast to slow MyHC isoforms in both the soleus and EDL. When OX animals are allowed to run, alterations in MyHC isoforms are still observed in the EDL but not in the soleus. When physical activity is combined with estrogen treatment no alterations are observed in both muscles. In conclusion, this study shows that ovariectomy induces alterations in the contractile properties of skeletal muscles and that physical activity in combination with estrogen treatment are associated with the maintenance of slow and fast muscle characteristics.
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| 5. |
- Kostareva, Anna, et al.
(author)
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Mice expressing L345P mutant desmin exhibit morphological and functional changes of skeletal and cardiac mitochondria
- 2008
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In: Journal of Muscle Research and Cell Motility. - : Springer Science and Business Media LLC. - 0142-4319 .- 1573-2657. ; 29:1, s. 25-36
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Journal article (peer-reviewed)abstract
- Desmin mutations underlie inherited myopathies/cardiomyopathies with varying severity and involvement of the skeletal and cardiac muscles. We developed a transgenic mouse model expressing low level of the L345P desmin mutation (DESMUT mice) in order to uncover changes in skeletal and cardiac muscles caused by this mutation. The most striking ultrastructural changes in muscle from DESMUT mice were mitochondrial swelling and vacuolization. The mitochondrial Ca2+ level was significantly increased in skeletal and cardiac myocytes from DESMUT mice compared to wild type cells during and after contractions. In isolated DESMUT soleus muscles, contractile function and recovery from fatigue were impaired. A SHIRPA screening test for neuromuscular performance demonstrated decreased motor function in DESMUT compared to WT mice. Echocardiographic changes in DESMUT mice included left ventricular wall hypertrophy and a decreased left ventricular chamber dimension. The results imply that low levels of L345P desmin acts, at least partially, by a dominant negative effect on mitochondria.
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| 6. |
- Monemi, M, et al.
(author)
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Myosin heavy chain composition of the human lateral pterygoid and digastric muscles in young adults and elderly.
- 2000
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In: Journal of Muscle Research and Cell Motility. - 0142-4319 .- 1573-2657. ; 21:4, s. 303-312
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Journal article (peer-reviewed)abstract
- The myosin heavy chain (MyHC) content in different parts of, two jaw opening muscle, the human lateral pterygoid and the digastric muscles of five young adult and five elderly subjects (mean age 22 and 73 years, respectively) was determined, using gel electrophoresis and immunohistochemical methods. The lateral pterygoid of both young and elderly contained predominantly slow MyHC, and fast A MyHC was the major fast isoform. In contrast, the digastric was composed of slow, fast A and fast X MyHCs in about equal proportions in both age groups. About half of the lateral pterygoid fibres contained mixtures of slow and fast MyHCs, often together with alpha-cardiac MyHC. In the digastric, co-existence of slow and fast MyHCs was rare, and alpha-cardiac MyHC was lacking. On the other hand, co-expression of fast A and fast X MyHCs was found more often in the digastric than in the lateral pterygoid. In both age groups about half of the digastric IIB fibres contained solely fast X MyHC. In the lateral pterygoid, type IIB fibres with pure fast X MyHC was found in only one subject. The lateral pterygoid in elderly showed a significant amount of fibres with solely fast A MyHC, which were occasionally found in young adults. In the digastric, no significant differences were found between young and elderly, although the muscles of elderly contained lower mean value of slow MyHC, as compared to that of young muscles. It is concluded that the lateral pterygoid and the digastric muscles differ not only in the MyHC composition but also in modifications of the MyHC phenotypes during aging, suggesting that they have separate roles in jaw opening function.
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| 7. |
- Månsson, Alf
(author)
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Actomyosin based contraction : one mechanokinetic model from single molecules to muscle?
- 2016
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In: Journal of Muscle Research and Cell Motility. - : Springer Science and Business Media LLC. - 0142-4319 .- 1573-2657. ; 37:6, s. 181-194
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Journal article (peer-reviewed)abstract
- Bridging the gaps between experimental systems on different hierarchical scales is needed to overcome remaining challenges in the understanding of muscle contraction. Here, a mathematical model with well-characterized structural and biochemical actomyosin states is developed to that end. We hypothesize that this model accounts for generation of force and motion from single motor molecules to the large ensembles of muscle. In partial support of this idea, a wide range of contractile phenomena are reproduced without the need to invoke cooperative interactions or ad hoc states/transitions. However, remaining limitations exist, associated with ambiguities in available data for model definition e.g.: (1) the affinity of weakly bound cross-bridges, (2) the characteristics of the cross-bridge elasticity and (3) the exact mechanistic relationship between the force-generating transition and phosphate release in the actomyosin ATPase. Further, the simulated number of attached myosin heads in the in vitro motility assay differs several-fold from duty ratios, (fraction of strongly attached ATPase cycle times) derived in standard analysis. After addressing the mentioned issues the model should be useful in fundamental studies, for engineering of myosin motors as well as for studies of muscle disease and drug development.
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| 8. |
- Månsson, Alf
(author)
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The effects of inorganic phosphate on muscle force development and energetics : challenges in modelling related to experimental uncertainties
- 2021
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In: Journal of Muscle Research and Cell Motility. - : Springer. - 0142-4319 .- 1573-2657. ; 42, s. 33-46
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Journal article (peer-reviewed)abstract
- Muscle force and power are developed by myosin cross-bridges, which cyclically attach to actin, undergo a force-generating transition and detach under turnover of ATP. The force-generating transition is intimately associated with release of inorganic phosphate (Pi) but the exact sequence of events in relation to the actual Pi release step is controversial. Details of this process are reflected in the relationships between [Pi] and the developed force and shortening velocity. In order to account for these relationships, models have proposed branched kinetic pathways or loose coupling between biochemical and force-generating transitions. A key hypothesis underlying the present study is that such complexities are not required to explain changes in the force-velocity relationship and ATP turnover rate with altered [Pi]. We therefore set out to test if models without branched kinetic paths and Pi-release occurring before the main force-generating transition can account for effects of varied [Pi] (0.1-25 mM). The models tested, one assuming either linear or non-linear cross-bridge elasticity, account well for critical aspects of muscle contraction at 0.5 mM Pi but their capacity to account for the maximum power output vary. We find that the models, within experimental uncertainties, account for the relationship between [Pi] and isometric force as well as between [Pi] and the velocity of shortening at low loads. However, in apparent contradiction with available experimental findings, the tested models produce an anomalous force-velocity relationship at elevated [Pi] and high loads with more than one possible velocity for a given load. Nevertheless, considering experimental uncertainties and effects of sarcomere non-uniformities, these discrepancies are insufficient to refute the tested models in favour of more complex alternatives.
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| 9. |
- Månsson, Alf
(author)
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Translational actomyosin research : fundamental insights and applications hand in hand.
- 2012
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In: Journal of Muscle Research and Cell Motility. - : Springer Science and Business Media LLC. - 0142-4319 .- 1573-2657. ; 33:3-4, s. 219-233
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Research review (peer-reviewed)abstract
- This review describes the development towards actomyosin based nanodevices taking a starting point in pioneering studies in the 1990s based on conventional in vitro motility assays. References are given to parallel developments using the kinesin-microtubule motor system. The early developments focused on achieving cargo-transportation using actin filaments as cargo-loaded shuttles propelled by surface-adsorbed heavy meromyosin along micro- and nanofabricated channels. These efforts prompted extensive studies of surface-motor interactions contributing with new insights of general relevance in surface and colloid chemistry. As a result of these early efforts, a range of complex devices have now emerged, spanning applications in medical diagnostics, biocomputation and formation of complex nanostructures by self-organization. In addition to giving a comprehensive account of the developments towards real-world applications an important goal of the present review is to demonstrate important connections between the applied studies and fundamental biophysical studies of actomyosin and muscle function. Thus the manipulation of the motor proteins towards applications has resulted in new insights into methodological aspects of the in vitro motiliy assay. Other developments have advanced the understanding of the dynamic materials properties of actin filaments.
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| 10. |
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| 11. |
- Ochala, Julien, et al.
(author)
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Myofilament lattice structure in presence of a skeletal myopathy-related tropomyosin mutation
- 2013
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In: Journal of Muscle Research and Cell Motility. - : Springer Science and Business Media LLC. - 0142-4319 .- 1573-2657. ; 34:3-4, s. 171-175
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Journal article (peer-reviewed)abstract
- Human tropomyosin mutations deregulate skeletal muscle contraction at the cellular level. One key feature is the slowing of the kinetics of force development. The aim of the present study was to characterize the potential underlying molecular mechanisms by recording and analyzing the X-ray diffraction patterns of human membrane-permeabilized muscle cells expressing a particular beta-tropomyosin mutation (E41K). During resting conditions, the d(1,0) lattice spacing, Delta(1,0) and I-1,I-1 to I-1,I-0 ratio were not different from control values. These results suggest that, in presence of the E41K beta-tropomyosin mutation, the myofilament lattice geometry is well maintained and therefore may not have any detrimental influence on the contraction mechanisms and thus, on the rate of force generation.
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| 15. |
- Rahman, Mohammad A., et al.
(author)
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Comparative analysis of widely used methods to remove nonfunctional myosin heads for the in vitro motility assay
- 2018
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In: Journal of Muscle Research and Cell Motility. - : Springer. - 0142-4319 .- 1573-2657. ; 39:5-6, s. 175-187
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Journal article (peer-reviewed)abstract
- The in vitro motility assay allows studies of muscle contraction through observation of actin filament propulsion by surface-adsorbed myosin motors or motor fragments isolated from muscle. A possible problem is that motility may be compromised by nonfunctional, "dead", motors, obtained in the isolation process. Here we investigate the effects on motile function of two approaches designed to eliminate the effects of these dead motors. We first tested the removal of heavy meromyosin (HMM) molecules with ATP-insensitive "dead" heads by pelleting them with actin filaments, using ultracentrifugation in the presence of 1 mM MgATP ("affinity purification"). Alternatively we incubated motility assay flow cells, after HMM surface adsorption, with non-fluorescent "blocking actin" (1 µM) to block the dead heads. Both affinity purification and use of blocking actin increased the fraction of motile filaments compared to control conditions. However, affinity purification significantly reduced the actin sliding speed in five out of seven experiments on silanized surfaces and in one out of four experiments on nitrocellulose surfaces. Similar effects on velocity were not observed with the use of blocking actin. However, a reduced speed was also seen (without affinity purification) if HMM or myosin subfragment 1 was mixed with 1 mM MgATP before and during surface adsorption. We conclude that affinity purification can produce unexpected effects that may complicate the interpretation of in vitro motility assays and other experiments with surface adsorbed HMM, e.g. single molecule mechanics experiments. The presence of MgATP during incubation with myosin motor fragments is critical for the complicating effects.
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| 16. |
- Yu, F, et al.
(author)
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Human single masseter muscle fibers contain unique combinations of myosin and myosin binding protein C isoforms
- 2002
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In: Journal of Muscle Research and Cell Motility. - 0142-4319 .- 1573-2657. ; 23, s. 317-
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Journal article (peer-reviewed)abstract
- Striated craniofacial and limb muscles differ in their embryological origin, regulatory program during myogenesis, and innervation. In an attempt to explore the effects of these differences on the striated muscle phenotype in humans, the expression of myosin and myosin-associated thick filament proteins were studied at the single fiber level both in the human jaw-closing masseter muscle and in two limb muscles (biceps brachii and quadriceps femoris muscles). In the masseter, unique combinations of myosin heavy chain (MyHC) and myosin binding protein C (MyBP-C) isoforms were observed at the single fiber level. Compared to the limb muscles, the MyHC isoform expression was more complex in the masseter while the opposite was observed for MyBP-C. In limb muscles, a coordinated expression of three MyHC and three MyBP-C isoforms were observed, i.e., single fibers contained one or two MyHC isoforms, and up to three MyBP-C isoforms. Also, the relative content of the different MyBP-C isoforms correlated with the MyHC isoform expression. In the masseter, on the other hand, up to five different MyHC isoforms could be observed in the same fiber, but only one MyBP-C isoform was identified irrespective MyHC isoform expression. This MyBP-C isoform had a migration rate similar to the slow MyBP-C isoform in limb muscle fibers. In conclusion, a unique myofibrillar protein isoform expression was observed in the human masseter muscle fibers, suggesting significant differences in structural and functional properties between muscle fibers from human masseter and limb muscles.
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| 17. |
- Arheden, Håkan, et al.
(author)
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Force-velocity relation and rate of ATP hydrolysis in osmotically compressed skinned smooth muscle of the guinea pig
- 1987
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In: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 8:2, s. 151-160
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Journal article (peer-reviewed)abstract
- Chemically skinned guinea pig taenia coli fibre bundles showed a concentration-dependent decrease in width when incubated in media containing Dextran T500 (0-0.2 g ml-1). The maximal reduction in width, observed at 0.2 g ml-1 dextran, was 32%. The effect was reversible upon removal of dextran. Isometric force was slightly increased (about 10%) at the lowest dextran concentration (0.025 g ml-1) but decreased at higher concentrations (40% decrease at 0.2 g/ml-1). The energetic tension cost (ATP turnover/force) was decreased by about 40% after dextran addition. Force development and relaxation were markedly slower in 0.1 g ml-1 and absent in 0.2 g ml-1 dextran. In isotonic quick-release experiments 0.025 g ml-1 dextran did not influence maximal shortening velocity (Vmax) and relative stiffness, whereas 0.1 g ml-1 markedly increased stiffness and decreased Vmax to about 27%. Vanadate induced relaxation in the activated muscle (pCa 4.5) both in the absence and presence (0.1 g ml-1) of dextran and increased the rate of relaxation (pCa 9) at 0.1 g ml-1 dextran. The isometric rate of crossbridge turnover, as reflected by the energetic tension cost and the rate of relaxation, was decreased at all degrees of osmotic compression. Crossbridge turnover rate during shortening (Vmax) was unaffected at an osmotic compression of 12% (width) but was decreased at higher compression (32%).
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| 18. |
- Arner, Anders, et al.
(author)
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Smooth, slow and smart muscle motors.
- 2003
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In: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 24:2-3, s. 165-173
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Journal article (peer-reviewed)abstract
- Smooth muscle is a slow and economical muscle with a large variability in contractile properties. This review describes results regarding the relation between expression of myosin isoforms and the contraction of smooth muscle. The focus of the review is on studies of the organised contractile system in the smooth muscle tissue. The role of the myosin heavy chain variants formed by alternative splicing in the myosin heavy chain tail (SM1, SM2 isoforms) and head (SM-A SM-B isoforms) regions, as well as the role of essential light chains (LC17a, LC17b isoforms) for the variability of contractile properties are discussed. Smooth muscle also has the ability to alter its contractile properties in response to altered functional demands in vivo, e.g. during hypertrophic growth of urinary bladder, intestine, uterus and vessels and in response to altered hormone levels. These alterations involve changes in myosin expression and altered contractile kinetics. Non-muscle myosin has been shown to have a contractile function in some smooth muscle tissues and recent data on the kinetic properties of non-muscle myosin filaments in smooth muscle tissue are described.
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| 20. |
- Balogh, Johanna, et al.
(author)
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Lower active force generation and improved fatigue resistance in skeletal muscle from desmin deficient mice.
- 2003
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In: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 24:7, s. 453-459
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Journal article (peer-reviewed)abstract
- The mechanical effects of the intermediate filament protein desmin was examined in desmin deficient mice (Des-/-) and their wild type control (Des+/+). Active force generation was determined in intact soleus muscles and in skinned single fibres from soleus and psoas. A decreased force generation of skinned muscle fibres from Des-/- mice and a tendency towards decreased active force in intact soleus muscle were detected. Concentrations of the contractile protein actin and myosin were not altered in Des-/- muscles. Ca(2+)-sensitivity of skinned single fibres in Des-/- muscles was unchanged compared to Des+/+. Using a protocol with repeated short tetani an increased fatigue resistance was found in the intact soleus muscles from Des-/- mice. In conclusion, desmin intermediate filaments are required for optimal generation or transmission of active force in skeletal muscle. Although other studies have shown that the desmin intermediate filaments appear to influence Ca(2+)-handling, the Ca(2+)-sensitivity of the contractile filaments is not altered in skeletal muscle of Des-/- mice. Previous studies have reported a switch towards slower myosin isoforms in slow skeletal muscle of Des-/- mice. The increased fatigue resistance show that this change is reflected in the physiological function of the muscle.
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| 25. |
- Klinth, J, et al.
(author)
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Cardiotonic bipyridine amrinone slows myosin-induced actin filament sliding at saturating [MgATP]
- 2003
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In: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 24:1, s. 15-32
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Journal article (peer-reviewed)abstract
- Previously reported effects of amrinone on skeletal muscle function suggest that the drug reduces the rate constant of myosin cross-bridge dissociation. We have used the in vitro motility assay to further elucidate the mechanism underlying this effect and to aid these studies a new, improved,. lament tracking software was developed in the Matlab(TM) environment. The experiments were carried out at 30degreesC using heavy meromyosin from fast rabbit muscle and rhodamine-phalloidin labeled actin. laments. A slowing effect of amrinone on. lament sliding velocity at 1 mM MgATP was observed at drug concentrations >0.3 mM. This effect showed signs of saturation at the highest drug concentrations (1-2 mM) that could be readily tested. The sliding velocity exhibited hyperbolic dependence on [ MgATP] with a V-max of 7.2 +/- 0.9 mum/s and a K-M of 0.18 +/- 0.02 mM. Amrinone (1 mM) reduced V-max by 32 +/- 5% (P < 0.01) and K-M by 42 &PLUSMN; 8% (P < 0.05; n = 4). These results are accounted for in the most straightforward way by a model where amrinone acts directly on the actomyosin system and reduces the rate constant of MgADP release. Such a well-defined effect on the myosin cross-bridge cycle makes the drug a potentially useful pharmacological tool for further studies of myosin function both in vitro and in the ordered. lament array of a living muscle fiber.
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| 31. |
- Swärd, Karl, et al.
(author)
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Contractile effects of polycations in permeabilized smooth muscle
- 1998
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In: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 19:5, s. 463-472
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Journal article (peer-reviewed)abstract
- The polycations spermine, neomycin and polylysine potentiated Ca(2+)-activated force in beta-escin permeabilized guinea-pig ileum strips. The effect was inhibited by the calmodulin antagonists trifluoperazine, mastoparan and W13. Potentiation was slow or absent in chi-toxin permeabilized strips, indicating dependence on penetration of the polycations into cells. The effects of spermine and neomycin were maintained after extensive permeabilization by beta-escin, which eliminated the contractile effect of GTPgammaS. Replacement of ATP by CTP, which is not a substrate for myosin light chain kinase, inhibited contractile potentiation. Potentiation of Ca(2+)-activated contractions was associated with increased phosphorylation of the myosin regulatory light chains (LC20). A contractile effect of polylysine and neomycin was also seen in Ca(2+)-free medium and after partial LC20 thiophosphorylation, indicating that phosphorylation-independent processes may contribute to the response. Although spermine does not cause contraction in Ca(2+)-free medium at physiological [MgATP], it did so when [MgATP] was lowered to 40 micron. Similar to high-[Mg2+], the rate of contraction on addition of ATP to strips incubated with microcystin-LR in inhibit phosphatase activity was increased by the polycations, but only at [Ca2+] < 0.3 micron. The results suggest that polycations increase Ca(2+)-activated force by inhibiting myosin phosphatase activity, thereby increasing myosin LC20 phosphorylation. However, additional activation mechanisms, evident at low [Ca2+] and at low [ATP] and possibly involving direct activation of myosin, contribute to their effect.
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| 34. |
- Österman, Å, et al.
(author)
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Effects of 2,3-butanedione monoxime on activation of contraction and crossbridge kinetics in intact and chemically skinned smooth muscle fibres from guinea pig taenia coli
- 1993
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In: Journal of Muscle Research and Cell Motility. - 0142-4319. ; 14:2, s. 186-194
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Journal article (peer-reviewed)abstract
- The effects of 2,3-butanedione monoxime (BDM) were studied in smooth muscle fibres from guinea pig taenia coli. In intact muscle, active force during contractions induced by high-K+ was inhibited by about 10% in 1 mM BDM and by approximately 70% in 10 mM BDM. Intracellular [Ca2+] during contraction, measured with the fura-2 technique, was reduced in the presence of BDM. The reduction in force and [Ca2+] in the presence of 1 and 10 mM BDM could be reproduced by reduction in extracellular Ca2+, suggesting that BDM influences the Ca2+ entry or release. In skinned muscle preparations, BDM decreased the Ca2+ sensitivity of active force. This change could be explained by a decreased level of myosin light chain phosphorylation. In fibres maximally activated by thiophosphorylation, the effect of BDM on force occurred at higher concentrations; 10 mM gave no reduction of force and 60 mM 15% reduction. The maximal shortening velocity (Vmax) and force were unaffected by 30 mM BDM in thiophosphorylated muscle and decreased almost in parallel in Ca(2+)-activated contractions. The present results suggest that BDM inhibits myosin light chain phosphorylation, directly decreases force generation at the crossbridge level and inhibits the Ca2+ translocation in smooth muscle. The effect on force in skinned fibres is observed at higher BDM concentrations than those reported to be required for inhibition of force in striated muscle. The inhibition of force in intact smooth muscle could be explained by an influence on Ca2+ translocation.
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