Single actomyosin motor interactions in skeletal muscle
Zeno Földes‐PappShih‐Chu LiaoBen BarbieriKarol GryczynskiRafał LuchowskiZygmunt GryczyńskiIgnacy GryczyńskiJulian BorejdoTiefeng You
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We present a study of intramuscular motion during contraction of skeletal muscle myofibrils. Myofibrillar actin was labeled with fluorescent dye so that the ratio of fluorescently labeled to unlabeled protein was 1:105. Such sparse labeling assured that there was on average only one actin-marker present in the focus at a given time. From the intensity signal in the two orthogonal detection channels, significant fluctuations, similar to fluorescent burst in diffusion-based single-molecule detection schemes, were identified via a threshold algorithm and analyzed with respect to their intensity and polarization. When only rigor complexes were formed, the fluctuations of polarized intensity were characterized by unimodal Gaussian photon distributions. During contraction, in contrast, bimodal Gaussian photon distributions were observed above the rigor background threshold. This suggests that the bimodal Gaussian photon distributions represent pre- and post-power stroke conformations. Clusters of polarized photons indicated an anisotropy decay of single actomyosin motors of ~ 9 s during muscle contraction.Keywords:
Myofibril
On isolated isthmus of oviduct of the rabbit, Isocorydine (Isoc) (3 mu mol/L) decreased significantly the frequency of spontaneous contraction and muscle tension, but not the amplitude of contraction. The tension and frequency of spontaneous contraction can be suppressed by Isoc at concentrations from 3 to 300 mumol/L. The amplitude of contraction was decreased only at 300 mu mol/L. It is suggested that the frequency and tension of spontaneous contraction of isthmic muscle are more sensitive to Isoc than the amplitude. Isoc antagonized the norepinephrine-induced contraction of the oviduct. The transport of ova through the oviduct reduced by hCG could be delayed by Isoc.
Oviduct
Muscle tension
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Continuous activity in excised and curarized frog sartorius muscles reduced twitch tension, contraction rate, and half-relaxation rate, and increased contraction and half-relaxation times. These changes are essentially the same as those reported by others for single fibers. 0.05 mm 2,4-dinitrophenol (DNP), 1 mm NaN 3 , and 1 mm KCN reduced twitch and tetanus tension in rested muscles. DNP and KCN shortened contraction and half-relaxation times, but NaN 3 induced a late prolongation. DNP and NaN 3 reduced contraction and half-relaxation rates, but KCN enhanced them. DNP and NaN 3 accentuated fatigue declines in tension output. KCN consistently induced twitch treppe, while tetanus tension declined as in unpoisoned fatigue. All the agents enhanced fatigue prolongations of contraction and half-relaxation times. DNP and NaN 3 accelerated the fatigue declines of contraction and half-relaxation rates, but KCN retarded them. All inhibitor effects were at least partially reversible. These results differ in many respects from equivalent results obtained with mouse muscles. Known inhibitor mechanisms do not as yet account adequately for the present findings.
Contractility
Time to peak
Bufo marinus
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A protein component that modified the interaction between actin and myosin was released from myofibrils on Ca2+-treatment, accompanying the weakening of Z disks. For its release 10(-4) M Ca2+ was required. The presence of the component facilitated the dissociation of thin and thick filaments from myofibrils and delayed superprecipitation of reconstituted actomyosin, independently of Ca2+ concentration. The component is probably a constituent of Z disks. In postmortem muscle, it is possible that the component is released from Z disks with an increased concentration of Ca2+, and that it weakens rigor linkages formed between actin and myosin, giving rise to lengthening of rigor-shortened sarcomeres.
Myofibril
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Single smooth muscle cells were isolated from vas deferens of guinea pig and effect of cocaine on calcium contraction of the individual cells under partially depolarized condition was examined. Among the isolated cells, a few cells were contracted by 20 mM calcium chloride in medium containing 60 mM potassium chloride. Cocaine increased the ratio of contracted cells. The result suggested that cocaine facilitated calcium contraction of individual cells in the tissue and induced larger contraction of the tissue.
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Objective:Based on the knowledge of special structure of muscle and a mechanochemical actin-activated myosin ATPase cycle four-state model,the relationship between the muscle contraction force and the contraction velocity is discussed.According to up-building a mechanical model,the relationship between the muscle contraction force and the contraction velocity is discussed thoroughly.Methods:With experimental results of single molecule myosin the relationship between the muscle contraction force and the contraction velocity is proposed from the view of physics by the chemical kinetic method and biochemical thermodynamic theory,and the relationship between the muscle contraction force and the contraction velocity is calculated.Results:We find the relationship is similar with the Formula Hill.The theoretical results are consistent with that of experiment.The chemical reaction of muscle contraction is accommodated automatically according to the change of load in muscle,the force of friction is relative to the load in muscle contraction.Conclusions:The model is fit to discussing the relation between the muscle contraction force and the contraction velocity and the method of physics is also fit to studying the system in this article.
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High-K medium produces a tonic contraction in guinea pig taenia coli. If muscle strips are preincubated in glucose-free medium, K produces only a phasic contraction. A comparison of Ca 45 entry and tissue Ca changes in the two responses were made. Both responses are accompanied by an enhanced uptake of Ca 45 . In addition to an increased Ca 45 uptake, a significant rise of tissue Ca was observed during the tonic contraction. No detectable changes in tissue Ca were noted in the phasic contraction. In light of modern theories of muscle contraction, it was proposed that in the phasic contraction, sufficient Ca is released from a cellular site to initiate contraction, whereas in the tonic contraction enough Ca crosses the membrane to initiate contraction. The transmembrane Ca transport involved in the latter response appeared to be dependent on metabolism.
Taenia coli
Tonic (physiology)
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1. The flight muscles of blowflies are easily dispersed in appropriate media to form suspensions of myofibrils which are highly suitable for phase contrast observation of the band changes associated with ATP-induced contraction. 2. Fresh myofibrils show a simple band pattern in which the A substance is uniformly distributed throughout the sarcomere, while the pattern characteristic of glycerinated material is identical with that generally regarded as typical of relaxed vertebrate myofibrils (A, I, H, Z, and M bands present). 3. Unrestrained myofibrils of both fresh and glycerinated muscle shorten by not more than about 20 per cent on exposure to ATP. In both cases the A substance migrates during contraction and accumulates in dense bands in the Z region, while material also accumulates in the M region. It is proposed that these dense contraction bands be designated the C(z), and C(m) bands respectively. In restrained myofibrils, the I band does not disappear, but the C(z) and C(m) bands still appear in the presence of ATP. 4. The birefringence of the myofibrils decreases somewhat during contraction, but the shift of A substance does not result in an increase of birefringence in the C(z) and C(m) bands. It seems therefore that the A substance, if it is oriented parallel with the fibre axis in the relaxed myofibril, must exist in a coiled or folded configuration in the C hands of contracted myofibrils. 5. The fine structure of the flight muscle has been determined from electron microscopic examination of ultrathin sections. The myofibrils are of roughly hexagonal cross-section and consist of a regular single hexagonal array of compound myofilaments the cores of which extend continuously throughout all bands of the sarcomere in all states of contraction or relaxation so far investigated. 6. Each myofilament is joined laterally with its six nearest neighbours by thin filamentous bridges which repeat at regular intervals along the fibre axis and are present in the A, I, and Z, but not in the H or M bands. When stained with PTA, the myofilaments display a compound structure. In the A band, a lightly staining medullary region about 40 A in diameter is surrounded by a densely staining cortex, the over-all diameter of the myofilament being about 120 A. This thick cortex is absent in the I and H bands, but a thinner cortex is often visible. 7. It is suggested that the basic structure is a longitudinally continuous framework of F actin filaments, which are linked periodically by the lateral bridges (possibly tropomyosin). The A substance is free under certain conditions to migrate to the Z bands to form the C(z) bands. The material forming the C(m) bands possibly represents another component of the A substance. The results do not clearly indicate whether myosin is confined to the A bands or distributed throughout the sarcomere.
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Postmortem changes in the actin-myosin interaction were studied by determining the amount of thick and thin filaments dissociated by ATP. The amount of separated filaments was very small in myofibrils prepared from muscles in rigor, while it increased markedly during post-rigor storage of muscles. Electron microscopically, separated thick and thin filaments prepared from stored muscles were similar to freshly prepared ones and no signs of proteolytic degradation of either type of filament could be observed. A protein which was released from myofibrils (probably from Z discs) on Ca2+-treatment seemed to be most closely related to the post-rigor dissociation of thick filaments from thin filaments.
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