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  • 1
    Electronic Resource
    Electronic Resource
    Sarcomere shortening in striated muscle occurs in stepwise fashion (1977)
    [s.l.] : Nature Publishing Group
    Nature 268 (1977), S. 757-759 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Cardiac and skeletal muscle specimens were mounted in an apparatus (Fig. 1), components of which have been described1. The muscle was transilluminated with laser light (Spectra Physics He-Ne laser, Model 120, A=0.6238 Ann). The diffraction pattern was collected at the rear focal plane of a water ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/268757a0
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  • 2
    Electronic Resource
    Electronic Resource
    Active tension generation in isolated skeletal myofibrils (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 498-510 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Single or double myofibrils isolated from rabbit psoas muscle were suspended between a fine needle and an optical force transducer. By using a photodiode array, the length of every sarcomere along the specimen could be measured. Relaxed specimens exhibited uniform sarcomere lengths and their passive length-tension curve was comparable to that of larger specimens. Most specimens could be activated and relaxed four to five times before active force levels began to decline; some specimens lasted for 10–15 activation cycles. Active tension (20–22°C) was reproducible from contraction to contraction. The contractile response was dependent on initial sarcomere length. If initially activated at sarcomere lengths of ≥2.7 μm, one group of sarcomeres usually shortened to sarcomere lengths of 1.8–2.0 μm, while the remaining sarcomeres were stretched to longer lengths. Myofibrils that were carefully activated at shorter initial sarcomere lengths usually contracted homogeneously. Both homogeneous and inhomogeneous contractions produced high levels of active tension. Calcium sensitivity was found to be comparable to that in larger preparations; myofibrils immersed in pCa 6.0 solution generated 30% of maximal tension, while pCa 5.5–4.5 resulted in full activation. Active tension at full overlap of thick and thin filaments ranged from 0.34 to 0.94 N mm-2 (mean of 0.59 N mm-2±0.13 sd. n=65). Even allowing for a maximum of 20% nonmyofibrillar space in skinned or intact muscle fibres, the mean tension generated by isolated myofibrils per cross-sectional area is higher than by fibre preparations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00297212
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  • 3
    Electronic Resource
    Electronic Resource
    Limits of titin extension in single cardiac myofibrils (1996)
    Springer
    Journal of muscle research and cell motility 17 (1996), S. 425-438 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Passive force and dynamic stiffness were measured in relaxed, single myofibrils from rabbit ventricle over a wide range of sarcomere lengths, from ∼2–5μm. Myofibril stretch up to sarcomere lengths of ∼3 μm resulted in a steady increase in both force and stiffness. The shape of the length-force and the length-stiffness curves remained fully reproducible for repeated extensions to a sarcomere length of ∼2.7 μm. Above this length, myofibrillar viscoelastic properties were apparently changed irreversibly, likely due to structural alterations within the titin (connectin) filaments. Stretch beyond ∼3 μm sarcomere length resulted in a markedly reduced slope of the passive force curve, while the stiffness curve became flat. Thus, cardiac sarcomeres apparently reach a strain limit near a length of 3 μm. Above the strain limit, both curve types frequently showed a series of inflections, which we assumed to result from the disruption of titin-thick filament bonds and consequent addition of previously bound A-band titin segments to the elastic I-band titin portion. Indeed, we confirmed in immunofluorescence microscopic studies, using a monoclonal antibody against titin near the A/I junction, that upon sarcomere stretch beyond the strain limit length, the previously stationary antibody epitopes suddenly moved into the I-band, indicating A-band titin release. Altogether, the passive force/stiffness-length relation of cardiac myofibrils was qualitatively similar to, but quantitatively different from, that reported for skeletal myofibrils. From these results, we inferred that cardiac myofibrils have an approximately two times greater relative I-band titin extensibility than skeletal myofibrils. This could hint at differences in the maximum passive force-bearing capacity of titin filaments in the two muscle types.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00123359
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  • 4
    Electronic Resource
    Electronic Resource
    Filament lengths in frog semitendinosus and tibialis anterior muscle fibres (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 167-172 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary In frog semitendinosus muscle the descending limb of the length-tension curve is shifted rightward relative to that of tibialis anterior. Both the plateau right corner and the zero-force intercept are equally shifted. To investigate the reason for this shift, we compared filament lengths in the two muscles. Single fibres were mechanically skinned, stretched to reveal filaments clearly, incubated in a solution containing one of several antibodies to enhance filament visualization, and examined by electron microscopy. We found no differences of filament length. Thick filament lengths were 1.62 and 1.61 μm, respectively. I-segment lengths were measured by two methods. With the first, filament length was the same for both muscles, 1.95 or 1.98 μm, depending on the value taken for the troponin repeat; with the second it was 1.92 and 1.94 μm, respectively, for the two muscles. These differences are insignificant. Thus, the reported differences of shape of the length-tension curve are not explainable in terms of differences of filament length.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00115451
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  • 5
    Electronic Resource
    Electronic Resource
    Interaction between titin and thin filaments in intact cardiac muscle (1997)
    Springer
    Journal of muscle research and cell motility 18 (1997), S. 345-351 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract A ’freeze break‘ technique and immunoelectronmicroscopy were used to study the elastic properties of cardiactitin filaments. Small bundles consisting of a few fibres fromfreshly prepared dog papillary muscle were quickly frozen andbroken under liquid nitrogen to fracture sarcomeres in planesperpendicular to the filament axes. Breaks occurred at each ofseveral regions along the sarcomeres. The still-frozen specimenswere thawed during fixation to allow elastic filaments toretract. The broken muscle segments were then treated withmonoclonal titin antibody 9D10 which labelled a unique epitope inthe I-band. In sarcomeres broken at the A-I junction, the titinfilaments reacted toward the Z-line, independently of the thinfilaments. The retracted epitopes did not reach the Z-line;retraction stopped at the N1-line level. In sarcomeres brokennear the Z-line, the titin filaments retracted in the oppositedirection, to the tip of the thick filaments. When the breakoccurred in the A-band, by contrast, the titin-epitope positionwas unaffected. On the basis of these results, and despite thereported interaction of titin and actin in vitro, it appears thatcardiac titin molecules form elastic filaments that arefunctionally independent of the thin filaments. Near the Z-line,however, the titin filaments seem to associate firmly with thethin filaments
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1018626210300
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  • 6
    Electronic Resource
    Electronic Resource
    Stepwise shortening of muscle fibre segments (1987)
    Springer
    Journal of muscle research and cell motility 8 (1987), S. 242-251 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Shortening dynamics were measured in single fibres of frog skeletal muscle using a system that could track the spacing between hairs mounted on the fibre surface. Segment length changes were predominantly stepwise. The objective of the study was to identify potential artifacts and check their relevance. Several possible causes of artifactual steps were evaluated quantitatively and ruled out. In addition, the surface marker method and an independent length-detection method based on light diffraction were used simultaneously. The concurrence of results confirmed that it is highly unlikely that stepwise shortening could arise out of instrument artifact. Possible mechanisms underlying the phenomenon are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01574592
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  • 7
    Electronic Resource
    Electronic Resource
    Elastic properties of the titin filament in the Z-line region of vertebrate striated muscle (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 416-422 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The characteristics of the titin filament in the vicinity of the Z-line were investigated using immunoelectron microscopy. We used monoclonal titin antibodies T-11 and T-12 on single fibres of frog skeletal muscle, and on Z-line-extracted fibres. It is well established that the I-band region of titin is elastic. We find, however, that the elastic properties are not uniform. The T-12 epitope, which binds near the Z-line at the N1-line level, hardly changes position relative to the Z-line as the sarcomere is stretched. This demonstrates the functional inextensibility of the N1-Z-line region. After extreme stretch (above 6-μm sarcomere length), this zone finally does elongate; thus, the titin molecule in this region is intrisically elastic. The functional inextensibility seen at shorter sarcomere lengths may, therefore, be a result of binding of titin to the actin filament in the zone near the Z-line. When the Z-line was extracted, the T-12 epitope remained in the same position as in the unextracted fibres; it did not retract from the Z-line. Failure to retract implies that functional anchoring of titin is not exclusive to the Z-line, but includes some site closer to the A-band. Combined with the results of the above-mentioned stretch experiment, this result implies a likely binding of titin to the thin filament either focally at the N1 line or all along the entire N1-Z region. Thus, this region of titin is functionally stiff, but intrinsically elastic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00121293
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  • 8
    Electronic Resource
    Electronic Resource
    Contraction-induced movements of water in single fibres of frog skeletal muscle (1993)
    Springer
    Journal of muscle research and cell motility 14 (1993), S. 573-584 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Although X-ray diffraction measurements imply almost constant filament separation during isometric contraction, such constancy does not hold at the level of the isolated cell; cell cross-section increases substantially during isometric contraction. This expansion could arise from accumulation of water drawn from other fibre regions, or from water drawn into the cell from outside. To distinguish between these hypotheses, we froze single fibres of frog skeletal muscle that were jacketed by a thin layer of water. Frozen fibres were freeze-substituted, sectioned transversely, and examined in the electron microscope. In fibres frozen during contraction, we found large amounts of water just beneath the sarcolemma, less in deeper regions, and almost none in the fibre core. Such gradients were absent or diminished in fibres frozen in the relaxed state. The water was not confined to the myofibril space alone; we found large water spaces between myofibrils, particularly near mitochondria. Accumulation of water between myofibrils and around mitochondria implies that the driving force for water movement probably lies outside the filament lattice, and may therefore be osmotic. The fact that the distribution was nonuniform-highest near the sarcolemma and lowest in the core-implies that the water was likely drawn from the thin jacket surrounding the cell. Thus, the contractile cycle appears to be associated with water entry into and exit from the cell.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00141554
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  • 9
    Electronic Resource
    Electronic Resource
    Quantal length changes in single contracting sarcomeres (1999)
    Springer
    Journal of muscle research and cell motility 20 (1999), S. 529-538 
    Details
    ISSN: 1573-2657
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract The time course of shortening was investigated in the single sarcomere, the smallest contractile unit that retains natural structure. We projected the striation patterns of single bumblebee flight-muscle myofibrils onto a linear photodiode array, which was scanned periodically to produce repetitive traces of intensity vs. position along the array. Sarcomere length was taken as the span between adjacent A-band or Z-line centroids. When myofibrils were ramp-released by a motor, individual sarcomeres shortened in steps punctuated by pauses. The single sarcomere-shortening trace was consistently stepwise both in activated and relaxed specimens. Although step size was variable, the size distribution showed a signature-like feature: the histogram comprised distinct peaks that were spaced quasi-regularly. In the activated myofibrils the interpeak separation corresponded to 2.71 nm per half-sarcomere. This value is equal to the linear advance of actin subunits along the thin filament. Thus, actin filaments translate over thick filaments by steps that may be integer multiples of the actin-subunit spacing.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1005590401721
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  • 10
    Electronic Resource
    Electronic Resource
    Visualization of the transverse cytoskeletal network in insect-flight muscle by scanning-electron microscopy (1995)
    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 32 (1995), S. 226-232 
    Details
    ISSN: 0886-1544
    Keywords: Z-line interconnections ; honey-bee flight muscle ; transverse cytoskeletal network ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Located at the level of the Z-line, the transverse cytoskeletal network of insectflight muscle interconnects adjacent myofibrils with one another, and interconnects peripheral myofibrils with the cell membrane. This network has been presumed to keep myofibrils in register, or to distribute tension laterally among myofibrils. In this study, we used scanning-electron microscopy to reveal details of the three-dimensional arrangement of this network. The network is seen to interconnect longitudinal elements of the cytoskeletal network which surround each myofibril. The arrangement is not unlike that seen in vertebrate skeletal muscle. Interestingly, the transverse network makes contact with cell components such as dense bodies and mitochondria. Such contacts imply potential roles over and above those noted above. The network may be involved not only in mechanical function, but possibly also in intracellular communication. © 1995 Wiley-Liss, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/cm.970320306
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