Article Information

• PDF (709 kb)

PubMed

• Articles by G. Mutungi
• Articles by K.W. Ranatunga

Related Articles

• A Non-Cross-Bridge Stiffness in Activated Frog Muscle Fibers...

  A Non-Cross-Bridge Stiffness in Activated Frog Muscle Fibers Biophysical Journal, Volume 82, Issue 6, 1 June 2002, Pages 3118-3127 Maria A. Bagni, Giovanni Cecchi, Barbara Colombini and Francesco Colomo Abstract Force responses to fast ramp stretches of various amplitude and velocity, applied during tetanic contractions, were measured in single intact fibers from frog tibialis anterior muscle. Experiments were performed at 14°C at ∼2.1m sarcomere length on fibers bathed in Ringer’s solution containing various concentrations of 2,3-butanedione monoxime (BDM) to greatly reduce the isometric tension. The fast tension transient produced by the stretch was followed by a period, lasting until relaxation, during which the tension remained constant to a value that greatly exceeded the isometric tension. The excess of tension was termed “static tension,” and the ratio between the force and the accompanying sarcomere length change was termed “static stiffness.” The static stiffness was independent of the active tension developed by the fiber, and independent of stretch amplitude and stretching velocity in the whole range tested; it increased with sarcomere length in the range 2.1–2.8m, to decrease again at longer lengths. Static stiffness increased well ahead of tension during the tetanus rise, and fell ahead of tension during relaxation. These results suggest that activation increased the stiffness of some sarcomeric structure(s) outside the cross-bridges. Abstract | Full Text | PDF (133 kb)

• Effects of the Number of Actin-Bound S1 and Axial Force on X...

  Effects of the Number of Actin-Bound S1 and Axial Force on X-Ray Patterns of Intact Skeletal Muscle Biophysical Journal, Volume 90, Issue 3, 1 February 2006, Pages 975-984 P.J. Griffiths, M.A. Bagni, B. Colombini, H. Amenitsch, S. Bernstorff, S. Funari, C.C. Ashley and G. Cecchi Abstract Effects of the number of actin-bound S1 and of axial tension on x-ray patterns from tetanized, intact skeletal muscle fibers were investigated. The muscle relaxant, BDM, reduced tetanic M3 meridional x-ray reflection intensity (), M3 spacing (), and the equatorial / ratio in a manner consistent with a reduction in the fraction of S1 bound to actin rather than by generation of low-force S1-actin isomers. At complete force suppression, was 78% of its relaxed value. BDM distorted dynamic responses to sinusoidal length oscillations in a manner consistent with an increased cross-bridge contribution to total sarcomere compliance, rather than a changed S1 lever orientation in BDM. When the number of actin-bound S1 was varied by altering myofilament overlap, tetanic at low overlap was similar to that in high [BDM] (79% of relaxed ). Tetanic dependence on active tension in overlap experiments differed from that observed with BDM. At high BDM, tetanic approached its relaxed value (14.34nm), whereas tetanic at low overlap was 14.50nm, close to its value at full overlap (14.56nm). This difference in tetanic behavior was explicable by a nonlinear thick filament compliance which is extended by both active and passive tension. Abstract | Full Text | PDF (176 kb)

• Spontaneous Oscillatory Contraction without Regulatory Prote...

  Spontaneous Oscillatory Contraction without Regulatory Proteins in Actin Filament-Reconstituted Fibers Biophysical Journal, Volume 75, Issue 3, 1 September 1998, Pages 1439-1445 Hideaki Fujita and Shin’ichi Ishiwata Abstract Skinned skeletal and cardiac muscle fibers exhibit spontaneous oscillatory contraction (SPOC) in the presence of MgATP, MgADP, and inorganic phosphate (P), but the molecular mechanism underlying this phenomenon is not yet clear. We have investigated the role of regulatory proteins in SPOC using cardiac muscle fibers of which the actin filaments had been reconstituted without tropomyosin and troponin, according to a previously reported method (Fujita et al., 1996. 71:2307–2318). That is, thin filaments in glycerinated cardiac muscle fibers were selectively removed by treatment with gelsolin. Then, by adding exogenous actin to these thin filament-free cardiac muscle fibers under polymerizing conditions, actin filaments were reconstituted. The actin filament-reconstituted cardiac muscle fibers generated active tension in a Ca-insensitive manner because of the lack of regulatory proteins. Herein we have developed a new solvent condition under which SPOC occurs, even in actin filament-reconstituted fibers: the coexistence of 2,3-butanedione 2-monoxime (BDM), a reversible inhibitor of actomyosin interactions, with MgATP, MgADP and P. The role of BDM in the mechanism of SPOC in the actin filament-reconstituted fibers was analogous to that of the inhibitory function of the tropomyosin-troponin complex (-Ca) in the control fibers. The present results suggest that SPOC is a phenomenon that is intrinsic to the actomyosin motor itself. Abstract | Full Text | PDF (289 kb)

• …more

Abstract

Tension responses to ramp stretches of 1–3% Lo (fiber length) in amplitude were examined in resting muscle fibers of the rat at temperatures ranging from 10 degrees C to 36 degrees C. Experiments were done using bundles of approximately 10 intact fibers isolated from the extensor digitorum longus (a fast muscle) and the soleus (a slow muscle). At low temperatures (below approximately 20 degrees C), the tension response consisted of an initial rise to a peak during the ramp followed by a complex tension decay to a plateau level; the tension decay occurred at approximately constant sarcomere length. The tension decay after a standard stretch at approximately 3–4.Lo/s contained a fast, an intermediate, and a (small amplitude) slow component, which at 10 degrees C (sarcomere length approximately 2.5 microns) were approximately 2000.s-1, approximately 150.s-1, and approximately 25.s-1 for fast fibers and approximately 2000.s-1, approximately 70.s-1 and approximately 8.s-1 for slow fibers, respectively. The fast component may represent the decay of interfilamentary viscous resistance, and the intermediate component may be due to viscoelasticity in the gap (titin, connectin) filament. The two- to threefold fast-slow muscle difference in the rate of passive tension relaxation (in the intermediate and the slow components) compares with previously reported differences in the speed of their active contractions; this suggests that "passive viscoelasticity" is appropriately matched to contraction speed in different muscle fiber types. At approximately 35 degrees C, the fast and intermediate components of tension relaxation were followed by a delayed tension rise at approximately 10.s-1 (fast fibers) and 2.5.s-1 (slow fibers); the delayed tension rise was accompanied by sarcomere shortening. BDM (5–10 mM) reduced the active twitch and tetanic tension responses and the delayed tension rise at 35 degrees C; the results indicate stretch sensitive activation in mammalian sarcomeres at physiological temperatures.