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- Sarcomere length dependence of the force-velocity relation i...Sarcomere length dependence of the force-velocity relation in single frog muscle fibers
Biophysical Journal, Volume 55, Issue 3, 1 March 1989, Pages 499-507
H.L. Granzier, D.H. Burns and G.H. Pollack
AbstractThe force-velocity relation of single frog fibers was measured at sarcomere lengths of 2.15, 2.65, and 3.15 microns. Sarcomere length was obtained on-line with a system that measures the distance between two markers attached to the surface of the fiber, approximately 800 microns apart. Maximal shortening velocity, determined by extrapolating the Hill equation, was similar at the three sarcomere lengths: 6.5, 6.0, and 5.7 microns/s at sarcomere lengths of 2.15, 2.65, and 3.15 microns, respectively. For loads not close to zero the shortening velocity decreased with increasing sarcomere length. This was the case when force was expressed as a percentage of the maximal force at optimal fiber length or as a percentage of the sarcomere-isometric force at the respective sarcomere lengths. The force-velocity relation was discontinuous around zero velocity: load clamps above the level that kept sarcomeres isometric resulted in stretch that was much slower than when the load was decreased below isometric by a similar amount. We fitted the force-velocity relation for slow shortening (less than 600 nm/s) and for slow stretch (less than 200 nm/s) with linear regression lines. At a sarcomere length of 2.15 microns the slopes of these lines was 8.6 times higher for shortening than for stretch. At 2.65 and 3.15 microns the values were 21.8 and 14.1, respectively. At a sarcomere length of 2.15 microm, the velocity of stretch abruptly increased at loads that were 160–170% of the sarcomere isometric load, i.e., the muscle yielded. However, at a sarcomere length of 2.65 and 3.15 microm yield was absent at such loads. Even the highest loads tested (260%) resulted in only slow stretch.(ABSTRACT TRUNCATED AT 250 WORDS)
Abstract | PDF (1064 kb) - Magnitude of Sarcomere Extension Correlates with Initial Sar...Magnitude of Sarcomere Extension Correlates with Initial Sarcomere Length during Lengthening of Activated Single Fibers from Soleus Muscle of Rats
Biophysical Journal, Volume 95, Issue 4, 1 August 2008, Pages 1890-1901
Appaji Panchangam, Dennis R. Claflin, Mark L. Palmer and John A. Faulkner
AbstractA laser-diffraction technique was developed that rapidly reports the lengths of sarcomeres () in serially connected sectors of permeabilized single fibers. The apparatus translates a laser beam along the entire length of a fiber segment within 2ms, with brief stops at each of 20 contiguous sectors. We tested the hypothesis that during lengthening contractions, when maximally activated fibers are stretched, sectors that contain the longer sarcomeres undergo greater increases in than those containing shorter sarcomeres. Fibers (=16) were obtained from the soleus muscles of adult male rats and the middle portions (length=1.05±0.11mm; mean±SD) were investigated. Single stretches of strain 27% and a strain rate of 54% s were initiated at maximum isometric stress and resulted in a 19±9% loss in isometric stress. The data on revealed that 1), the stretch was not distributed uniformly among the sectors, and 2), during the stretch, sectors at long before the stretch elongated more than those at short lengths. The findings support the hypothesis that during stretches of maximally activated skeletal muscles, sarcomeres at longer lengths are more susceptible to damage by excessive strain.
Abstract | Full Text | PDF (741 kb) - Force Kinetics and Individual Sarcomere Dynamics in Cardiac ...Force Kinetics and Individual Sarcomere Dynamics in Cardiac Myofibrils after Rapid Ca Changes
Biophysical Journal, Volume 83, Issue 4, 1 October 2002, Pages 2152-2161
R. Stehle, M. Krüger and G. Pfitzer
AbstractKinetics of force development and relaxation after rapid application and removal of Ca were measured by atomic force cantilevers on subcellular bundles of myofibrils prepared from guinea pig left ventricles. Changes in the structure of individual sarcomeres were simultaneously recorded by video microscopy. Upon Ca application, force developed with an exponential rate constant almost identical to , the rate constant of force redevelopment measured during steady-state Ca activation; this indicates that reflects isometric cross-bridge turnover kinetics. The kinetics of force relaxation after sudden Ca removal were markedly biphasic. An initial slow linear decline (rate constant ) lasting for a time was abruptly followed by an ∼20 times faster exponential decay (rate constant ). is similar to measured at low activating [Ca], indicating that reflects isometric cross-bridge turnover kinetics under relaxed-like conditions (see also Tesi et al., 2002. . . 83:2142–2151). Video microscopy revealed the following: invariably at a single sarcomere suddenly lengthened and returned to a relaxed-type structure. Originating from this sarcomere, structural relaxation propagated from one sarcomere to the next. Propagated sarcomeric relaxation, along with effects of stretch and P on relaxation kinetics, supports an intersarcomeric chemomechanical coupling mechanism for rapid striated muscle relaxation in which cross-bridges conserve chemical energy by strain-induced rebinding of P.
Abstract | Full Text | PDF (408 kb) - …more
Copyright © 1973 The Biophysical Society. All rights reserved.
Biophysical Journal, Volume 13, Issue 9, 857-876, 1 September 1973
doi:10.1016/S0006-3495(73)86031-X
Articles
Optical Diffraction Studies of Muscle Fibers
Masataka Kawai and Irwin D. Kuntz
Abstract
A new technique to monitor light diffraction patterns electrically is applied to frog semitendinosus muscle fibers at various levels of stretch. The intensity of the diffraction lines, sarcomere length change, and the length-dispersion (line width) were calculated by fast analogue circuits and displayed in real time. A heliumneon laser (wavelength 6328Å) was used as a light source. It was found that the intensity of the first-order diffraction line drops significantly (30–50%) at an optimal sarcomere length of 2.8μm on isometric tetanic stimulation. Such stimulation produced contraction of half-sarcomeres by about 22 nm presumably by stretching inactive elements such as tendons. The dispersion of the sarcomere lengths is extremely small, and it is proportional to the sarcomere length (less than 4%). The dispersion increases on stimulation. These changes on isometric tetanic stimulation were dependent on sarcomere length. No vibration or oscillation in the averaged length of the sarcomeres was found during isometric tetanus within a resolution of 3 nm; however, our observation of increased length dispersion of the sarcomeres together with detection of the averaged shortening of the sarcomere lengths suggests the presence of asynchronous cyclic motions between thick and thin filaments. An alternative explanation is simply an increase of the length dispersion of sarcomeres without cyclic motions.
