| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Department of Pharmacology,
Department of Physiology and Pharmacology,
, University of Lund, Solvegatan 10, Lund, Sweden
, University of St Andrews, St Andrews, Fife, Scotland
1. A study has been made of changes in sarcomere length and tension which occur during relaxation from isometric (`fixed ends') tetani in isolated muscle fibres of the frog. Sarcomere lengths were calculated from measurements of the separation of the zero-to-first-order intensity maxima in diffraction patterns generated by illuminating small segments of fibre with a He—Ne laser. Diffraction spectra were recorded continuously on cine-film using the method of `streak' photography.
2. Many sarcomeres in a muscle fibre are found to undergo active shortening during relaxation, at the expense of others located elsewhere which become passively extended. The time of onset of changes in sarcomere length coincides with the well known `shoulder' on the tension record, and their amplitude is maximal at the time when isometric force approaches zero. The original pattern of sarcomere lengths is only re-established after tension has disappeared.
3. The variability in the pattern of sarcomere length changes during relaxation was studied in a sample of twenty fibres, by making `streak' recordings from successive 1 mm segments along the entire length of each fibre. This survey showed that segments which elongate are located predominantly, though not exclusively, close to the fibre ends. The fractional length of the fibre which underwent shortening was found to vary considerably in different preparations. In many `streak' recordings the first order line fragmented into several distinct intensity maxima.
4. The effects of varying the initial fibre length on the time course of the tension decay and on the accompanying changes in sarcomere length were studied. The range of fibre lengths investigated corresponded with sarcomere spacings of 1·9-3·2 µm. The rate constant, R, for the exponential (later) component of the tension decay decreased with increasing fibre length and this was accompanied by a reduction in the mean amplitude of sarcomere shortening [Formula: see text] and lengthening [Formula: see text]. However, the time interval during which sarcomeres shortened or elongated increased, and so the mean velocities of sarcomere length changes ([Formula: see text] and [Formula: see text]) also displayed an inverse dependence upon fibre length.
5. The effects of altering temperature (0-20 °C) on the time course of the changes in sarcomere length and tension were investigated. The time to onset of the length changes, t1, the time to maximum amplitude, t2, and the time to full recovery, t3, all decreased exponentially with increasing temperature, but to differing extents. Temperature co-efficients for the velocity of sarcomere length changes during the interval t2 — t1 and for the fast tension decay were 2·47 ([Formula: see text]), 2·54 ([Formula: see text]) and 2·45 (R). The rate of the slow tension decay (before the tension `shoulder') also increased with temperature, with a Q10 of 2·43.
6. The complex patterns of sarcomere length changes seen during relaxation appear to be due to variations in the duration of mechanical activity in different fibre segments. A model is presented which shows that the characteristic form of the tension decay can be accounted for by the progressive emergence of local inequalities in the relative strengths of adjacent sarcomeres, as relaxation proceeds.
The experiments were performed at this address.
This article has been cited by other articles:
|
|
 |
|
  G. Todd, J. L. Taylor, J. E. Butler, P. G. Martin, R. B. Gorman, and S. C. Gandevia Use of motor cortex stimulation to measure simultaneously the changes in dynamic muscle properties and voluntary activation in human muscles J Appl Physiol, May 1, 2007; 102(5): 1756 - 1766. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 I. A. Telley, J. Denoth, E. Stussi, G. Pfitzer, and R. Stehle Half-Sarcomere Dynamics in Myofibrils during Activation and Relaxation Studied by Tracking Fluorescent Markers Biophys. J., January 15, 2006; 90(2): 514 - 530. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 A. Soman, T. L. Hedrick, and A. A. Biewener Regional patterns of pectoralis fascicle strain in the pigeon Columba livia during level flight J. Exp. Biol., February 15, 2005; 208(4): 771 - 786. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. Radzyukevich and K. A. P. Edman Effects of intracellular acidification and varied temperature on force, stiffness, and speed of shortening in frog muscle fibers Am J Physiol Cell Physiol, July 1, 2004; 287(1): C106 - C113. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. Stehle, M. Kruger, and G. Pfitzer Force Kinetics and Individual Sarcomere Dynamics in Cardiac Myofibrils after Rapid Ca2+ Changes Biophys. J., October 1, 2002; 83(4): 2152 - 2161. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Coirault, D. Chemla, and Y. Lecarpentier Relaxation of diaphragm muscle J Appl Physiol, October 1, 1999; 87(4): 1243 - 1252. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Jiang and F. J. Julian Effects of ramp shortening during linear phase of relaxation on [Ca2+]i in intact skeletal muscle fibers Am J Physiol Cell Physiol, January 1, 1999; 276(1): C152 - C160. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y.-B. Sun, C. Caputo, and K. A. P. Edman Effects of BAPTA on force and Ca2+ transient during isometric contraction of frog muscle fibers Am J Physiol Cell Physiol, August 1, 1998; 275(2): C375 - C381. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
P. A. Wahr, J. D. Johnson, and Jack. A. Rall Determinants of relaxation rate in skinned frog skeletal muscle fibers Am J Physiol Cell Physiol, June 1, 1998; 274(6): C1608 - C1615. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
Y. Jiang, M. F. Patterson, D. L. Morgan, and F. J. Julian Basis for late rise in fura 2 R signal reporting [Ca2+]i during relaxation in intact rat ventricular trabeculae Am J Physiol Cell Physiol, May 1, 1998; 274(5): C1273 - C1282. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. Coirault, D. Chemla, J.-C. Pourny, F. Lambert, and Y. Lecarpentier Instantaneous force-velocity-length relationship in diaphragmatic sarcomere J Appl Physiol, February 1, 1997; 82(2): 404 - 412. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
Address for reprints.