| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Received December 23, 2004
Revised January 26, 2005
Accepted after revision March 2, 2005
1 La Trobe University
* To whom correspondence should be addressed. E-mail: e.verburg{at}latrobe.edu.au.
This study investigated the effects of elevated, physiological levels of intracellular free [Ca2+] on depolarisation-induced force responses and on passive and active force production by the contractile apparatus in mechanically-skinned fibres of toad iliofibularis muscle. Excitation-contraction (EC) coupling was retained after skinning and force responses could be elicited by depolarisation of the transverse-tubular (T-) system. Raising the cytoplasmic [Ca2+] to ~1 µM or above for 3 min caused an irreversible reduction in the depolarisation-induced force response by interrupting the coupling between the voltage sensors in the T-system and the Ca2+ release channels in the sarcoplasmic reticulum. This uncoupling showed a steep [Ca2+]-dependency, with 50% uncoupling at ~1.9 µM Ca2+. The uncoupling occurring with 2 µM Ca2+ was largely prevented by the calpain inhibitor, leupeptin (1 mM). Raising the cytoplasmic [Ca2+] above 1 microM also caused an irreversible decline in passive force production in stretched skinned fibres in a manner graded by [Ca2+] though at a much slower relative rate than loss of coupling. The progressive loss of passive force could be rapidly stopped by lowering [Ca2+] to 10 nM, and was almost completely inhibited by 1 mM leupeptin but not by 10 µM calpastatin. Muscle homogenates pre-activated by Ca2+-exposure also evidently contained a diffusible factor that caused damage to passive force production in a Ca2+-dependent manner. Western blotting showed a) that calpain-3 was present in the skinned fibres and was activated by the Ca2+-exposure, and b) that the Ca2+-exposure in stretched skinned fibres resulted in proteolysis of titin. We conclude that the disruption of EC-coupling occurring at elevated levels of [Ca2+] is likely to be caused at least in part by Ca2+-activated proteases, most likely by calpain-3, though a role of calpain-1 is not excluded.
This article has been cited by other articles:
|
|
 |
|
  B.-T. Zhang, S. S. Yeung, D. G. Allen, L. Qin, and E. W. Yeung Role of the calcium-calpain pathway in cytoskeletal damage after eccentric contractions J Appl Physiol, July 1, 2008; 105(1): 352 - 357. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. Ng, J. M. Metzger, D. R. Claflin, and J. A. Faulkner Poloxamer 188 reduces the contraction-induced force decline in lumbrical muscles from mdx mice Am J Physiol Cell Physiol, July 1, 2008; 295(1): C146 - C150. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. R. Claflin and S. V. Brooks Direct observation of failing fibers in muscles of dystrophic mice provides mechanistic insight into muscular dystrophy Am J Physiol Cell Physiol, February 1, 2008; 294(2): C651 - C658. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 D. G. Allen, G. D. Lamb, and H. Westerblad Skeletal Muscle Fatigue: Cellular Mechanisms Physiol Rev, January 1, 2008; 88(1): 287 - 332. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. G. Allen, G. D. Lamb, and H. Westerblad Impaired calcium release during fatigue J Appl Physiol, January 1, 2008; 104(1): 296 - 305. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 B. S. Launikonis and E. Rios Store-operated Ca2+ entry during intracellular Ca2+ release in mammalian skeletal muscle J. Physiol., August 15, 2007; 583(1): 81 - 97. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
G. D. Lamb Calpains in muscle: selective and protective? J. Physiol., August 1, 2007; 582(3): 897 - 897. [Full Text] [PDF]
|
|
|
|
|
|
P. Gailly, F. De Backer, M. Van Schoor, and J. M. Gillis In situ measurements of calpain activity in isolated muscle fibres from normal and dystrophin-lacking mdx mice J. Physiol., August 1, 2007; 582(3): 1261 - 1275. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
C. van der Poel and D. G. Stephenson Effects of elevated physiological temperatures on sarcoplasmic reticulum function in mechanically skinned muscle fibers of the rat Am J Physiol Cell Physiol, July 1, 2007; 293(1): C133 - C141. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
I. C. H. Smith and D. J. Newham Fatigue and functional performance of human biceps muscle following concentric or eccentric contractions J Appl Physiol, January 1, 2007; 102(1): 207 - 213. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. M. Murphy, E. Verburg, and G. D. Lamb Ca2+ activation of diffusible and bound pools of {micro}-calpain in rat skeletal muscle J. Physiol., October 15, 2006; 576(2): 595 - 612. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
E. Verburg, T. L. Dutka, and G. D. Lamb Long-lasting muscle fatigue: partial disruption of excitation-contraction coupling by elevated cytosolic Ca2+ concentration during contractions Am J Physiol Cell Physiol, April 1, 2006; 290(4): C1199 - C1208. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. R. Moopanar and D. G. Allen The activity-induced reduction of myofibrillar Ca2+ sensitivity in mouse skeletal muscle is reversed by dithiothreitol J. Physiol., February 15, 2006; 571(1): 191 - 200. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
R. M. Murphy, R. J. Snow, and G. D. Lamb {micro}-Calpain and calpain-3 are not autolyzed with exhaustive exercise in humans Am J Physiol Cell Physiol, January 1, 2006; 290(1): C116 - C122. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. G Allen, N. P Whitehead, and E. W Yeung Mechanisms of stretch-induced muscle damage in normal and dystrophic muscle: role of ionic changes J. Physiol., September 15, 2005; 567(3): 723 - 735. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
