| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
|
|
|
|||||||
|
|||||||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
1 Zoology, La Trobe University, Bundoora, Victoria, Australia
* To whom correspondence should be addressed. E-mail: t.dutka{at}latrobe.edu.au.
When muscle fibers are repeatedly stimulated they may become depolarized and force output decline. Excitation of the transverse-tubular (T-) system is critical for activation, but its role in muscle fatigue is poorly understood. Here, mechanically-skinned fibers from rat fast-twitch muscle were used because the sarcolemma is absent but the T-system retains normal excitability and its properties can be studied in isolation. The T-system membrane was fully polarized by bathing the skinned fiber in an internal solution with 126 mM K+ (control solution) or set at partially depolarised levels (~-63 mV and -58 mV) in solutions with 66 or 55 mM K+ respectively, and action potentials (APs) triggered in the sealed T-system by field stimulation. Prolonged depolarization of the T-system reduced tetanic force proportionately more than twitch force, with greater effect at higher stimulation frequency (responses at 20 Hz and 100 Hz reduced to 71 and 62 % in 66 mM K+, and to 54 and 35 % in 55 mM K+, respectively). Double pulse stimulation showed that depolarization increased the repriming period (estimated minimum time before a second AP can be produced) from ~4 ms to ~7.5 and 15 ms in the 66 and 55 mM K+ solutions respectively. These results demonstrate that T-system depolarization reduces tetanic force by impairing AP repriming, rather than by preventing AP generation per se or by inactivating the T-system voltage-sensors. The findings also explain why it is advantageous to reduce the rate of motoneuron stimulation to muscles during repeated or prolonged periods of activity.
This article has been cited by other articles:
|
|
 |
|
  S. P. Cairns and M. I. Lindinger Do multiple ionic interactions contribute to skeletal muscle fatigue? J. Physiol., September 1, 2008; 586(17): 4039 - 4054. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
T. L. Dutka, R. M. Murphy, D. G. Stephenson, and G. D. Lamb Chloride conductance in the transverse tubular system of rat skeletal muscle fibres: importance in excitation-contraction coupling and fatigue J. Physiol., February 1, 2008; 586(3): 875 - 887. [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]
|
|
|
|
 |
|
 T. L. Dutka and G. D. Lamb Na+-K+ pumps in the transverse tubular system of skeletal muscle fibers preferentially use ATP from glycolysis Am J Physiol Cell Physiol, September 1, 2007; 293(3): C967 - C977. [Abstract] [Full Text] [PDF]
|
|
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH |
| Visit Other APS Journals Online |
