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E-C coupling failure in mouse EDL muscle after in vivo eccentric contractions
C P Ingalls1, G L Warren, J H Williams
1Muscle Biology Laboratory, Texas A&M University, College Station, Texas 77843-4243, USA. Ingalls@unix.tamu.edu
Journal of Applied Physiology (Bethesda, Md. : 1985)
|July 9, 1998
Summary
Eccentric contractions cause muscle force loss primarily due to excitation-contraction coupling failure. This defect, located at the t-tubule and sarcoplasmic reticulum interface, impairs calcium handling and reduces muscle force output.
Area of Science:
- Muscle Physiology
- Cellular Biology
- Biomedical Research
Background:
- Eccentric contractions can cause muscle damage and force loss.
- Excitation-contraction (E-C) coupling is crucial for muscle function.
- Understanding E-C coupling failure mechanisms is vital for muscle injury recovery.
Purpose of the Study:
- To quantify the contribution of E-C coupling failure to force loss after eccentric contractions in mouse EDL muscles.
- To identify the specific mechanisms underlying E-C coupling defects post-injury.
- To investigate changes in calcium handling and sarcoplasmic reticulum function.
Main Methods:
- In vivo eccentric contraction injury in mouse EDL muscles.
- In vitro measurement of maximal isometric tetanic force (Po) and contracture forces (caffeine, 4-chloro-m-cresol, K+).
- Assessment of sarcoplasmic reticulum (SR) Ca2+ release and uptake rates, and intracellular Ca2+ concentration ([Ca2+]i) using confocal microscopy.
Main Results:
- E-C coupling failure accounts for 57-75% of force loss within 5 days post-injury.
- Force loss is comparable to K+-induced force reduction, suggesting a defect at the t-tubule-SR interface.
- Elevated resting [Ca2+]i and reduced peak tetanic [Ca2+]i were observed immediately post-injury, with impaired SR Ca2+ handling developing by day 3.
Conclusions:
- The primary cause of force decrement after eccentric contractions is E-C coupling failure.
- The t-tubule-SR interface is a key site of injury-induced E-C coupling defects.
- Impaired calcium handling and SR function contribute to persistent force deficits.