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Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges

Slowing of relaxation is an important characteristic of skeletal muscle fatigue. The aim of the present study was to quantify the relative contribution of altered Ca(2+) handling (calcium component) and factors down-stream to Ca(2+) (cross-bridge component) to the slowing of relaxation in fatigued f...

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Autores principales: Westerblad, Håkan, Lännergren, Jan, Allen, David G.
Formato: Texto
Lenguaje:English
Publicado: The Rockefeller University Press 1997
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2217069/
https://www.ncbi.nlm.nih.gov/pubmed/9089444
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author Westerblad, Håkan
Lännergren, Jan
Allen, David G.
author_facet Westerblad, Håkan
Lännergren, Jan
Allen, David G.
author_sort Westerblad, Håkan
collection PubMed
description Slowing of relaxation is an important characteristic of skeletal muscle fatigue. The aim of the present study was to quantify the relative contribution of altered Ca(2+) handling (calcium component) and factors down-stream to Ca(2+) (cross-bridge component) to the slowing of relaxation in fatigued fibers of Xenopus and mouse. Two types of Xenopus fibers were used: easily fatigued, type 1 fibers and fatigue resistant, type 2 fibers. In these Xenopus fibers the free myoplasmic [Ca(2+)] ([Ca(2+)](i)) was measured with indo-1, and the relaxation of Ca(2+)-derived force, constructed from tetanic [Ca(2+)](i) records and in vivo [Ca(2+)](i)-force curves, was analyzed. An alternative method was used in both Xenopus and mouse fibers: fibers were rapidly shortened during the initial phase of relaxation, and the time to the peak of force redevelopment was measured. These two methods gave similar results and showed proportional slowing of the calcium and cross-bridge components of relaxation in both fatigued type 1 and type 2 Xenopus fibers, whereas only the cross-bridge component was slowed in fatigued mouse fibers. Ca(2+) removal from the myoplasm during relaxation was markedly less effective in Xenopus fibers as compared to mouse fibers. Fatigued Xenopus fibers displayed a reduced rate of sarcoplasmic reticulum Ca(2+) uptake and increased sarcoplasmic reticulum Ca(2+) leak. Some fibers were stretched at various times during relaxation. The resistance to these stretches was increased during fatigue, especially in Xenopus fibers, which indicates that longitudinal movements during relaxation had become less pronounced and this might contribute to the increased cross-bridge component of relaxation in fatigue. In conclusion, slowing of relaxation in fatigued Xenopus fibers is caused by impaired Ca(2+) handling and altered cross-bridge kinetics, whereas the slowing in mouse fibers is only due to altered cross-bridge kinetics.
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spelling pubmed-22170692008-04-22 Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges Westerblad, Håkan Lännergren, Jan Allen, David G. J Gen Physiol Article Slowing of relaxation is an important characteristic of skeletal muscle fatigue. The aim of the present study was to quantify the relative contribution of altered Ca(2+) handling (calcium component) and factors down-stream to Ca(2+) (cross-bridge component) to the slowing of relaxation in fatigued fibers of Xenopus and mouse. Two types of Xenopus fibers were used: easily fatigued, type 1 fibers and fatigue resistant, type 2 fibers. In these Xenopus fibers the free myoplasmic [Ca(2+)] ([Ca(2+)](i)) was measured with indo-1, and the relaxation of Ca(2+)-derived force, constructed from tetanic [Ca(2+)](i) records and in vivo [Ca(2+)](i)-force curves, was analyzed. An alternative method was used in both Xenopus and mouse fibers: fibers were rapidly shortened during the initial phase of relaxation, and the time to the peak of force redevelopment was measured. These two methods gave similar results and showed proportional slowing of the calcium and cross-bridge components of relaxation in both fatigued type 1 and type 2 Xenopus fibers, whereas only the cross-bridge component was slowed in fatigued mouse fibers. Ca(2+) removal from the myoplasm during relaxation was markedly less effective in Xenopus fibers as compared to mouse fibers. Fatigued Xenopus fibers displayed a reduced rate of sarcoplasmic reticulum Ca(2+) uptake and increased sarcoplasmic reticulum Ca(2+) leak. Some fibers were stretched at various times during relaxation. The resistance to these stretches was increased during fatigue, especially in Xenopus fibers, which indicates that longitudinal movements during relaxation had become less pronounced and this might contribute to the increased cross-bridge component of relaxation in fatigue. In conclusion, slowing of relaxation in fatigued Xenopus fibers is caused by impaired Ca(2+) handling and altered cross-bridge kinetics, whereas the slowing in mouse fibers is only due to altered cross-bridge kinetics. The Rockefeller University Press 1997-03-01 /pmc/articles/PMC2217069/ /pubmed/9089444 Text en This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 4.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/4.0/).
spellingShingle Article
Westerblad, Håkan
Lännergren, Jan
Allen, David G.
Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges
title Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges
title_full Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges
title_fullStr Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges
title_full_unstemmed Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges
title_short Slowed Relaxation in Fatigued Skeletal Muscle Fibers of Xenopus and Mouse : Contribution of [Ca(2+)](i) and Cross-bridges
title_sort slowed relaxation in fatigued skeletal muscle fibers of xenopus and mouse : contribution of [ca(2+)](i) and cross-bridges
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2217069/
https://www.ncbi.nlm.nih.gov/pubmed/9089444
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