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This Article Full Text Full Text (PDF) Supplemental Information All Versions of this Article: 294/3/R948    most recent 00541.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (3) Citing Articles via Google Scholar Google Scholar Articles by Karatzaferi, C. Articles by Cooke, R. Search for Related Content PubMed PubMed Citation Articles by Karatzaferi, C. Articles by Cooke, R.

ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

Inhibition of shortening velocity of skinned skeletal muscle fibers in conditions that mimic fatigue

¹Institute of Human Performance and Rehabilitation, Center for Research and Technology Thessaly, and ²Department of Physical Education and Sport Science, University of Thessaly, Trikala, Greece; and ³Department of Biochemistry and Biophysics, Cardiovascular Research Institute, University of California, San Francisco, California

Submitted 27 July 2007 ; accepted in final form 11 December 2007

The mechanisms responsible for the inhibition of shortening velocity that occurs during muscle fatigue have not been completely elucidated. Phosphorylation of the myosin regulatory light chain (RLC) occurs during heavy use; however, previous reports on its role in affecting velocity have been equivocal. To further understand the process of fatigue, we varied the levels of myosin RLC phosphorylation (from 10 to >50%) and the concentrations of protons (from pH 7 to 6.2) and phosphate (from 5 to 30 mM), all of which change during fatigue. We measured the mechanics of permeable rabbit psoas fibers at a temperature closer to physiological (30°C), using a temperature jump protocol to briefly activate the fibers at the higher temperature to preserve sarcomere homogeneity. Although lowered pH alone had an effect on velocity, it was the three factors together, i.e., high phosphorylation, low pH, and high phosphate, that acted synergistically to inhibit fiber velocity by 40%. Our data demonstrate that in conditions that simulate physiological muscle fatigue, myosin phosphorylation does contribute to the inhibition of contraction velocity of fully activated fast muscle fibers.

mechanics; myosin; pH

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