Received April 1, 2004
Revised May 19, 2004
Accepted after revision July 2, 2004
Resistance to fatigue of individual Xenopus single skeletal muscle fibers is correlated with mitochondrial volume density
Creed M Stary 1,
Odile Mathieu-Costello 1,
Michael C Hogan 1*
1 UC San Diego, Dept Medicine
* To whom correspondence should be addressed. E-mail: mchogan{at}ucsd.edu.
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Abstract |
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The purpose of the present study was to compare the individual fatigue characteristics of isolated single skeletal muscle fibers with their mitochondrial volume density, using direct histological morphometry. Single muscle fibers (n=14) were microdissected from lumbrical muscle of adult female Xenopus laevis, and force was measured while fibers were stimulated (tetanic contractions of 200 ms trains with 70 Hz stimuli at 9 V) at progressively increasing frequencies (2min each at 0.25, 0.33, 0.5, and 1 contractions/sec) until fatigue (<50% initial maximal force) had been established. Following the end of the fatigue protocol the volume density of mitochondria was determined by electron microscopy. Time to fatigue varied among the individual fibers from 3.3 min to 10 min. Mitochondrial volume densities ranged from 3.0% to 9.2%, and were positively correlated (r = 0.93) with time to fatigue of corresponding individual fibers. These results, using direct histological measurements of mitochondrial volume density: 1) support on a single cell basis the notion that oxidative capacity is a major determinant of muscle fatigue resistance; and 2) the fatigue profile of a single cell can be used to predict oxidative capacity.
Key Words:
Microscopy, Mitochondria, VO2
