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First published online March 14, 2008
Journal of Experimental Biology 211, 1041-1049 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013722
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Persistence of motor unit and muscle fiber types in the presence of inactivity

Roland R. Roy1,*, David J. Pierotti2, Alan Garfinkel3, Hui Zhong1, Kenneth M. Baldwin4 and V. Reggie Edgerton1,3

1 Brain Research Institute, University of California, Los Angeles, CA 90024-1761, USA
2 Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ 86001-5640, USA
3 Department of Physiological Science, University of California, Los Angeles, CA 90024-1761, USA
4 Department of Physiology and Biophysics, University of California, Irvine, CA 92697, USA


Figure 1
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  		Fig. 1. The relationship between normalized succinate dehydrogenase (SDH) and normalized myofibrillar adenosine triphosphatase (mATPase) activity for the motor unit fibers in the tibialis anterior (TA) of all control (A) and all spinal cord isolated (SI, B) cats. Note the clusters for each fiber type, particularly for the type I and type IIx fibers.

 

Figure 2
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  		Fig. 2. The relationship between normalized {alpha}-glycerophosphate dehydrogenase (GPD) and normalized mATPase activity for the motor unit fibers in the TA of all control (A) and all SI (B) cats. Again, note the clusters for each fiber type, particularly for the type I and type IIx fibers. Abbreviations as in Fig. 1.

 

Figure 3
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  		Fig. 3. The relationship between normalized SDH and mATPase (A,C) and normalized mATPase and GPD (B,D) activity for type I motor unit fibers (glycogen depleted) and type I non-motor unit fibers (not glycogen depleted, located within the territory of the motor unit fibers) in a slow TA motor unit from a control (A,B) and a SI (C,D) cat is shown. In addition, data for all type I fibers across all cats are included for comparative purposes. Note that the ranges in the enzyme activities of motor unit fibers generally overlap those of non-motor unit fibers in both the control and SI cats. Abbreviations as in Figs 1 and 2.

 

Figure 4
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  		Fig. 4. The relationship between normalized SDH and mATPase (A,C) and normalized mATPase and GPD (B,D) activity for type IIa motor unit fibers (glycogen depleted) and type IIa non-motor unit fibers (not glycogen depleted, located within the territory of the motor unit fibers) in a fast TA motor unit from a control (A,B) and a SI (C,D) cat is shown. In addition, data for all type IIa fibers across all cats are included for comparative purposes. Note that the ranges in the enzyme activities of motor unit fibers generally overlap those of non-motor unit fibers in both the control and SI cats. Abbreviations as in Figs 1 and 2.

 

Figure 5
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  		Fig. 5. The relationship between normalized SDH and mATPase (A,C) and normalized mATPase and GPD (B,D) activity for type IIx motor unit fibers (glycogen depleted) and type IIx non-motor unit fibers (not glycogen depleted, located within the territory of the motor unit fibers) in a fast TA motor unit from a control (A,B) and a SI (C,D) cat is shown. In addition, data for all type IIx fibers across all cats are included for comparative purposes. Note that the ranges in the enzyme activities of motor unit fibers generally overlap those of non-motor unit fibers in both the control and SI cats. Abbreviations as in Figs 1 and 2.

 

Figure 6
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  		Fig. 6. A 3-D representation of the relationship among SDH, GPD and mATPase activities in the fibers of the motor units from all control (A) and all SI (B) cats. Note the presence of three clusters of fiber types for both the control and the SI cats. Abbreviations as in Figs 1 and 2.

 

Figure 7
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  		Fig. 7. Location of centroids of control (C) and SI (E) fibers in each of the three fiber types (type I, 1; type IIa, 2; and type IIx, 3). Metric re-scaling (see text in Results section) produced a new coordinate system (dimension 1 and dimension 2) in which the six centroids had maximum separation.

 

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© The Company of Biologists Ltd 2008