Long-term effects of spinal cord transection on fast and slow rat skeletal muscle. II. Morphometric properties.
Morphometric properties of rat soleus and extensor digitorum longus muscles were studied 1 year following complete thoracic spinal cord transection (spinal cord level T9). Both muscles demonstrated almost complete type 1 to type 2 muscle fiber type conversion after 1 year. Muscle fiber atrophy was observed in both muscles. Type 2 fiber atrophy occurred to about the same extent in both muscles. Atrophy was most severe for the soleus type 1 fibers (50% decrease in size). Calculations based on the fiber type and size changes observed indicate that the percentage of the muscle cross-sectional area occupied by each fiber type was almost the same for both muscles 1 year after transection. Discriminant analysis of the data indicated that the percentage of type 2 fibers present in the muscle was the best discriminator between the various groups. These morphometric data provided a basis for understanding the contractile results presented in the previous study as well as insights into the mechanism of transformation in skeletal muscle. Furthermore, inherent differences between type 1 and type 2 fibers were demonstrated between predominantly slow and predominantly fast muscles. Thus, after almost one-half a lifetime of transection, rat muscles are almost completely transformed to fast muscle, and, regardless of initial conditions, have nearly identical properties.
D000251:Adenosine Triphosphatases / Q000378:metabolism; D000818:Animals; D009132:Muscles / Q000032:analysis* / Q000201:enzymology; D009133:Muscular Atrophy / Q000473:pathology; D009210:Myofibrils / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D013116:Spinal Cord / Q000502:physiology*; D013223:Statistics as Topic; D013997:Time Factors
D000251:Adenosine Triphosphatases