Degeneration-regeneration as a mechanism contributing to the fast to slow conversion of chronically stimulated fast-twitch rabbit muscle.
Extensor digitorum longus muscles of male adult White New Zealand rabbits were indirectly stimulated at 10 Hz for 12 h daily for periods ranging up to 28 days. After four weeks the stimulated muscles showed a nearly uniform profile of high succinate dehydrogenase activity and, when incubated after acid preincubation for myofibrillar adenosine triphosphatase, displayed more dark- and intermediate-staining fibers than their contralateral counterparts. Muscles stimulated from between 6 to 21 days revealed degenerative foci and phagocytosis of degenerated fibers. These fibers were mostly of the fast-twitch, glycolytic type. Small myofibers, which often contained central nuclei, and structures identified as myoblasts or myotubes, reacted with a monoclonal antibody prepared against embryonic myosin heavy chains. The data suggest that under the employed conditions the fast to slow conversion of chronically stimulated fast-twitch rabbit muscle is not exclusively caused by adult fiber transformation, but results in part from the substitution of fast-twitch glycolytic fibers with newly formed fibers that have a high oxidative profile.
D000251:Adenosine Triphosphatases / Q000032:analysis; D000818:Animals; D002467:Cell Nucleus / Q000648:ultrastructure; D006651:Histocytochemistry; D007700:Kinetics; D008297:Male; D008854:Microscopy, Electron; D009132:Muscles / Q000201:enzymology / Q000502:physiology* / Q000648:ultrastructure; D009218:Myosins / Q000032:analysis; D011817:Rabbits; D012038:Regeneration
D000251:Adenosine Triphosphatases; D009218:Myosins