Partial fast-to-slow conversion of regenerating rat fast-twitch muscle by chronic low-frequency stimulation.
Chronic low-frequency stimulation (CLFS) of rat fast-twitch muscles induces sequential transitions in myosin heavy chain (MHC) expression from MHCIIb --> MHCIId/x --> MHCIIa. However, the 'final' step of the fast-to-slow transition, i.e., the upregulation of MHCI, has been observed only after extremely long stimulation periods. Assuming that fibre degeneration/regeneration might be involved in the upregulation of slow myosin, we investigated the effects of CLFS on extensor digitorum longus (EDL) muscles regenerating after bupivacaine-induced fibre necrosis. Normal, non-regenerating muscles responded to both 30- and 60-day CLFS with fast MHC isoform transitions (MHCIIb --> MHCIId --> MHCIIa) and only slight increases in MHCI. CLFS of regenerating EDL muscles caused similar transitions among the fast isoforms but, in addition, caused significant increases in MHCI (to approximately 30% relative concentration). Stimulation periods of 30 and 60 days induced similar changes in the regenerating bupivacaine-treated muscles, indicating that the upregulation of slow myosin was restricted to regenerating fibres, but only during an early stage of regeneration. These results suggest that satellite cells and/or regenerating fast rat muscle fibres are capable of switching directly to a slow program under the influence of CLFS and, therefore, appear to be more malleable than adult fibres.
Pette
Dirk
D
Department of Biology, University of Konstanz, D-78457 Konstanz, Germany. dirk.pette@uni-konstanz.de
Sketelj
Janez
J
Skorjanc
Dejan
D
Leisner
Elmi
E
Traub
Irmtrud
I
Bajrović
Fajko
F
D000818:Animals; D002045:Bupivacaine / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D004558:Electric Stimulation; D008297:Male; D009119:Muscle Contraction / Q000502:physiology; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000166:cytology / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000166:cytology / Q000254:growth & development* / Q000378:metabolism*; D009133:Muscular Atrophy / Q000139:chemically induced / Q000378:metabolism / Q000503:physiopathology; D018995:Myosin Heavy Chains / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D032496:Satellite Cells, Skeletal Muscle / Q000166:cytology / Q000378:metabolism
D020033:Protein Isoforms; D018995:Myosin Heavy Chains; D002045:Bupivacaine