Effects of unweighting and clenbuterol on myosin light and heavy chains in fast and slow muscles of rat.
To investigate the plasticity of slow and fast muscles undergoing slow-to-fast transition, rat soleus (SOL), gastrocnemius (GAS), and extensor digitorum longus (EDL) muscles were exposed for 14 days to 1) unweighting by hindlimb suspension (HU), or 2) treatment with the beta(2)-adrenergic agonist clenbuterol (CB), or 3) a combination of both (HU-CB). In general, HU elicited atrophy, CB induced hypertrophy, and HU-CB partially counteracted the HU-induced atrophy. Analyses of myosin heavy (MHC) and light chain (MLC) isoforms revealed HU- and CB-induced slow-to-fast transitions in SOL (increases of MHCIIa with small amounts of MHCIId and MHCIIb) and the upregulation of the slow MHCIa isoform. The HU- and CB-induced changes in GAS consisted of increases in MHCIId and MHCIIb ("fast-to-faster transitions"). Changes in the MLC composition of SOL and GAS consisted of slow-to-fast transitions and mainly encompassed an exchange of MLC1s with MLC1f. In addition, MLC3f was elevated whenever MHCIId and MHCIIb isoforms were increased. Because the EDL is predominantly composed of type IID and IIB fibers, HU, CB, and HU-CB had no significant effect on the MHC and MLC patterns.
Stevens
L
L
Laboratoire de Plasticité Neuromusculaire, Université des Sciences et Technologies de Lille, F-59655 Villeneuve d'Ascq, France. dirk.pette@uni-konstanz.de
Firinga
C
C
Gohlsch
B
B
Bastide
B
B
Mounier
Y
Y
Pette
D
D
D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D001284:Atrophy; D001835:Body Weight / Q000187:drug effects; D002976:Clenbuterol / Q000494:pharmacology*; D006614:Hindlimb; D019417:Hindlimb Suspension; D006984:Hypertrophy; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D018995:Myosin Heavy Chains / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism*; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar
D000318:Adrenergic beta-Agonists; D018994:Myosin Light Chains; D018995:Myosin Heavy Chains; D002976:Clenbuterol