title: beta-Adrenoceptor signaling in regenerating skeletal muscle after beta-agonist administration.
abstract: Stimulating the beta-adrenoceptor (beta-AR) signaling pathway can enhance the functional repair of skeletal muscle after injury, but long-term use of beta-AR agonists causes beta-AR downregulation, which may limit their therapeutic effectiveness. The aim was to examine beta-AR signaling during early regeneration in rat fast-twitch [extensor digitorum longus (EDL)] and slow-twitch (soleus) muscles after bupivacaine injury and test the hypothesis that, during regeneration, beta-agonist administration does not cause beta-AR desensitization. Rats received either the beta-AR agonist fenoterol (1.4 mgxkg(-1)xday(-1) ip) or saline for 7 days postinjury. Fenoterol reduced beta-AR density in regenerating soleus muscles by 42%. Regenerating EDL muscles showed a threefold increase in beta-AR density, and, again, these values were 43% lower with fenoterol treatment. An amplified adenylate cyclase (AC) response to isoproterenol was observed in cell membrane fragments from EDL and soleus muscles 7 days postinjury. Fenoterol attenuated this increase in regenerating EDL muscles but not soleus muscles. beta-AR signaling mechanisms were assessed using AC stimulants (NaF, forskolin, and Mn(2+)). Although beta-agonist treatment reduces beta-AR density in regenerating muscles, these muscles can produce large cAMP responses relative to healthy (uninjured) muscles. Desensitization of beta-AR signaling in regenerating muscles is prevented by altered rates of beta-AR synthesis and/or degradation, changes in G protein populations and coupling efficiency, and altered AC activity. These mechanisms have important therapeutic implications for modulating beta-AR signaling to enhance muscle repair after injury.
authors.affiliation: Basic and Clinical Myology Laboratory, Dept. of Physiology, The Univ. of Melbourne, Victoria, 3010 Australia.
authors.forename: Felice
authors.initials: F
authors.lastname: Beitzel
authors.forename: Martin N
authors.initials: MN
authors.lastname: Sillence
authors.forename: Gordon S
authors.initials: GS
authors.lastname: Lynch
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D019204:GTP-Binding Proteins / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects* / Q000378:metabolism / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011916:Rats, Inbred F344; D011943:Receptors, Adrenergic, beta / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012038:Regeneration / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D000318:Adrenergic beta-Agonists; D012333:RNA, Messenger; D011943:Receptors, Adrenergic, beta; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases