title: Effects of bite-opening and cyclosporin A on the mRNA levels of myosin heavy chain and the muscle mass in rat masseter.
abstract: To gain more insight into the mechanism of muscle plasticity in response to mechanical overload, we analyzed the effects of bite -opening (BO, 3 mm increase in the vertical dimension for 2 weeks) and/or a calcineurin (CaN) inhibitor, cyclosporin A (CsA, 10 mg/kg body weight, once daily for 2 weeks, ip) treatment on the myosin heavy chain (MHC I, IIa, IId/x, IIb) mRNA levels, using real-time RT-PCR with specific primers and on the muscle mass in rat masseter. As compared with normal control (n = 6), the BO treatment (n = 6) significantly increased the MHC I (p < 0.05) and the IIa mRNA levels (p < 0.01), and the CsA treatment (n = 6) significantly decreased the MHC I mRNA level (p < 0.01) in association with the significant decrease in the MHC IIb mRNA level (p < 0.05). The BO + CsA treatment (n = 6) significantly increased the MHC IIa mRNA level (p < 0.01) in association with the significant decrease in the MHC IIb mRNA level (p < 0.01), as compared with control. The masseter muscle mass was significantly decreased by either the CsA (p < 0.05) or the BO + CsA treatment (p < 0.001), but slightly increased by the BO treatment. These results suggest that in rat masseter the BO treatment produces not only the up-regulation of MHC IIa mRNA independently of CaN-signaling pathways, but also the MHC mRNA transition from IIa to I and the muscle mass maintenance mainly of type IIb fiber through the CaN-signaling pathways.
authors.affiliation: Department of Orthodontics, Tsurumi University School of Dental Medicine, Tsurumi-ku, Yokohama 230-8501, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Arai
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Ohnuki
authors.forename: Daisuke
authors.initials: D
authors.lastname: Umeki
authors.forename: Yasutake
authors.initials: Y
authors.lastname: Saeki
mesh_terms: D000818:Animals; D001835:Body Weight / Q000187:drug effects; D065095:Calcineurin Inhibitors; D016572:Cyclosporine / Q000494:pharmacology*; D008406:Masseter Muscle / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D018995:Myosin Heavy Chains / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D017090:Occlusal Splints; D009929:Organ Size / Q000187:drug effects; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014716:Vertical Dimension
chemical_list: D065095:Calcineurin Inhibitors; D012333:RNA, Messenger; D016572:Cyclosporine; D018995:Myosin Heavy Chains