title: Immobilization with atrophy induces de novo expression of neuronal nicotinic α7 acetylcholine receptors in muscle contributing to neurotransmission.
abstract: BACKGROUND
  Mature acetylcholine receptor (AChR) isoform normally mediates muscle contraction. The hypothesis that α7AChRs up-regulate during immobilization and contribute to neurotransmission was tested pharmacologically using specific blockers to mature (waglerin-1), immature (αA-OIVA), and α7AChRs (methyllycaconitine), and nonspecific muscle AChR antagonist, α-bungarotoxin.
  
  
  METHODS
  Mice were immobilized; contralateral limbs were controls. Fourteen days later, anesthetized mice were mechanically ventilated. Nerve-stimulated tibialis muscle contractions on both sides were recorded, and blockers enumerated above sequentially administered via jugular vein. Data are mean ± standard error.
  
  
  RESULTS
  Immobilization (N = 7) induced tibialis muscle atrophy (40.6 ± 2.8 vs. 52.1 ± 2.0 mg; P < 0.01) and decrease of twitch tension (34.8 ± 1.1 vs. 42.9 ± 1.5 g; P < 0.01). Waglerin-1 (0.3 ± 0.05 μg/g) significantly (P = 0.001; N = 9) depressed twitch tension on contralateral (≥97%) versus immobilized side (approximately 45%). Additional waglerin-1 (total dose 1.06 ± 0.12 μg/g or approximately 15.0 × ED50 in normals) could not depress twitch of 80% or greater on immobilized side. Immature AChR blocker, αA-OIVA (17.0 ± 0.25 μg/g) did not change tension bilaterally. Administration of α-bungarotoxin (N = 4) or methyllycaconitine (N = 3) caused 96% or greater suppression of the remaining twitch tension on immobilized side. Methyllycaconitine, administered first (N = 3), caused equipotent inhibition by waglerin-1 on both sides. Protein expression of α7AChRs was significantly (N = 3; P < 0.01) increased on the immobilized side.
  
  
  CONCLUSIONS
  Ineffectiveness of waglerin-1 suggests that the twitch tension during immobilization is maintained by receptors other than mature AChRs. Because αA-OIVA caused no neuromuscular changes, it can be concluded that immature AChRs contribute minimally to neurotransmission. During immobilization approximately 20% of twitch tension is maintained by up-regulation of α-bungarotoxin- and methyllycaconitine-sensitive α7AChRs.
authors.affiliation: From Massachusetts General Hospital, Shriners Hospitals for Children®, Boston, Massachusetts, and Harvard Medical School, Boston, Massachusetts (S.L., H.-s.Y., T.S., M.A.S.K.); the Peptide Core Facility, Massachusetts General Hospital (A.K.); the Signal Transduction Laboratory, Massachusetts General Hospital, and Harvard Medical School (M.K.), the Clinical and Biochemical Pharmacology Laboratory, Massachusetts General Hospital, Shriners Hospitals for Children®, and Harvard Medical School (J.A.J.M.). Current positions: Sang-gye Paik Hospital, College of Medicine, In-Je University, Seoul, South Korea (S.L.), Department of Anesthesiology, Asan Medical Center, University of Ulsan, Seoul, South Korea (H.-s.Y.), Asahikawa University, Asahikawa, Japan (T.S.).
authors.forename: Sangseok
authors.initials: S
authors.lastname: Lee
authors.forename: Hong-Seuk
authors.initials: HS
authors.lastname: Yang
authors.forename: Tomoki
authors.initials: T
authors.lastname: Sasakawa
authors.forename: Mohammed A S
authors.initials: MA
authors.lastname: Khan
authors.forename: Ashok
authors.initials: A
authors.lastname: Khatri
authors.forename: Masao
authors.initials: M
authors.lastname: Kaneki
authors.forename: J A Jeevendra
authors.initials: JA
authors.lastname: Martyn
mesh_terms: D000818:Animals; D001284:Atrophy; D015153:Blotting, Western; D002038:Bungarotoxins / Q000494:pharmacology; D020916:Conotoxins / Q000494:pharmacology; D003435:Crotalid Venoms / Q000494:pharmacology; D007103:Immobilization / Q000009:adverse effects*; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000294:innervation* / Q000378:metabolism* / Q000473:pathology; D009213:Myography; D009469:Neuromuscular Junction / Q000187:drug effects; D010456:Peptides, Cyclic / Q000494:pharmacology; D009435:Synaptic Transmission / Q000502:physiology*; D064569:alpha7 Nicotinic Acetylcholine Receptor / Q000096:biosynthesis* / Q000187:drug effects
chemical_list: D002038:Bungarotoxins; D020916:Conotoxins; D003435:Crotalid Venoms; D010456:Peptides, Cyclic; D064569:alpha7 Nicotinic Acetylcholine Receptor; C492637:alphaA-conotoxin OIVA; C077895:waglerin