title: Altered fast- and slow-twitch muscle fibre characteristics in female mice with a (S248F) knock-in mutation of the brain neuronal nicotinic acetylcholine receptor.
abstract: We generated a mouse line with a missense mutation (S248F) in the gene (CHRNA4) encoding the alpha4 subunit of neuronal nicotinic acetylcholine receptor (nAChR). Mutant mice demonstrate brief nicotine induced dystonia that resembles the clinical events seen in patients with the same mutation. Drug-induced dystonia is more pronounced in female mice, thus our aim was to determine if the S248F mutation changed the properties of fast- and slow-twitch muscle fibres from female mutant mice. Reverse transcriptase-PCR confirmed CHRNA4 gene expression in the brain but not skeletal muscles in normal and mutant mice. Ca(2+) and Sr(2+) force activation curves were obtained using skinned muscle fibres prepared from slow-twitch (soleus) and fast-twitch (EDL) muscles. Two significant results were found: (1) the (pCa(50) - pSr(50)) value from EDL fibres was smaller in mutant mice than in wild type (1.01 vs. 1.30), (2) the percentage force produced at pSr 5.5 was larger in mutants than in wild type (5.76 vs. 0.24%). Both results indicate a shift to slow-twitch characteristics in the mutant. This conclusion is supported by the identification of the myosin heavy chain (MHC) isoforms. Mutant EDL fibres expressed MHC I (usually only found in slow-twitch fibres) as well as MHC IIa. Despite the lack of spontaneous dystonic events, our findings suggest that mutant mice may be having subclinical events or the mutation results in a chronic alteration to muscle neural input.
authors.affiliation: School of Life and Environmental Sciences, Deakin University, VIC, Australia. djcan@deakin.edu.au
authors.forename: David J
authors.initials: DJ
authors.lastname: Cannata
authors.forename: David I
authors.initials: DI
authors.lastname: Finkelstein
authors.forename: Ilse
authors.initials: I
authors.lastname: Gantois
authors.forename: Yaroslav
authors.initials: Y
authors.lastname: Teper
authors.forename: John
authors.initials: J
authors.lastname: Drago
authors.forename: Jan M
authors.initials: JM
authors.lastname: West
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism / Q000502:physiology; D002118:Calcium / Q000494:pharmacology; D004195:Disease Models, Animal; D004421:Dystonia / Q000139:chemically induced / Q000235:genetics / Q000503:physiopathology*; D005260:Female; D055879:Gene Knock-In Techniques; D006614:Hindlimb / Q000503:physiopathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018656:Muscle Fibers, Fast-Twitch / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D020125:Mutation, Missense; D018995:Myosin Heavy Chains / Q000378:metabolism; D009538:Nicotine / Q000633:toxicity; D020033:Protein Isoforms / Q000378:metabolism; D011978:Receptors, Nicotinic / Q000235:genetics*; D013324:Strontium / Q000494:pharmacology
chemical_list: D002118:Calcium; D018995:Myosin Heavy Chains; D009538:Nicotine; D020033:Protein Isoforms; D011978:Receptors, Nicotinic; D013324:Strontium