title: Nerve influence on myosin light chain phosphorylation in slow and fast skeletal muscles.
abstract: Neural stimulation controls the contractile properties of skeletal muscle fibres through transcriptional regulation of a number of proteins, including myosin isoforms. To study whether neural stimulation is also involved in the control of post-translational modifications of myosin, we analysed the phosphorylation of alkali myosin light chains (MLC1) and regulatory myosin light chains (MLC2) in rat slow (soleus) and fast (extensor digitorum longus EDL) muscles using 2D-gel electrophoresis and mass spectrometry. In control rats, soleus and EDL muscles differed in the proportion of the fast and slow isoforms of MLC1 and MLC2 that they contained, and also in the distribution of the variants with distinct isoelectric points identified on 2D gels. Denervation induced a slow-to-fast transition in myosin isoforms and increased MLC2 phosphorylation in soleus, whereas the opposite changes in myosin isoform expression and MLC2 phosphorylation were observed in EDL. Chronic low-frequency stimulation of EDL, with a pattern mimicking that of soleus, induced a fast-to-slow transition in myosin isoforms, accompanied by a decreased MLC2 phosphorylation. Chronic administration (10 mg x kg(-1) x d(-1) intraperitoneally) of cyclosporin A, a known inhibitor of calcineurin, did not change significantly the distribution of fast and slow MLC2 isoforms or the phosphorylation of MLC2. All changes in MLC2 phosphorylation were paralleled by changes in MLC kinase expression without any variation of the phosphatase subunit, PP1. No variation in MLC1 phosphorylation was detectable after denervation or cyclosporin A administration. These results suggest that the low-frequency neural discharge, typical of soleus, determines low levels of MLC2 phosphorylation together with expression of slow myosin, and that MLC2 phosphorylation is regulated by controlling MLC kinase expression through calcineurin-independent pathways.
authors.affiliation: Department of Anatomy and Physiology, University of Padova, Italy.
authors.forename: Cyril
authors.initials: C
authors.lastname: Bozzo
authors.forename: Barbara
authors.initials: B
authors.lastname: Spolaore
authors.forename: Luana
authors.initials: L
authors.lastname: Toniolo
authors.forename: Laurence
authors.initials: L
authors.lastname: Stevens
authors.forename: Bruno
authors.initials: B
authors.lastname: Bastide
authors.forename: Caroline
authors.initials: C
authors.lastname: Cieniewski-Bernard
authors.forename: Angelo
authors.initials: A
authors.lastname: Fontana
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Mounier
authors.forename: Carlo
authors.initials: C
authors.lastname: Reggiani
mesh_terms: D000818:Animals; D065095:Calcineurin Inhibitors; D016572:Cyclosporine / Q000494:pharmacology; D003714:Denervation; D004558:Electric Stimulation; D015180:Electrophoresis, Gel, Two-Dimensional; D004791:Enzyme Inhibitors / Q000494:pharmacology; D008297:Male; D013058:Mass Spectrometry; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism*; D018994:Myosin Light Chains / Q000235:genetics / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism; D010766:Phosphorylation; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000601:surgery; D013997:Time Factors
chemical_list: D065095:Calcineurin Inhibitors; D004791:Enzyme Inhibitors; D018994:Myosin Light Chains; D020033:Protein Isoforms; D016572:Cyclosporine; D009219:Myosin-Light-Chain Kinase