title: Sphingomyelinase depresses force and calcium sensitivity of the contractile apparatus in mouse diaphragm muscle fibers.
abstract: Diseases that result in muscle weakness, e.g., heart failure, are characterized by elevated sphingomyelinase (SMase) activity. In intact muscle, SMase increases oxidants that contribute to diminished muscle force. However, the source of oxidants, specific processes of muscle contraction that are dysfunctional, and biochemical changes underlying the weakness elicited by SMase remain unknown. We tested three hypotheses: 1) SMase-induced depression of muscle force is mediated by mitochondrial reactive oxygen species (ROS), 2) SMase depresses force and calcium sensitivity of the contractile apparatus, and 3) SMase promotes oxidation and phosphorylation of myofibrillar proteins. Our experiments included intact muscle bundles, permeabilized single fibers, and isolated myofibrillar proteins. The mitochondrial-targeted antioxidant d-Arg-2',6'-dimethyl-Tyr-Lys-Phe-NH(2), decreased cytosolic oxidants and protected intact muscle bundles from weakness stimulated by SMase. SMase depressed maximal calcium-activated force by 20% in permeabilized single fibers (in kN/m(2): control 117 ± 6; SMase 93 ± 8; P < 0.05). Calcium sensitivity of permeabilized single fibers decreased from 5.98 ± 0.03 (control) to 5.91 ± 0.02 (SMase; P < 0.05). Myofibrillar protein nitrotyrosines, carbonyls, and phosphorylation were unaltered by SMase. Our study shows that the fall in specific force of intact muscle elicited by SMase is mediated by mitochondrial ROS and can be attributed largely to dysfunction of the contractile apparatus.
authors.affiliation: Department of Physiology and Center for Muscle Biology, University of Kentucky, Lexington, Kentucky 40536-0298, USA.
authors.forename: Leonardo F
authors.initials: LF
authors.lastname: Ferreira
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Moylan
authors.forename: Shawn
authors.initials: S
authors.lastname: Stasko
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Smith
authors.forename: Kenneth S
authors.initials: KS
authors.lastname: Campbell
authors.forename: Michael B
authors.initials: MB
authors.lastname: Reid
mesh_terms: D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002463:Cell Membrane Permeability; D003600:Cytosol / Q000201:enzymology; D003964:Diaphragm / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D004558:Electric Stimulation; D056966:Excitation Contraction Coupling; D051379:Mice; D008810:Mice, Inbred C57BL; D008931:Mitochondria, Muscle / Q000201:enzymology; D009119:Muscle Contraction / Q000187:drug effects; D018485:Muscle Fibers, Skeletal / Q000187:drug effects / Q000201:enzymology*; D053580:Muscle Strength / Q000187:drug effects; D009210:Myofibrils / Q000201:enzymology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D010766:Phosphorylation; D050050:Protein Carbonylation; D011499:Protein Processing, Post-Translational; D017382:Reactive Oxygen Species / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D014443:Tyrosine / Q000031:analogs & derivatives / Q000378:metabolism
chemical_list: D000975:Antioxidants; D017382:Reactive Oxygen Species; C002744:3-nitrotyrosine; D014443:Tyrosine; D013108:Sphingomyelin Phosphodiesterase