title: Nitric oxide synthase-1 is enriched in fast-twitch oxidative myofibers.
abstract: Nitric oxide synthase-1 (NOS-1) is found in high concentrations in skeletal muscles, where its synthesis product nitric oxide (NO) is reported to be involved in a number of processes, including the modulation of the oxidative metabolism of myofibers. Performing immunoblot analysis and quantification of formazan produced by its specific NADPH diaphorase activity, we found NOS-1 to be enriched in rat skeletal muscles with a high proportion of fast-twitch myofibers. Since these myofibers represent a metabolically heterogeneous subpopulation, we extended our investigation to the level of individual myofibers. Using serial sections we combined myosin heavy chain-based fiber-typing with quantitative succinate dehydrogenase histochemistry to determine three groups of fiber-types, comprising fast-oxidative, fast-glycolytic and slow-oxidative myofibers. Image analysis showed that NOS-1 diaphorase activity is significantly enriched in fast-oxidative myofibers compared with fast-glycolytic and slow-oxidative ones. In order to characterize potential biological effects of the fiber-type-specific enrichment of NOS-1, we performed cytochrome oxidase histochemistry in the presence of the NO donors NOC-9 and SNAP. Both NO donors reduced cytochrome oxidase activity in all myofibers investigated with almost identical semi-maximal inhibition rates, although fast-oxidative and slow-oxidative myofibers contained twice as much basal catalytic activity than fast-glycolytic ones. In summary, we suggest that the NOS-1/NO system of skeletal muscles exerts its biological role especially in fast-oxidative myofibers, since these myofibers express more NOS-1 than fast-glycolytic or slow-oxidative ones and also contain the highest concentrations of cytochrome oxidases as potential target molecules of NO.
authors.affiliation: Institute of Anatomy, Universitätsklinikum Benjamin Franklin, Freie Universität Berlin, Königin-Luise-Str. 15, 14195 Berlin-Dahlem, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Planitzer
authors.forename: A
authors.initials: A
authors.lastname: Miethke
authors.forename: O
authors.initials: O
authors.lastname: Baum
mesh_terms: D000818:Animals; D003576:Electron Transport Complex IV / Q000378:metabolism; D015151:Immunoblotting; D007150:Immunohistochemistry; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000166:cytology / Q000201:enzymology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D018995:Myosin Heavy Chains / Q000378:metabolism; D020030:Nitric Oxide Donors / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052248:Nitric Oxide Synthase Type I; D051381:Rats; D017208:Rats, Wistar; D013223:Statistics as Topic; D013385:Succinate Dehydrogenase / Q000378:metabolism
chemical_list: D020030:Nitric Oxide Donors; D019001:Nitric Oxide Synthase; D052248:Nitric Oxide Synthase Type I; C496322:Nos1 protein, rat; D013385:Succinate Dehydrogenase; D003576:Electron Transport Complex IV; D018995:Myosin Heavy Chains