title: Exercise capacity of mice genetically lacking muscle glycogen synthase: in mice, muscle glycogen is not essential for exercise.
abstract: The glucose storage polymer glycogen is generally considered to be an important source of energy for skeletal muscle contraction and a factor in exercise endurance. A genetically modified mouse model lacking muscle glycogen was used to examine whether the absence of the polysaccharide affects the ability of mice to run on a treadmill. The MGSKO mouse has the GYS1 gene, encoding the muscle isoform of glycogen synthase, disrupted so that skeletal muscle totally lacks glycogen. The morphology of the soleus and quadriceps muscles from MGSKO mice appeared normal. MGSKO-null mice, along with wild type littermates, were exercised to exhaustion. There were no significant differences in the work performed by MGSKO mice as compared with their wild type littermates. The amount of liver glycogen consumed during exercise was similar for MGSKO and wild type animals. Fasting reduced exercise endurance, and after overnight fasting, there was a trend to reduced exercise endurance for the MGSKO mice. These studies provide genetic evidence that in mice muscle glycogen is not essential for strenuous exercise and has relatively little effect on endurance.
authors.affiliation: Department of Biochemistry and Molecular Biology and Indiana University Center for Diabetes Research, Indiana University School of Medicine, Indianapolis, Indiana 46202-5122, USA.
authors.forename: Bartholomew A
authors.initials: BA
authors.lastname: Pederson
authors.forename: Carlie R
authors.initials: CR
authors.lastname: Cope
authors.forename: Jill M
authors.initials: JM
authors.lastname: Schroeder
authors.forename: Micah W
authors.initials: MW
authors.lastname: Smith
authors.forename: José M
authors.initials: JM
authors.lastname: Irimia
authors.forename: Beth L
authors.initials: BL
authors.lastname: Thurberg
authors.forename: Anna A
authors.initials: AA
authors.lastname: DePaoli-Roach
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Roach
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D001835:Body Weight; D005260:Female; D006003:Glycogen / Q000737:chemistry / Q000378:metabolism; D006006:Glycogen Synthase / Q000235:genetics* / Q000378:metabolism*; D006019:Glycolysis; D006579:Heterozygote; D007773:Lactates / Q000378:metabolism; D008099:Liver / Q000378:metabolism; D008112:Liver Glycogen / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018482:Muscle, Skeletal / Q000378:metabolism; D009132:Muscles / Q000201:enzymology*; D010805:Physical Conditioning, Animal; D011108:Polymers / Q000737:chemistry; D011134:Polysaccharides / Q000737:chemistry; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D007773:Lactates; D008112:Liver Glycogen; D011108:Polymers; D011134:Polysaccharides; D006003:Glycogen; D006006:Glycogen Synthase