title: Energy metabolism in single human muscle fibers during contraction without and with epinephrine infusion.
abstract: The concentrations of glycogen, ATP, and phosphocreatine were analyzed in types I and II muscle fibers separated from biopsy samples of the quadriceps femoris muscle in five healthy volunteers. Muscle samples were obtained before and after 64 s of intermittent electrical stimulation. The experiment was carried out without and with epinephrine (Epi) infusion. Before stimulation the glycogen concentration was 11% higher in type II than in type I fibers (P less than 0.05). During electrical stimulation, rapid glycogenolysis occurred in type II fibers with hardly any detectable glycogenolysis in type I fibers. The calculated rates of glycogenolysis were 0.18 +/- 0.14 and 3.54 +/- 0.53 mmol glucose.kg dry muscle-1.s-1 in types I and II fibers, respectively. Epi infusion increased the rate of glycogenolysis during electrical stimulation in type I fibers (10-fold) but did not enhance the rate in type II fibers (P greater than 0.05). It is considered that, during short-term maximal muscle contraction, rapid muscle glycogenolysis occurs predominantly in type II fibers even though types I and II fibers are recruited and that, when Epi stimulation of glycogenolysis occurs, this is predominantly limited to type I fibers.
authors.affiliation: Department of Clinical Chemistry II, Huddinge University Hospital, Karolinska Institute, Sweden.
authors.forename: P L
authors.initials: PL
authors.lastname: Greenhaff
authors.forename: J M
authors.initials: JM
authors.lastname: Ren
authors.forename: K
authors.initials: K
authors.lastname: Söderlund
authors.forename: E
authors.initials: E
authors.lastname: Hultman
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D004734:Energy Metabolism / Q000187:drug effects; D004837:Epinephrine / Q000008:administration & dosage / Q000494:pharmacology*; D005260:Female; D006003:Glycogen / Q000378:metabolism; D006801:Humans; D007262:Infusions, Intravenous; D007700:Kinetics; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009132:Muscles / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010725:Phosphocreatine / Q000378:metabolism; D012016:Reference Values
chemical_list: D010725:Phosphocreatine; D000255:Adenosine Triphosphate; D006003:Glycogen; D004837:Epinephrine