title: Contraction-mediated glycogenolysis in mouse skeletal muscle lacking creatine kinase: the role of phosphorylase b activation.
abstract: Skeletal muscle that is deficient in creatine kinase (CK-/-) exhibits accelerated glycogenolysis during contraction. Understanding this phenomenon could provide insight into the control of glycogenolysis during contraction. Therefore, glycogen breakdown was investigated in isolated extensor digitorum longus CK-/- muscle. Muscles were stimulated to produce repeated tetani for 20 s in the presence of sodium cyanide to block mitochondrial respiration. Accumulation of lactate after stimulation was similar in wild-type (WT) and CK-/- muscles, whereas accumulation of glucose-6-phosphate was twofold higher in CK-/- muscles, indicating greater glycogenolysis in CK-/- muscles. Total phosphorylase activity was decreased by almost 30 % in CK-/- muscle (P < 0.001). Phosphorylase fractional activity (-/+ 3.3 mM AMP) was similar in both groups in the basal state (about 10 %), but increased to a smaller extent in CK-/- muscles after stimulation (39 +/- 4 % vs. 52 +/- 4 % in WT, P < 0.05). Inorganic phosphate, the substrate for phosphorylase, increased marginally in CK-/- muscles after stimulation (basal = 25.3 +/- 2.2 micromol (g dry muscle)-1; stimulated = 33.9 +/- 2.3 micromol (g dry muscle)-1), but substantially in WT muscles (basal = 11.4 +/- 0.7 micromol (g dry muscle)-1; stimulated = 54.2 +/- 4.5 micromol (g dry muscle)-1). Kinetic studies of phosphorylase b (dephosphorylated enzyme) from muscle extracts in vitro demonstrated higher relative activities in CK-/- muscles (60-135 %) in response to low AMP concentrations (up to 50 microM) in both the basal state and after stimulation (P < 0.05), whereas no differences in activity between CK-/- and WT muscles were observed at high AMP concentrations (> 100 microM). These data indicate that allosteric activation of phosphorylase b accounts for the accelerated glycogenolysis in CK-/- muscle during contraction.
authors.affiliation: Department of Physiology and Pharmacology, Karolinska Institutet, 17177 Stockholm, Sweden. abram.katz@fyfa.ki.se
authors.forename: Abram
authors.initials: A
authors.lastname: Katz
authors.forename: Daniel C
authors.initials: DC
authors.lastname: Andersson
authors.forename: Josephine
authors.initials: J
authors.lastname: Yu
authors.forename: Barbara
authors.initials: B
authors.lastname: Norman
authors.forename: Marie E
authors.initials: ME
authors.lastname: Sandstrom
authors.forename: Be
authors.initials: B
authors.lastname: Wieringa
authors.forename: Hakan
authors.initials: H
authors.lastname: Westerblad
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D003401:Creatine / Q000378:metabolism; D003402:Creatine Kinase / Q000235:genetics*; D004558:Electric Stimulation; D004789:Enzyme Activation / Q000187:drug effects; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006003:Glycogen / Q000378:metabolism*; D024981:Glycogen Phosphorylase / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D066298:In Vitro Techniques; D007288:Inosine / Q000378:metabolism; D007291:Inosine Monophosphate / Q000378:metabolism; D019344:Lactic Acid / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009119:Muscle Contraction / Q000502:physiology*; D018763:Muscle Fatigue / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism*; D010725:Phosphocreatine / Q000378:metabolism; D010762:Phosphorylase a / Q000378:metabolism; D010763:Phosphorylase b / Q000378:metabolism*; D012966:Sodium Cyanide / Q000494:pharmacology
chemical_list: D010725:Phosphocreatine; D007291:Inosine Monophosphate; D019344:Lactic Acid; D000249:Adenosine Monophosphate; D019298:Glucose-6-Phosphate; D007288:Inosine; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D006003:Glycogen; D024981:Glycogen Phosphorylase; D010762:Phosphorylase a; D010763:Phosphorylase b; D006006:Glycogen Synthase; D003402:Creatine Kinase; D003401:Creatine; D012966:Sodium Cyanide