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This Article Full Text Full Text (PDF) All Versions of this Article: 553/2/523    most recent jphysiol.2003.051078v1 Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Katz, A. Articles by Westerblad, H. Search for Related Content PubMed PubMed Citation Articles by Katz, A. Articles by Westerblad, H.

Contraction-mediated glycogenolysis in mouse skeletal muscle lacking creatine kinase: the role of phosphorylase b activation

Abram Katz, Daniel C. Andersson, Josephine Yu, Barbara Norman*, Marie E. Sandström, Bé Wieringa† and Häkan Westerblad

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 µmol (g dry muscle)^-1; stimulated = 33.9 ± 2.3 µmol (g dry muscle)^-1), but substantially in WT muscles (basal = 11.4 ± 0.7 µmol (g dry muscle)^-1; stimulated = 54.2 ± 4.5 µmol (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 µM) 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 µM). These data indicate that allosteric activation of phosphorylase b accounts for the accelerated glycogenolysis in CK^-/- muscle during contraction.

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