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

@entity908 @entity1391 @entity880 @entity860 @entity116 @entity17376 @entity3776
Skeletal muscle that is deficient in @entity908 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 @entity116 for 20 s in the presence of @entity17376 to block mitochondrial respiration. Accumulation of @entity880 after stimulation was similar in wild-type (WT) and CK-/- muscles, whereas accumulation of @entity3776 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 @entity860 ) 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 @entity1391 , 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 @entity860 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 @entity860 concentrations (> 100 microM). These data indicate that allosteric activation of phosphorylase b accounts for the accelerated glycogenolysis in CK-/- muscle during contraction.
