Authors: Marie E Sandström Fabio Abbate Daniel C Andersson ShiJin Zhang Håkan Westerblad Abram Katz
Publish Date: 2004/04/14
Volume: 448, Issue: 5, Pages: 533-538
Abstract
Glycogen supercompensation increase in muscle glycogen content above basal is an established phenomenon induced by unknown mechanisms It consists of both insulindependent and independent components Here we investigate insulinindependent glycogen supercompensation in isolated intact extensor digitorum longus muscles from mice Muscles were stimulated electrically incubated in vitro with 55 mM glucose for up to 16 h and then analysed for glycogen glucose uptake and enzyme activities Basal glycogen was 84±6 µmol glucosyl units/g dry muscle and was depleted by 80 after 10 min contraction Glycogen increased after contraction reaching a peak value of 113±9 µmol glucosyl units/g dry muscle P005 vs basal by 6 h and returned to basal values by 16 h 84±8 Maximal activities of glycogen synthase phosphorylase and αglucosidase were not significantly altered by contraction or during the 6h recovery period Glycogen synthase fractional activity 017/72 mM glucose6P inversely related to phosphorylation state of the enzyme was increased about twofold early after contraction but then decreased and was slightly lower than baseline during the period of supercompensation 4–6 h Phosphorylase fractional activity ±adenosine monophosphate directly related to phosphorylation state of the enzyme decreased to 60 of basal after contraction and decreased further during the initial 4 h of recovery to 40 of basal P001 vs basal After 4 h recovery glucose uptake was slightly 50 higher in the stimulated than in the nonstimulated muscle P001 Thus insulinindependent glycogen supercompensation involves inactivation of phosphorylase and hence an inhibition of glycogen breakdown
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