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Regulation of glycogen synthesis in rat skeletal muscle after glycogen-depleting contractile activity: effects of adrenaline on glycogen synthesis and activation of glycogen synthase and glycogen phosphorylase.

ABSTRACT: We investigated the effects of insulin and adrenaline on the rate of glycogen synthesis in skeletal muscles after electrical stimulation in vitro. The contractile activity decreased the glycogen concentration by 62%. After contractile activity, the glycogen stores were fully replenished at a constant and high rate for 3 h when 10 m-i.u./ml insulin was present. In the absence of insulin, only 65% of the initial glycogen stores was replenished. Adrenaline decreased insulin-stimulated glycogen synthesis. Surprisingly, adrenaline did not inhibit glycogen synthesis stimulated by glycogen-depleting contractile activity. In agreement with this, the fractional activity of glycogen synthase was high when adrenaline was present after exercise, whereas adrenaline decreased the fractional activity of glycogen synthase to a low level during stimulation with insulin. Furthermore, adrenaline activated glycogen phosphorylase almost completely during stimulation with insulin, whereas a much lower activation of glycogen phosphorylase was observed after contractile activity. Thus adrenaline does not inhibit contraction-stimulated glycogen synthesis.

SUBMITTER: Franch J

PROVIDER: S-EPMC1220635 | biostudies-other | 1999 Nov

REPOSITORIES: biostudies-other

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Project description:The mitochondrial and endoplasmic reticulum unfolded protein responses (UPR(mt) and UPR(ER)) are important for cellular homeostasis during stimulus-induced increases in protein synthesis. Exercise triggers the synthesis of mitochondrial proteins, regulated in part by peroxisome proliferator activator receptor-? coactivator 1? (PGC-1?). To investigate the role of the UPR in exercise-induced adaptations, we subjected rats to 3 h of chronic contractile activity (CCA) for 1, 2, 3, 5, or 7 days followed by 3 h of recovery. Mitochondrial biogenesis signaling, through PGC-1? mRNA, increased 14-fold after 1 day of CCA. This resulted in 10-32% increases in cytochrome c oxidase activity, indicative of mitochondrial content, between days 3 and 7, as well as increases in the autophagic degradation of p62 and microtubule-associated proteins 1A/1B light chain 3A (LC3)-II protein. Before these adaptations, the UPR(ER) transcripts activating transcription factor-4, spliced X-box-binding protein 1, and binding immunoglobulin protein were elevated (1.3- to 3.8-fold) at days 1-3, while CCAAT/enhancer-binding protein homologous protein (CHOP) and chaperones binding immunoglobulin protein and heat shock protein (HSP) 70 were elevated at mRNA and protein levels (1.5- to 3.9-fold) at days 1-7 of CCA. The mitochondrial chaperones 10-kDa chaperonin, HSP60, and 75-kDa mitochondrial HSP, the protease ATP-dependent Clp protease proteolytic subunit, and the regulatory protein sirtuin-3 of the UPR(mt) were concurrently induced 10-80% between days 1 and 7 To test the role of the UPR in CCA-induced remodeling, we treated animals with the endoplasmic reticulum stress suppressor tauroursodeoxycholic acid and subjected them to 2 or 7 days of CCA. Tauroursodeoxycholic acid attenuated CHOP and HSP70 protein induction; however, this failed to impact mitochondrial remodeling. Our data indicate that signaling to the UPR is rapidly activated following acute contractile activity, that this is attenuated with repeated bouts, and that the UPR is involved in chronic adaptations to CCA; however, this appears to be independent of CHOP signaling.

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Regulation of glycogen synthesis in rat skeletal muscle after glycogen-depleting contractile activity: effects of adrenaline on glycogen synthesis and activation of glycogen synthase and glycogen phosphorylase.

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