title: Glycogenin protein and mRNA expression in response to changing glycogen concentration in exercise and recovery.
abstract: Glycogenin (GN-1) is essential for the formation of a glycogen granule; however, rarely has it been studied when glycogen concentration changes in exercise and recovery. It is unclear whether GN-1 is degraded or is liberated and exists as apoprotein (apo)-GN-1 (unglycosylated). To examine this, we measured GN-1 protein and mRNA level at rest, at exhaustion (EXH), and during 5 h of recovery in which the rate of glycogen restoration was influenced by carbohydrate (CHO) provision. Ten males cycled (65% VO2 max) to volitional EXH (117.8 +/- 4.2 min) on two separate occasions. Subjects were administered carbohydrate (CHO; 1 g.kg(-1).h(-1) Gatorlode) or water [placebo (PL)] during 5 h of recovery. Muscle biopsies were taken at rest, at EXH, and following 30, 60, 120, and 300 min of recovery. At EXH, total glycogen concentration was reduced (P < 0.05). However, GN-1 protein and mRNA content did not change. By 5 h of recovery, glycogen was resynthesized to approximately 60% of rest in the CHO trial and remained unchanged in the PL trial. GN-1 protein and mRNA level did not increase during recovery in either trial. We observed modest amounts of apo-GN-1 at EXH, suggesting complete degradation of some granules. These data suggest that GN-1 is conserved, possibly as very small, or nascent, granules when glycogen concentration is low. This would provide the ability to rapidly restore glycogen during early recovery.
authors.affiliation: Department of Human Health and Nutritional Sciences, University of Guelph, Guelph, ON, Canada N1G 2W1. rjwilson@uoguelph.ca
authors.forename: Rhonda J
authors.initials: RJ
authors.lastname: Wilson
authors.forename: Jenny E
authors.initials: JE
authors.lastname: Gusba
authors.forename: Deborah L
authors.initials: DL
authors.lastname: Robinson
authors.forename: Terry E
authors.initials: TE
authors.lastname: Graham
mesh_terms: D000328:Adult; D001642:Bicycling; D001786:Blood Glucose / Q000378:metabolism; D002241:Carbohydrates / Q000494:pharmacology; D015444:Exercise / Q000502:physiology*; D005964:Glucosyltransferases / Q000235:genetics* / Q000378:metabolism*; D006003:Glycogen / Q000235:genetics / Q000378:metabolism*; D006023:Glycoproteins / Q000235:genetics* / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D007328:Insulin / Q000097:blood; D008297:Male; D018482:Muscle, Skeletal / Q000378:metabolism*; D009994:Osmolar Concentration; D010807:Physical Endurance / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism*; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D002241:Carbohydrates; D006023:Glycoproteins; D007328:Insulin; D012333:RNA, Messenger; C051887:glycogenin; D006003:Glycogen; D005964:Glucosyltransferases