title: Glycogen metabolism in rat heart muscle cultures after hypoxia.
abstract: Elevated glycogen levels in heart have been shown to have cardioprotective effects against ischemic injury. We have therefore established a model for elevating glycogen content in primary rat cardiac cells grown in culture and examined potential mechanisms for the elevation (glycogen supercompensation). Glycogen was depleted by exposing the cells to hypoxia for 2 h in the absence of glucose in the medium. This was followed by incubating the cells with 28 mM glucose in normoxia for up to 120 h. Hypoxia decreased glycogen content to about 15% of control, oxygenated cells. This was followed by a continuous increase in glycogen in the hypoxia treated cells during the 120 h recovery period in normoxia. By 48 h after termination of hypoxia, the glycogen content had returned to baseline levels and by 120 h glycogen was about 150% of control. The increase in glycogen at 120 h was associated with comparable relative increases in glucose uptake (approximately 180% of control) and the protein level of the glut-1 transporter (approximately 170% of control), whereas the protein level of the glut-4 transporter was decreased to < 10% of control. By 120 h, the hypoxia-treated cells also exhibited marked increases in the total (approximately 170% of control) and fractional activity of glycogen synthase (control, approximately 15%; hypoxia-treated, approximately 30%). Concomitantly, the hypoxia-treated cells also exhibited marked decreases in the total (approximately 50% of control) and fractional activity of glycogen phosphorylase (control, approximately 50%; hypoxia-treated, approximately 25%). Thus, we have established a model of glycogen supercompensation in cultures of cardiac cells that is explained by concerted increases in glucose uptake and glycogen synthase activity and decreases in phosphorylase activity. This model should prove useful in studying the cardioprotective effects of glycogen.
authors.affiliation: Gonda (Goldshmied) Medical Diagnostic Research Center, Faculty of Life Sciences, Bar-Ilan University, Ramat Gan, Israel.
authors.forename: Ayelet
authors.initials: A
authors.lastname: Vigoda
authors.forename: Liaman K
authors.initials: LK
authors.lastname: Mamedova
authors.forename: Vladimir
authors.initials: V
authors.lastname: Shneyvays
authors.forename: Abram
authors.initials: A
authors.lastname: Katz
authors.forename: Asher
authors.initials: A
authors.lastname: Shainberg
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D003402:Creatine Kinase / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D006003:Glycogen / Q000378:metabolism*; D024981:Glycogen Phosphorylase / Q000378:metabolism; D006006:Glycogen Synthase / Q000378:metabolism; D000860:Hypoxia; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D009206:Myocardium / Q000378:metabolism*; D051381:Rats; D013997:Time Factors
chemical_list: D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495679:Slc2a1 protein, rat; C495694:Slc2a4 protein, rat; D000255:Adenosine Triphosphate; D006003:Glycogen; D024981:Glycogen Phosphorylase; D006006:Glycogen Synthase; D003402:Creatine Kinase; D005947:Glucose