title: Contraction- and hypoxia-stimulated glucose transport is mediated by a Ca2+-dependent mechanism in slow-twitch rat soleus muscle.
abstract: Increases in contraction-stimulated glucose transport in fast-twitch rat epitrochlearis muscle are mediated by AMPK- and Ca2+/calmodulin-dependent protein kinase (CAMK)-dependent signaling pathways. However, recent studies provide evidence suggesting that contraction-stimulated glucose transport in slow-twitch skeletal muscle is mediated through an AMPK-independent pathway. The purpose of the present study was to test the hypothesis that contraction-stimulated glucose transport in rat slow-twitch soleus muscle is mediated by an AMPK-independent/Ca2+-dependent pathway. Caffeine, a sarcoplasmic reticulum (SR) Ca2+-releasing agent, at a concentration that does not cause muscle contractions or decreases in high-energy phosphates, led to an approximately 2-fold increase in 2-deoxyglucose (2-DG) uptake in isolated split soleus muscles. This increase in glucose transport was prevented by the SR calcium channel blocker dantrolene and the CAMK inhibitor KN93. Conversely, 5-aminoimidazole-4-carboxamide-1-beta-D-ribofuranoside (AICAR), an AMPK activator, had no effect on 2-DG uptake in isolated split soleus muscles yet resulted in an approximately 2-fold increase in the phosphorylation of AMPK and its downstream substrate acetyl-CoA carboxylase. The hypoxia-induced increase in 2-DG uptake was prevented by dantrolene and KN93, whereas hypoxia-stimulated phosphorylation of AMPK was unaltered by these agents. Tetanic muscle contractions resulted in an approximately 3.5-fold increase in 2-DG uptake that was prevented by KN93, which did not prevent AMPK phosphorylation. Taken in concert, our results provide evidence that hypoxia- and contraction-stimulated glucose transport is mediated entirely through a Ca2+-dependent mechanism in rat slow-twitch muscle.
authors.affiliation: Division of Geriatrics and Nutritional Sciences, Department of Medicine, Washington Univ. School of Medicine, Applied Physiology, Campus Box 8113, 4566 Scott Ave., St. Louis, MO 63110, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Wright
authors.forename: Paige C
authors.initials: PC
authors.lastname: Geiger
authors.forename: John O
authors.initials: JO
authors.lastname: Holloszy
authors.forename: Dong-Ho
authors.initials: DH
authors.lastname: Han
mesh_terms: D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism / Q000502:physiology*; D002121:Calcium Channel Blockers / Q000494:pharmacology; D015687:Cell Hypoxia / Q000502:physiology; D003620:Dantrolene / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism / Q000502:physiology*; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism / Q000502:physiology; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D012265:Ribonucleotides / Q000494:pharmacology
chemical_list: D002121:Calcium Channel Blockers; D047428:Protein Kinase Inhibitors; D012265:Ribonucleotides; D000620:Aminoimidazole Carboxamide; D002110:Caffeine; C031143:AICA ribonucleotide; D003620:Dantrolene; D005947:Glucose; D002118:Calcium