title: Low-intensity contraction activates the alpha1-isoform of 5'-AMP-activated protein kinase in rat skeletal muscle.
abstract: Skeletal muscle expresses two catalytic subunits, alpha1 and alpha2, of the 5'-AMP-activated protein kinase (AMPK), which has been implicated in contraction-stimulated glucose transport and fatty acid oxidation. Muscle contraction activates the alpha2-containing AMPK complex (AMPKalpha2), but this activation may occur with or without activation of the alpha1-containing AMPK complex (AMPKalpha1), suggesting that AMPKalpha2 is the major isoform responsible for contraction-induced metabolic events in skeletal muscle. We report for the first time that AMPKalpha1, but not AMPKalpha2, can be activated in contracting skeletal muscle. Rat epitrochlearis muscles were isolated and incubated in Krebs-Ringer bicarbonate buffer containing pyruvate. In muscles stimulated to contract at a frequency of 1 and 2 Hz during the last 2 min of incubation, AMPKalpha1 activity increased twofold and AMPKalpha2 activity remained unchanged. Muscle stimulation did not change the muscle AMP concentration or the AMP-to-ATP ratio. AMPK activation was associated with increased phosphorylation of Thr(172) of the alpha-subunit, the primary activation site. Muscle stimulation increased the phosphorylation of acetyl-CoA carboxylase (ACC), a downstream target of AMPK, and the rate of 3-O-methyl-d-glucose transport. In contrast, increasing the frequency (>or=5 Hz) or duration (>or=5 min) of contraction activated AMPKalpha1 and AMPKalpha2 and increased AMP concentration and the AMP/ATP ratio. These results suggest that 1) AMPKalpha1 is the predominant isoform activated by AMP-independent phosphorylation in low-intensity contracting muscle, 2) AMPKalpha2 is activated by an AMP-dependent mechanism in high-intensity contracting muscle, and 3) activation of each isoform enhances glucose transport and ACC phosphorylation in skeletal muscle.
authors.affiliation: Laboratory of Nutrition Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8501, Japan.
authors.forename: Taro
authors.initials: T
authors.lastname: Toyoda
authors.forename: Satsuki
authors.initials: S
authors.lastname: Tanaka
authors.forename: Ken
authors.initials: K
authors.lastname: Ebihara
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Masuzaki
authors.forename: Kiminori
authors.initials: K
authors.lastname: Hosoda
authors.forename: Kenji
authors.initials: K
authors.lastname: Sato
authors.forename: Tohru
authors.initials: T
authors.lastname: Fushiki
authors.forename: Kazuwa
authors.initials: K
authors.lastname: Nakao
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Hayashi
mesh_terms: D019325:3-O-Methylglucose / Q000378:metabolism; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000032:analysis; D000255:Adenosine Triphosphate / Q000032:analysis; D000818:Animals; D015153:Blotting, Western; D004558:Electric Stimulation; D004789:Enzyme Activation; D066298:In Vitro Techniques; D008297:Male; D009097:Multienzyme Complexes / Q000378:metabolism*; D009119:Muscle Contraction / Q000502:physiology*; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000502:physiology*; D010766:Phosphorylation; D020033:Protein Isoforms; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley; D013912:Threonine / Q000378:metabolism
chemical_list: D009097:Multienzyme Complexes; D020033:Protein Isoforms; D019325:3-O-Methylglucose; D013912:Threonine; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D000103:Acetyl-CoA Carboxylase