Low-intensity contraction activates the alpha1-isoform of 5'-AMP-activated protein kinase in rat skeletal muscle.
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.
Toyoda
Taro
T
Laboratory of Nutrition Chemistry, Division of Food Science and Biotechnology, Graduate School of Agriculture, Kyoto University, Kyoto, 606-8501, Japan.
Tanaka
Satsuki
S
Ebihara
Ken
K
Masuzaki
Hiroaki
H
Hosoda
Kiminori
K
Sato
Kenji
K
Fushiki
Tohru
T
Nakao
Kazuwa
K
Hayashi
Tatsuya
T
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
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