Exercise Induces Isoform-Specific Increase in 5'AMP-Activated Protein Kinase Activity in Human Skeletal Muscle Nobuharu Fujii,* Tatsuya Hayashi,* Michael F. Hirshman,* Jeremy T. Smith,* Susan A. Habinowski,† Lennart Kaijser,‡ James Mu,§ Olle Ljungqvist, ¶,  Morris J. Birnbaum,§ Lee A. Witters,† Anders Thorell, ¶ and Laurie J. Goodyear* ,1 *Research Division, Joslin Diabetes Center, and Department of Medicine, Brigham and Women’s Hospital and Harvard Medical School, Boston, Massachusetts 02215; †Endocrine-Metabolism Division, Department of Medicine and Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755-3833; ‡Department of Clinical Physiology and Department of Surgery, Huddinge University Hospital, Karolinska Institute, 141 86 Huddinge, Sweden; §Howard Hughes Medical Institute, Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104; and ¶ Center of Gastrointestinal Disease, Ersta Hospital, Karolinska Institute, 116 91 Stockholm, Sweden Received June 12, 2000 The 5AMP-activated protein kinase (AMPK) is stim- ulated by contractile activity in rat skeletal muscle. AMPK has emerged as an important signaling inter- mediary in the regulation of cell metabolism being linked to exercise-induced changes in muscle glucose and fatty acid metabolism. In the present study, we determined the effects of exercise on isoform-specific AMPK activity (1 and 2) in human skeletal muscle. Needle biopsies of vastus lateralis muscle were ob- tained from seven healthy subjects at rest, after 20 and 60 min of cycle ergometer exercise at 70% of VO 2 max, and 30 min following the 60 min exercise bout. In com- parison to the resting state, AMPK 2 activity signifi- cantly increased at 20 and 60 min of exercise, and remained at a higher level with 30 min of recovery. AMPK 1 activity tended to slightly decrease with 20 min of exercise at 70%VO 2 max; however, the change was not statistically significant. AMPK 1 activities were at basal levels at 60 min of exercise and 30 min of recovery. On a separate day, the same subjects exer- cised for 20 min at 50% of VO 2 max. Exercise at this intensity did not change 2 activity, and similar to exercise at 70% of VO 2 max, there was no significant change in 1 activity. In conclusion, exercise at a higher intensity for only 20 min leads to increases in AMPK 2 activity but not 1 activity. These results suggest that the 2-containing AMPK complex, rather than 1, may be involved in the metabolic responses to exercise in human skeletal muscle. © 2000 Academic Press Key Words: AMPK; exercise; glucose transport; skel- etal muscle; contraction, human. The AMP-activated protein kinase (AMPK) is a member of a metabolite-sensing protein kinase family that acts as a fuel gauge monitoring cellular energy levels (1–3). When the cell senses low fuel (decreased ATP), AMPK acts to switch off ATP-consuming path- ways and switch on alternative pathways for ATP re- generation. AMPK is activated by an increase in the AMP:ATP and creatine:phosphocreatine ratios, via a complex mechanism that involves allosteric modifica- tion, phosphorylation by an AMPK kinase, and de- creases in phosphatase activities (1, 2). In rat skeletal muscle, physical exercise (4 – 6), nerve stimulation to produce muscle contractions in situ (7, 8), and contrac- tion in vitro (9 –11) all significantly increase AMPK activity. The AMPK heterotrimer consists of one catalytic subunit () and two noncatalytic subunits ( and ) (1, 2). The noncatalytic subunits are essential for opti- mum enzyme activity and may participate in substrate targeting (12). Two distinct isoforms of the AMPK cat- alytic subunit have been described. The 1 isoform has a wide tissue distribution, whereas 2 is predomi- This work was supported by Grants AR42338, AR45670 (to L.J.G), and DK35712 (to L.A.W) from the National Institutes of Health, Grant 09101 from the Swedish Medical Research Council (to O.L.), and grants from the Foundation for Total Health Promotion, the Meiji Life Foundation of Health and Welfare, the Nakatomi Foun- dation, and the Descente and Ishimoto Memorial Foundation for the Promotion for Sports Science (to H.T.). N.F. is supported by a post- doctoral fellowship for research abroad from the Japan Society for the Promotion of Science. T.H. was a Mary K. Iacocca Fellow at the Joslin Diabetes Center. 1 To whom correspondence should be addressed at Research Divi- sion, Joslin Diabetes Center, One Joslin Place, Boston, MA 02215. Fax: 617-732-2650. E-mail: Laurie.Goodyear@joslin.harvard.edu. Biochemical and Biophysical Research Communications 273, 1150 –1155 (2000) doi:10.1006/bbrc.2000.3073, available online at http://www.idealibrary.com on 1150 0006-291X/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved.