Alpha-catalytic subunits of 5'AMP-activated protein kinase display fiber-specific expression and are upregulated by chronic low-frequency stimulation in rat muscle.
5'-AMP-activated protein kinase (AMPK) signaling initiates adaptive changes in skeletal muscle fibers that restore homeostatic energy balance. The purpose of this investigation was to examine, in rats, the fiber-type protein expression patterns of the alpha-catalytic subunit isoforms in various skeletal muscles, and changes in their respective contents within the tibialis anterior (TA) after chronic low-frequency electrical stimulation (CLFS; 10 Hz, 10 h daily), applied for 4 +/- 1.2 or 25 +/- 4.8 days. Immunocytochemical staining of soleus (SOL) and medial gastrocnemius (MG) showed that 86 +/- 4.1 to 97 +/- 1.4% of type IIA fibers stained for both the alpha1- and alpha2-isoforms progressively decreased to 63 +/- 12.2% of type IID/X and 9 +/- 2.4% of IIB fibers. 39 +/- 11.4% of IID/X and 83 +/- 7.9% of IIB fibers expressed only the alpha2 isoform in the MG, much of which was localized within nuclei. alpha1 and alpha2 contents, assessed by immunoblot, were lowest in the white gastrocnemius [WG; 80% myosin heavy chain (MHC) IIb; 20% MHCIId/x]. Compared with the WG, alpha1 content was 1.6 +/- 0.08 (P < 0.001) and 1.8 +/- 0.04 (P < 0.0001)-fold greater in the red gastrocnemius (RG: 13%, MHCIIa) and SOL (21%, MHCIIa), respectively, and increased in proportion to MHCIIa content. Similarly, alpha2 content was 1.4 +/- 0.10 (P < 0.02) and 1.5 +/- 0.07 (P < 0.001)-fold greater in RG and SOL compared with WG. CLFS induced 1.43 +/- 0.13 (P < 0.007) and 1.33 +/- 0.08 (P < 0.009)-fold increases in the alpha1 and alpha2 contents of the TA and coincided with the transition of faster type IIB and IID/X fibers toward IIA fibers. These findings indicate that fiber types differ with regard to their capacity for AMPK signaling and that this potential is increased by CLFS.
Putman
Charles T
CT
Faculty of Physical Education and Recreation and The Centre for Neuroscience, Faculty of Medicine & Dentistry, University of Alberta, E-417 Van Vliet Centre, Edmonton, Alberta, Canada. tputman@ualberta.ca
Martins
Karen J B
KJ
Gallo
Maria E
ME
Lopaschuk
Gary D
GD
Pearcey
Jean A
JA
MacLean
Ian M
IM
Saranchuk
Ryan J
RJ
Pette
Dirk
D
D055372:AMP-Activated Protein Kinases; D000818:Animals; D015153:Blotting, Western; D002384:Catalysis; D002467:Cell Nucleus / Q000378:metabolism; D004558:Electric Stimulation; D004591:Electrophoresis, Polyacrylamide Gel; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000096:biosynthesis / Q000235:genetics; D008297:Male; D009097:Multienzyme Complexes / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D018656:Muscle Fibers, Fast-Twitch / Q000201:enzymology / Q000502:physiology; D018485:Muscle Fibers, Skeletal / Q000201:enzymology* / Q000502:physiology; D018657:Muscle Fibers, Slow-Twitch / Q000201:enzymology / Q000502:physiology; D018482:Muscle, Skeletal / Q000201:enzymology* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015854:Up-Regulation / Q000502:physiology
D007527:Isoenzymes; D009097:Multienzyme Complexes; D017346:Protein Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D018995:Myosin Heavy Chains