HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: 293/3/R1325    most recent 00609.2006v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Putman, C. T. Articles by Pette, D. Search for Related Content PubMed PubMed Citation Articles by Putman, C. T. Articles by Pette, D.

ENVIRONMENTAL, EXERCISE AND RESPIRATORY PHYSIOLOGY

-Catalytic subunits of 5'AMP-activated protein kinase display fiber-specific expression and are upregulated by chronic low-frequency stimulation in rat muscle

¹Exercise Biochemistry Laboratory, Faculty of Physical Education and Recreation; ²Centre for Neuroscience and ³Departments of Pharmacology and Paediatrics, Faculty of Medicine and Dentistry; University of Alberta, Edmonton, Alberta, Canada; and ⁴Department of Biology, Faculty of Science, University of Konstanz, Konstanz, Germany

Submitted 25 August 2006 ; accepted in final form 6 June 2007

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 -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 1- and 2-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 2 isoform in the MG, much of which was localized within nuclei. 1 and 2 contents, assessed by immunoblot, were lowest in the white gastrocnemius [WG; 80% myosin heavy chain (MHC) IIb; 20% MHCIId/x]. Compared with the WG, 1 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, 2 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 1 and 2 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.

myosin heavy chain; fast-twitch muscle; slow-twitch muscle