Expression of AMP-activated Protein Kinase Subunit Isoforms in Masseter and Tibialis Anterior Muscles of Mice before and after Weaning

AMP-activated protein kinase (AMPK) acts as a fuel gauge during musclar exercise and stress-induced energy crisis. The function of the masseter muscle changes during postnatal development, along with an alteration in the type of muscle fibers. We investigated expressions of AMPK subunit isoforms in the masseter muscle by quantitative real-time RT-PCR and Western blotting, and compared them with those in the tibialis anterior muscle in 2-, 4-, and 9-week-old mice. The most abundantly expressed isoform of the catalytic subunit was α2, and those of the regulatory subunits were β1, β2, and γ1 in both types of muscle; mRNA expression of all the main isoforms in the masseter muscle was higher than that in the tibialis anterior muscle. Expression of α protein increased with development in both muscle types. Messenger RNA expression of regulatory subunit isoforms β1 and γ1 in the masseter muscle rose, together with an increase in the amounts of their corresponding proteins. On the other hand, mRNA expression of these isoforms in the tibialis anterior muscle decreased with development, while their corresponding proteins increased at a similar rate to that of the development of the α subunit. This altered expression of AMPK subunit isoforms in each muscle during postnatal development may be related to the changing function of each type of muscle.