Na,K-ATPase Activity in Mouse Muscle is Regulated by AMPK and PGC-1α

Na,K-ATPase activity, which is crucial for skeletal muscle function, undergoes acute and long-term regulation in response to muscle activity. The aim of the present study was to test the hypothesis that AMP kinase (AMPK) and the transcriptional coactivator PGC-1 alpha are underlying factors in long-term regulation of Na,K-ATPase isoform (alpha,beta and PLM) abundance and Na(+) affinity. Repeated treatment of mice with the AMPK activator AICAR decreased total PLM protein content but increased PLM phosphorylation, whereas the number of alpha- and beta-subunits remained unchanged. The K (m) for Na(+) stimulation of Na,K-ATPase was reduced (higher affinity) after AICAR treatment. PLM abundance was increased in AMPK kinase-dead mice compared with control mice, but PLM phosphorylation and Na,K-ATPase Na(+) affinity remained unchanged. Na,K-ATPase activity and subunit distribution were also measured in mice with different degrees of PGC-1 alpha expression. Protein abundances of alpha 1 and alpha 2 were reduced in PGC-1 alpha +/- and -/- mice, and the beta(1)/beta(2) ratio was increased with PGC-1 alpha overexpression (TG mice). PLM protein abundance was decreased in TG mice, but phosphorylation status was unchanged. Na,K-ATPase V (max) was decreased in PCG-1 alpha TG and KO mice. Experimentally in vitro induced phosphorylation of PLM increased Na,K-ATPase Na(+) affinity, confirming that PLM phosphorylation is important for Na,K-ATPase function. In conclusion, both AMPK and PGC-1 alpha regulate PLM abundance, AMPK regulates PLM phosphorylation and PGC-1 alpha expression influences Na,K-ATPase alpha(1) and alpha(2) content and beta(1)/beta(2) isoform ratio. Phosphorylation of the Na,K-ATPase subunit PLM is an important regulatory mechanism.