Protein kinase Cα activity is important for contraction-induced FXYD1 phosphorylation in skeletal muscle

d Thomassen M, Rose AJ, Jensen TE, Maarbjerg SJ, Bune L, Leitges M, Richter EA, Bangsbo J, Nordsborg NB. Protein kinase C alpha activity is important for contraction-induced FXYD1 phosphorylation in skeletal muscle. Am J Physiol Regul Integr Comp Physiol 301: R1808-R1814, 2011. First published September 28, 2011; doi:10.1152/ajpregu.00066.2011.-Exercise-induced phosphorylation of FXYD1 is a potential important regulator of Na+-K+-pump activity. It was investigated whether skeletal muscle contractions induce phosphorylation of FXYD1 and whether protein kinase C alpha (PKC alpha) activity is a prerequisite for this possible mechanism. In part 1, human muscle biopsies were obtained at rest, after 30 s of high-intensity exercise (166 +/- 31% of (V) over dotO(2max)) and after a subsequent 20 min of moderate-intensity exercise (79 +/- 8% of (V) over dotO(2max)). In general, FXYD1 phosphorylation was increased compared with rest both after 30 s (P < 0.05) and 20 min (P < 0.001), and more so after 20 min compared with 30 s (P < 0.05). Specifically, FXYD1 ser63, ser68, and combined ser68 and thr69 phosphorylation were 26-45% higher (P < 0.05) after 20 min of exercise than at rest. In part 2, FXYD1 phosphorylation was investigated in electrically stimulated soleus and EDL muscles from PKC alpha knockout (KO) and wild-type (WT) mice. Contractile activity caused FXYD1 ser68 phosphorylation to be increased (P < 0.001) in WT soleus muscles but to be reduced (P < 0.001) in WT extensor digitorum longus. In contrast, contractile activity did not affect FXYD1 ser68 phosphorylation in the KO mice. In conclusion, exercise induces FXYD1 phosphorylation at multiple sites in human skeletal muscle. In mouse muscles, contraction-induced changes in FXYD1 ser68 phosphorylation are fiber-type specific and dependent on PKC alpha activity.