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Fibre type‐specific change in FXYD1 phosphorylation during acute intense exercise in humans
Author(s) -
Thomassen Martin,
Murphy Robyn M.,
Bangsbo Jens
Publication year - 2013
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2012.247312
Subject(s) - phosphorylation , microbiology and biotechnology , chemistry , biophysics , biology
Key pointsMost human experiments examine proteins at the whole muscle level, and knowledge of fibre type specificity is mainly obtained in animal muscles. We used a new methodology and provide novel findings at the single fibre level. Potassium changes across muscle cell membranes may be important for development of fatigue during exercise. The Na + –K + pump with the regulatory phospholemman (FXYD1) subunit and the ATP‐dependent K + channel Kir6.2 play crucial roles in potassium regulation. We show that in humans Na + –K + pump α2 is expressed to a greater extent in type II than in type I fibres and Kir6.2 is expressed primarily in type I fibres. During exercise, phosphorylation of FXYD1 serine 68 is increased only in type II fibres, indicating differences in Na + –K + pump activity. These results show that human Kir6.2 and Na + –K + pump subunit expression and FXYD1 phosphorylation are fibre type specific, which may influence exercise‐induced potassium regulation and fatigue development.Abstract The aim of the present study was to examine fibre type‐specific Na + –K + pump subunit expression and exercise‐induced alterations in phospholemman (FXYD1) phosphorylation in humans. Segments of human skeletal muscle fibres were dissected and fibre typed, and protein expression was determined by Western blotting. The protein expression of the Na + –K + pump α2 isoform was lower in type I than in type II fibres (0.63 ± 0.04 a.u. vs . 1.00 ± 0.07 a.u., P < 0.001), while protein expression of the Na + –K + pump α1 and β1 isoforms was not different. Protein expression of the ATP‐dependent potassium channel Kir6.2 was higher in type I compared with type II fibres. In both type I ( P < 0.01) and type II fibres ( P < 0.001) the AB_FXYD1 signal was lower after exercise compared with rest, indicating an increase in unspecific FXYD1 phosphorylation. The FXYD1 serine 68 phosphorylation was higher ( P < 0.001) after exercise compared with rest in type II fibres (1.90 ± 0.25 vs . 1.00 ± 0.08) and not changed in type I fibres. Total FXYD1 was not expressed in a fibre type‐specific manner. Expression of phosphofructokinase was lower ( P < 0.001) in type I than in type II fibres, whereas citrate synthase and 3‐hydroxyacyl‐CoA dehydrogenase were more abundant ( P < 0.001) in type I fibres. In conclusion, FXYD1 phosphorylation at serine 68 increased after an acute bout of intense exercise in human type II fibres, while AB_FXYD1 signal intensity was lower in both type I and type II fibres, indicating fibre type‐specific differences in FXYD1 phosphorylation on serine 63, serine 68 and threonine 69. This, together with the observation of a higher abundance of the Na + –K + pump α2 isoform protein in type II fibres, is likely to have importance for the exercise‐induced human Na + –K + pump activity in the different fibre types.