Intense exercise up-regulates Na(+),K(+)-ATPase isoform mRNA, but not protein expression in human skeletal muscle

Characterization of expression of, and consequently also the acute exercise effects on, Na(+),K(+)-ATPase isoforms in human skeletal muscle remains incomplete and was therefore investigated. Fifteen healthy subjects (eight males, seven females) performed fatiguing, knee extensor exercise at ∼40% of their maximal work output per contraction. A vastus lateralis muscle biopsy was taken at rest, fatigue and 3 and 24 h postexercise, and analysed for Na(+),K(+)-ATPase α(1), α(2), α(3), β(1), β(2) and β(3) mRNA and crude homogenate protein expression, using Real-Time RT-PCR and immunoblotting, respectively. Each individual expressed gene transcripts and protein bands for each Na(+),K(+)-ATPase isoform. Each isoform was also expressed in a primary human skeletal muscle cell culture. Intense exercise (352 ± 69 s; mean ±s.e.m.) immediately increased α(3) and β(2) mRNA by 2.4- and 1.7-fold, respectively (P < 0.05), whilst α(1) and α(2) mRNA were increased by 2.5- and 3.5-fold at 24 h and 3 h postexercise, respectively (P < 0.05). No significant change occurred for β(1) and β(3) mRNA, reflecting variable time-dependent responses. When the average postexercise value was contrasted to rest, mRNA increased for α(1), α(2), α(3), β(1), β(2) and β(3) isoforms, by 1.4-, 2.2-, 1.4-, 1.1-, 1.0- and 1.0-fold, respectively (P < 0.05). However, exercise did not alter the protein abundance of the α(1)–α(3) and β(1)–β(3) isoforms. Thus, human skeletal muscle expresses each of the Na(+),K(+)-ATPase α(1), α(2), α(3), β(1), β(2) and β(3) isoforms, evidenced at both transcription and protein levels. Whilst brief exercise increased Na(+),K(+)-ATPase isoform mRNA expression, there was no effect on isoform protein expression, suggesting that the exercise challenge was insufficient for muscle Na(+),K(+)-ATPase up-regulation