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The Na + ,K + -ATPase (NKA) is important in regulating trans-membrane ion gradients, cellular excitability and muscle function. We investigated the effects of resistance training in healthy young adults on the adaptability of NKA content and of the specific α and β isoforms in human skeletal muscle. MethodsTwenty-one healthy young males (22.9 ±4.6 y; 1.80 ±0.70 m, 85.1 ±17.8 kg, mean±SD) underwent 7 weeks of resistance training, training three time per week (RT, n=16) or control (CON, n=5). The training program was effective with a 39% gain in leg press muscle strength (p=0.001). A resting vastus lateralis muscle biopsy was taken before and following RT or CON and assayed for NKA content ([ 3 H]ouabain binding site content) and NKA isoform (α1, α2, β1, β2) abundances. ResultsAfter RT, each of NKA content (12%, 311 ±76 vs 349 ±76 pmol.g wet weight -1 , p=0.01), NKA α1 (32%, p=0.01) and α2 (10%, p<0.01) isoforms were increased, whereas β1 (p=0.18) and β2 (p=0.22) isoforms were unchanged. NKA content and isoform abundances were unchanged during CON. ConclusionsResistance training increased muscle NKA content through upregulation of both α1 and α2 isoforms, which were independent of β isoform changes. In animal models, modulations in α1 and α2 isoform abundances in skeletal muscle may affect fatigue resistance during exercise, muscle hypertrophy and strength. Whether similar in-vivo functional benefits of these NKA isoform adaptations occurs in human muscle with resistance training remains to be determined.

We investigated the effects of testosterone suppression, hindlimb immobilization, and recovery on skeletal muscle Na+,K+-ATPase (NKA), measured via [3H]ouabain binding site content (OB) and NKA isoform abundances (α1–3, β1–2). Male rats underwent castration or sham surgery plus 7 days of rest, 10 days of unilateral immobilization (cast), and 14 days of recovery, with soleus muscles obtained at each time from cast and noncast legs. Testosterone reduction did not modify OB or NKA isoforms in nonimmobilized control muscles. With sham surgery, OB was lower after immobilization in the cast leg than in both the noncast leg (−26%, P = 0.023) and the nonimmobilized control (−34%, P  = 0.001), but OB subsequently recovered. With castration, OB was lower after immobilization in the cast leg than in the nonimmobilized control (−34%, P  = 0.001), and remained depressed at recovery (−34%, P = 0.001). NKA isoforms did not differ after immobilization or recovery in the sham group. After castration, α2 in the cast leg was ~60% lower than in the noncast leg ( P = 0.004) and nonimmobilized control ( P = 0.004) and after recovery remained lower than the nonimmobilized control (−42%, P = 0.039). After immobilization, β1 was lower in the cast than the noncast leg (−26%, P = 0.018), with β2 lower in the cast leg than in the noncast leg (−71%, P = 0.004) and nonimmobilized control (−65%, P = 0.012). No differences existed for α1 or α3. Thus, both OB and α2 decreased after immobilization and recovery in the castration group, with α2, β1, and β2 isoform abundances decreased with immobilization compared with the sham group. Therefore, testosterone suppression in rats impaired restoration of immobilization-induced lowered number of functional NKA and α2 isoforms in soleus muscle. NEW & NOTEWORTHY: The Na+,K+-ATPase (NKA) is vital in muscle excitability and function. In rats, immobilization depressed soleus muscle NKA, with declines in [3H]ouabain binding, which was restored after 14 days recovery. After testosterone suppression by castration, immobilization depressed [3H]ouabain binding, depressed α2, β1, and β2 isoforms, and abolished subsequent recovery in [3H]ouabain binding and α2 isoforms. This may have implications for functional recovery for inactive men with lowered testosterone levels, such as in prostate cancer or aging.