Malleability of human skeletal muscle Na+-K+-ATPase pump with short-term training

To investigate the hypothesis that short-term submaximal training would result in changes in Na+-K+-ATPase content, activity, and isoform distribution in skeletal muscle, seven healthy, untrained men [peak aerobic power (peak oxygen consumption; VO2 peak) = 45.6 ml(.)kg(-1.)min(-1) (SE 5.4)] cycled for 2 h/day at 60-65% VO2 peak for 6 days. Muscle tissue, sampled from the vastus lateralis before training (0 days) and after 3 and 6 days of training and analyzed for Na+-K+-ATPase content, as assessed by the vanadate facilitated [H-3]ouabain-binding technique, was increased (P < 0.05) at 3 days (294 +/- 8.6 pmol/g wet wt) and 6 days (308 15 pmol/g wet wt) of training compared with 0 days (272 +/- 9.7 pmol/g wet wt). Maximal Na+-K+-ATPase activity as evaluated by the 3-O-methylfluorescein phosphatase assay was increased (P < 0.05) by 6 days (53.4 +/- 5.9 nmol(.)h(-1.)mg protein(-1)) but not by 3 days (35.9 +/- 4.5 nmol(.)h(-1.)mg protein(-1)) compared with 0 days (37.8 +/- 3.7 nmol(.)h(-1.)mg protein(-1)) of training. Relative isoform distribution, measured by Western blot techniques, indicated increases (P < 0.05) in alpha(2)-content by 3 days and beta(1)-content by 6 days of training. These results indicate that prolonged aerobic exercise represents a potent stimulus for the rapid adaptation of Na+-K+-ATPase content, isoform, and activity characteristics.