Dissociation between changes in muscle Na+-K+-ATPase isoform abundance and activity with consecutive days of exercise and recovery

The early plasticity of vastus lateralis Na+-K+-ATPaseto the abrupt onset of prolonged submaximal cycling was studied in 12 untrained participants ((V) over dot(O2 peak) 44.8 +/- 2.0 ml.kg(-1).min(-1), mean +/- SE) using a 6-day protocol (3 days of exercise plus 3 days of recovery). Tissue samples were extracted prior to (Pre) and following exercise (Post) on day 1 (E1) and day 3 (E3) and on each day of recovery (R1, R2, R3) and analyzed for changes in maximal protein (beta(max)) (vanadate-facilitated [H-3] ouabain binding), alpha- and beta-isoform concentration (quantitative immunoblotting) and maximal Na+-K+-ATPase activity (V-max) (3O- methylfluorescein K+-stimulated phosphatase assay). For beta(max) (pmol/g wet wt), an increase (P < 0.05) of 11.8% was observed at R1 compared with E1-Pre (340 +/- 14 vs 304 +/- 17). For the alpha-isoforms alpha(1), alpha(2), and alpha(3), increases (P < 0.05) of 46, 42, and 31% were observed at R1, respectively. For the beta-isoform, beta(1) and beta(2) increased (P < 0.05) by 19 and 28% at R1, whereas beta(3) increased (P < 0.05) by 18% at R2. With the exception of alpha(2) and alpha(3), the increases in the isoforms persisted at R3. Exercise resulted in an average decrease (P < 0.05) in V-max by 14.3%. No differences were observed in V-max at E1 - Pre and E3 - Pre or between R1, R2, and R3. It is concluded that 3 days of prolonged exercise is a powerful stimulus for the rapid upregulation of the Na+-K+-ATPase subunit isoforms. Contrary to our hypothesis, the increase in subunit expression is not accompanied by increases the maximal catalytic activity.