Human skeletal muscle Na, K-ATPase concentration quantified by 3H-ouabain binding to intact biopsies before and after moderate physical conditioning.

The putative effect of moderate training on human skeletal muscle Na,K-ATPase concentration and thus on the capacity for active uptake of potassium was evaluated. In 15 conscripts the Na,K-pump concentration was determined in vastus lateralis muscle by measurement of 3H-ouabain binding to intact muscle biopsies before and after 10 weeks of physical training. All subjects had improved physical fitness, body weight was reduced by 3% (P less than 0.001), Cooper's test showed an improvement by 7% (P less than 0.05) and leg circumference 10 cm above the knee joint had increased by 3% (P less than 0.001). Mean Na,K-pump concentration +/- S.E.M. in vastus lateralis muscles was 308 +/- 13 (N = 15) and 300 +/- 7 (N = 15) pmol x g wet wt.-1 (P less than 0.60) before and after training, respectively. Thus, in human subjects moderate improvement of physical performance may occur without any change in skeletal muscle Na,K-pump concentration. It may be, however, that change in the acute regulation of skeletal muscle Na,K-ATPase--i.e. augmented activity of existing Na,K-pumps--may reduce exercise-induced rise in plasma potassium concentration after moderate physical conditioning. Since the circumference of the legs had increased, the total amount of Na,K-ATPase in the legs had probably increased. Hence, moderate training may induce muscle hypertrophy with a balanced synthesis of muscle mass and Na,K-pumps.