Exercise-induced translocation of Na+-K+ pump subunits to the plasma membrane in human skeletal muscle

Six human subjects performed one-legged knee extensor exercise (90 +/- 4 W) until fatigue (exercise time 4.6 +/- 0.8 min). Needle biopsies were obtain ed from vastus lateralis muscle before and immediately after exercise. Prod uction of giant sarcolemmal vesicles from the biopsy material was used as a membrane purification procedure, and Na+-K+ pump alpha- and beta-subunits were quantified by Western blotting. Exercise significantly increased (P < 0.05) the vesicular membrane content of the alpha(2)-, total alpha-, and be ta(1)-subunits by 70 +/- 29, 35 +/- 10, and 26 +/- 5%, respectively. The me mbrane content of oil was not changed by exercise, and the densities of sub units in muscle homogenates were unchanged. The ratio of vesicular to crude muscle homogenate content of the alpha(2)-, total alpha-, and beta(1)-subu nits was elevated during exercise by 67 +/- 33 (P < 0.05), 23 +/- 6 (P < 0. 05), and 40 +/- 14% (P = 0.06), respectively. It is concluded that transloc ation of subunits is an important mechanism involved in the short time upre gulation of the Na+-K+ pumps in association with human muscle activity.