AREGU April 47/4

Juel, Carsten, Jens Jung Nielsen, and Jens Bangsbo. Exercise-induced translocation of Na1-K1 pump subunits to the plasma membrane in human skeletal muscle. Am J Physiol Regulatory Integrative Comp Physiol 278: R1107– R1110, 2000.—Six human subjects performed one-legged knee extensor exercise (90 6 4 W) until fatigue (exercise time 4.6 6 0.8 min). Needle biopsies were obtained from vastus lateralis muscle before and immediately after exercise. Production of giant sarcolemmal vesicles from the biopsy material was used as a membrane purification procedure, and Na1-K1 pump aand b-subunits were quantified by Western blotting. Exercise significantly increased (P , 0.05) the vesicular membrane content of the a2-, total a-, and b1-subunits by 70 6 29, 35 6 10, and 26 6 5%, respectively. The membrane content of a1 was not changed by exercise, and the densities of subunits in muscle homogenates were unchanged. The ratio of vesicular to crude muscle homogenate content of the a2-, total a-, and b1-subunits was elevated during exercise by 67 6 33 (P , 0.05), 23 6 6 (P , 0.05), and 40 6 14% (P 5 0.06), respectively. It is concluded that translocation of subunits is an important mechanism involved in the short time upregulation of the Na1-K1 pumps in association with human muscle activity.