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 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 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 beta(1)-subunits by 70 +/- 29, 35 +/- 10, and 26 +/- 5%, respectively. The membrane content of alpha(1) 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 alpha(2)-, total alpha-, and beta(1)-subunits 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 translocation of subunits is an important mechanism involved in the short time upregulation of the Na(+)-K(+) pumps in association with human muscle activity.     

Cell sodium-induced recruitment of Na(+)-K(+)-ATPase pumps in rabbit cortical collecting tubules is aldosterone-dependent

The influence of intracellular sodium concentration ( [Na+]i) on the number of Na(+)-K(+)-ATPase pumps was examined in cortical collecting tubules (CCD) of kidneys from rabbits in different aldosterone conditions. Specific [3H]ouabain binding was measured in isolated CCD with various [Na+]i. Experiments were performed on adrenalectomized rabbits receiving only a substitutive dose of dexamethasone and on adrenalectomized rabbits replete with aldosterone. In aldosterone-replete rabbits, the number of binding sites increased linearly with [Na+]i, from 16 fmol/nl tubular volume at 15 mM Na+i to 39 fmol/nl tubular volume at 140 mM Na+i. Neither actinomycin D (5 microM) nor cycloheximide (10 microM) prevented this [Na+]i-dependent increase. In adrenalectomized rabbits, the number of ouabain-binding sites was reduced and did not increase with [Na+]i. These results are in favor of the presence of a "latent" pool of pumps in CCD, rapidly recruited under [Na+]i influence. Aldosterone appears to be required for the constitution and/or activation of this pool.     

Postischemic Na(+)-K(+)-ATPase reactivation is delayed in the absence of glycolytic ATP in isolated rat hearts

Normalization of intracellular sodium (Na) after postischemic reperfusion depends on reactivation of the sarcolemmal Na(+)-K(+)-ATPase. To evaluate the requirement of glycolytic ATP for Na(+)-K(+)-ATPase function during postischemic reperfusion, 5-s time-resolution 23Na NMR was performed in isolated perfused rat hearts. During 20 min of ischemia, Na increased approximately twofold. In glucose-reperfused hearts with or without prior preischemic glycogen depletion, Na decreased immediately upon postischemic reperfusion. In glycogen-depleted pyruvate-reperfused hearts, however, the decrease of Na was delayed by approximately 25 s, and application of the pyruvate dehydrogenase (PDH) activator dichloroacetate (DA) did not shorten this delay. After 30 min of reperfusion, Na had almost normalized in all groups and contractile recovery was highest in the DA-treated hearts. In conclusion, some degree of functional coupling of glycolytic ATP and Na(+)-K(+)-ATPase activity exists, but glycolysis is not essential for recovery of Na homeostasis and contractility after prolonged reperfusion. Furthermore, the delayed Na(+)-K(+)-ATPase reactivation observed in pyruvate-reperfused hearts is not due to inhibition of PDH.