STUDIES ON THE EFFECT OF SODIUM AND POTASSIUM ON THE ATPase ACTIVITY AND CALCIUM UPTAKE OF THE SKELETAL MUSCLE MICROSOMES

Abstract

1. Calcium uptake by rabbit skeletal muscle microsomes was stimulated by the addition of Na+ or K+ alone or both, but the synergistic action of Na+ and K+ was not remarkable.2. The stimulation of calcium uptake was the highest at the concentration of 20 mM of Na+ or 40mM of K+.3. The pH optimum of calcium uptake was 6.8. The pH optimum of ATPase activity was about 78 in the case of Mg2+ alone or Mg2++Na+, and about 7.4 in the case of Mg2++ Na++K+4. ATPase activity was also stimulated by the addition of Na+ or K+, but the synergistic action of Na+ and K+ was not observed. Ouabain did not affect the stimulated ATPase activity.5. ATPase activity was stimulated by a low concentration of Ca2+ in the presence of Na+ and K+ alone or both regardless of the presence of oxalate. In the presence of Mg2+ alone the ATPase activity was stimulated slightly by the addition of Ca2+, but in the presence of oxalate the ATPase activity with Mg2+ alone was not stimulated by the presence of Ca2+.6. The addition of salyrgan depressed the ATPase activity to a certain level. The ATPase which links to Ca2+ uptake was considered to be Na+-K+ stimulated, Ca2+ stimulated ouabain insensitive and salyrgan sensitive enzyme.