[ATPase activity and ATP-dependent accumulation of Ca2+ in skeletal muscle nuclei. Effects of denervation and electric stimulation].

The dependence of the ATPase activity of skeletal muscle nuclei on divalent cations was studied. An addition of Ca2+ significantly increased the activity of nuclear ATPase. Mg2+ exerted an activating effect in the presence of 10(-5) M Ca2+ and an inhibiting effect in the presence of 2 x 10(-3) M Ca2+. Predominant localization of Ca-ATPase in the nucleoli and in the internal nuclear envelope was demonstrated by an electron microscopic histochemical technique. ATP increased the uptake of 45Ca by muscle nuclei; the optimal conditions for this incorporation were established. The changes in Ca-ATPase activities and in the ATP-dependent uptake of 45Ca induced by denervation and electric stimulation were found to be synchronous and unidirectional.