Stimulation of cardiac sarcolemmal (Na+--K+) ATPase activity by phosphorylase kinase

Following preincubation with phosphorylase kinase, ATPase activities of heart sarcolemmal membranes were increased: total ATPase from 9.38+/-0.65 to 15.25+/-0.90 and ouabain-sensitive (Na+--K+)ATPase from 1.67+/-0.17 to 3.12+/-0.33 micron moles Pi/mg protein/h (mean +/- S.E. of 3 experiments); (Ca2+)ATPase and (Mg2+--Ca2+)-ATPase activities were not significantly altered due to phosphorylase kinase. Under these conditions, phosphorylase kinase catalyzed phosphorylation of sarcolemmal membranes. The kinase-catalyzed phosphorylation of membranes was increased by Ca2+ ions: at pH 6.8, 30% increase in phosphorylation was observed whereas at pH 8.5, 267% increase was noted due to this action. These findings support the view that Ca2+-dependent phosphorylation of membranes regulates (Na+--K+)ATPase.