Cyclic GMP Regulation of the Plasma Membrane (Ca²⁺-Mg²⁺) ATPase in Vascular Smooth Muscle

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Plasma membrane (Ca₂₊-Mg₂₊) ATPase purified from bovine aortic microsomes by calmodulin affinity chromatography was incorporated into soybean phospholipid liposomes. In the reconstituted proteoliposomes, a protein corresponding to the ATPase was phosphorylated by [γ-³²P] ATP in the presence of cGMP and cGMPdependent protein kinase. Both the affinity for Ca²⁺ and the maximum Ca²⁺ uptake activity by the proteoliposomes were increased by the cGMP-dependent phosphorylation, and there was good parallelism between the Ca²⁺-uptake rate and the extent of phosphorylation. These results strongly suggest that the Ca²⁺-transport ATPase of the vascular smooth muscle plasma membrane is regulated through its cGMP-dependent phosphorylation.