Mechanism of Ca²⁺-regulation in Aorta

Abstract

A new acid-stable phosphorylation was found to be formed in the presence of ATP and Ca²⁺ in a microsomal protein isolated from bovine aortic smooth muscle. The microsomes also showed Ca²⁺-uptake activity. Both of the Ca²⁺ dependency of the phosphorylation and the Ca²⁺-uptake were in the same range (1-10μM) and the patterns were quite identical to those of rabbit skeletal microsomes. The molecular weight of the phosphorylated protein estimated with SDS-gel electrophoresis was approximately 105, 000. The phosphoprotein was labile at alkaline pH after the denaturation and its decomposition was accelerated by hydroxylamine. The phosphorylation formed in aortic microsomes was thus quite similar to the acid-stable phosphorylated intermediate of the Ca²⁺-transport ATPase of sarcoplasmic reticulum from skeletal and cardiac muscles. These data suggest that the Ca²⁺-dependent phosphorylation of the protein is formed as a reaction intermediate of the Ca²⁺, Mg²⁺-ATPase of the aortic microsomes.