Mechanism of Ca²⁺-regulation in Aorta (IV)

Abstract

ATP-dependent Ca²⁺ uptake by microsomes, isolated from bovine aortic and mesenteric smooth muscle, was inhibited by Ca²⁺ ionophore: A23187, and Ca²⁺ release from the microsomes was induced immediately after adding A23187. However, Ca²⁺, Mg²⁺-ATPase activity of those microsomes was not affected. Rate of A23187-induced Ca²⁺ release was not slowered by divalent cations: Ca²⁺, Mg²⁺, and Sr²⁺ at high concentrations (1mM). LDL also inhibited ATP-dependent and ATP-independent Ca²⁺ uptake by the microsomes, but did not induce Ca²⁺-release from the microsomes. Thus, site of the LDL action of the microsomes was suggested to be outer membrane binding sites of Ca²⁺.