Liver glucose-6-phosphatase activity is not modulated by physiological intracellular Ca²⁺ concentrations

1. In the presence of MgATP and increasing amounts of added Ca²⁺, isolated liver microsomal vesicles accumulate approx. 10 nmol of Ca²⁺/mg of protein and buffer ambient free Ca²⁺ at increasing concentrations (0.22-10.9 μM). Under these experimental conditions, microsomal glucose-6-phosphatase activity is unaffected by the concentration of extravesicular free Ca²⁺. 2. Different levels of intravesicular Ca²⁺ were obtained by treating microsomes with the Ca²⁺ ionophore A23187 and by stimulating active microsomal Ca²⁺ accumulation with P₁ (3 mM). In both instances, microsomal glucose-6-phosphatase activity is unaffected by the level of intravesicular Ca²⁺.