ATP-dependent Ca²⁺ accumulation in intracellular membranes of guinea pig macrophages after saponin treatment

Ca²⁺ transport system in the intracellular membranes was studied by using saponin-treated macrophages of the guinea pig, in which the plasma membranes could be selectively destroyed. Saponin-treated macrophages could accumulate 3.1 nmoles Ca²⁺ 4 × 10⁶ macrophages in the presence of Mg-ATP and sodium azide with an apparent affinity constant of 6 × 10⁶ M^-1. In the absence of sodium azide, the value of Ca²⁺ uptake of saponin-treated macrophages was 95 nmoles/4 × 10⁶ macrophages, and its affinity constant for Ca²⁺ was 3 × 10⁵ M^-1. Saponin-treated macrophages may be suitable for the studies of Ca²⁺ transport systems in the intracellular membranes.