Ca²⁺ Release in the Endoplasmic Reticulum of Guinea Pig Peritoneal Macrophages

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Passive permeability of the endoplasmic reticulum of saponin-treated macrophages to Ca²⁺ was studied by the filtration method using ⁴⁵Ca. The Ca²⁺ release from the endoplasmic reticulum of macrophages was enhanced by the presence of submicromolar concentrations of Ca²⁺ in the medium. The Ca²⁺ release was enhanced by caffeine, and suppressed by MgCl₂. These phenomena are similar to the Ca²⁺-induced Ca²⁺ release reported for the sarcoplasmic reticulum of skeletal muscle. On the other hand, adenine suppressed the Ca²⁺ release from the endoplasmic reticulum, while it reportedly enhanced the Ca²⁺-induced Ca²⁺ release of the skeletal muscle. The threshold concentration of Ca²⁺ for the Ca²⁺-induced Ca²⁺ release was approximately 10^-8 M in the presence of 0.95mM MgCl₂ in macrophages. The spontaneous spreading of macrophages and spontaneous migration of macrophages were inhibited by adenine, and also by caffeine in spite of the enhancement of the Ca²⁺-induced Ca²⁺ release.