Changes of intracellular free Ca²⁺ in macrophages following N-formyl chemotactic peptide stimulation. direct measurement by the loading of quin 2

The changes in the intracellu1a, free Ca²⁺ in Guinea pig peritoneal macrophages induced by N-formyl chemotactic peptides were examined using a fluorescent Ca²⁺ indicator, quin 2. The ATP contents of quin 2-loaded macrophages were also examined. The intracellular free Ca²⁺ was immediately raised about 4-fold by the addition of chemotactic peptides both in the presence and absence of extracellular Ca²⁺ and returned to the basal level within 6 min. A mitochondrial uncoupler had no effect on basal free Ca²⁺ concentration and the increase in intracellular free Ca²⁺ induced by chemotactic peptides. A23187 increased the intracellular free Ca²⁺ concentration and minimized the increase by chemotactic peptides. Chiorpromazine also gradually increased the basal level, in agreement with our previous report that this drug induced Ca²⁺ release from the store sites. The results indicate that the increase in the intracellular free Ca²⁺ induced by chemotactic peptides is due to Ca²⁺ release from the membraneous store site(s), other than mitochondria. Extracellular Ca²⁺ was raised by the addition of a chemotactic peptide, when assayed inCa²⁺-free saline using guin 2. The second addition of the chemotactic peptide, after the intracellular free Ca²⁺ concentration had returned to the basal level, was ineffective. Recovery of the free Ca²⁺ change induced by chemotactic peptide was observed only when the macrophages were freshly incubated in Ca²⁺-containing saline for more than 20 min at 37°C. These results suggest that the Ca released from the store site(s) may be effluxed through the plasma membrane.Quin 2 loaded in macrophages may interfere with mitochondrial ATP synthesis.