Changes of Intracellular Free Ca2+ in Macrophages Following N-Formyl Chemotactic Peptide Stimulation. Direct Measurement by the Loading of Quin 21

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Abstract
The changes in the intracellu1a, free Ca 2+ in guinea pig peritoneal macrophages induced by N -formyl chemotactic peptides were examined using a fluorescent Ca 2+ indicator, quin 2. The ATP contents of quin 2-loaded macrophages were also examined. The intracellular free Ca 2+ was immediately raised about 4-fold by the addition of chemotactic peptides both in the presence and absence of extracellular Ca 2+ and returned to the basal level within 6 min. A mitochondrial uncoupler had no effect on basal free Ca 2+ concentration and the increase in intracellular free Ca 2+ induced by chemotactic peptides. A23187 increased the intracellular free Ca 2+ 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 Ca 2+ release from the store sites. The results indicate that the increase in the intracellular free Ca 2+ induced by chemotactic peptides is due to Ca 2+ release from the membraneous store site(s), other than mitochondria. Extracellular Ca 2+ was raised by the addition of a chemotactic peptide, when assayed inCa 2+ -free saline using guin 2. The second addition of the chemotactic peptide, after the intracellular free Ca 2+ concentration had returned to the basal level, was ineffective. Recovery of the free Ca 2+ change induced by chemotactic peptide was observed only when the macrophages were freshly incubated in Ca 2+ -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.