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 intracellular 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. Chlorpromazine 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 in free Ca2+-free saline using quin 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 degrees C. These results suggest that the Ca2+ released from the store site(s) may be effluxed through the plasma membrane. Quin 2 loaded in macrophages may interfere with mitochondrial ATP synthesis.