Changes of Intracellular Free Ca²⁺ in Macrophages Following N-Formyl Chemotactic Peptide Stimulation. Direct Measurement by the Loading of Quin 2

Abstract

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 6min. A mitochondrial uncoupler had no effect on basal free Ca²⁺ concentration and the increase in intracellular free Ca²⁺ induced by chemotactic peptides. A 23187 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 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 20min at 37°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.