Regulation of cytosolic free Ca 2+ in cultured rat alveolar macrophages (NR8383)

Ca 2+ mobilization in the rat alveolar macrophage cell line NR8383 was examined with the Ca 2+ ‐sensitive fluorescent probe Fura‐2. ATP and norepinephrine elicited a 108 and 46% increase, respectively, in cytosolic free Ca 2+ concentration ([Ca 2+ ] i ). Acetylcholine, nicotine, isoproterenol, substance P, and vasoactive intestinal polypeptide did not alter [Ca 2+ ] i . Inositol 1,4,5‐trisphosphate (IP 3 ) formation was also activated by ATP. The carbohydraterich cell wall preparation, zymosan, induced a gradual [Ca 2+ ] i increase only in the presence of external Ca 2+ , but did not activate IP 3 formation. This increase was abolished by laminarin and by removal of extracellular Ca 2+ , suggesting that the [Ca 2+ ] i increase was activated by β‐glucan receptors and mediated by Ca 2+ influx. This influx was significantly reduced by SKF96365, but not by nifedipine, ω‐conotoxin GVIA, ω‐agatoxin IVA, or flunarizine. These results suggest that release of intracellular Ca 2+ in NR8383 cells is regulated by P 2 ‐purinoceptors and that zymosan causes Ca 2+ influx via a receptor‐operated pathway. J. Leukoc. Biol. 62: 341–348; 1997.