REGULATIONS OF CYTOSOLIC-FREE CA2+ IN CULTURED RAT ALVEOLAR MACROPHAGES (NR8383)

Ca2+ mobilization in the rat alveolar macrophage cell line NR8383 was examined with the Ca2+-sensitive fluorescent probe Fura-2. ATP and nor epinephrine elicited a 108 and 46% increase, respectively, in cytosoli c free Ca2+ concentration ([Ca2+](i)). Acetylcholine, nicotine, isopro terenol, substance P, and vasoactive intestinal polypeptide did not al ter [Ca2+](i). Inositol 1,4,5-trisphosphate (IP3) formation was also a ctivated by ATP. The carbohydrate-rich cell wall preparation, zymosan, induced a gradual [Ca2+](i) increase only in the presence of external Ca2+, but did not activate IP3 formation. This increase was abolished by laminarin and by removal of extracellular Ca2+, suggesting that th e [Ca2+](i) Increase was activated by B-glucan receptors and mediated by Ca2+ influx. This influx was significantly reduced by SKF96365, but not by nifedipine, omega-conotoxin GVIA, omega-agatoxin TVA, or fluna rizine. These results suggest that release of intracellular Ca2+ in MR 8383 cells is regulated by P-2-purinoceptors and that zymosan causes C a2+ influx via a receptor-operated pathway.