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FMLP-induced arachidonic acid release, phospholipid metabolism, and calcium mobilization in human monocytes.
R W Godfrey1, R M Manzi, B D Jensen
1Department of Experimental Pathology, SmithKline and French Laboratories, Swedeland, Pennsylvania 19406.
Abstract:
Radiolabeled human peripheral blood monocytes released [3H]arachidonic acid upon challenge with the calcium ionophore A23187 (10 microM), or f-Met-Leu-Phe (FMLP, 1 microM). Chromatographic analysis of [3H]arachidonic acid labeled phospholipids showed that stimulation by FMLP reduced the amount of labeled phosphatidylcholine exclusively. Treatment of the monocytes with 10(-3) M dibutyryl cyclic AMP (d-cAMP) or 5 X 10(-4) M isobutylmethylxanthine (IBMX) substantially inhibited [3H]arachidonic acid release (30%) and depletion from labeled phosphatidylcholine (PC) in FMLP--but not calcium ionophore--stimulated cells. Using the fluorescent probe Indo-1, the FMLP-induced cytosolic calcium increase was unaffected by 10(-3) M dibutyryl cyclic AMP. The results suggest that FMLP-stimulated phospholipase activity is regulated by cyclic AMP, but not by depressing receptor-medicated increases in cytoplasmic free calcium.