Calcium regulation of phosphatidyl inositol turnover in macrophage activation by formyl peptides

Stimulation by the tripeptide N‐formyl norleucyl leucyl phenylalanine (FNLLP) of the guinea pig alveolar macrophage gives rise to transient production of superoxide anion (O 2 − ). Components of the phosphatidyl inositol (PI) cycle (phosphatidic acid) (PA), phosphatidyl inositol‐4,5‐bisphosphate (TPI) and phosphatidyl inositol‐4‐phosphate (DPI) were monitored using 32 P in order to examine the possible association of this cycle with the FNLLP‐stimulated production of O 2 − . Macrophage stimulation by FNLLP led to an increased flux of metabolites through the PI cycle. The level of 32 P label in both TPI and DPI rapidly decreased upon exposure to FNLLP, followed by a 5‐min period during which the 32 P label in TPI and DPI approached prestimulated levels. During this period, there was a fivefold increase in 32 P‐PA. It is suggested that diacylglycerol (DAG) is the O 2 − production. The importance of continued cycling of PI in the stimulated mechanism is demonstrated by the inhibition by LiCl of the extent, but not the initial rate, of both O 2 − production and the formation of 32 P‐PA upon peptide stimulation after 1‐h preincuexamined. It has previously been demonstrated that intracellular availability of calcium can influence the rate and extent of O 2 − production. In cells preloaded with quin‐2, which acts as a high‐affinity sink for calcium in the cytosol, the initial rate of FNLLP‐stimulated O 2 − production is inhibited in low (10 μM) extracellular calcium medium. High extracellular calcium (1 mM) completely reverses this inhibition and also significantly extends the time course of O 2 − production in both quin‐2 and control cells (Stickle et al., 1984). In parallel with these effects on O 2 − production, varying calcium conditions is demonstrated to influence the rate and extent of PA formation. These same calcium conditions were found to have little or no effect on the initial unstimulated levels of TPI, DPI, and PA. These results indicate that the influence of an intracellular pool of calcium on O 2 − production may be via its influence on stimulated PI turnover.