Breakdown and synthesis of polyphosphoinositides in fMetLeuPhe-stimulated neutrophils

The interconversions of the inositol-containing lipids (PI, PI-P and PI-P2) and their products (DG, inositol phosphates and PA) in human and rabbit neutrophils stimulated with fMetLeuPhe and PMA have been examined. PMA causes only the phosphorylation of PI to PI-P whereas fMetLeuPhe causes phosphorylation of both PI and PI-P yielding PI-P2 and the hydrolysis of all three lipids. While the predominant reaction is breakdown of PI to PA catalysed by phospholipase D, approx. 2% of PI is converted to polyphosphoinositides and then broken down by the phospholipase C route yielding inositol phosphates and DG. The latter reaction occurs without detectable lag and is a function of receptor occupancy. The amount of inositol trisphosphate thus formed would be sufficient to release Ca2+ from intracellular stores.