Loss of Phosphatidylinositol and Gain in Phosphatidate in Neutrophils Stimulated with Fmet-Leu-Phe

Neutrophils stimulated with fMetLeuPhe show a loss of phosphatidylinositol (PI) and a gain in phosphatidate (PA). In cells prelabeled with 32Pi, it would be expected that the newly synthesized PA would have the same specific radioactivity as cellular ATP provided that PI loss is catalyzed by phospholipase C and the resultant diacylglycerol is phosphorylated by ATP. Instead, the specific radioactivity of the newly-formed PA was found to be less than a tenth of the specific radioactivity of ATP. The source of the newly formed PA is most likely to be PI because: (1) Increase in PA mass is accompanied by an equivalent decrease in mass of PI. (2) In cells pulse-labeled with [3H]glycerol, label lost from PI is recovered in PA. (3) Specific radioactivity of the new [32P]PA is similar to the specific radioactivity of [32P]PI. The most plausible explanation for these results is that PI is directly converted to PA by phospholipase D action. This conclusion is supported by observations that neither inositol phosphates nor diacylglycerol increase at the expense of PI or polyphosphoinositides in fMetLeuPhestimulated cells.