Modification of positional distribution of fatty acids in phosphatidylinositol of rabbit neutrophils stimulated with formylmethionyl-leucyl-phenylalanine.

ABSTRACT

The effects of formylmethionyl-leucyl-phenylalanine (fMet-Leu-Phe) on the positional distribution of fatty acids in phosphatidylinositol (PI), phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were investigated with rabbit neutrophils. The proportion of arachidonate at the C-2 position of PI was 35.0% in resting neutrophils and declined to 30.8% after 5 min stimulation with the peptide at a concentration of 10(-7) M. In contrast, the profiles of the positional distribution of fatty acids in PC and PE were not affected upon stimulation with fMet-Leu-Phe. The phospholipid composition of rabbit neutrophils was examined at different time intervals following the addition of fMet-Leu-Phe. PI and PC, but no other phospholipids, exhibited significant changes in their quantities. The quantity of PC decreased at 5 min with a concurrent increase in that of lysophosphatidylcholine (lysoPC), suggesting a phospholipase A2 action on PC. The quantity of PI, on the other hand, decreased at 1 min with an accompanying increase in phosphatidic acid when the profile of the positional distribution of fatty acids in PI remained unchanged. No lysophosphatidylinositol (lysoPI) was detected. This indicates the enhancement of the PI cycle in the fMet-Leu-Phe-stimulated neutrophils. The augmented PI cycle in response to fMet-Leu-Phe was further supported by the finding that [3H]arachidonyl-diacylglycerol and -phosphatidic acid accumulated at the expense of [3H]arachidonylPI in rabbit neutrophils prelabelled with [3H]arachidonate. Restoration of the content of PI to the higher than the original level at 5 min after stimulation with fMet-Leu-Phe, however, leads to the suggestion that de novo synthesis of PI as well as PI resynthesis along the closed cycle of PI has occurred at 5 min and that this newly synthesized PI, via a de novo pathway with a different pattern of the positional fatty acyl composition, is the cause of the decreased proportion of arachidonate.