Platelet-activating factor stimulates metabolism of phosphoinositides via phospholipase A2 in primary cultured rat hepatocytes.
Addition of platelet-activating factor (PAF) to cells doubly labeled with [14C]glycerol plus [3H]arachidonic acid resulted in a transient decrease of [14C]glycerol-labeled phosphatidylinositol (PI) and a transient increase of [14C]glycerol-labeled lysophosphatidylinositol (LPI). [3H]Arachidonate-labeled PI, on the other hand, decreased in a time-dependent manner. The radioactivity in phosphatidylethanolamine, phosphatidylcholine, sphingomyelin, and phosphatidylserine did not change significantly. The 3H/14C ratio decreased in PI in a time-dependent manner, suggesting the involvement of a phospholipase A2 activity. Although PAF also induced a gradual increase of diacylglycerol (DG), the increase of [14C]glycerol-labeled DG paralleled the loss of triacyl [14C]glycerol and the 3H/14C ratio of DG was 16 times smaller than that of PI. Thus, DG seemed not to be derived from PI. In myo- [3H]inositol-prelabeled cells, PAF induced a transient decrease of [3H]phosphatidylinositol-4,5-bis-phosphate (TPI) and [3H]phosphatidylinositol-4-phosphate (DPI) at 1 min. PAF stimulation of cultured hepatocytes prelabeled with 32Pi induced a transient decrease of [32P]polyphosphoinositides at 20 sec to 1 min. [32P]LPI appeared within 10 sec after stimulation and paralleled the loss of [32P]PI. [3H]Inositol triphosphate, [3H]inositol diphosphate, and [3H]inositol phosphate, which increased in a time-dependent manner upon stimulation with adrenaline, did not accumulate with the stimulation due to PAF. These observations indicate that PAF causes degradation of inositol phospholipids via phospholipase A2 and induces a subsequent resynthesis of these phospholipids.
D000818:Animals; D002478:Cells, Cultured; D004837:Epinephrine / Q000494:pharmacology; D007294:Inositol / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000201:enzymology / Q000378:metabolism*; D008297:Male; D010716:Phosphatidylinositols / Q000378:metabolism*; D010740:Phospholipases / Q000502:physiology*; D010741:Phospholipases A / Q000502:physiology*; D054467:Phospholipases A2; D010761:Phosphorus Radioisotopes; D010972:Platelet Activating Factor / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D010716:Phosphatidylinositols; D010761:Phosphorus Radioisotopes; D010972:Platelet Activating Factor; D007294:Inositol; D010740:Phospholipases; D010741:Phospholipases A; D054467:Phospholipases A2; D004837:Epinephrine