Acetylglyceryl ether phosphorylcholine (AGEPC; platelet-activating factor)-induced stimulation of rabbit platelets: correlation between phosphatidic acid level, 45Ca2+ uptake, and [3H]serotonin secretion.

When 32Pi-labeled rabbit platelets were incubated with 5 X 10(-10) M 1-O-alkyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC), either in the presence or absence (0.1 mM EGTA) of added Ca2+, there was a three- to five-fold increase in the [32P]phosphatidic acid (PA) pool within 15 to 20 s. This event was followed by a gradual decrease in the [32P]PA level to near basal level in 5 min. AGEPC effected this change in [32P]PA in a characteristic dose- and time-dependent manner. Polar head group analogs of AGEPC, such as AGEDME and AGEMME, also effected an increase in PA labeling at levels comparable to those previously reported for their activity toward rabbit platelets [K. Satouchi, R. N. Pinckard, L. M., McManus, and D. J. Hanahan (1981) J. Biol. Chem. 256, 4425-4432]. Other analogs, i.e., lysoGEPC and the enantiomer, sn-1-AGEPC, which are inactive toward rabbit platelets, also showed no effect on the level of [32P]PA. The finding that the PA level in rabbit platelets could be manipulated by the addition of AGEPC, without any added Ca2+, provided an excellent model system for establishing a correlation between the uptake of Ca2+, serotonin release, and PA level. Thus, PA must be regarded as a sensitive indicator of a reaction mechanism important to the platelet response to AGEPC, and could be the focal point in promoting calcium uptake during the stimulation process.