Protein-stimulated enrichment of human platelet membranes in linoleylphosphatidylcholines. Effect upon adenylate cyclase and fluidity.

In order to study the effect of linoleyl enrichment of platelet membranes upon adenylate cyclase activity and membrane fluidity, manipulations of platelet phospholipids are carried out with phosphatidylcholine-loaded high-density lipoproteins (HDL) or phospholipid-exchange protein and phospholipid-cholesterol mixed vesicles. Incubation with HDL does not appear to be valuable for this purpose. On the other hand, phospholipid-exchange protein and mixed vesicles can be used successfully. Phospholipid-exchange protein stimulated 3-fold the spontaneous exchange of 2-linoleylphosphatidylcholine between the vesicles and the platelets. Linoleyl enrichment of platelets by dilinoleylphosphatidylcholine is about 25% and by 2-linoleylphosphatidylcholine is about 45-50%. The unsaturation index remains constant when the enrichment is performed using dilinoleylphosphatidylcholine but it increases with 2-linoleylphosphatidylcholine. Basal and prostaglandin E1-stimulated adenylate cyclase activities are not modified by dilinoleylphosphatidylcholine, while they increase significantly in the case of 2-linoleylphosphatidylcholine. There is no significant variation in diphenyl hexatriene fluorescence polarization parameters, either with dilinoleylphosphatidylcholine or with 2-linoleylphosphatidylcholine.