ROLE OF AUTOCRINE STIMULATION FOR THE EFFECTS OF CYCLIC-AMP ON PROTEIN AND LIPID PHOSPHORYLATION IN PLATELETS ACTIVATED BY PARTICLES

We have compared responses in platelets stimulated with the particulat e materials, Intralipid (liposome-suspension) and a potential contrast medium IEEC thyl-acetylamino)-2,4,6-triiodo-benzenecarboxylate coated with human serum albumin), with and without forskolin and inhibitors of autocrine stimulation (IAS: an ADP-removing system of creatine phos phate/creatine phosphokinase; RGDS to prevent fibrinogen/fibronectin b inding to GPIIb/IIIa; SQ 29.548 as a TXA(2) receptor antagonist; cypro heptadine as a serotonin receptor antagonist; BN 52021 as a platelet-a ctivating factor receptor antagonist). The pattern of tyrosine-phospho rylated proteins, phosphorylation of initial lipids and phosphorylatio n of pleckstrin (P47) were used as markers for early signal transducin g responses, while secretion of ADP+ATP and beta-N-acetyl-glycosaminid ase were used as final responses. Intralipid showed no platelet activa tion except for some weak tyrosine protein phosphorylation that was in hibited by elevated cAMP, IEEC induced strong platelet activation that was partly inhibited by increased levels of cAMP and IAS. The inhibit ion of elevated cAMP seemed to be due to removal of the G protein-medi ated activation from secreted autocrine stimulators either by IAS or f orskolin, The remaining activity is a pure effect from IEEC which is n ot affected by elevated cAMP. (C) 1998 Federation of European Biochemi cal Societies.