COLLAGEN-INDUCED PLATELET-AGGREGATION AND RELEASE REACTION - ROLE OF RAS PROTEIN

The relationship between the platelet collagen receptor and ras protei n was examined by immunoprecipitation of control and collagen stimulat ed platelets with both antibodies. Both ras protein and receptor are c oprecipitated by both antibodies. The coprecipitated samples contained GTP and GDP which were separated by thin layer chromatography. The ef fect of guanine nucleotide binding protein (G-protein, 21(ras)) on pla telet aggregation was examined by using a guanine triphosphate analogu e (GTP-gamma-S) Results of streptolysin O permeabilized experiments sh ow that the addition of the analogue to permeabilized platelet-rich pl asma causes platelet aggregation and release of ATP in a dose-dependen t fashion. The aggregation induced by GTP-gamma-S could not be obtaine d with GDP, GDP-B-S, or 5'-GMP, suggesting that the effect of GDP-gamm a-s is specific. The platelet aggregation induced by the analogue was inhibited in dose-dependent manner GTP-gamma-S induced thromboxane B2 formation was also decreased by Formation of thromboxane B2 was also b locked by the addition of PMSF and ethanol suggesting that GTP-gamma-S increases arachidonic acid release from permeabilized platelets. Thes e results suggest that both GTP-gamma-S and GTP enhance phospholipase A2 activity which releases arachidonic acid in permeabilized platelets and subsequently causes platelets to aggregate. Published by Elsevier Science Ltd.