Degradation of different molecular species of phosphatidylinositol in thrombin-stimulated human platelets.

The relative degradation of the various molecular species of phosphatidylinositol in response to thrombin was studied in human platelets. For this purpose, platelets were prelabeled with [2-3H]glycerol and the loss of radioactivity from the saturated, monoenoic, dienoic, trienoic, tetraenoic, and greater than tetraenoic [3H]phosphatidylinositols was determined after conversion to their 1,2-diacylglycerol acetate derivatives and fractionation by argentation thin layer chromatography. Within 90 s, when the thrombin-dependent degradation of total [3H] phosphatidylinositol amounted to 49.5%, the percentage loss of radioactivity from the tetraenoic (1-stearoyl 2-arachidonoyl) species and greater than tetraenes was significantly greater than that for the other molecular classes and approximately twice that for the monoenes. Furthermore, the extent of degradation tended to decrease with decreasing unsaturation of the phosphatidylinositols in intact platelets. These results indicate that the thrombin-dependent hydrolysis of phosphatidylinositol in intact human platelets exhibits a preferential degradation of 1-acyl (predominantly stearoyl plus oleoyl) 2-arachidonoyl species relative to other molecular species which may possibly be of importance in platelet aggregation.