EFFECTS OF THROMBIN AND THE THROMBIN RECEPTOR ACTIVATING PEPTIDE, SFLLRN, ON REDISTRIBUTION OF PLATELET ALPHA-GRANULE CONTENTS ARE SIMILAR AND INDEPENDENT OF THE EXTENT OF THROMBOXANE FORMATION

Immunocytochemistry with gold-labeled antibodies was used to compare the effects of stimulation of human platelets with thrombin (1 U/ml) and the thrombin receptor activating peptide, SFLLRN (20 mu M). After 3 min, redistribution of fibrinogen, von Willebrand factor, and P-selectin (GMP-140, CD62) was examined, the percentages of [C-14]serotonin and beta-thromboglobulin released from prelabeled platelets were measured, and the amount of thromboxane B-2 formed was assayed. Upon stimulation with either thrombin or SFLLRN, the platelets had changed from their normal disc shape to spheroidal forms with short pseudopodia. Few alpha-granules remained the open canalicular system was expanded (more so with SFLLRN) and contained most of the fibrinogen and von Willebrand factor, although small amounts were evident on the platelet surface. Most of the P-selectin was on the surface. Both thrombin and SFLLRN caused complete release of beta-thromboglobulin and 88.3 and 77.5% release of [C-14]serotonin, respectively. However, formation of TXB(2) caused by thrombin was 10 times greater than that caused by SFLLRN (969 +/- 173 vs 76 +/- 22 ng/10(9) platelets). Thus, the redistribution of platelet alpha-granule contents is similar with thrombin or SFLLRN stimulation and is unaffected by the extent of thromboxane formation. (C) 1995 Academic Press, Inc.