Localization of granular components in ADP- and/or teleocidin-stimulated human blood platelets as revealed by immunocytochemical methods.

Morphological aspects of the platelet release reaction induced by adenosine 5'-diphosphate (ADP) and/or teleocidin (a tumor promoter) in the presence of aspirin were studied by transmission electron microscopy. Human platelet-rich plasma treated with reagents at 37 degrees C for 1-5 min was fixed with aldehyde and embedded in Epon or Lowicryl K4M. Addition of ADP (10 microM) resulted in the centralization of granules without granule release, while teleocidin (100 ng/ml) induced the swelling of the open canalicular system (OCS) and the release of alpha-granules without centralization of these granules. When both ADP and teleocidin were added successively, a synergistic effect was predominant; and both alpha- and dense-granules were discharged from the cytoplasm. Postembedding immunocytochemical studies employing specific antibodies against various granular components in combination with protein A gold as a label revealed that, following the administration of teleocidin, several components of alpha-granules such as beta-thromboglobulin and platelet factor 4 moved into the swollen OCS, while the dense-granule component, serotonin, did not. When both teleocidin and ADP were administered, both alpha-granular and dense-granular components moved into the swollen OCS.