Exocytosis of secretory organelles from blood platelets incubated with cationic polypeptides.

The blood platelet release reaction involves the secretion, in parallel, of specific chemical constituents stored in intracellular organelles to the plasma without loss of substances suggestive of cell damage. The present investigation has employed an unusual effect of cationic polypeptides to follow the platelet secretory process. When platelets were incubated with polybrene and polylysine, the agents were taken up and deposited in cytoplasmic organelles. The matrix of granules developed a lattice-like substructure not produced by other chemical agents, and dark zones of granules and dense bodies became more electron opaque. Subsequently, the platelets exposed to cationic polypeptides underwent the shape change and internal transformation similar to that produced by potent aggregating agents. Granules and dense bodies appeared in the open canalicular system and were extruded in a relatively intact state from the altered platelets. No differences were observed in the response of normal, afibrinogenemic or thrombasthenic platelets to incubation with polybrene and polylysine. The results indicate that cationic polypeptides can stimulate the extrusion of secretory organelles, and support the previous reports suggesting that channels of the open canalicular system serve as conduits for discharging the products of the release reaction.