Interactions of Polylysine With Platelets

Platelet aggregation induced by the cationic polypeptide, polylysine, differs in many respects from aggregation induced by ADP. Polylysine causes immediate, irreversible aggregation and the aggregates form a tight mosaic with electrondense material between the membranes and coating the surface. Inhibitors of ADP-induced aggregation or of the platelet release reaction do not inhibit polylysine, but negatively charged polymers (heparin and mucopolysaccharides) are inhibitory and also cause deaggregation. In contrast to agents such as thrombin, polylysine does not cause the release of serotonin, ATP, or ADP from the platelet granules, but it does cause a leak of adenine nucleotides and lactic dehydrogenase from the platelet cytoplasm. This leak from the cytoplasm can be inhibited by prostaglandin E₁. Polylysine inhibits serotonin uptake by platelets, but ADP does not. Low concentrations of polylysine inhibit ADP or thrombin-induced aggregation and thrombin-induced release. Collagen-induced release and aggregation are potentiated by polylysine. Both ADP and polylysine cause increased C¹⁴O₂ production from platelets incubated with glucose-6-¹⁴C. Prostaglandin E₁ inhibits this stimulation by both these agents. Mucopolysaccharides and heparin inhibit only the polylysine-induced stimulation of metabolism. The increased aerobic metabolism observed with both ADP and polylysine may be related to changes that occur when platelets change shape and adhere to each other and it may not be a specific reaction to ADP.