[THE EFFECTS OF LYS-PLASMINOGEN ON HUMAN PLATELET SECRETION].

The effects of Lys-plasminoge on platelet α-granule secretion were studied. The level of P-selectin exposed on the surface of plasma membranes of washed human platelets was measured by flow cytometry as a market of α-granule secretion. It was shown that Lys-plasminogen facilitates partial release of α-granules, but impedes thrombin-induced platelet exocytosis. It is suggested that Lys-plasminogen may affect platelet secretion rather through interaction of its non-catalytic (kringle) domains with membrane receptors than due to contaminating plasmin activity. In contrast to Lys-form, native proenzyme (Glu-plasminogen) had no effects on α-granule releasing. Here, we provide the first experimental demonstration that Lys-form of plasminogen is able to modulate platelet α-granule secretion, and this effect can be considered as one of the plausible mechanisms of its anti-aggregating activity.