Concurrent and separate inside-out transition of platelet apoptosis and activation markers to the platelet surface.

The cell plasma membrane is tightly coupled with the vital processes of apoptosis and activation. In the current study, we investigated exposure of the apoptosis marker phosphatidylserine (PS) and activation marker P-selectin (CD62) on the plasma membrane of anucleate platelets. We found that, depending on triggering stimuli, the plasma membrane of human platelets may exist in four states with predominant exposure of (i) PS but not CD62 (75·9 ± 2·8% of total cells), (ii) CD62 but not PS (86·2 ± 1·3%), (iii) both PS and CD62 (89·6 ± 1·0%) or (iv) neither PS nor CD62 (87·9-97·5%), when platelets were treated at optimal conditions with pro-apoptotic BH3 mimetic ABT-737, thrombin, calcium ionophore A23187 or control diluents, respectively. The dynamics of PS exposure induced by ABT-737 is a slow temperature-dependent process requiring 90 min treatment at 37°C rather than at room temperature for obtaining high levels of PS exposure. In contrast, thrombin-induced CD62 exposure and A23187-induced PS and CD62 exposure showed fast temperature-independent dynamics. This model of selective and concurrent stimulation of PS and/or CD62 transition to the platelet surface provides an experimental horizon for elucidating the roles of plasma membrane markers of platelet apoptosis and activation in platelet clearance.