Platelet interaction with active and TLCK-inactivated α-thrombin

Abstract

Interaction of α-thrombin with platelets causes a dose-dependent depolarization of the trans-membrane potential which can be measured by monitoring the fluorescence of a cyanine dye. Inactivation with tosyllysylchloromethylketone abolishes the ability of thrombin to either initiate platelet aggregation or to cause the change in potential observed with unmodified thrombin. Preincubation of washed platelets with inactivated thrombin lowers the subsequent membrane potential change in response to 0.005 to 0.05 U/ml of active thrombin. The extent of that competition is a function of quantities of modified and native thrombin used. The data presented here are fully compatible with the concept that two distinct thrombin binding modes, with different affinities, exist on the platelet surface.