ИСТИНА

Background: Activated platelets form two distinct subpopulations, one of which is characterized by high intracellular calcium concentration, loss of mitochondrial membrane potential and phosphatidylserine (PS) exposure. However, there is little information about detailed relationship between dynamics of these three processes. Aims: To elucidate the sequence of events leading to PS exposure. Methods: Washed gel-filtered platelets were loaded with FuraRed and tetramethylrhodamine, labeled with annexin V and immobilized on a fibrinogen coverslips, activated with TRAP or thrombin and registered using confocal microscopy in real time. for experimental planning and analysis, we used a computational model of PAR1-stimulated platelet signal transduction that described interactions between cytosol, dense tubular system and mitochondria. The set of ordinary differential equation was solved using COPASI software (www.copasi.org). Results: TRAP stimulation induced spiking in cytosolic calcium that gradually disappeared as a result of PAR1 inactivation. In some platelets, spiking led to a significant accumulation of calcium in mitochondria via the mitochondrial uniporter. This resulted in a mitochondrial permeability transition pore opening, loss of mitochondrial membrane potential, and the PS exposure (all three processes taking place with no detectable time shift). Interestingly, the procoagulant platelets initially had significantly higher average calcium concentration in their resting state than those that did not expose PS, suggesting a possible cause for the difference in their subsequent fate. Conclusion: Procoagulant platelets form as a result of mitochondria overloading with calcium following a prolonged period of cytosolic calcium spiking. Initial cytosolic calcium level in a resting platelet can pre-dispose it to becoming either procoagulant (if high) or non-procoagulant upon activation. Disclosure of Interest: None declared.