Differential integrin activity mediated by platelet collagen receptor engagement under flow conditions

The platelet receptors glycoprotein (Gp)VI, integrin α (2) β (1) and GpIb/V/IX mediate platelet adhesion and activation during thrombogenesis. Increases of intracellular Ca (2+) ([Ca (2+) ] (i) ) are key signals during platelet activation; however, their relative importance in coupling different collagen receptors to functional responses under shear conditions remains unclear. To study shear-dependent, receptor-specific platelet responses, we used collagen or combinations of receptor-specific collagen-mimetic peptides as substrates for platelet adhesion and activation in whole human blood under arterial flow conditions and compared real-time and endpoint parameters of thrombus formation alongside [Ca (2+) ] (i) measurements using confocal imaging. All three collagen receptors coupled to [Ca (2+) ] (i) signals, but these varied in amplitude and temporal pattern alongside variable integrin activation. GpVI engagement produced large, sustained [Ca (2+) ] (i) signals leading to realtime increases in integrins α (2) β (1) − and α (IIb) β (3) -mediated platelet adhesion. α (IIb) β (3) -dependent platelet aggregation was dependent on P (2) Y (12) signalling. Co-engagement of α (2) β (1) and GpIb/V/IX generated transient [Ca (2+) ] (i) spikes and low amplitude [Ca (2+) ] (i) responses that potentiated GpVI-dependent [Ca (2+) ] (i) signalling. Therefore α (2) β (1) GpIb/V/IX and GpVI synergise to generate [Ca (2+) ] (i) signals that regulate platelet behaviour and thrombus formation. Antagonism of secondary signalling pathways reveals distinct, separate roles for α (IIb) β (3) in stable platelet adhesion and aggregation. Supplementary Material to this article is available online at www.thrombosis-online.com .