FIGURE 2.

Dok-2^−/− platelets exhibit increased platelet-platelet interactions through an increased α_IIbβ₃-dependent tether lifetime. A, whole blood from WT or Dok-2^−/− mice was pretreated with the integrin α_IIbβ₃ inhibitor GPI562 (10 μm) prior to perfusion through type I collagen (50 μg/ml)-coated microslides at 1,800 s⁻¹ for 3 min, and the number of adherent platelets (per 25% of field) was determined as described under “Experimental Procedures.” ns, not significant. B, WT whole blood was perfused over immobilized collagen (50 μg/ml) for 1 min to allow thrombi to form. Non-adherent platelets were removed, and WT or Dok-2^−/− whole blood was perfused over the preformed thrombi. The interaction lifetime (s) of adherent platelets was determined by quantifying the number of frames for which a platelet remained attached to preformed thrombi (25 frames = 1 s). ***, p < 0.001. C–E, whole blood from WT or Dok-2 mice was perfused across spread platelets of the same genotype (●, WT^[spread]+WT; ○, Dok-2^{−/−[spread]} + Dok-2^−/−) or alternative genotypes (■, Dok-2^{−/−[spread]}+WT; □, WT^[spread] + Dok-2^−/−). C and E, the number of incoming platelets attached to a spread ([spread]) platelet of the indicated genotype. D, the tether lifetime of adherent platelets (s), which was determined by quantifying the number of frames for which a platelet remained attached to a spread platelet (25 frames = 1 s). These results represent six independent experiments (mean ± S.E.).