Effect of deficiency of SLP-76 on granule release and annexin V binding after costimulation with thrombin and convulxin.

Granule release in SLP-76^+/− (A) or SLP-76^−/− (B) platelets was monitored by flow cytometric measurement of surface expression of P-selectin in unstimulated platelets (dotted line) or after costimulation with 0.5 U/mL thrombin and 250 ng/mL convulxin (solid line). Annexin V binding to SLP-76^+/− (C) or SLP-76^−/− (D) platelets was measured by flow cytometry in unstimulated platelets (dotted line) or after costimulation with thrombin and convulxin (solid line). (E) The percentage of platelets staining positively for annexin V binding, defined as region M1 as shown in panels C and D, was determined for SLP-76^+/− (open bars; n = 4) or SLP-76^−/−(filled bars; n = 4) platelets that were either left unstimulated (control) or stimulated with thrombin (0.5 U/mL) plus convulxin (250 ng/mL), or ionomycin (3 μM). *P < .05 versus SLP-76^+/− platelets.