Activation of FOG1 ki/ki platelets by several agonists is impaired. (A) Relative mean fluorescent intensity of P-selectin on platelets from WT (white bars) or FOG1 ki/ki (gray bars) mice after activation with the thrombin receptor agonist AYP peptide (500μM, left) or the collagen receptor agonist convulxin (24nM, right). The dotted line represents the baseline signal for nonactivated platelets for both WT and ki/ki mice. N = 6, each done in duplicate. Data are mean ± SD. (B) WT or ki/ki platelets were stimulated with thrombin (1 U/mL, left) or convulxin (24nM, right), and supernatants were assayed for PF4 release by ELISA. N = 4, each done in duplicate. Data are mean ± SD. (C) Representative platelet aggregation analysis of WT platelets using a low dose of thrombin (0.08 U/mL) and FOG1 ki/ki platelets using this same dose or a 12.5-fold higher dose (1 U/mL). Aggregation was measured by percentage light transmission. Results are representative of 4 experiments. (D) Representative analysis of platelet ATP secretion in response to thrombin treatment as described in panel C. ATP secretion was measured by a sensitive luminescent assay simultaneously with measurement of aggregation.