Agonist-induced platelet prothrombinase activity and average [Ca²⁺]_i values. GFP was activated with 10 μg/mL collagen (A and D), 0.1 U/mL thrombin (B and E), or collagen plus thrombin (C and F ) for 10 minutes with (+) or without (−) stirring. Left panels (A through C): prothrombinase activity, as picomoles thrombin formed per 10⁸ platelets in 3 minutes for collagen, and in 1 minute for thrombin, and collagen plus thrombin. Right panels (D through F ): average [Ca²⁺]_i for the entire activation period, calculated as described in Materials and Methods. Results are shown as means ± SE for normal subjects (n = 19), δ-SPD patients with the Hermansky-Pudlak syndrome (HPS, n = 10), and patients with thrombasthenia (TSA, n = 5): P values: *<.05; **<.01, ***<.001.