Effect of Src kinase inhibition and cGMP modulation on [Ca²⁺]_i elevations in platelets interacting with acid-soluble type I collagen under flow. Blood cell suspensions (Figure 1 legend contains details) were perfused at the shear rate of 250 seconds over immobilized collagen, without or with prior incubation for 10 minutes at 37°C with various concentrations of (A) the Src kinase inhibitor PP2 or (B) the cGMP analog 8-bromo-cyclic guanosine monophosphate (8-Br-cGMP). Platelets in which at least one [Ca²⁺]_i elevation occurred were considered activated, and those exhibiting α-like or γ-like Ca²⁺ peaks were enumerated. Results are shown relative to the values observed in untreated blood cell suspensions (control). Data are the mean ± 95% CI of 3 (A) or 4 (B) different experiments.