Inhibition of specific [Ca⁺⁺]_ioscillations in platelets interacting with immobilized VWF. A blood cell suspension, prepared as described in the legend to Figure 2, was perfused over immobilized VWF at the shear rate of 3000 s^–1 for 90 seconds. Surface interacting platelets were identified, and their [Ca⁺⁺]_i was monitored in real time for the next 30 seconds during translocation or stationary adhesion. Typical α/β and γ Ca⁺⁺ peaks are identified in the control platelets. The same peaks were also seen after treatment with ASA (400 μM) or the anti-P2Y₁₂ inhibitor (AR-C69931MX, 1 μM). In contrast, after addition of the P2Y₁ inhibitor (MRS2216, 12.5 μM), no type γ [Ca⁺⁺]_i oscillations occurred, whereas α/β peaks were apparently unchanged. Comparable results were obtained in 4 different experiments.