Ectodomain shedding of GPIbα and GPVI from the surface of apoptotic platelets. Washed human platelets were preincubated with vehicle (DMSO), Q-VD-Oph (Q-VD: 50μM), or GM6001 (GM: 100μM) before treatment with vehicle (DMSO) or ABT-737 (1μM) for the indicated times or 180 minutes (Ai,iii). (A) Platelets were fixed and the surface expression of GPIbα (i-ii), and GPVI (iii-iv) was examined by flow cytometry, as described in supplemental Methods. In some experiments (B), platelets were lysed under nonreducing conditions and GPIbα and GPVI were immunoblotted, as described in supplemental Methods. Images and flow cytometry profiles (Ai,iii,B) are taken from 1 experiment representative of 3 independent experiments. (Aii,iv) Date are the mean ± SEM (n = 3). ns indicates not significant. *P < .05. **P < .01. ***P < .001.