Immunodetection of Gα_i1, Gα_i2, Gα_i3, Gα_z, and Gα_q in membranes prepared from normal or patient platelets. Platelet membranes were prepared from normal (N) or patient (P) blood as described in “Patient, materials, and methods.” Protein (40 μg) was loaded onto a 10% gel and proteins were separated by SDS-PAGE. Proteins were transferred to PVDF membranes by electroblotting and probed with specific antisera against different Gα subunits. (A) Gα_i2 and Gα_q detected in platelet membranes from 2 separate experiments and Gα_i3 detected in platelet membranes from a single preparation. (B) Gα_i1 detected in 2 separate membrane preparations prepared during 2 separate visits. This blot was stripped and reprobed with anti Gα_i3 as a loading control. (C) Gα_z detected in 2 separate membrane preparations prepared from 2 separate visits. (D) Gα_i1 detected by a second anti-Gα_i1 antibody (AB-2). The blot was stripped 3 times and successively probed with anti Gα_z, p85 PI-3K, and c-Src antibodies, respectively.