GST-Gi2α pulldown of RGS18 from human platelet lysates. Human platelets. (A) Lysates were prepared from resting platelets and from platelets incubated with forskolin (20 µM), PGI₂ (15 µM), or the PAR1 agonist peptide, SFLLRN (50 µM). The lysates were then incubated with GST-Gi2α coupled to glutathione beads in the presence of GDP plus AlF₄⁻ or GDP alone as indicated. Bound proteins were subjected to electrophoresis and probed with RGS18 and Gi2α antibodies to detect RGS18 and GST-Gi2α fusion protein, respectively. (B) Summary of 3 experiments expressed as the percentage of the result obtained with resting platelets (mean ± SEM). P values are relative to resting platelets. IB, immunoblotting.