RXR binds and inhibits Gq signaling in human platelets. (A) Top panel shows a typical Rac activation assay blot; lower panel shows densitometry measurements (arbitrary units) from 3 blots. Rac activation was measured at 30 seconds after U46619 stimulation. 9cRA was given as standard as a 3-minute pretreatment. For densitometry measurements vehicle pretreatment (control), U46619 (1 \#956;M), 9cRA (10 \#956;M), and 9cRA followed by U46619 (9c+U4; 9cRA 10 \#956;M; U46619 1\#956;M) are shown. *P < .05 by repeated measures 1-way ANOVA, followed by Bonferroni post test. (B) 9cRA (0.1-20 \#956;M) inhibits U46619-induced (U4; 1 \#956;M intracellular Ca²⁺ release in washed platelets. Figure represents the mean ± SEM changes in Ca²⁺ release (nM) in 4 × 10⁸ platelets. (C) RXR binds Gq_/11 in a ligand-dependent fashion. Human PRP was treated with 9cRA (10 \#956;M) for 3 minutes. Platelet lysates were immunoprecipitated (IP) with anti-Gq_/11 and Western blotted (WB) for RXR\#945; (top panel) or Gq_/11 (lower panel). (D) Densitometry measurements (arbitrary units) from 3 blots for RXR\#945; expression detected after 9cRA (10 \#956;M; 3 minutes) treatment and Gq_/11 IP. *P < .05 by unpaired t test. (E) RXR binds Gq_/11 but not Gi/o/t/z/gust in a ligand-dependent fashion. Human PRP was treated with 9cRA (10 \#956;M) for 3 minutes. Platelet lysates were immunoprecipitated (IP) with anti-RXR\#945; and Western blotted (WB) for Gq_/11 (top panel) or Gi/o/t/z/gust (lower panel); arrow indicates 40-kDa band.