GRK2 and arrestin2 regulate UTP-mediated arterial contraction 199 Figure 4 GRK2 inhibition decreases P2Y2-receptor desensitization induced by UTP. MSMCs were co-transfected with 0.5 mg eGFP-PH and either pcDNA3 (control), D110A,K220RGRK2, D110A,K220RGRK3, K215RGRK5, or K215RGRK6 (0.5 mg). Cells were subjected to the standard R1/Rmax/R2 protocol (see Section 2). Representative traces show IP3 changes in cells transfected with pcDNA3 (A), D110A,K220RGRK2 (B), D110A,K220RGRK3 (C ), K215RGRK5 (D), or K215RGRK6 (E). P2Y receptor desensitization was determined as the relative (%) change in R2 response compared with R1. (F ) Cumulative data are presented as means + SEM from 13 – 19 cells from MSMC preparations from four or more different animals. Statistical signiﬁcance is indicated as asterisk **P , 0.01 vs. vector-transfected MSMCs (one-way ANOVA; Dunnett’s post hoc test).