MAPK signaling from the OXTR is mediated by GRK6. A, HEK-293 cells expressing the OXTR and treated with siRNA directed against GRK6 demonstrated a significant decrease in maximal pERK signaling at 2, 5, 10, and 30 minutes (*, P < .0001). Two-way ANOVA demonstrated that the 2 curves differed significantly (P < .0001). B, There were no differences in the pERK signal between cells treated with CTL siRNA and siRNA directed against GRK5 (P = .28). C, Cells treated with siRNA directed against GRK2 demonstrated significantly enhanced pERK expression at 2, 5, 30, and 60 minutes compared with cells treated with CTL siRNA (*, P < .0001) (C). Two-way ANOVA demonstrated that the 2 curves differed significantly (P < .0001).