(a) Left: Representative traces showing 10 μM epinephrine (Epi)-stimulated yellow/cyan (Y/C) emission ratio changes from HEK293T cells co-expressing endoEKAR4, SNAP-β2AR, and endo-Nb37 in the presence or absence of 10 μM U0126 (+MEKi) or 10 μM SB-590885 (+Rafi). Solid lines indicate the mean, and shaded areas show SEM. Right: Maximum endoEKAR4 responses. (b) Representative Proximily Ligation Assay (PLA) images for the Gαs × Raf1 association under the indicated conditions. (c) Bar graph of PLA quantification. (d) Quantification of PLA particle density for Gαs × MEK1. Bar graphs and scatter plots depict the mean ± SEM. *P < 0.05, **P < 0.01, ****P < 0.0001; ordinary one-way ANOVA followed by Holm-Šídák’s multiple-comparison test (a), two-way ANOVA followed by Turkey’s multiple-comparison test (c, d). Negative control curve and data points in (a) are reproduced from Fig. 2e.