Kinetics of Gα_q/PLCβ₁ interaction. (A) Cartoon of Gα_q-CFP, PLCβ₁-YFP, and cognate G proteins. (B) Confocal images of a pair of cells coexpressing Gα_q-CFP and PLCβ₁-YFP. Bar, 10 µm. (C) FRETr photometry time course for a single cell undergoing a 5-s exposure to 10 µM oxo-M. The top panel shows CFP_C fluorescence (blue trace, left axis) and YFP_C fluorescence (yellow trace, right axis), and the bottom panel shows the ratio, YFP_C/CFP_C (black). Sampling frequency: 2 Hz during baseline and 20 Hz during agonist. (D) Mean time course for 5-s exposures to oxo-M in 10 cells. Mean ± SEM. Note the different time scales for onset and washout. For clarity in display, points from fast sampling were pooled in 200-ms bins. (E) FRETr concentration–response time course for a single cell. Oxo-M from 10 nM to 50 µM as labeled. For clarity in display, trace is smoothed. (F) FRETr concentration–response curve from steady-state values in E for four cells. Mean ± SEM.