Kinetics of PIP₂ hydrolysis. (A) Cartoon of PH(PLCδ₁)-CFP, PH(PLCδ₁)-YFP, Kv7.2/7.3 channels, and PIP₂. PLC hydrolyzes PIP₂ to send PH probes to the cytosol. (B) Confocal images of three cells expressing PH-CFP and PH-YFP. Bar, 10 µm. (C) FRETr photometry time course for a single cell undergoing a 20-s exposure to 10 mM 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 throughout. (D) Mean time course for 20-s exposures to oxo-M in 22 cells. Mean ± SEM. Note the different time scales for onset and washout. For clarity in display, points were pooled in 1-s bins for onset and 10-s bins for washout. (E) FRETr concentration–response time course for a single cell. Oxo-M from 1 nM to 10 µM as labeled. (F) FRETr concentration–response curve from steady-state values in E for 12 cells. Mean ± SEM.