pH-sensitivity and chloride sensitivity of mCl-YFP measured by local perfusion of individual cells.

<p>(<b>A</b>) The pH-sensitivity of mCl-YFP fluorescence with a pK_a of 5.88 calibrated with a fixed 0.2 mM Cl⁻ solution containing 100 µM TBT and 50 µM Nigericin. F₀ is the initial fluorescence at pH 7.20. For each data point, fluorescence data of more than 35 cells were averaged. Note in each case that the pK_a is far removed from physiological pH. (<b>B</b>) The chloride sensitivity of mCl-YFP with a K_d of 14.4 mM at a fixed 0.2 mM Cl⁻ solution using 100 µM TBT and 50 µM nigericin at pH 7.20. F₀ is the initial fluorescence under 0.2 mM Cl⁻. For each data point, fluorescence data of more than 25 cells were averaged. The sensitivity is doubled compared to previous YFP-based Cl⁻ sensors, and within the physiological range of cellular Cl⁻ changes.