Figure 3.

(a) Experimental setup. An acousto-optic tunable filter (AOTF) on the excitation path dynamically controlled the wavelength and intensity of illumination. A patch clamp amplifier provided control over the membrane potential. A camera recorded fluorescence. A shutter (not shown) after the AOTF blocked all light from reaching the sample during dark intervals. The AOTF, patch clamp apparatus, and camera were synchronized via custom software. (b) Voltage-sensitive fluorescence of Arch(D95H) expressed in a HEK cell under constant illumination at 640 nm. The fluorescence more than doubled between V_m = −150 and +150 mV. (c) Fluorescence of Arch(D95Q) increased 7-fold between −150 and +150 mV, though most of the sensitivity was at positive voltages, above the physiological range.