Figure 3: FRET-opsin sensors report voltage depolarization via decreases in emission intensity from the fluorescence donor.
From: Imaging neural spiking in brain tissue using FRET-opsin protein voltage sensors
(a) Optical step responses of cultured HEK293T cells transfected with MacQ, and cultured neurons transfected with MacQ-mOrange2 and MacQ-mCitrine (440 Hz frame rate). The MacQ VSD increased its fluorescence intensity with increased voltage depolarization (left). The donor fluorescent proteins of the FRET-opsin sensors exhibited decreases in fluorescence intensity with increased depolarization (middle, right). We held neurons at −70 mV at the start of each trace and stepped to command voltages ranging from −140 mV to +100 mV. (b) Steady state fluorescence responses of MacQ-mOrange2 and MacQ-mCitrine as a function of neuronal membrane voltage. Illumination at the specimen plane was 1,400 mW mm−2 (λ=633 nm) for the MacQ studies, and 15 mW mm−2 (λ=530 nm and 505 nm, for MacQ-mOrange and MacQ-mCitrine, respectively) for the FRET-opsin sensors. Error bars are s.e.m.
