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. Author manuscript; available in PMC: 2014 Nov 28.
Published in final edited form as: Nat Commun. 2014 Apr 22;5:3674. doi: 10.1038/ncomms4674

Figure 3. FRET-opsin sensors report voltage depolarization via decreases in emission intensity from the fluorescence donor.

Figure 3

(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 1400 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.