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. Author manuscript; available in PMC: 2017 Aug 15.
Published in final edited form as: Nat Neurosci. 2016 Aug 26;19(9):1142–1153. doi: 10.1038/nn.4359

Table 2.

Selected genetically encoded transmitter indicators (GETIs)

GETI Maximum ΔF/F
in vitro/
on neuronsa 		Glu-free
brightness
in vitro
(mM−1 cm−1)b 		Glu-bound
brightness
in vitro
(mM−1 cm−1)b 		Kd
in vitro/
on neurons
(µM)		 kon
(M−1 s−1)		 koff
(s−1)		 Refs.
FLIPE +0.1/+0.04 (ECFP) 7.8c 8.0 0.6/ND 100 × 106 60 43
−0.1/−0.04 (Venus) 4.0 3.7
SuperGluSnFR +0.14/0.19 (ECFP) 9.4d 9.6 2.5/2.5 30 × 106 75 128
−0.13/−0.17 (Citrine) 1.9 1.5
iGluSnFR +4.5/+1.0 5.3d 29d 110/4.9 ND ND 46
a

Fluorescence change from zero to saturating glutamate in vitro at 25 °C at the emission peak of each channel. This number is empirically measured and, for the acceptor fluorophore in FRET sensors, is influenced by cross-excitation and bleed-through. As event detection is often optimized by single-channel imaging of FRET indicators23,83, the two channels are shown separately.

b

Estimated molar brightness produced by each fluorophore. For FRET sensors, glutamate-free/saturated brightness for the donor channel is calculated as the product of donor peak extinction coefficient and donor quantum yield multiplied by 1 – E, where E is glutamate-free/saturated FRET efficiency. Glutamate-free/saturated brightness for the acceptor channel is calculated as the product of donor peak extinction coefficient and acceptor quantum yield multiplied by E. Specific values for these parameters are noted below. These numbers do not account for cross-excitation and bleed-through of the other channel, but provide an estimate of the contribution of each fluorophore to indicator brightness.

c

Peak ECFP extinction coefficient is 28 mM−1 cm−1 at 433 nm, ECFP quantum yield is 0.37 (ref. 129), Venus quantum yield is 0.57 (ref. 130), and glutamate-free/saturated E of 0.25/0.23 is derived from published emission spectra in HBSS. dCitrine quantum yield is 0.76 (ref. 130), and glutamate-free/saturated E of 0.09/0.07 is derived from published emission spectra.

d

Brightness in the glutamate-bound state at pH 7.4 was first estimated from published data showing 90% of maximal brightness at pH 7.4, assuming maximal brightness is similar to that of EGFP. Glutamate-free brightness in vitro was then obtained by dividing by ΔF/F + 1. NA, not applicable. ND, not determined. Measurements were performed at room temperature. A maximum of two significant digits are used; some values measured from published graphs are less precise.