Table 1.
Comparison of biophysical properties of calcium indicators used in this work. Values were derived from measurements by Chen et al.28 for GCaMP6s and by Gee et al.57 for fluo-4, in in vitro (cell-free) environments under saturating calcium conditions at neutral pH. Parameters are λmax (ex): wavelength of fluorescence excitation maximum; λmax (em): wavelength of emission maximum; εmax: absorption coefficient at the excitation maximum; QY: fluorescence quantum yield; EC50: midpoint of calcium binding curve; Hill slope for the calcium binding curve; koff: off-rate for calcium unbinding; DR: fluorescence dynamic range from zero to saturating calcium concentration.
| GCaMP6s28 | Fluo-457 | |
|---|---|---|
| λmax (ex) (nm) | 497 | 494 |
| λmax (em) (nm) | 515 | 516 |
| εmax (M−1cm−1) | 68500 | 88000 |
| QY | 0.61 | 0.14 |
| EC50 (nM) | 144 | 345 |
| Hill slope | 2.9 | 1.0 |
| koff (s−1) | 1.1 | 369a |
| DR (F∞/F0) | 63 | >100 |
ameasured for fluo-358.