Figure 6.

Each class depends on a different set of factors for the Ca²⁺-induced fluorescence change. Shown are Ca²⁺-saturated/free ratios (Sat/Free) of ρ_e, φ_e, ε_e(λ_Rmax), and σ_2,e(λ_Rmax) of (A) jRGECO1a, (B) K-GECO1, and (C) jREX-GECO1. Insets: Ca²⁺-saturated/free F₁ and F₂ ratios were both calculated from the independent measurements of ρ_e, φ_e, ε_e, and σ_2,e (tan) and measured directly (green) as described for Fig. 5. The horizontal dashed line marks a Ca²⁺-saturated/free (Sat/Free) ratio of 1 (no change) for each plot. Error bars represent estimated SDs.