(A,G) Time courses of TMEM16F WT and Q559K activation by 15 µM Ca2+ in 150 mM NaCl. The currents were recorded when the patches were held at +80 mV. (B, E, H, K) Recordings of reversal potential with a hyperpolarizing ramp protocol following constant holding at +80 mV. For the demonstrated traces, the solutions were applied in the order of 150 mM, 45 mM and 15 mM NaCl, and back to 150 mM NaCl (not shown). Ca2+-free solution was applied at the end to confirm the seal. (C, F, I, L) Detail amplification showing tail currents in B, E, H, K recorded at +80 mV following the hyperpolarizing ramp. Note that in F, the tail current is not significantly bigger than endogenous current (gray trace), excluding the feasibility to calculate Erev out of it. (D, J) Current magnitudes activated by 15 µM Ca2+ in 150 mM NaCl were plotted against the Erev values measured with 15 mM NaCl intracellular solution, indicating that there is no correlation.