Ionic permeability ratios (PX/PCl) and anion selectivity sequences of WT and mutant TMEM16A channels
| Channel . | PX/PCl . | Selectivity sequence . | ||||
|---|---|---|---|---|---|---|
| SCN− . | NO3− . | I− . | Br− . | Cl− . | ||
| WT TMEM16A + 0.2 µM Ca2+ | 4.01 ± 0.38 (5) | 1.90 ± 0.06 (5) | 3.18 ± 0.40 (5) | 1.77 ± 0.06 (5) | 1 (5) | SCN− > I− > NO3− > Br− > Cl− |
| I641A – Ca2+ | 1.67 ± 0.11 (6) | 1.22 ± 0.03 (6) | 1.92 ± 0.14 (6) | 1.43 ± 0.03 (6) | 1 (6) | I− > SCN− > Br− > NO3− > Cl− |
| I641A + 0.2 µM Ca2+ | 1.22 ± 0.05 (6) | 1.05 ± 0.05 (6) | 1.38 ± 0.05 (6) | 1.28 ± 0.03 (6) | 1 (6) | I− > Br− = SCN− > NO3− = Cl− |
| G644P + 0.2 µM Ca2+ | 1.43 ± 0.05 (8) | 1.37 ± 0.05 (9) | 1.45 ± 0.04 (8) | 1.26 ± 0.04 (10) | 1 (11) | SCN− = I− = NO3− = Br− > Cl− |
| E702Q + 5 µM Ca2+ | 1.89 ± 0.18 (7) | 1.59 ± 0.11 (7) | 1.99 ± 0.11 (6) | 1.56 ± 0.06 (6) | 1 (32) | I− > SCN− > NO3− = Br− > Cl− |
| E702Q + 12 µM Ca2+ | 1.31 ± 0.04 (5) | 1.09 ± 0.01 (5) | 1.32 ± 0.04 (5) | 1.31 ± 0.04 (5) | 1(5) | I−> SCN− = Br− > NO3− > Cl− |
| E705Q + 12 µM Ca2+ | 1.60 ± 0.09 (6) | 2.06 ± 0.18 (7) | 2.13 ± 0.21 (6) | 1.76 ± 0.13 (6) | 1 (29) | I− > NO3− > Br− > SCN− > Cl− |
| E702Q/E705Q + 12 µM Ca2+ | 1.02 ± 0.05 (5) | 1.29 ± 0.04 (5) | 1.64 ± 0.05 (5) | 1.32 ± 0.03 (5) | 1 (5) | I− > NO3− > Br− > SCN− = Cl− |
| 5Q – Ca2+ | 3.70 ± 0.36 (8) | 2.56 ± 0.2 (8) | 3.26 ± 0.16 (10) | 1.79 ± 0.05 (12) | 1 (12) | SCN− > I− > NO3− > Br− > Cl− |
| 5Q + 12 µM Ca2+ | 1.27 ± 0.07 (8) | 1.30 ± 0.07 (8) | 1.42 ± 0.08 (7) | 1.23 ± 0.01 (8) | 1 (8) | SCN− = I− = NO3− = Br− ≥ Cl− |
| 5Q/I641A – Ca2+ | 1.31 ± 0.05 (7) | 0.94 ± 0.03 (5) | 1.24 ± 0.03 (6) | 1.12 ± 0.01 (6) | 1 (7) | SCN− > I− > Br− > NO3− = Cl− |
| 5Q/G644P – Ca2+ | 1.43 ± 0.05 (6) | 1.08 ± 0.03 (6) | 1.38 ± 0.03 (6) | 1.18 ± 0.03 (6) | 1 (6) | SCN− > I− > Br− > NO3− > Cl− |
| Channel . | PX/PCl . | Selectivity sequence . | ||||
|---|---|---|---|---|---|---|
| SCN− . | NO3− . | I− . | Br− . | Cl− . | ||
| WT TMEM16A + 0.2 µM Ca2+ | 4.01 ± 0.38 (5) | 1.90 ± 0.06 (5) | 3.18 ± 0.40 (5) | 1.77 ± 0.06 (5) | 1 (5) | SCN− > I− > NO3− > Br− > Cl− |
| I641A – Ca2+ | 1.67 ± 0.11 (6) | 1.22 ± 0.03 (6) | 1.92 ± 0.14 (6) | 1.43 ± 0.03 (6) | 1 (6) | I− > SCN− > Br− > NO3− > Cl− |
| I641A + 0.2 µM Ca2+ | 1.22 ± 0.05 (6) | 1.05 ± 0.05 (6) | 1.38 ± 0.05 (6) | 1.28 ± 0.03 (6) | 1 (6) | I− > Br− = SCN− > NO3− = Cl− |
| G644P + 0.2 µM Ca2+ | 1.43 ± 0.05 (8) | 1.37 ± 0.05 (9) | 1.45 ± 0.04 (8) | 1.26 ± 0.04 (10) | 1 (11) | SCN− = I− = NO3− = Br− > Cl− |
| E702Q + 5 µM Ca2+ | 1.89 ± 0.18 (7) | 1.59 ± 0.11 (7) | 1.99 ± 0.11 (6) | 1.56 ± 0.06 (6) | 1 (32) | I− > SCN− > NO3− = Br− > Cl− |
| E702Q + 12 µM Ca2+ | 1.31 ± 0.04 (5) | 1.09 ± 0.01 (5) | 1.32 ± 0.04 (5) | 1.31 ± 0.04 (5) | 1(5) | I−> SCN− = Br− > NO3− > Cl− |
| E705Q + 12 µM Ca2+ | 1.60 ± 0.09 (6) | 2.06 ± 0.18 (7) | 2.13 ± 0.21 (6) | 1.76 ± 0.13 (6) | 1 (29) | I− > NO3− > Br− > SCN− > Cl− |
| E702Q/E705Q + 12 µM Ca2+ | 1.02 ± 0.05 (5) | 1.29 ± 0.04 (5) | 1.64 ± 0.05 (5) | 1.32 ± 0.03 (5) | 1 (5) | I− > NO3− > Br− > SCN− = Cl− |
| 5Q – Ca2+ | 3.70 ± 0.36 (8) | 2.56 ± 0.2 (8) | 3.26 ± 0.16 (10) | 1.79 ± 0.05 (12) | 1 (12) | SCN− > I− > NO3− > Br− > Cl− |
| 5Q + 12 µM Ca2+ | 1.27 ± 0.07 (8) | 1.30 ± 0.07 (8) | 1.42 ± 0.08 (7) | 1.23 ± 0.01 (8) | 1 (8) | SCN− = I− = NO3− = Br− ≥ Cl− |
| 5Q/I641A – Ca2+ | 1.31 ± 0.05 (7) | 0.94 ± 0.03 (5) | 1.24 ± 0.03 (6) | 1.12 ± 0.01 (6) | 1 (7) | SCN− > I− > Br− > NO3− = Cl− |
| 5Q/G644P – Ca2+ | 1.43 ± 0.05 (6) | 1.08 ± 0.03 (6) | 1.38 ± 0.03 (6) | 1.18 ± 0.03 (6) | 1 (6) | SCN− > I− > Br− > NO3− > Cl− |
We computed the permeability ratios using Goldman–Hodgkin–Katz (Eq. 3) and the shifts induced by replacing the total [Cl−]e with SCN−, NO3−, I−, or Br−. The number of independent reversal potential measurements used to calculate PX/PCl is indicated in parentheses. 5Q, channel with five acidic residues of site 1 Ca2+ pocket mutated to Q. Pipette solutions contained 0 or the indicated [Ca2+]i in µM; [Cl−]i = 40 mM, pHe = pHi = 7.3.