Functional properties of the WT_E702Q concatemer. (A) Representative currents of the E702Q mutant at 80 and −80 mV. (B) Rundown-corrected concentration–response relations of the E702Q mutant at 80 and −80 mV (n = 13–14 for each data point). Solid lines are the best fit to the Hill equation. Dash­ed lines indicate the relations of WT mTMEM16A at 80 and −80 mV. (C) Na⁺ versus Cl⁻ selectivity of the E702Q mutant. (left) I-V plots recorded at 150 mM extracellular and the indicated intracellular NaCl concentrations at 1 mM (n = 5) [Ca²⁺]_free. (right) Relation between intracellular [NaCl] and E_rev at 1 mM (n = 5) [Ca²⁺]_free. The line indicates the Nernst potential of Cl⁻. (D) Merged and averaged variance-<I> plot and pooled data (n = 10) of the E702Q mutant obtained at 1 mM [Ca²⁺]_free at 80 mV. (E) Representative currents of the WT_E702Q concatemer at 80 and −80 mV. (A and E) Blue and red dots indicate the reference pulses used for rundown correction at 80 and −80 mV, respectively (see Materials and methods). (F) Rundown-corrected concentration–response relation of the WT_E702Q concatemer at 80 mV (n = 8–18 for each data point). The solid line is the best fit to the triphasic Hill equation. Dashed lines indicate the fist activation of WT (green) and E702Q (orange) at 80 mV. (G) Rundown-corrected concentration–response relations of the WT_E702Q concatemer at 80 and −80 mV (n = 8–18 for each data point). Lines are the best fit to a triphasic Hill equation. (H) Merged and averaged variance-<I> plot and pooled data (n = 9) of the WT_E702Q concatemer obtained at 2 µM [Ca²⁺]_free at 80 mV. (D and H, left) The dotted lines indicate the mean P_{O max} across patches. (D and H, right) Dotted lines indicate the corresponding value of WT mTMEM16A. In B–D and F–H, data are presented as mean and errors as SEM.