Functional properties of WT mTMEM16A. (A) Representative currents of WT mTMEM16A at 80 and −80 mV. Numbers show [Ca²⁺]_free (µM) on the intracellular side of the excised patch. Each sweep was recorded using the voltage and piezo protocol shown in Fig. S1 A. Individual sweeps are separated by a regular time interval (17–20 s, programmed in Clampex) and are concatenated to form a single trace. Blue and red dots indicate the reference pulses used for rundown correction at 80 and −80 mV, respectively (see Materials and methods). Currents at low (left) and high Ca²⁺ (right) were recorded from different patches. (B) Rundown-corrected concentration–response relations of WT mTMEM16A at 80 and −80 mV (n = 4–12 for each data point). Lines are the best fit to a biphasic Hill equation. (C) Na⁺ versus Cl⁻ selectivity of WT mTMEM16A. I-V plots of the instantaneous current in response to the indicated voltage steps at 150 mM extracellular and the indicated intracellular NaCl concentrations at 2 µM (n = 6, left) and 1 mM (n = 6–7, middle) [Ca²⁺]_free. Data are mean values of normalized I-V plots from individual patches unless otherwise stated. (right) Relation between intracellular [NaCl] and reversal potential (E_rev) at 2 µM (n = 6) and 1 mM (n = 6–7) [Ca²⁺]_free. The line indicates the Nernst potential of Cl⁻. (D) Merged and averaged variance-<I> plots of WT mTMEM16A obtained at 2 µM (n = 21, left) and 1 mM (n = 10, middle) [Ca²⁺]_free at 80 mV. The solid lines are the best fit to the noise parabola equation. Dotted lines indicate the mean P_{O max} across patches. Other variance-<I> plots were constructed in the same way unless otherwise stated. (right) Pooled data of individual i and P_{O max} values obtained from individual patches expressing WT mTMEM16A at 2 µM (n = 21) and 1 mM (n = 10) [Ca²⁺]_free. n.s., P > 0.05; ***, P ≤ 0.001. In B–D, data are presented as mean and errors as SEM.