Pore properties of the wild-type TMEM16A channel, K584Q mutant, and the MT-WT(K584Q) and MT(K584Q)-WT heterodimeric channels, where MT refers to the E698C subunit. WT(K584Q) and MT(K584Q), respectively, represent the WT and E698C subunits harboring K584Q mutation. [Cl⁻]_i = [Cl⁻]_o = 140 mM in all recordings. (A) Recordings of the K584Q mutant in 20 µM [Ca²⁺] (left) in response to a voltage step family from −80 to 80 mV (right). Leak current has been subtracted. (B) I-V relationships of the K584Q mutant obtained from a ramp voltage protocol (−80 to 80 mV) in 20 mM [Ca²⁺] (black) and 20 µM [Ca²⁺] (red) and from a voltage step protocol like that shown in A (red squares, n = 5). For the two ramp I-V curves, the width of each curve represents the SEM of the averaged current of each digitized data point in the I-V curve. RI = 0.45 ± 0.01 (n = 7) and 0.48 ± 0.01 (n = 5) for the I-V curves in 20 µM [Ca²⁺] and 20 mM [Ca²⁺], respectively. (C) Comparison of the I-V curve rectifications between the wild-type channel and K584Q mutant (left) and between E698C-WT (abbreviated as MT-WT; blue) and MT(K584Q)-WT (red, middle) or MT-WT(K584Q) (red, right). All I-V curves were obtained with 20 µM [Ca²⁺]. Four to seven normalized I-V curves were averaged. The width of each I-V curve represents the SEM of the averaged values. RIs for WT, K584Q, MT-WT, MT(K584Q)-WT, and MT-WT(K584Q) were 1.00 ± 0.02, 0.45 ± 0.01, 0.78 ± 0.06, 0.78 ± 0.05, and 0.47 ± 0.04, respectively.