(A and B) Quantification of the apparent calcium sensitivity of E698Q and E701Q (Yu et al., 2012) mutant TMEM16A channels. (A) Representative current traces of E698Q and E701Q mutants in response to intracellular solutions with different calcium concentrations recorded at +60 mV. Table indicates the concentration of calcium used. (B) Calcium dose–response curves of the mTMEM16A channels at +60 mV. Smooth curves represent fits to the Hill equation. (C) Sequence alignment of the calcium-activated TMEM16 channels. h16A, m16A, x16A, m16B, m16F and Fly16 are the human TMEM16A (Uniprot ID #Q5XXA6), mouse TMEM16A (Uniprot ID #Q8BHY3-2), Xenopus TMEM16A (Uniprot ID #B5SVV6), mouse TMEM16B (Uniprot ID #Q8CFW1), mouse TMEM16F (Uniprot ID #Q6P9J9) and Drosophila TMEM16 channels (Uniprot ID #Q86P24), respectively. Highly conserved acidic residues that are potentially exposed to the cytoplasm are highlighted in red. Some residues with conserved oxygen-containing side chains in m16F and Fly16 are highlighted in green. Putative transmembrane (TM) segments are highlighted in cyan. The controversial TM6 segments are highlighted in gray and labeled as TM6′ and TM6″, respectively. ‘In’ and ‘Out’ indicate the intracellular and extracellular side of the membrane, respectively.