Anoctamin 1 (ANO1) is an anion channel that is activated by changes in cytosolic Ca2＋ concentration and noxious heat. Although the critical roles of ANO1 have been elucidated in various cell types, the control of its gating mechanisms by Ca2＋ and heat remain more elusive. To investigate critical amino acid residues for modulation of Ca2＋ and heat sensing, we constructed a randomized mutant library for ANO1. Among 695 random mutants, reduced Ca2＋ sensitivity was observed in two mutants (mutant 84 and 87). Consequently, the E143A mutant showed reduced sensitivity to Ca2＋ but not to high temperatures, whereas the E705V mutant exhibited reduced sensitivity to both Ca2＋ and noxious heat. These results suggest that the glutamic acids (E) at 143 and 705 residues in ANO1 are critical for modulation of Ca2＋ and/or heat responses. Furthermore, these findings help to provide a better understanding of the Ca2＋-mediated activation and heat-sensing mechanism of ANO1. [BMB Reports 2018; 51(5): 236-241].