pH_i regulates TMEM16A ion channel activity. (A) Representative TMEM16A currents recorded from inside-out patches perfused with intracellular solutions containing 0.5 µM Ca²⁺ at different pH_i values. Currents were elicited by voltage steps from −100 to +100 mV with 20-mV increments. The holding potential was −60 mV. All the traces shown were from the same patch. (B) Mean G-V relations of the TMEM16A channels under different pH_i values at 0.5 µM Ca²⁺. Relative conductance was determined by measuring the amplitude of tail currents 400 µs after repolarization to a fixed membrane potential (−60 mV). The smooth curves represent Boltzmann fits: G/G_max = 1/{1 + exp[−ze(V − V_1/2)/kT]}. G_max is tail current amplitude in response to depolarization to +100 mV in 0.5 µM Ca²⁺ at pH_i 8.9. Error bar represents SEM (n = 7). (C) Mean conductance of TMEM16A at different pH_i values was normalized to the maximum conductance at pH_i 8.9 at different voltages and then plotted as a function of pH_i (G-pH_i relationship). Data were fitted with linear regression curves, and the mean slopes from fits were 0.27, 0.28, 0.29, 0.3, and 0.29 for 20, 40, 60, 80, and 100 mV, respectively (n = 7).