Activation efficiency is reduced at physiological pH. Single-channel openings at pH 7.4, all with an energy-based internal and a 10-s delay, as a comparison versus standard external solution at pH 8.0. (A and B) Currents at pH 7.4 with a 10-s delay between applications. (C) Dwell time histogram of the latency to first opening with a 10-s delay and an energy-based internal. The histogram was best fit by two exponentials (dashed lines). (D) Mean (±SEM) success rate. **P < 0.01, Student’s t test, P = 0.002. (E) Mean (±SEM) efficiency (η) of activation. ***P < 0.001, Student’s t test, P = 0.0008.