Charge loss at the OFF is pH_EXT dependent. (A) Mean Q_ON- and Q_OFF-V from individual experiments normalized with respect to Q_ON,MAX at pH 7.4. Increasing pH_EXT caused a larger loss of charge in Q_OFF (see Charge loss by R232H deprotonation for details). (B) Q_ON,MAX values for individual experiments were normalized with respect to Q_MAX at pH 7.4 (Q_MAX,pH7.4), showing that the maximum Q_ON net charge is independent of pH_EXT. (C) pH_EXT dependence of the V_1/2 value of the Q_ON. The slight shift of V_1/2 by pH_EXT is not significantly different (P < 0.05). (D) The pH_EXT dependence of the apparent charge of the fitted Boltzmann distributions to the Q_ON is not significant (P < 0.01). Error bars are SD.