Figure 4. Effects of pH on single channel activity.

Concentration-dependent inhibition of single channel activity by acidic pH. Single channel currents were recorded from an inside-out patch under the same conditions as Fig. 1. At a V_m of −120 mV, two active channels were seen at pH_i 7.4, both of which had a slope conductance of 22 pS (top, P_open = 0.873). These currents were completely inhibited at pH_i 5.4 (middle, P_open = 0.000). Channel activity resumed after washout (bottom, P_open = 0.863). Labels on the right: c, closure; 1, the first opening; 2, the second opening.