A, representative current traces recorded at pH 7.4 (left) and pH 5.5 (right) using the activation protocol described in Fig. 1A. B, superimposed traces taken from the same cell at pH 7.4 and 5.5, showing the current recorded at +60 and -60 mV test and tail potentials, respectively. C, normalized current is plotted as a function of the membrane voltage (mV) at pH 7.4 (open squares) and pH 5.5 (filled squares; n = 15). D, current amplitude measured at pH 7.4 and 5.5 and recorded at +60 mV (n = 21, *P < 0.0015). E, t1/2 was measured at pH 7.4 and pH 5.5 at +60 mV. F, τdeact were obtained at pH 7.4 and 5.5 from the monoexponential fit of the tail currents measured at -60 mV from a prepulse potential of +30 mV (n = 21; *P < 0.001).