EXPERIMENTAL FIGURE 22-11 Probability of channel opening and current flux through individual voltage-gated K⁺ channels increases with the extent of membrane depolarization. These patch-clamp tracings were obtained from patches of neuronal plasma membrane clamped at three different potentials, +50, +20, and –10 mV. The upward deviations in the current indicate the opening of K⁺ channels and movement of K⁺ ions outward (cytosolic to exoplasmic face) across the membrane. Increasing the membrane depolarization (i.e., the clamping voltage) from –10 mV to +50 mV increases the probability a channel will open, the time it stays open, and the amount of electric current (numbers of ions) that passes through it. pA = picoamperes.

[Data from B. Pallota et al., 1981, Nature 293:471, as modified by B. Hille, 1992, Ion Channels of Excitable Membranes, 2d ed., Sinauer, p. 122.]