FIGURE 8.

Bipolar V_j-gating of N2E+G5K hemichannels. (A) A cell-attached record of a single N2E+G5K hemichannel at holding potentials ranging from 60 to −120 mV. The channel closes to substates by V_j-gating at positive potentials, with P_open decreasing as the holding potential becomes more positive. Closures attributable to V_j-gating are also observed at negative potentials with their frequency increasing as the holding potential becomes more negative, as exemplified by the trace obtained at a holding potential of −120 mV. The asterisk denotes the time when the applied voltage was stepped to 0 mV to determine the zero current level. (B) The current-voltage relation of two N2E+G5K hemichannels recorded in a cell-attached patch configuration obtained with ±120-mV voltage ramp. Two sequential traces are shown in this panel. Closures attributable to V_j-gating are observed at both positive and negative potentials but occur sooner and are more prevalent positive holding potentials. The boxed region is expanded in the insert to illustrate brief closures ascribable to V_j-gating. The record also illustrates the inward rectification of the N2E + G5K channel. Records were obtained with pipette and bath solutions composed of 140 mM KCl, 1 mM EDTA, and 10 mM HEPES, pH 7.6.