Effect of deglycosylation on gating currents from the nonconducting (W434F) mutant Shaker K_V channel. (A) Gating currents from an oocyte expressing nonconductive Shaker K_V channels before (black) and after (red) 5-min exposure to PNGase F. Gating currents were elicited in response to voltage steps from −100 mV to the voltage shown on the traces by using the cut-open oocyte voltage clamp. (B) Voltage dependence of the gating charge before and after PNGase F treatment from the experiment shown in A. Solid lines represent Boltzmann fits. The best parameter values for the total amount of charge (Q_tot) and the midpoint voltage (V_1/2) were 2.42 nC and −55.4 mV before treatment and 1.94 nC and −48.7 mV after PNGase F treatment, respectively. The reduction in Q_tot was observed in all experiments. It progresses with a slow time constant (∼60 min) to ∼30% of the initial value of Q_tot. The reason for this response is unknown presently, but it appears to be specific for the nonconducting W434F mutant channel. (C) Normalized voltage dependence of the steady-state charge distribution. The plot shows the charge distribution before (black symbols) and after (red symbols) PNGase F treatment from seven experiments. In all experiments, the V_1/2 shifted to the right in the voltage axes. (D) Box plot of the changes in V_1/2 from the seven experiments.