Figure 9.

Despite fast unblocking, α + β3b tail currents exhibit a residual voltage-dependent blockade at negative potentials. In A, the instantaneous I-V curve obtained with 10 μM Ca²+ (○) is replotted (from Fig. 8 C) along with the fit for the case where G_max was constrained to 2.0 (•). Predictions based on the values given in Table and used for the simulations in Fig. 15 are also shown (□; also see Online Supplemental Materials available at http://www.jgp.org/cgi/content/full/117/6/583/DC1). In B, based on the values for K₂(V) obtained from the fit shown in A, fractional occupancy in O*_n (○) and I_n (•) was calculated and plotted as a function of the potential at which the tail current was measured. In C, tail current amplitudes (normalized to −100 mV) were measured for three patches before (•) and after (○) removal of inactivation with trypsin. In D, the ratio (○) of tail current amplitude at 100 μs before trypsin application to that after removal of inactivation is plotted as a function of repolarization potential. Note the correspondence of these values to those for O*_n in panel B. The solid line is a fit of the following equation:fV=f _max1+K0exp^−zFVRT,where f_max = 0.613, K(0) = 3.32 and z = −0.503.