The dependence of fractional unblock on Po may not discriminate among various state-dependent blocking models. Fractional unblock was determined based on generation of families of Po versus voltage curves over a range of Ca²⁺ assuming various blocking schemes. (A) Dotted and solid lines correspond, respectively, to dependence of fractional unblock on Po for +60 and +100 mV, based on the open-channel block model given by Scheme 1a. Filled and open circles correspond to predictions based on Scheme 2a at +100 and +60 mV, respectively. (B) For Scheme 2b, fractional unblock exhibits a slight dependence on Po. (C) For Scheme 2b′, based on values derived from the fit of GV curves (Fig. 4 G), fractional unblock exhibits a strong dependence on Po. (D) Fractional unblock is plotted as a function of Po for Scheme 3a. (E) Fractional unblock is plotted as a function of Po for Scheme 3b. (F) Fractional unblock is plotted as a function of Po based on fitted values for Scheme 3b′ (Fig. 4 H), exhibiting largely Po-independent fractional unblock.