Fig. 1.

Block by Fe²⁺ of currents carried by Ca²⁺ with the II-V protocol. A, sample currents recorded by using the protocols illustrated below the middle records, under control conditions (left), after the addition of Fe²⁺ (middle), and after washout of Fe²⁺ (right) (3-kHz Gaussian filter). Currents are shown in 40-mV increments. B, II-V relationships from the protocol used in A, under control conditions (0 mM Fe²⁺) and with two concentrations of Fe²⁺ (n = 4 for each concentration). C, expanded view of II-V relationships. D, chord conductances calculated for the data in B. E, inhibition by Fe²⁺, expressed as the ratio of the chord conductance with Fe²⁺ to the chord conductance under control conditions. Data are not shown near the reversal potential, where errors in conductance calculations can be large. Solid curves, fits to the model described by Woodhull (1973). Symbols shown in B apply to B to E.