Figure 1. Electrophysiological measurements of BK channels in ARPE-19 cells. A: Shown is the pulse protocol used to measure Ca²⁺-activated potassium currents. From a holding potential of −40 mV the cells were stimulated by 20 potential steps of 50 ms duration from −130 mV with 10 mV increment. B: Shown are control currents evoked in Ringer solution by the pulse protocol shown in A. C: Shown is the same cell as in A in the presence of the specific BK channel antagonist iberiotoxin (100 nM). D: Shown is the iberiotoxin-sensitive current of the same cell (A-B). E: The current-voltage relationship of the steady-state current displayed here, illustrates that only outward current was blocked by iberiotoxin. Shown are the data from the cell measured in A-C. Abbreviations: Control without iberiotoxin represents ●; iberiotoxin-insensitive represents ■; iberiotoxin-sensitive represents ▼. F: The comparison of current densities at +50 mV measured before and after application of 100 nM iberiotoxin illustrates the reduction of outward currents by the addition of the blocker (n=6). G: Shown here is the current-voltage relationship of normalized mean iberiotoxin-sensitive currents fitted with a Boltzmann equation (V1/2=5.23 mV, k=9.58 mV, n=4).