FIGURE 2.
His-337/His-491 residues are critical for block of KCa2.2 and KCa2.3 currents by apamin and organic blockers. A–C, outside-out patch (A and C) and whole-cell (B) macroscopic currents evoked by ramps from −80 to 80 mV in the absence (black trace) and the presence of a supramaximal concentration of apamin (100 nm) (gray trace). Mutation of the outer pore His residue in KCa2.2(H337N) (A) and KCa2.3(H491N) (B) produced currents that were insensitive to the bee venom toxin. Mutation of His-337 in KCa2.2 to the positively charged arginine (H337R) also produced currents that were apamin-insensitive (C). D, graph showing the mean ± S.E. inhibition by 100 nm apamin of macroscopic current from each mutant. E, graph showing the lack of block of KCa2.2(H337N) by the organic blockers UCL1684 (20 nm) and d-TC (100 μm) when compared with block of WT KCa2.2- and KCa2.3-mediated current.