FIGURE 6.

The removal of two histidine residues in mSLO3 subregion B does not affect pH sensitivity of mSLO3 channels. The I-V relationships are shown for: WT bSLO3 currents (top panel), WT mSLO3 currents (middle panel), and mSLO3−2 His mutant currents (bottom panel) in control conditions (filled symbols) and in the presence of 20 mm NH₄Cl to alkalinize the intracellular medium (open symbols). The increases in the normalized current produced by intracellular alkalinization with NH₄Cl measured at the value of the V½ of activation for each channel were 0.30 ± 0.009 to 0.36 ± 0.02 for WT bSLO3 (n = 7) at 0 mV, 0.8 ± 0.008 to 1.6 ± 0.14 at +70 mV for WT mSLO3 (n = 9), and 0.54 ± 0.01 to 1.1 ± 0.06 at +50 mV for the mSLO3–2 His mutant (n = 9). Note that intracellular alkalinization has less effect on WT bSLO3 than on WT mSLO3 channels, whereas the effect is very similar for both the WT mSLO3 channel and the mSLO3 mutant channel lacking two histidines (mSLO3 −2 His).