Figure 2
From: Identification of a proton sensor that regulates conductance and open time of single hERG channels
Extracellular acidosis reduces single hERG1a and 1b channel conductance. (ai and bi). Representative traces of single hERG1a (bi) and hERG1b (bi) channels at -80 mV, originating from recording with pipette solution pH of 7.4 or pH 6.3. Channel activity was observed following a voltage step to +20 mV, imposed as indicated by the arrows. Openings are shown as downward deflections, with dashed lines to represent the closed (C) and open (O) state. (ai) Single channel openings from two patches containing hERG1a channels, one with an electrode solution of pH 7.4 (upper 2 traces, from a single recording) and another with an electrode solution of pH 6.3 (lower 2 traces, from a single recording). (bi) hERG1b channel openings from two patches, one with an electrode solution of pH 7.4 (upper 2 traces from a single recording) and another with an electrode solution of pH 6.3 (lower 2 traces from a single recording). Horizontal scale bar represents 500 ms and vertical scale bar represents 1 pA. Single-channel current-voltage (I-V) relationships for hERG1a (aii) and hERG1b (bii) channels at the two pH values. Channel amplitudes were derived from amplitude histograms fitted with a single Gaussian distribution (not shown). Plots were fitted with a linear relationship (solid line) constrained to pass through zero (dashed line) to achieve slope conductance 12.3 ± 0.2 pS for pH 7.4 (n = 10 cells) and 9.3 ± 0.1 pS for pH 6.3 (n = 9 cells; P < 0.0001, unpaired students t-test) for hERG1a channels (aii). Slope conductance values for hERG1b channels (bii) are 11.3 ± 0.2 pS for pH 7.4 (n = 7 cells) and 7.7 ± 0.4 pS for pH 6.3 (n = 6 cells; P < 0.0001, unpaired students t-test). SEM bars are small and obscured by the symbols for some points. (aiii and biii) Open-time duration histograms produced at -80 mV by combining data from 10 patches in pH 7.4 for hERG1a (aiii) and 7 patches for hERG1b (biii). Histograms were fit with a single exponential function with time constants of 5.0 ms (hERG1a) and 4.7 ms (hERG1b). (aiv and Biv) Combined open-time duration histograms for 9 patches in pH 6.3 at -80 mV for hERG1a (aiv) and hERG1b (biv). Histograms were fit with a single exponential function with time constants 3.1 ms (hERG1a) and 2.9 ms (hERG1b). (av and bv) Plots of open time vs membrane potential for hERG1a (av) and hERG1b (bv) channels, with exponential fits at 7.4 and pH 6.3. Channel open time decreased with membrane depolarization, with the voltage dependence of the change in open time with voltage being lost in pH 6.3. ‘****’ and ‘**’ denote significance of P < 0.0001 and P < 0.01 respectively (2-way ANOVA).
