XB-IMG-124879
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Figure 6. Low pH abolishes Mg2+ modulation of delay and activation kinetics in I287D+F324D channels. (A) Representative currents recorded at pH 5.5 (top) or pH 8.0 (middle) at +20 mV in the absence (solid trace) or at +30 mV (+20 mV at pH 5.5 only) in the presence (dashed trace) of Mg2+ have been scaled and overlaid. (Bottom) Representative currents recorded at pH 5.5 in the absence of Mg2+ (solid trace; +20 mV) or at pH 8.0 in the presence of Mg2+ (dashed trace; +30 mV) have been scaled and overlaid. Arrows indicate start of voltage pulse (t = 0). (B) Bar graph shows τact values measured at pH 5.5, 6.5, 7.5, or 8.0 in the absence (open bars; +20 mV) or presence (filled bars; +30 mV, except for +20 mV at pH 5.5) of Mg2+. Data are provided as mean ± SEM; n = 8–11. Asterisk (*), τact values measured in the presence and absence of Mg2+ differ significantly; P < 0.05 by ANOVA. Values of τact for I287D+F324D in the absence of Mg2+ were 15 ± 1 ms (pH 5.5), 7 ± 0.3 ms (pH 6.5), 9 ± 1 ms (pH 7.5), and 8 ± 0.4 ms (pH 8). Values of τact for I287D+F324D in the presence of Mg2+ were 14 ± 2 ms (pH 5.5), 14 ± 1 ms (pH 6.5), 16 ± 1 ms (pH 7.5), and 17 ± 1 ms (pH 8). (C) Bar graph shows delay before pore opening measured at pH 5.5, 6.5, 7.5, or 8.0 in the absence (open bars; +20 mV) or presence (filled bars; +30 mV, except for +20 mV at pH 5.5) of Mg2+. Data are provided as mean ± SEM; n = 9–15. Asterisk (*), delay values measured in the presence and absence of Mg2+ differ significantly; P < 0.05 by ANOVA. Values of the delay for I287D+F324D in the absence of Mg2+ were: pH 5.5, 5.7 ± 0.2 ms; pH 6.5, 1.5 ± 0.1 ms; pH 7.5, 3.5 ± 0.2 ms; pH 8.0, 2.9 ± 0.2 ms. Values of the delay for I287D+F324D in the presence of Mg2+ were: pH 5.5, 5.0 ± 0.4 ms; pH 6.5, 3.6 ± 0.2 ms; pH 7.5, 6.7 ± 0.4 ms; pH 8.0, 7.3 ± 0.3 ms. Image published in: Lin MC et al. (2010) © 2010 Lin et al. Creative Commons Attribution-NonCommercial-ShareAlike license Larger Image Printer Friendly View |