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. 2008 Nov;132(5):547–562. doi: 10.1085/jgp.200810051

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© 2008 Jara-Oseguera et al.

This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.jgp.org/misc/terms.shtml). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

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Figure 6. — Kinetics of TPrA block depends on the extracellular sodium concentration. (A) Single-channel openings (left) in the absence of TPrA (left trace) and the presence of 2 mM TPrA (right trace) with isometric 130-mM NaCl solutions at 40 mV. The right panel depicts the normalized amplitude histogram from multiple traces as in the left panel. The β distribution fit yielded parameters of β = 8,563.7 s⁻¹ and α = 10,971 s⁻¹. (B) Single-channel openings (left) in the absence of TPrA (left trace) and the presence of 2 mM TPrA (right trace) with 10 mM NaCl in the extracellular and 130 mM in the intracellular solution at 40 mV. The right panel shows the normalized amplitude histogram with the β distribution fit superimposed. The parameters of the fit are: β = 26,919 s⁻¹, α = 11,661 s⁻¹. The amplitude histogram under low extracellular sodium conditions is left-shifted, indicating faster blocker kinetics under these conditions. (C) On-rates obtained from fits of the β distribution to histograms as in B under low sodium conditions, obtained from two different patches (filled circles). The black line is a fit to an exponential of the form:
The values of the fit parameters are: k_on(0) = 1.57 × 10⁶ M⁻¹ s⁻¹; z_on = 0.72 e_o. The gray line corresponds to the fit to the on-rate under isometric 130 mM NaCl conditions in Fig. 5 C (open circles). Error bars are smaller than the symbols. The data indicate that the relief of block observed as a plateau for the on-rate at more positive potentials is a result of interactions between the blocker and the Na⁺ ions in the selectivity filter, and not due to diffusion limitation. Group data are presented as mean ± SEM.

graphic file with name M7.gif — Kinetics of TPrA block depends on the extracellular sodium concentration. (A) Single-channel openings (left) in the absence of TPrA (left trace) and the presence of 2 mM TPrA (right trace) with isometric 130-mM NaCl solutions at 40 mV. The right panel depicts the normalized amplitude histogram from multiple traces as in the left panel. The β distribution fit yielded parameters of β = 8,563.7 s⁻¹ and α = 10,971 s⁻¹. (B) Single-channel openings (left) in the absence of TPrA (left trace) and the presence of 2 mM TPrA (right trace) with 10 mM NaCl in the extracellular and 130 mM in the intracellular solution at 40 mV. The right panel shows the normalized amplitude histogram with the β distribution fit superimposed. The parameters of the fit are: β = 26,919 s⁻¹, α = 11,661 s⁻¹. The amplitude histogram under low extracellular sodium conditions is left-shifted, indicating faster blocker kinetics under these conditions. (C) On-rates obtained from fits of the β distribution to histograms as in B under low sodium conditions, obtained from two different patches (filled circles). The black line is a fit to an exponential of the form:
The values of the fit parameters are: k_on(0) = 1.57 × 10⁶ M⁻¹ s⁻¹; z_on = 0.72 e_o. The gray line corresponds to the fit to the on-rate under isometric 130 mM NaCl conditions in Fig. 5 C (open circles). Error bars are smaller than the symbols. The data indicate that the relief of block observed as a plateau for the on-rate at more positive potentials is a result of interactions between the blocker and the Na⁺ ions in the selectivity filter, and not due to diffusion limitation. Group data are presented as mean ± SEM.